xnu-6153.101.6.tar.gz

[apple/xnu.git] / osfmk / vm / vm_object.c

/*
 * Copyright (c) 2000-2018 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/*
 * Mach Operating System
 * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University
 * All Rights Reserved.
 *
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 */
/*
 *      File:   vm/vm_object.c
 *      Author: Avadis Tevanian, Jr., Michael Wayne Young
 *
 *      Virtual memory object module.
 */

#include <debug.h>
#include <mach_pagemap.h>
#include <task_swapper.h>

#include <mach/mach_types.h>
#include <mach/memory_object.h>
#include <mach/memory_object_default.h>
#include <mach/memory_object_control_server.h>
#include <mach/vm_param.h>

#include <mach/sdt.h>

#include <ipc/ipc_types.h>
#include <ipc/ipc_port.h>

#include <kern/kern_types.h>
#include <kern/assert.h>
#include <kern/queue.h>
#include <kern/kalloc.h>
#include <kern/zalloc.h>
#include <kern/host.h>
#include <kern/host_statistics.h>
#include <kern/processor.h>
#include <kern/misc_protos.h>
#include <kern/policy_internal.h>

#include <vm/memory_object.h>
#include <vm/vm_compressor_pager.h>
#include <vm/vm_fault.h>
#include <vm/vm_map.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_protos.h>
#include <vm/vm_purgeable_internal.h>

#include <vm/vm_compressor.h>

#if CONFIG_PHANTOM_CACHE
#include <vm/vm_phantom_cache.h>
#endif

#if VM_OBJECT_ACCESS_TRACKING
uint64_t vm_object_access_tracking_reads = 0;
uint64_t vm_object_access_tracking_writes = 0;
#endif /* VM_OBJECT_ACCESS_TRACKING */

boolean_t vm_object_collapse_compressor_allowed = TRUE;

struct vm_counters vm_counters;

#if VM_OBJECT_TRACKING
boolean_t vm_object_tracking_inited = FALSE;
btlog_t *vm_object_tracking_btlog;

void
vm_object_tracking_init(void)
{
        int vm_object_tracking;

        vm_object_tracking = 1;
        PE_parse_boot_argn("vm_object_tracking", &vm_object_tracking,
            sizeof(vm_object_tracking));

        if (vm_object_tracking) {
                vm_object_tracking_btlog = btlog_create(
                        VM_OBJECT_TRACKING_NUM_RECORDS,
                        VM_OBJECT_TRACKING_BTDEPTH,
                        TRUE /* caller_will_remove_entries_for_element? */);
                assert(vm_object_tracking_btlog);
                vm_object_tracking_inited = TRUE;
        }
}
#endif /* VM_OBJECT_TRACKING */

/*
 *      Virtual memory objects maintain the actual data
 *      associated with allocated virtual memory.  A given
 *      page of memory exists within exactly one object.
 *
 *      An object is only deallocated when all "references"
 *      are given up.
 *
 *      Associated with each object is a list of all resident
 *      memory pages belonging to that object; this list is
 *      maintained by the "vm_page" module, but locked by the object's
 *      lock.
 *
 *      Each object also records the memory object reference
 *      that is used by the kernel to request and write
 *      back data (the memory object, field "pager"), etc...
 *
 *      Virtual memory objects are allocated to provide
 *      zero-filled memory (vm_allocate) or map a user-defined
 *      memory object into a virtual address space (vm_map).
 *
 *      Virtual memory objects that refer to a user-defined
 *      memory object are called "permanent", because all changes
 *      made in virtual memory are reflected back to the
 *      memory manager, which may then store it permanently.
 *      Other virtual memory objects are called "temporary",
 *      meaning that changes need be written back only when
 *      necessary to reclaim pages, and that storage associated
 *      with the object can be discarded once it is no longer
 *      mapped.
 *
 *      A permanent memory object may be mapped into more
 *      than one virtual address space.  Moreover, two threads
 *      may attempt to make the first mapping of a memory
 *      object concurrently.  Only one thread is allowed to
 *      complete this mapping; all others wait for the
 *      "pager_initialized" field is asserted, indicating
 *      that the first thread has initialized all of the
 *      necessary fields in the virtual memory object structure.
 *
 *      The kernel relies on a *default memory manager* to
 *      provide backing storage for the zero-filled virtual
 *      memory objects.  The pager memory objects associated
 *      with these temporary virtual memory objects are only
 *      requested from the default memory manager when it
 *      becomes necessary.  Virtual memory objects
 *      that depend on the default memory manager are called
 *      "internal".  The "pager_created" field is provided to
 *      indicate whether these ports have ever been allocated.
 *
 *      The kernel may also create virtual memory objects to
 *      hold changed pages after a copy-on-write operation.
 *      In this case, the virtual memory object (and its
 *      backing storage -- its memory object) only contain
 *      those pages that have been changed.  The "shadow"
 *      field refers to the virtual memory object that contains
 *      the remainder of the contents.  The "shadow_offset"
 *      field indicates where in the "shadow" these contents begin.
 *      The "copy" field refers to a virtual memory object
 *      to which changed pages must be copied before changing
 *      this object, in order to implement another form
 *      of copy-on-write optimization.
 *
 *      The virtual memory object structure also records
 *      the attributes associated with its memory object.
 *      The "pager_ready", "can_persist" and "copy_strategy"
 *      fields represent those attributes.  The "cached_list"
 *      field is used in the implementation of the persistence
 *      attribute.
 *
 * ZZZ Continue this comment.
 */

/* Forward declarations for internal functions. */
static kern_return_t    vm_object_terminate(
        vm_object_t     object);

static kern_return_t    vm_object_copy_call(
        vm_object_t             src_object,
        vm_object_offset_t      src_offset,
        vm_object_size_t        size,
        vm_object_t             *_result_object);

static void             vm_object_do_collapse(
        vm_object_t     object,
        vm_object_t     backing_object);

static void             vm_object_do_bypass(
        vm_object_t     object,
        vm_object_t     backing_object);

static void             vm_object_release_pager(
        memory_object_t pager);

zone_t          vm_object_zone;         /* vm backing store zone */

/*
 *      All wired-down kernel memory belongs to a single virtual
 *      memory object (kernel_object) to avoid wasting data structures.
 */
static struct vm_object                 kernel_object_store __attribute__((aligned(VM_PACKED_POINTER_ALIGNMENT)));
vm_object_t                             kernel_object;

static struct vm_object                 compressor_object_store __attribute__((aligned(VM_PACKED_POINTER_ALIGNMENT)));
vm_object_t                             compressor_object = &compressor_object_store;

/*
 *      The submap object is used as a placeholder for vm_map_submap
 *      operations.  The object is declared in vm_map.c because it
 *      is exported by the vm_map module.  The storage is declared
 *      here because it must be initialized here.
 */
static struct vm_object                 vm_submap_object_store __attribute__((aligned(VM_PACKED_POINTER_ALIGNMENT)));

/*
 *      Virtual memory objects are initialized from
 *      a template (see vm_object_allocate).
 *
 *      When adding a new field to the virtual memory
 *      object structure, be sure to add initialization
 *      (see _vm_object_allocate()).
 */
static struct vm_object                 vm_object_template;

unsigned int vm_page_purged_wired = 0;
unsigned int vm_page_purged_busy = 0;
unsigned int vm_page_purged_others = 0;

static queue_head_t     vm_object_cached_list;
static uint32_t         vm_object_cache_pages_freed = 0;
static uint32_t         vm_object_cache_pages_moved = 0;
static uint32_t         vm_object_cache_pages_skipped = 0;
static uint32_t         vm_object_cache_adds = 0;
static uint32_t         vm_object_cached_count = 0;
static lck_mtx_t        vm_object_cached_lock_data;
static lck_mtx_ext_t    vm_object_cached_lock_data_ext;

static uint32_t         vm_object_page_grab_failed = 0;
static uint32_t         vm_object_page_grab_skipped = 0;
static uint32_t         vm_object_page_grab_returned = 0;
static uint32_t         vm_object_page_grab_pmapped = 0;
static uint32_t         vm_object_page_grab_reactivations = 0;

#define vm_object_cache_lock_spin()             \
                lck_mtx_lock_spin(&vm_object_cached_lock_data)
#define vm_object_cache_unlock()        \
                lck_mtx_unlock(&vm_object_cached_lock_data)

static void     vm_object_cache_remove_locked(vm_object_t);


static void vm_object_reap(vm_object_t object);
static void vm_object_reap_async(vm_object_t object);
static void vm_object_reaper_thread(void);

static lck_mtx_t        vm_object_reaper_lock_data;
static lck_mtx_ext_t    vm_object_reaper_lock_data_ext;

static queue_head_t vm_object_reaper_queue; /* protected by vm_object_reaper_lock() */
unsigned int vm_object_reap_count = 0;
unsigned int vm_object_reap_count_async = 0;

#define vm_object_reaper_lock()         \
                lck_mtx_lock(&vm_object_reaper_lock_data)
#define vm_object_reaper_lock_spin()            \
                lck_mtx_lock_spin(&vm_object_reaper_lock_data)
#define vm_object_reaper_unlock()       \
                lck_mtx_unlock(&vm_object_reaper_lock_data)

#if CONFIG_IOSCHED
/* I/O Re-prioritization request list */
queue_head_t    io_reprioritize_list;
lck_spin_t      io_reprioritize_list_lock;

#define IO_REPRIORITIZE_LIST_LOCK()     \
                lck_spin_lock_grp(&io_reprioritize_list_lock, &vm_object_lck_grp)
#define IO_REPRIORITIZE_LIST_UNLOCK()   \
                lck_spin_unlock(&io_reprioritize_list_lock)

#define MAX_IO_REPRIORITIZE_REQS        8192
zone_t          io_reprioritize_req_zone;

/* I/O Re-prioritization thread */
int io_reprioritize_wakeup = 0;
static void io_reprioritize_thread(void *param __unused, wait_result_t wr __unused);

#define IO_REPRIO_THREAD_WAKEUP()       thread_wakeup((event_t)&io_reprioritize_wakeup)
#define IO_REPRIO_THREAD_CONTINUATION()                                 \
{                                                               \
        assert_wait(&io_reprioritize_wakeup, THREAD_UNINT);     \
        thread_block(io_reprioritize_thread);                   \
}

void vm_page_request_reprioritize(vm_object_t, uint64_t, uint32_t, int);
void vm_page_handle_prio_inversion(vm_object_t, vm_page_t);
void vm_decmp_upl_reprioritize(upl_t, int);
#endif

#if 0
#undef KERNEL_DEBUG
#define KERNEL_DEBUG KERNEL_DEBUG_CONSTANT
#endif


/*
 *      vm_object_allocate:
 *
 *      Returns a new object with the given size.
 */

__private_extern__ void
_vm_object_allocate(
        vm_object_size_t        size,
        vm_object_t             object)
{
        *object = vm_object_template;
        vm_page_queue_init(&object->memq);
#if UPL_DEBUG || CONFIG_IOSCHED
        queue_init(&object->uplq);
#endif
        vm_object_lock_init(object);
        object->vo_size = size;

#if VM_OBJECT_TRACKING_OP_CREATED
        if (vm_object_tracking_inited) {
                void    *bt[VM_OBJECT_TRACKING_BTDEPTH];
                int     numsaved = 0;

                numsaved = OSBacktrace(bt, VM_OBJECT_TRACKING_BTDEPTH);
                btlog_add_entry(vm_object_tracking_btlog,
                    object,
                    VM_OBJECT_TRACKING_OP_CREATED,
                    bt,
                    numsaved);
        }
#endif /* VM_OBJECT_TRACKING_OP_CREATED */
}

__private_extern__ vm_object_t
vm_object_allocate(
        vm_object_size_t        size)
{
        vm_object_t object;

        object = (vm_object_t) zalloc(vm_object_zone);

//      dbgLog(object, size, 0, 2);                     /* (TEST/DEBUG) */

        if (object != VM_OBJECT_NULL) {
                _vm_object_allocate(size, object);
        }

        return object;
}


lck_grp_t               vm_object_lck_grp;
lck_grp_t               vm_object_cache_lck_grp;
lck_grp_attr_t          vm_object_lck_grp_attr;
lck_attr_t              vm_object_lck_attr;
lck_attr_t              kernel_object_lck_attr;
lck_attr_t              compressor_object_lck_attr;

extern void vm_named_entry_init(void);

int workaround_41447923 = 0;

/*
 *      vm_object_bootstrap:
 *
 *      Initialize the VM objects module.
 */
__private_extern__ void
vm_object_bootstrap(void)
{
        vm_size_t       vm_object_size;

        assert(sizeof(mo_ipc_object_bits_t) == sizeof(ipc_object_bits_t));

        vm_object_size = (sizeof(struct vm_object) + (VM_PACKED_POINTER_ALIGNMENT - 1)) & ~(VM_PACKED_POINTER_ALIGNMENT - 1);

        vm_object_zone = zinit(vm_object_size,
            round_page(512 * 1024),
            round_page(12 * 1024),
            "vm objects");
        zone_change(vm_object_zone, Z_CALLERACCT, FALSE); /* don't charge caller */
        zone_change(vm_object_zone, Z_NOENCRYPT, TRUE);
        zone_change(vm_object_zone, Z_ALIGNMENT_REQUIRED, TRUE);

        vm_object_init_lck_grp();

        queue_init(&vm_object_cached_list);

        lck_mtx_init_ext(&vm_object_cached_lock_data,
            &vm_object_cached_lock_data_ext,
            &vm_object_cache_lck_grp,
            &vm_object_lck_attr);

        queue_init(&vm_object_reaper_queue);

        lck_mtx_init_ext(&vm_object_reaper_lock_data,
            &vm_object_reaper_lock_data_ext,
            &vm_object_lck_grp,
            &vm_object_lck_attr);


        /*
         *      Fill in a template object, for quick initialization
         */

        /* memq; Lock; init after allocation */

        vm_object_template.memq.prev = 0;
        vm_object_template.memq.next = 0;
#if 0
        /*
         * We can't call vm_object_lock_init() here because that will
         * allocate some memory and VM is not fully initialized yet.
         * The lock will be initialized for each allocated object in
         * _vm_object_allocate(), so we don't need to initialize it in
         * the vm_object_template.
         */
        vm_object_lock_init(&vm_object_template);
#endif
#if DEVELOPMENT || DEBUG
        vm_object_template.Lock_owner = 0;
#endif
        vm_object_template.vo_size = 0;
        vm_object_template.memq_hint = VM_PAGE_NULL;
        vm_object_template.ref_count = 1;
#if     TASK_SWAPPER
        vm_object_template.res_count = 1;
#endif  /* TASK_SWAPPER */
        vm_object_template.resident_page_count = 0;
        vm_object_template.wired_page_count = 0;
        vm_object_template.reusable_page_count = 0;
        vm_object_template.copy = VM_OBJECT_NULL;
        vm_object_template.shadow = VM_OBJECT_NULL;
        vm_object_template.vo_shadow_offset = (vm_object_offset_t) 0;
        vm_object_template.pager = MEMORY_OBJECT_NULL;
        vm_object_template.paging_offset = 0;
        vm_object_template.pager_control = MEMORY_OBJECT_CONTROL_NULL;
        vm_object_template.copy_strategy = MEMORY_OBJECT_COPY_SYMMETRIC;
        vm_object_template.paging_in_progress = 0;
#if __LP64__
        vm_object_template.__object1_unused_bits = 0;
#endif /* __LP64__ */
        vm_object_template.activity_in_progress = 0;

        /* Begin bitfields */
        vm_object_template.all_wanted = 0; /* all bits FALSE */
        vm_object_template.pager_created = FALSE;
        vm_object_template.pager_initialized = FALSE;
        vm_object_template.pager_ready = FALSE;
        vm_object_template.pager_trusted = FALSE;
        vm_object_template.can_persist = FALSE;
        vm_object_template.internal = TRUE;
        vm_object_template.private = FALSE;
        vm_object_template.pageout = FALSE;
        vm_object_template.alive = TRUE;
        vm_object_template.purgable = VM_PURGABLE_DENY;
        vm_object_template.purgeable_when_ripe = FALSE;
        vm_object_template.purgeable_only_by_kernel = FALSE;
        vm_object_template.shadowed = FALSE;
        vm_object_template.true_share = FALSE;
        vm_object_template.terminating = FALSE;
        vm_object_template.named = FALSE;
        vm_object_template.shadow_severed = FALSE;
        vm_object_template.phys_contiguous = FALSE;
        vm_object_template.nophyscache = FALSE;
        /* End bitfields */

        vm_object_template.cached_list.prev = NULL;
        vm_object_template.cached_list.next = NULL;

        vm_object_template.last_alloc = (vm_object_offset_t) 0;
        vm_object_template.sequential = (vm_object_offset_t) 0;
        vm_object_template.pages_created = 0;
        vm_object_template.pages_used = 0;
        vm_object_template.scan_collisions = 0;
#if CONFIG_PHANTOM_CACHE
        vm_object_template.phantom_object_id = 0;
#endif
        vm_object_template.cow_hint = ~(vm_offset_t)0;

        /* cache bitfields */
        vm_object_template.wimg_bits = VM_WIMG_USE_DEFAULT;
        vm_object_template.set_cache_attr = FALSE;
        vm_object_template.object_is_shared_cache = FALSE;
        vm_object_template.code_signed = FALSE;
        vm_object_template.transposed = FALSE;
        vm_object_template.mapping_in_progress = FALSE;
        vm_object_template.phantom_isssd = FALSE;
        vm_object_template.volatile_empty = FALSE;
        vm_object_template.volatile_fault = FALSE;
        vm_object_template.all_reusable = FALSE;
        vm_object_template.blocked_access = FALSE;
        vm_object_template.vo_ledger_tag = VM_LEDGER_TAG_NONE;
        vm_object_template.vo_no_footprint = FALSE;
#if CONFIG_IOSCHED || UPL_DEBUG
        vm_object_template.uplq.prev = NULL;
        vm_object_template.uplq.next = NULL;
#endif /* UPL_DEBUG */
#ifdef VM_PIP_DEBUG
        bzero(&vm_object_template.pip_holders,
            sizeof(vm_object_template.pip_holders));
#endif /* VM_PIP_DEBUG */

        vm_object_template.objq.next = NULL;
        vm_object_template.objq.prev = NULL;
        vm_object_template.task_objq.next = NULL;
        vm_object_template.task_objq.prev = NULL;

        vm_object_template.purgeable_queue_type = PURGEABLE_Q_TYPE_MAX;
        vm_object_template.purgeable_queue_group = 0;

        vm_object_template.vo_cache_ts = 0;

        vm_object_template.wire_tag = VM_KERN_MEMORY_NONE;
#if !VM_TAG_ACTIVE_UPDATE
        vm_object_template.wired_objq.next = NULL;
        vm_object_template.wired_objq.prev = NULL;
#endif /* ! VM_TAG_ACTIVE_UPDATE */

        vm_object_template.io_tracking = FALSE;

#if CONFIG_SECLUDED_MEMORY
        vm_object_template.eligible_for_secluded = FALSE;
        vm_object_template.can_grab_secluded = FALSE;
#else /* CONFIG_SECLUDED_MEMORY */
        vm_object_template.__object3_unused_bits = 0;
#endif /* CONFIG_SECLUDED_MEMORY */

#if VM_OBJECT_ACCESS_TRACKING
        vm_object_template.access_tracking = FALSE;
        vm_object_template.access_tracking_reads = 0;
        vm_object_template.access_tracking_writes = 0;
#endif /* VM_OBJECT_ACCESS_TRACKING */

#if DEBUG
        bzero(&vm_object_template.purgeable_owner_bt[0],
            sizeof(vm_object_template.purgeable_owner_bt));
        vm_object_template.vo_purgeable_volatilizer = NULL;
        bzero(&vm_object_template.purgeable_volatilizer_bt[0],
            sizeof(vm_object_template.purgeable_volatilizer_bt));
#endif /* DEBUG */

        /*
         *      Initialize the "kernel object"
         */

        kernel_object = &kernel_object_store;

/*
 *      Note that in the following size specifications, we need to add 1 because
 *      VM_MAX_KERNEL_ADDRESS (vm_last_addr) is a maximum address, not a size.
 */

        _vm_object_allocate(VM_MAX_KERNEL_ADDRESS + 1,
            kernel_object);

        _vm_object_allocate(VM_MAX_KERNEL_ADDRESS + 1,
            compressor_object);
        kernel_object->copy_strategy = MEMORY_OBJECT_COPY_NONE;
        compressor_object->copy_strategy = MEMORY_OBJECT_COPY_NONE;
        kernel_object->no_tag_update = TRUE;

        /*
         *      Initialize the "submap object".  Make it as large as the
         *      kernel object so that no limit is imposed on submap sizes.
         */

        vm_submap_object = &vm_submap_object_store;
        _vm_object_allocate(VM_MAX_KERNEL_ADDRESS + 1,
            vm_submap_object);
        vm_submap_object->copy_strategy = MEMORY_OBJECT_COPY_NONE;

        /*
         * Create an "extra" reference to this object so that we never
         * try to deallocate it; zfree doesn't like to be called with
         * non-zone memory.
         */
        vm_object_reference(vm_submap_object);

        vm_named_entry_init();

        PE_parse_boot_argn("workaround_41447923", &workaround_41447923,
            sizeof(workaround_41447923));
}

#if CONFIG_IOSCHED
void
vm_io_reprioritize_init(void)
{
        kern_return_t   result;
        thread_t        thread = THREAD_NULL;

        /* Initialze the I/O reprioritization subsystem */
        lck_spin_init(&io_reprioritize_list_lock, &vm_object_lck_grp, &vm_object_lck_attr);
        queue_init(&io_reprioritize_list);

        io_reprioritize_req_zone = zinit(sizeof(struct io_reprioritize_req),
            MAX_IO_REPRIORITIZE_REQS * sizeof(struct io_reprioritize_req),
            4096, "io_reprioritize_req");
        zone_change(io_reprioritize_req_zone, Z_COLLECT, FALSE);

        result = kernel_thread_start_priority(io_reprioritize_thread, NULL, 95 /* MAXPRI_KERNEL */, &thread);
        if (result == KERN_SUCCESS) {
                thread_set_thread_name(thread, "VM_io_reprioritize_thread");
                thread_deallocate(thread);
        } else {
                panic("Could not create io_reprioritize_thread");
        }
}
#endif

void
vm_object_reaper_init(void)
{
        kern_return_t   kr;
        thread_t        thread;

        kr = kernel_thread_start_priority(
                (thread_continue_t) vm_object_reaper_thread,
                NULL,
                BASEPRI_VM,
                &thread);
        if (kr != KERN_SUCCESS) {
                panic("failed to launch vm_object_reaper_thread kr=0x%x", kr);
        }
        thread_set_thread_name(thread, "VM_object_reaper_thread");
        thread_deallocate(thread);
}

__private_extern__ void
vm_object_init(void)
{
        /*
         *      Finish initializing the kernel object.
         */
}


__private_extern__ void
vm_object_init_lck_grp(void)
{
        /*
         * initialze the vm_object lock world
         */
        lck_grp_attr_setdefault(&vm_object_lck_grp_attr);
        lck_grp_init(&vm_object_lck_grp, "vm_object", &vm_object_lck_grp_attr);
        lck_grp_init(&vm_object_cache_lck_grp, "vm_object_cache", &vm_object_lck_grp_attr);
        lck_attr_setdefault(&vm_object_lck_attr);
        lck_attr_setdefault(&kernel_object_lck_attr);
        lck_attr_cleardebug(&kernel_object_lck_attr);
        lck_attr_setdefault(&compressor_object_lck_attr);
        lck_attr_cleardebug(&compressor_object_lck_attr);
}


/*
 *      vm_object_deallocate:
 *
 *      Release a reference to the specified object,
 *      gained either through a vm_object_allocate
 *      or a vm_object_reference call.  When all references
 *      are gone, storage associated with this object
 *      may be relinquished.
 *
 *      No object may be locked.
 */
unsigned long vm_object_deallocate_shared_successes = 0;
unsigned long vm_object_deallocate_shared_failures = 0;
unsigned long vm_object_deallocate_shared_swap_failures = 0;

__private_extern__ void
vm_object_deallocate(
        vm_object_t     object)
{
        vm_object_t     shadow = VM_OBJECT_NULL;

//      if(object)dbgLog(object, object->ref_count, object->can_persist, 3);    /* (TEST/DEBUG) */
//      else dbgLog(object, 0, 0, 3);   /* (TEST/DEBUG) */

        if (object == VM_OBJECT_NULL) {
                return;
        }

        if (object == kernel_object || object == compressor_object) {
                vm_object_lock_shared(object);

                OSAddAtomic(-1, &object->ref_count);

                if (object->ref_count == 0) {
                        if (object == kernel_object) {
                                panic("vm_object_deallocate: losing kernel_object\n");
                        } else {
                                panic("vm_object_deallocate: losing compressor_object\n");
                        }
                }
                vm_object_unlock(object);
                return;
        }

        if (object->ref_count == 2 &&
            object->named) {
                /*
                 * This "named" object's reference count is about to
                 * drop from 2 to 1:
                 * we'll need to call memory_object_last_unmap().
                 */
        } else if (object->ref_count == 2 &&
            object->internal &&
            object->shadow != VM_OBJECT_NULL) {
                /*
                 * This internal object's reference count is about to
                 * drop from 2 to 1 and it has a shadow object:
                 * we'll want to try and collapse this object with its
                 * shadow.
                 */
        } else if (object->ref_count >= 2) {
                UInt32          original_ref_count;
                volatile UInt32 *ref_count_p;
                Boolean         atomic_swap;

                /*
                 * The object currently looks like it is not being
                 * kept alive solely by the reference we're about to release.
                 * Let's try and release our reference without taking
                 * all the locks we would need if we had to terminate the
                 * object (cache lock + exclusive object lock).
                 * Lock the object "shared" to make sure we don't race with
                 * anyone holding it "exclusive".
                 */
                vm_object_lock_shared(object);
                ref_count_p = (volatile UInt32 *) &object->ref_count;
                original_ref_count = object->ref_count;
                /*
                 * Test again as "ref_count" could have changed.
                 * "named" shouldn't change.
                 */
                if (original_ref_count == 2 &&
                    object->named) {
                        /* need to take slow path for m_o_last_unmap() */
                        atomic_swap = FALSE;
                } else if (original_ref_count == 2 &&
                    object->internal &&
                    object->shadow != VM_OBJECT_NULL) {
                        /* need to take slow path for vm_object_collapse() */
                        atomic_swap = FALSE;
                } else if (original_ref_count < 2) {
                        /* need to take slow path for vm_object_terminate() */
                        atomic_swap = FALSE;
                } else {
                        /* try an atomic update with the shared lock */
                        atomic_swap = OSCompareAndSwap(
                                original_ref_count,
                                original_ref_count - 1,
                                (UInt32 *) &object->ref_count);
                        if (atomic_swap == FALSE) {
                                vm_object_deallocate_shared_swap_failures++;
                                /* fall back to the slow path... */
                        }
                }

                vm_object_unlock(object);

                if (atomic_swap) {
                        /*
                         * ref_count was updated atomically !
                         */
                        vm_object_deallocate_shared_successes++;
                        return;
                }

                /*
                 * Someone else updated the ref_count at the same
                 * time and we lost the race.  Fall back to the usual
                 * slow but safe path...
                 */
                vm_object_deallocate_shared_failures++;
        }

        while (object != VM_OBJECT_NULL) {
                vm_object_lock(object);

                assert(object->ref_count > 0);

                /*
                 *      If the object has a named reference, and only
                 *      that reference would remain, inform the pager
                 *      about the last "mapping" reference going away.
                 */
                if ((object->ref_count == 2) && (object->named)) {
                        memory_object_t pager = object->pager;

                        /* Notify the Pager that there are no */
                        /* more mappers for this object */

                        if (pager != MEMORY_OBJECT_NULL) {
                                vm_object_mapping_wait(object, THREAD_UNINT);
                                vm_object_mapping_begin(object);
                                vm_object_unlock(object);

                                memory_object_last_unmap(pager);

                                vm_object_lock(object);
                                vm_object_mapping_end(object);
                        }
                        assert(object->ref_count > 0);
                }

                /*
                 *      Lose the reference. If other references
                 *      remain, then we are done, unless we need
                 *      to retry a cache trim.
                 *      If it is the last reference, then keep it
                 *      until any pending initialization is completed.
                 */

                /* if the object is terminating, it cannot go into */
                /* the cache and we obviously should not call      */
                /* terminate again.  */

                if ((object->ref_count > 1) || object->terminating) {
                        vm_object_lock_assert_exclusive(object);
                        object->ref_count--;
                        vm_object_res_deallocate(object);

                        if (object->ref_count == 1 &&
                            object->shadow != VM_OBJECT_NULL) {
                                /*
                                 * There's only one reference left on this
                                 * VM object.  We can't tell if it's a valid
                                 * one (from a mapping for example) or if this
                                 * object is just part of a possibly stale and
                                 * useless shadow chain.
                                 * We would like to try and collapse it into
                                 * its parent, but we don't have any pointers
                                 * back to this parent object.
                                 * But we can try and collapse this object with
                                 * its own shadows, in case these are useless
                                 * too...
                                 * We can't bypass this object though, since we
                                 * don't know if this last reference on it is
                                 * meaningful or not.
                                 */
                                vm_object_collapse(object, 0, FALSE);
                        }
                        vm_object_unlock(object);
                        return;
                }

                /*
                 *      We have to wait for initialization
                 *      before destroying or caching the object.
                 */

                if (object->pager_created && !object->pager_initialized) {
                        assert(!object->can_persist);
                        vm_object_assert_wait(object,
                            VM_OBJECT_EVENT_INITIALIZED,
                            THREAD_UNINT);
                        vm_object_unlock(object);

                        thread_block(THREAD_CONTINUE_NULL);
                        continue;
                }

                VM_OBJ_RES_DECR(object);        /* XXX ? */
                /*
                 *      Terminate this object. If it had a shadow,
                 *      then deallocate it; otherwise, if we need
                 *      to retry a cache trim, do so now; otherwise,
                 *      we are done. "pageout" objects have a shadow,
                 *      but maintain a "paging reference" rather than
                 *      a normal reference.
                 */
                shadow = object->pageout?VM_OBJECT_NULL:object->shadow;

                if (vm_object_terminate(object) != KERN_SUCCESS) {
                        return;
                }
                if (shadow != VM_OBJECT_NULL) {
                        object = shadow;
                        continue;
                }
                return;
        }
}



vm_page_t
vm_object_page_grab(
        vm_object_t     object)
{
        vm_page_t       p, next_p;
        int             p_limit = 0;
        int             p_skipped = 0;

        vm_object_lock_assert_exclusive(object);

        next_p = (vm_page_t)vm_page_queue_first(&object->memq);
        p_limit = MIN(50, object->resident_page_count);

        while (!vm_page_queue_end(&object->memq, (vm_page_queue_entry_t)next_p) && --p_limit > 0) {
                p = next_p;
                next_p = (vm_page_t)vm_page_queue_next(&next_p->vmp_listq);

                if (VM_PAGE_WIRED(p) || p->vmp_busy || p->vmp_cleaning || p->vmp_laundry || p->vmp_fictitious) {
                        goto move_page_in_obj;
                }

                if (p->vmp_pmapped || p->vmp_dirty || p->vmp_precious) {
                        vm_page_lockspin_queues();

                        if (p->vmp_pmapped) {
                                int refmod_state;

                                vm_object_page_grab_pmapped++;

                                if (p->vmp_reference == FALSE || p->vmp_dirty == FALSE) {
                                        refmod_state = pmap_get_refmod(VM_PAGE_GET_PHYS_PAGE(p));

                                        if (refmod_state & VM_MEM_REFERENCED) {
                                                p->vmp_reference = TRUE;
                                        }
                                        if (refmod_state & VM_MEM_MODIFIED) {
                                                SET_PAGE_DIRTY(p, FALSE);
                                        }
                                }
                                if (p->vmp_dirty == FALSE && p->vmp_precious == FALSE) {
                                        refmod_state = pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(p));

                                        if (refmod_state & VM_MEM_REFERENCED) {
                                                p->vmp_reference = TRUE;
                                        }
                                        if (refmod_state & VM_MEM_MODIFIED) {
                                                SET_PAGE_DIRTY(p, FALSE);
                                        }

                                        if (p->vmp_dirty == FALSE) {
                                                goto take_page;
                                        }
                                }
                        }
                        if ((p->vmp_q_state != VM_PAGE_ON_ACTIVE_Q) && p->vmp_reference == TRUE) {
                                vm_page_activate(p);

                                VM_STAT_INCR(reactivations);
                                vm_object_page_grab_reactivations++;
                        }
                        vm_page_unlock_queues();
move_page_in_obj:
                        vm_page_queue_remove(&object->memq, p, vmp_listq);
                        vm_page_queue_enter(&object->memq, p, vmp_listq);

                        p_skipped++;
                        continue;
                }
                vm_page_lockspin_queues();
take_page:
                vm_page_free_prepare_queues(p);
                vm_object_page_grab_returned++;
                vm_object_page_grab_skipped += p_skipped;

                vm_page_unlock_queues();

                vm_page_free_prepare_object(p, TRUE);

                return p;
        }
        vm_object_page_grab_skipped += p_skipped;
        vm_object_page_grab_failed++;

        return NULL;
}



#define EVICT_PREPARE_LIMIT     64
#define EVICT_AGE               10

static  clock_sec_t     vm_object_cache_aging_ts = 0;

static void
vm_object_cache_remove_locked(
        vm_object_t     object)
{
        assert(object->purgable == VM_PURGABLE_DENY);

        queue_remove(&vm_object_cached_list, object, vm_object_t, cached_list);
        object->cached_list.next = NULL;
        object->cached_list.prev = NULL;

        vm_object_cached_count--;
}

void
vm_object_cache_remove(
        vm_object_t     object)
{
        vm_object_cache_lock_spin();

        if (object->cached_list.next &&
            object->cached_list.prev) {
                vm_object_cache_remove_locked(object);
        }

        vm_object_cache_unlock();
}

void
vm_object_cache_add(
        vm_object_t     object)
{
        clock_sec_t sec;
        clock_nsec_t nsec;

        assert(object->purgable == VM_PURGABLE_DENY);

        if (object->resident_page_count == 0) {
                return;
        }
        clock_get_system_nanotime(&sec, &nsec);

        vm_object_cache_lock_spin();

        if (object->cached_list.next == NULL &&
            object->cached_list.prev == NULL) {
                queue_enter(&vm_object_cached_list, object, vm_object_t, cached_list);
                object->vo_cache_ts = sec + EVICT_AGE;
                object->vo_cache_pages_to_scan = object->resident_page_count;

                vm_object_cached_count++;
                vm_object_cache_adds++;
        }
        vm_object_cache_unlock();
}

int
vm_object_cache_evict(
        int     num_to_evict,
        int     max_objects_to_examine)
{
        vm_object_t     object = VM_OBJECT_NULL;
        vm_object_t     next_obj = VM_OBJECT_NULL;
        vm_page_t       local_free_q = VM_PAGE_NULL;
        vm_page_t       p;
        vm_page_t       next_p;
        int             object_cnt = 0;
        vm_page_t       ep_array[EVICT_PREPARE_LIMIT];
        int             ep_count;
        int             ep_limit;
        int             ep_index;
        int             ep_freed = 0;
        int             ep_moved = 0;
        uint32_t        ep_skipped = 0;
        clock_sec_t     sec;
        clock_nsec_t    nsec;

        KERNEL_DEBUG(0x13001ec | DBG_FUNC_START, 0, 0, 0, 0, 0);
        /*
         * do a couple of quick checks to see if it's
         * worthwhile grabbing the lock
         */
        if (queue_empty(&vm_object_cached_list)) {
                KERNEL_DEBUG(0x13001ec | DBG_FUNC_END, 0, 0, 0, 0, 0);
                return 0;
        }
        clock_get_system_nanotime(&sec, &nsec);

        /*
         * the object on the head of the queue has not
         * yet sufficiently aged
         */
        if (sec < vm_object_cache_aging_ts) {
                KERNEL_DEBUG(0x13001ec | DBG_FUNC_END, 0, 0, 0, 0, 0);
                return 0;
        }
        /*
         * don't need the queue lock to find
         * and lock an object on the cached list
         */
        vm_page_unlock_queues();

        vm_object_cache_lock_spin();

        for (;;) {
                next_obj = (vm_object_t)queue_first(&vm_object_cached_list);

                while (!queue_end(&vm_object_cached_list, (queue_entry_t)next_obj) && object_cnt++ < max_objects_to_examine) {
                        object = next_obj;
                        next_obj = (vm_object_t)queue_next(&next_obj->cached_list);

                        assert(object->purgable == VM_PURGABLE_DENY);

                        if (sec < object->vo_cache_ts) {
                                KERNEL_DEBUG(0x130020c, object, object->resident_page_count, object->vo_cache_ts, sec, 0);

                                vm_object_cache_aging_ts = object->vo_cache_ts;
                                object = VM_OBJECT_NULL;
                                break;
                        }
                        if (!vm_object_lock_try_scan(object)) {
                                /*
                                 * just skip over this guy for now... if we find
                                 * an object to steal pages from, we'll revist in a bit...
                                 * hopefully, the lock will have cleared
                                 */
                                KERNEL_DEBUG(0x13001f8, object, object->resident_page_count, 0, 0, 0);

                                object = VM_OBJECT_NULL;
                                continue;
                        }
                        if (vm_page_queue_empty(&object->memq) || object->vo_cache_pages_to_scan == 0) {
                                /*
                                 * this case really shouldn't happen, but it's not fatal
                                 * so deal with it... if we don't remove the object from
                                 * the list, we'll never move past it.
                                 */
                                KERNEL_DEBUG(0x13001fc, object, object->resident_page_count, ep_freed, ep_moved, 0);

                                vm_object_cache_remove_locked(object);
                                vm_object_unlock(object);
                                object = VM_OBJECT_NULL;
                                continue;
                        }
                        /*
                         * we have a locked object with pages...
                         * time to start harvesting
                         */
                        break;
                }
                vm_object_cache_unlock();

                if (object == VM_OBJECT_NULL) {
                        break;
                }

                /*
                 * object is locked at this point and
                 * has resident pages
                 */
                next_p = (vm_page_t)vm_page_queue_first(&object->memq);

                /*
                 * break the page scan into 2 pieces to minimize the time spent
                 * behind the page queue lock...
                 * the list of pages on these unused objects is likely to be cold
                 * w/r to the cpu cache which increases the time to scan the list
                 * tenfold...  and we may have a 'run' of pages we can't utilize that
                 * needs to be skipped over...
                 */
                if ((ep_limit = num_to_evict - (ep_freed + ep_moved)) > EVICT_PREPARE_LIMIT) {
                        ep_limit = EVICT_PREPARE_LIMIT;
                }
                ep_count = 0;

                while (!vm_page_queue_end(&object->memq, (vm_page_queue_entry_t)next_p) && object->vo_cache_pages_to_scan && ep_count < ep_limit) {
                        p = next_p;
                        next_p = (vm_page_t)vm_page_queue_next(&next_p->vmp_listq);

                        object->vo_cache_pages_to_scan--;

                        if (VM_PAGE_WIRED(p) || p->vmp_busy || p->vmp_cleaning || p->vmp_laundry) {
                                vm_page_queue_remove(&object->memq, p, vmp_listq);
                                vm_page_queue_enter(&object->memq, p, vmp_listq);

                                ep_skipped++;
                                continue;
                        }
                        if (p->vmp_wpmapped || p->vmp_dirty || p->vmp_precious) {
                                vm_page_queue_remove(&object->memq, p, vmp_listq);
                                vm_page_queue_enter(&object->memq, p, vmp_listq);

                                pmap_clear_reference(VM_PAGE_GET_PHYS_PAGE(p));
                        }
                        ep_array[ep_count++] = p;
                }
                KERNEL_DEBUG(0x13001f4 | DBG_FUNC_START, object, object->resident_page_count, ep_freed, ep_moved, 0);

                vm_page_lockspin_queues();

                for (ep_index = 0; ep_index < ep_count; ep_index++) {
                        p = ep_array[ep_index];

                        if (p->vmp_wpmapped || p->vmp_dirty || p->vmp_precious) {
                                p->vmp_reference = FALSE;
                                p->vmp_no_cache = FALSE;

                                /*
                                 * we've already filtered out pages that are in the laundry
                                 * so if we get here, this page can't be on the pageout queue
                                 */
                                vm_page_queues_remove(p, FALSE);
                                vm_page_enqueue_inactive(p, TRUE);

                                ep_moved++;
                        } else {
#if CONFIG_PHANTOM_CACHE
                                vm_phantom_cache_add_ghost(p);
#endif
                                vm_page_free_prepare_queues(p);

                                assert(p->vmp_pageq.next == 0 && p->vmp_pageq.prev == 0);
                                /*
                                 * Add this page to our list of reclaimed pages,
                                 * to be freed later.
                                 */
                                p->vmp_snext = local_free_q;
                                local_free_q = p;

                                ep_freed++;
                        }
                }
                vm_page_unlock_queues();

                KERNEL_DEBUG(0x13001f4 | DBG_FUNC_END, object, object->resident_page_count, ep_freed, ep_moved, 0);

                if (local_free_q) {
                        vm_page_free_list(local_free_q, TRUE);
                        local_free_q = VM_PAGE_NULL;
                }
                if (object->vo_cache_pages_to_scan == 0) {
                        KERNEL_DEBUG(0x1300208, object, object->resident_page_count, ep_freed, ep_moved, 0);

                        vm_object_cache_remove(object);

                        KERNEL_DEBUG(0x13001fc, object, object->resident_page_count, ep_freed, ep_moved, 0);
                }
                /*
                 * done with this object
                 */
                vm_object_unlock(object);
                object = VM_OBJECT_NULL;

                /*
                 * at this point, we are not holding any locks
                 */
                if ((ep_freed + ep_moved) >= num_to_evict) {
                        /*
                         * we've reached our target for the
                         * number of pages to evict
                         */
                        break;
                }
                vm_object_cache_lock_spin();
        }
        /*
         * put the page queues lock back to the caller's
         * idea of it
         */
        vm_page_lock_queues();

        vm_object_cache_pages_freed += ep_freed;
        vm_object_cache_pages_moved += ep_moved;
        vm_object_cache_pages_skipped += ep_skipped;

        KERNEL_DEBUG(0x13001ec | DBG_FUNC_END, ep_freed, 0, 0, 0, 0);
        return ep_freed;
}

/*
 *      Routine:        vm_object_terminate
 *      Purpose:
 *              Free all resources associated with a vm_object.
 *      In/out conditions:
 *              Upon entry, the object must be locked,
 *              and the object must have exactly one reference.
 *
 *              The shadow object reference is left alone.
 *
 *              The object must be unlocked if its found that pages
 *              must be flushed to a backing object.  If someone
 *              manages to map the object while it is being flushed
 *              the object is returned unlocked and unchanged.  Otherwise,
 *              upon exit, the cache will be unlocked, and the
 *              object will cease to exist.
 */
static kern_return_t
vm_object_terminate(
        vm_object_t     object)
{
        vm_object_t     shadow_object;

        vm_object_lock_assert_exclusive(object);

        if (!object->pageout && (!object->internal && object->can_persist) &&
            (object->pager != NULL || object->shadow_severed)) {
                /*
                 * Clear pager_trusted bit so that the pages get yanked
                 * out of the object instead of cleaned in place.  This
                 * prevents a deadlock in XMM and makes more sense anyway.
                 */
                object->pager_trusted = FALSE;

                vm_object_reap_pages(object, REAP_TERMINATE);
        }
        /*
         *      Make sure the object isn't already being terminated
         */
        if (object->terminating) {
                vm_object_lock_assert_exclusive(object);
                object->ref_count--;
                assert(object->ref_count > 0);
                vm_object_unlock(object);
                return KERN_FAILURE;
        }

        /*
         * Did somebody get a reference to the object while we were
         * cleaning it?
         */
        if (object->ref_count != 1) {
                vm_object_lock_assert_exclusive(object);
                object->ref_count--;
                assert(object->ref_count > 0);
                vm_object_res_deallocate(object);
                vm_object_unlock(object);
                return KERN_FAILURE;
        }

        /*
         *      Make sure no one can look us up now.
         */

        object->terminating = TRUE;
        object->alive = FALSE;

        if (!object->internal &&
            object->cached_list.next &&
            object->cached_list.prev) {
                vm_object_cache_remove(object);
        }

        /*
         *      Detach the object from its shadow if we are the shadow's
         *      copy. The reference we hold on the shadow must be dropped
         *      by our caller.
         */
        if (((shadow_object = object->shadow) != VM_OBJECT_NULL) &&
            !(object->pageout)) {
                vm_object_lock(shadow_object);
                if (shadow_object->copy == object) {
                        shadow_object->copy = VM_OBJECT_NULL;
                }
                vm_object_unlock(shadow_object);
        }

        if (object->paging_in_progress != 0 ||
            object->activity_in_progress != 0) {
                /*
                 * There are still some paging_in_progress references
                 * on this object, meaning that there are some paging
                 * or other I/O operations in progress for this VM object.
                 * Such operations take some paging_in_progress references
                 * up front to ensure that the object doesn't go away, but
                 * they may also need to acquire a reference on the VM object,
                 * to map it in kernel space, for example.  That means that
                 * they may end up releasing the last reference on the VM
                 * object, triggering its termination, while still holding
                 * paging_in_progress references.  Waiting for these
                 * pending paging_in_progress references to go away here would
                 * deadlock.
                 *
                 * To avoid deadlocking, we'll let the vm_object_reaper_thread
                 * complete the VM object termination if it still holds
                 * paging_in_progress references at this point.
                 *
                 * No new paging_in_progress should appear now that the
                 * VM object is "terminating" and not "alive".
                 */
                vm_object_reap_async(object);
                vm_object_unlock(object);
                /*
                 * Return KERN_FAILURE to let the caller know that we
                 * haven't completed the termination and it can't drop this
                 * object's reference on its shadow object yet.
                 * The reaper thread will take care of that once it has
                 * completed this object's termination.
                 */
                return KERN_FAILURE;
        }
        /*
         * complete the VM object termination
         */
        vm_object_reap(object);
        object = VM_OBJECT_NULL;

        /*
         * the object lock was released by vm_object_reap()
         *
         * KERN_SUCCESS means that this object has been terminated
         * and no longer needs its shadow object but still holds a
         * reference on it.
         * The caller is responsible for dropping that reference.
         * We can't call vm_object_deallocate() here because that
         * would create a recursion.
         */
        return KERN_SUCCESS;
}


/*
 * vm_object_reap():
 *
 * Complete the termination of a VM object after it's been marked
 * as "terminating" and "!alive" by vm_object_terminate().
 *
 * The VM object must be locked by caller.
 * The lock will be released on return and the VM object is no longer valid.
 */

void
vm_object_reap(
        vm_object_t object)
{
        memory_object_t         pager;

        vm_object_lock_assert_exclusive(object);
        assert(object->paging_in_progress == 0);
        assert(object->activity_in_progress == 0);

        vm_object_reap_count++;

        /*
         * Disown this purgeable object to cleanup its owner's purgeable
         * ledgers.  We need to do this before disconnecting the object
         * from its pager, to properly account for compressed pages.
         */
        if (object->internal &&
            (object->purgable != VM_PURGABLE_DENY ||
            object->vo_ledger_tag)) {
                int ledger_flags;
                kern_return_t kr;

                ledger_flags = 0;
                if (object->vo_no_footprint) {
                        ledger_flags |= VM_LEDGER_FLAG_NO_FOOTPRINT;
                }
                assert(!object->alive);
                assert(object->terminating);
                kr = vm_object_ownership_change(object,
                    object->vo_ledger_tag,   /* unchanged */
                    NULL,                    /* no owner */
                    ledger_flags,
                    FALSE);                  /* task_objq not locked */
                assert(kr == KERN_SUCCESS);
                assert(object->vo_owner == NULL);
        }

        pager = object->pager;
        object->pager = MEMORY_OBJECT_NULL;

        if (pager != MEMORY_OBJECT_NULL) {
                memory_object_control_disable(object->pager_control);
        }

        object->ref_count--;
#if     TASK_SWAPPER
        assert(object->res_count == 0);
#endif  /* TASK_SWAPPER */

        assert(object->ref_count == 0);

        /*
         * remove from purgeable queue if it's on
         */
        if (object->internal) {
                assert(VM_OBJECT_OWNER(object) == TASK_NULL);

                VM_OBJECT_UNWIRED(object);

                if (object->purgable == VM_PURGABLE_DENY) {
                        /* not purgeable: nothing to do */
                } else if (object->purgable == VM_PURGABLE_VOLATILE) {
                        purgeable_q_t queue;

                        queue = vm_purgeable_object_remove(object);
                        assert(queue);

                        if (object->purgeable_when_ripe) {
                                /*
                                 * Must take page lock for this -
                                 * using it to protect token queue
                                 */
                                vm_page_lock_queues();
                                vm_purgeable_token_delete_first(queue);

                                assert(queue->debug_count_objects >= 0);
                                vm_page_unlock_queues();
                        }

                        /*
                         * Update "vm_page_purgeable_count" in bulk and mark
                         * object as VM_PURGABLE_EMPTY to avoid updating
                         * "vm_page_purgeable_count" again in vm_page_remove()
                         * when reaping the pages.
                         */
                        unsigned int delta;
                        assert(object->resident_page_count >=
                            object->wired_page_count);
                        delta = (object->resident_page_count -
                            object->wired_page_count);
                        if (delta != 0) {
                                assert(vm_page_purgeable_count >= delta);
                                OSAddAtomic(-delta,
                                    (SInt32 *)&vm_page_purgeable_count);
                        }
                        if (object->wired_page_count != 0) {
                                assert(vm_page_purgeable_wired_count >=
                                    object->wired_page_count);
                                OSAddAtomic(-object->wired_page_count,
                                    (SInt32 *)&vm_page_purgeable_wired_count);
                        }
                        object->purgable = VM_PURGABLE_EMPTY;
                } else if (object->purgable == VM_PURGABLE_NONVOLATILE ||
                    object->purgable == VM_PURGABLE_EMPTY) {
                        /* remove from nonvolatile queue */
                        vm_purgeable_nonvolatile_dequeue(object);
                } else {
                        panic("object %p in unexpected purgeable state 0x%x\n",
                            object, object->purgable);
                }
                if (object->transposed &&
                    object->cached_list.next != NULL &&
                    object->cached_list.prev == NULL) {
                        /*
                         * object->cached_list.next "points" to the
                         * object that was transposed with this object.
                         */
                } else {
                        assert(object->cached_list.next == NULL);
                }
                assert(object->cached_list.prev == NULL);
        }

        if (object->pageout) {
                /*
                 * free all remaining pages tabled on
                 * this object
                 * clean up it's shadow
                 */
                assert(object->shadow != VM_OBJECT_NULL);

                vm_pageout_object_terminate(object);
        } else if (object->resident_page_count) {
                /*
                 * free all remaining pages tabled on
                 * this object
                 */
                vm_object_reap_pages(object, REAP_REAP);
        }
        assert(vm_page_queue_empty(&object->memq));
        assert(object->paging_in_progress == 0);
        assert(object->activity_in_progress == 0);
        assert(object->ref_count == 0);

        /*
         * If the pager has not already been released by
         * vm_object_destroy, we need to terminate it and
         * release our reference to it here.
         */
        if (pager != MEMORY_OBJECT_NULL) {
                vm_object_unlock(object);
                vm_object_release_pager(pager);
                vm_object_lock(object);
        }

        /* kick off anyone waiting on terminating */
        object->terminating = FALSE;
        vm_object_paging_begin(object);
        vm_object_paging_end(object);
        vm_object_unlock(object);

        object->shadow = VM_OBJECT_NULL;

#if VM_OBJECT_TRACKING
        if (vm_object_tracking_inited) {
                btlog_remove_entries_for_element(vm_object_tracking_btlog,
                    object);
        }
#endif /* VM_OBJECT_TRACKING */

        vm_object_lock_destroy(object);
        /*
         *      Free the space for the object.
         */
        zfree(vm_object_zone, object);
        object = VM_OBJECT_NULL;
}


unsigned int vm_max_batch = 256;

#define V_O_R_MAX_BATCH 128

#define BATCH_LIMIT(max)        (vm_max_batch >= max ? max : vm_max_batch)


#define VM_OBJ_REAP_FREELIST(_local_free_q, do_disconnect)              \
        MACRO_BEGIN                                                     \
        if (_local_free_q) {                                            \
                if (do_disconnect) {                                    \
                        vm_page_t m;                                    \
                        for (m = _local_free_q;                         \
                             m != VM_PAGE_NULL;                         \
                             m = m->vmp_snext) {                        \
                                if (m->vmp_pmapped) {                   \
                                        pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(m)); \
                                }                                       \
                        }                                               \
                }                                                       \
                vm_page_free_list(_local_free_q, TRUE);                 \
                _local_free_q = VM_PAGE_NULL;                           \
        }                                                               \
        MACRO_END


void
vm_object_reap_pages(
        vm_object_t     object,
        int             reap_type)
{
        vm_page_t       p;
        vm_page_t       next;
        vm_page_t       local_free_q = VM_PAGE_NULL;
        int             loop_count;
        boolean_t       disconnect_on_release;
        pmap_flush_context      pmap_flush_context_storage;

        if (reap_type == REAP_DATA_FLUSH) {
                /*
                 * We need to disconnect pages from all pmaps before
                 * releasing them to the free list
                 */
                disconnect_on_release = TRUE;
        } else {
                /*
                 * Either the caller has already disconnected the pages
                 * from all pmaps, or we disconnect them here as we add
                 * them to out local list of pages to be released.
                 * No need to re-disconnect them when we release the pages
                 * to the free list.
                 */
                disconnect_on_release = FALSE;
        }

restart_after_sleep:
        if (vm_page_queue_empty(&object->memq)) {
                return;
        }
        loop_count = BATCH_LIMIT(V_O_R_MAX_BATCH);

        if (reap_type == REAP_PURGEABLE) {
                pmap_flush_context_init(&pmap_flush_context_storage);
        }

        vm_page_lockspin_queues();

        next = (vm_page_t)vm_page_queue_first(&object->memq);

        while (!vm_page_queue_end(&object->memq, (vm_page_queue_entry_t)next)) {
                p = next;
                next = (vm_page_t)vm_page_queue_next(&next->vmp_listq);

                if (--loop_count == 0) {
                        vm_page_unlock_queues();

                        if (local_free_q) {
                                if (reap_type == REAP_PURGEABLE) {
                                        pmap_flush(&pmap_flush_context_storage);
                                        pmap_flush_context_init(&pmap_flush_context_storage);
                                }
                                /*
                                 * Free the pages we reclaimed so far
                                 * and take a little break to avoid
                                 * hogging the page queue lock too long
                                 */
                                VM_OBJ_REAP_FREELIST(local_free_q,
                                    disconnect_on_release);
                        } else {
                                mutex_pause(0);
                        }

                        loop_count = BATCH_LIMIT(V_O_R_MAX_BATCH);

                        vm_page_lockspin_queues();
                }
                if (reap_type == REAP_DATA_FLUSH || reap_type == REAP_TERMINATE) {
                        if (p->vmp_busy || p->vmp_cleaning) {
                                vm_page_unlock_queues();
                                /*
                                 * free the pages reclaimed so far
                                 */
                                VM_OBJ_REAP_FREELIST(local_free_q,
                                    disconnect_on_release);

                                PAGE_SLEEP(object, p, THREAD_UNINT);

                                goto restart_after_sleep;
                        }
                        if (p->vmp_laundry) {
                                vm_pageout_steal_laundry(p, TRUE);
                        }
                }
                switch (reap_type) {
                case REAP_DATA_FLUSH:
                        if (VM_PAGE_WIRED(p)) {
                                /*
                                 * this is an odd case... perhaps we should
                                 * zero-fill this page since we're conceptually
                                 * tossing its data at this point, but leaving
                                 * it on the object to honor the 'wire' contract
                                 */
                                continue;
                        }
                        break;

                case REAP_PURGEABLE:
                        if (VM_PAGE_WIRED(p)) {
                                /*
                                 * can't purge a wired page
                                 */
                                vm_page_purged_wired++;
                                continue;
                        }
                        if (p->vmp_laundry && !p->vmp_busy && !p->vmp_cleaning) {
                                vm_pageout_steal_laundry(p, TRUE);
                        }

                        if (p->vmp_cleaning || p->vmp_laundry || p->vmp_absent) {
                                /*
                                 * page is being acted upon,
                                 * so don't mess with it
                                 */
                                vm_page_purged_others++;
                                continue;
                        }
                        if (p->vmp_busy) {
                                /*
                                 * We can't reclaim a busy page but we can
                                 * make it more likely to be paged (it's not wired) to make
                                 * sure that it gets considered by
                                 * vm_pageout_scan() later.
                                 */
                                if (VM_PAGE_PAGEABLE(p)) {
                                        vm_page_deactivate(p);
                                }
                                vm_page_purged_busy++;
                                continue;
                        }

                        assert(VM_PAGE_OBJECT(p) != kernel_object);

                        /*
                         * we can discard this page...
                         */
                        if (p->vmp_pmapped == TRUE) {
                                /*
                                 * unmap the page
                                 */
                                pmap_disconnect_options(VM_PAGE_GET_PHYS_PAGE(p), PMAP_OPTIONS_NOFLUSH | PMAP_OPTIONS_NOREFMOD, (void *)&pmap_flush_context_storage);
                        }
                        vm_page_purged_count++;

                        break;

                case REAP_TERMINATE:
                        if (p->vmp_absent || p->vmp_private) {
                                /*
                                 *      For private pages, VM_PAGE_FREE just
                                 *      leaves the page structure around for
                                 *      its owner to clean up.  For absent
                                 *      pages, the structure is returned to
                                 *      the appropriate pool.
                                 */
                                break;
                        }
                        if (p->vmp_fictitious) {
                                assert(VM_PAGE_GET_PHYS_PAGE(p) == vm_page_guard_addr);
                                break;
                        }
                        if (!p->vmp_dirty && p->vmp_wpmapped) {
                                p->vmp_dirty = pmap_is_modified(VM_PAGE_GET_PHYS_PAGE(p));
                        }

                        if ((p->vmp_dirty || p->vmp_precious) && !p->vmp_error && object->alive) {
                                assert(!object->internal);

                                p->vmp_free_when_done = TRUE;

                                if (!p->vmp_laundry) {
                                        vm_page_queues_remove(p, TRUE);
                                        /*
                                         * flush page... page will be freed
                                         * upon completion of I/O
                                         */
                                        vm_pageout_cluster(p);
                                }
                                vm_page_unlock_queues();
                                /*
                                 * free the pages reclaimed so far
                                 */
                                VM_OBJ_REAP_FREELIST(local_free_q,
                                    disconnect_on_release);

                                vm_object_paging_wait(object, THREAD_UNINT);

                                goto restart_after_sleep;
                        }
                        break;

                case REAP_REAP:
                        break;
                }
                vm_page_free_prepare_queues(p);
                assert(p->vmp_pageq.next == 0 && p->vmp_pageq.prev == 0);
                /*
                 * Add this page to our list of reclaimed pages,
                 * to be freed later.
                 */
                p->vmp_snext = local_free_q;
                local_free_q = p;
        }
        vm_page_unlock_queues();

        /*
         * Free the remaining reclaimed pages
         */
        if (reap_type == REAP_PURGEABLE) {
                pmap_flush(&pmap_flush_context_storage);
        }

        VM_OBJ_REAP_FREELIST(local_free_q,
            disconnect_on_release);
}


void
vm_object_reap_async(
        vm_object_t     object)
{
        vm_object_lock_assert_exclusive(object);

        vm_object_reaper_lock_spin();

        vm_object_reap_count_async++;

        /* enqueue the VM object... */
        queue_enter(&vm_object_reaper_queue, object,
            vm_object_t, cached_list);

        vm_object_reaper_unlock();

        /* ... and wake up the reaper thread */
        thread_wakeup((event_t) &vm_object_reaper_queue);
}


void
vm_object_reaper_thread(void)
{
        vm_object_t     object, shadow_object;

        vm_object_reaper_lock_spin();

        while (!queue_empty(&vm_object_reaper_queue)) {
                queue_remove_first(&vm_object_reaper_queue,
                    object,
                    vm_object_t,
                    cached_list);

                vm_object_reaper_unlock();
                vm_object_lock(object);

                assert(object->terminating);
                assert(!object->alive);

                /*
                 * The pageout daemon might be playing with our pages.
                 * Now that the object is dead, it won't touch any more
                 * pages, but some pages might already be on their way out.
                 * Hence, we wait until the active paging activities have
                 * ceased before we break the association with the pager
                 * itself.
                 */
                while (object->paging_in_progress != 0 ||
                    object->activity_in_progress != 0) {
                        vm_object_wait(object,
                            VM_OBJECT_EVENT_PAGING_IN_PROGRESS,
                            THREAD_UNINT);
                        vm_object_lock(object);
                }

                shadow_object =
                    object->pageout ? VM_OBJECT_NULL : object->shadow;

                vm_object_reap(object);
                /* cache is unlocked and object is no longer valid */
                object = VM_OBJECT_NULL;

                if (shadow_object != VM_OBJECT_NULL) {
                        /*
                         * Drop the reference "object" was holding on
                         * its shadow object.
                         */
                        vm_object_deallocate(shadow_object);
                        shadow_object = VM_OBJECT_NULL;
                }
                vm_object_reaper_lock_spin();
        }

        /* wait for more work... */
        assert_wait((event_t) &vm_object_reaper_queue, THREAD_UNINT);

        vm_object_reaper_unlock();

        thread_block((thread_continue_t) vm_object_reaper_thread);
        /*NOTREACHED*/
}

/*
 *      Routine:        vm_object_release_pager
 *      Purpose:        Terminate the pager and, upon completion,
 *                      release our last reference to it.
 */
static void
vm_object_release_pager(
        memory_object_t pager)
{
        /*
         *      Terminate the pager.
         */

        (void) memory_object_terminate(pager);

        /*
         *      Release reference to pager.
         */
        memory_object_deallocate(pager);
}

/*
 *      Routine:        vm_object_destroy
 *      Purpose:
 *              Shut down a VM object, despite the
 *              presence of address map (or other) references
 *              to the vm_object.
 */
kern_return_t
vm_object_destroy(
        vm_object_t             object,
        __unused kern_return_t          reason)
{
        memory_object_t         old_pager;

        if (object == VM_OBJECT_NULL) {
                return KERN_SUCCESS;
        }

        /*
         *      Remove the pager association immediately.
         *
         *      This will prevent the memory manager from further
         *      meddling.  [If it wanted to flush data or make
         *      other changes, it should have done so before performing
         *      the destroy call.]
         */

        vm_object_lock(object);
        object->can_persist = FALSE;
        object->named = FALSE;
        object->alive = FALSE;

        old_pager = object->pager;
        object->pager = MEMORY_OBJECT_NULL;
        if (old_pager != MEMORY_OBJECT_NULL) {
                memory_object_control_disable(object->pager_control);
        }

        /*
         * Wait for the existing paging activity (that got
         * through before we nulled out the pager) to subside.
         */

        vm_object_paging_wait(object, THREAD_UNINT);
        vm_object_unlock(object);

        /*
         *      Terminate the object now.
         */
        if (old_pager != MEMORY_OBJECT_NULL) {
                vm_object_release_pager(old_pager);

                /*
                 * JMM - Release the caller's reference.  This assumes the
                 * caller had a reference to release, which is a big (but
                 * currently valid) assumption if this is driven from the
                 * vnode pager (it is holding a named reference when making
                 * this call)..
                 */
                vm_object_deallocate(object);
        }
        return KERN_SUCCESS;
}

/*
 * The "chunk" macros are used by routines below when looking for pages to deactivate.  These
 * exist because of the need to handle shadow chains.  When deactivating pages, we only
 * want to deactive the ones at the top most level in the object chain.  In order to do
 * this efficiently, the specified address range is divided up into "chunks" and we use
 * a bit map to keep track of which pages have already been processed as we descend down
 * the shadow chain.  These chunk macros hide the details of the bit map implementation
 * as much as we can.
 *
 * For convenience, we use a 64-bit data type as the bit map, and therefore a chunk is
 * set to 64 pages.  The bit map is indexed from the low-order end, so that the lowest
 * order bit represents page 0 in the current range and highest order bit represents
 * page 63.
 *
 * For further convenience, we also use negative logic for the page state in the bit map.
 * The bit is set to 1 to indicate it has not yet been seen, and to 0 to indicate it has
 * been processed.  This way we can simply test the 64-bit long word to see if it's zero
 * to easily tell if the whole range has been processed.  Therefore, the bit map starts
 * out with all the bits set.  The macros below hide all these details from the caller.
 */

#define PAGES_IN_A_CHUNK        64      /* The number of pages in the chunk must */
                                        /* be the same as the number of bits in  */
                                        /* the chunk_state_t type. We use 64     */
                                        /* just for convenience.                 */

#define CHUNK_SIZE      (PAGES_IN_A_CHUNK * PAGE_SIZE_64)       /* Size of a chunk in bytes */

typedef uint64_t        chunk_state_t;

/*
 * The bit map uses negative logic, so we start out with all 64 bits set to indicate
 * that no pages have been processed yet.  Also, if len is less than the full CHUNK_SIZE,
 * then we mark pages beyond the len as having been "processed" so that we don't waste time
 * looking at pages in that range.  This can save us from unnecessarily chasing down the
 * shadow chain.
 */

#define CHUNK_INIT(c, len)                                              \
        MACRO_BEGIN                                                     \
        uint64_t p;                                                     \
                                                                        \
        (c) = 0xffffffffffffffffLL;                                     \
                                                                        \
        for (p = (len) / PAGE_SIZE_64; p < PAGES_IN_A_CHUNK; p++)       \
                MARK_PAGE_HANDLED(c, p);                                \
        MACRO_END


/*
 * Return true if all pages in the chunk have not yet been processed.
 */

#define CHUNK_NOT_COMPLETE(c)   ((c) != 0)

/*
 * Return true if the page at offset 'p' in the bit map has already been handled
 * while processing a higher level object in the shadow chain.
 */

#define PAGE_ALREADY_HANDLED(c, p)      (((c) & (1ULL << (p))) == 0)

/*
 * Mark the page at offset 'p' in the bit map as having been processed.
 */

#define MARK_PAGE_HANDLED(c, p) \
MACRO_BEGIN \
        (c) = (c) & ~(1ULL << (p)); \
MACRO_END


/*
 * Return true if the page at the given offset has been paged out.  Object is
 * locked upon entry and returned locked.
 */

static boolean_t
page_is_paged_out(
        vm_object_t             object,
        vm_object_offset_t      offset)
{
        if (object->internal &&
            object->alive &&
            !object->terminating &&
            object->pager_ready) {
                if (VM_COMPRESSOR_PAGER_STATE_GET(object, offset)
                    == VM_EXTERNAL_STATE_EXISTS) {
                        return TRUE;
                }
        }
        return FALSE;
}



/*
 * madvise_free_debug
 *
 * To help debug madvise(MADV_FREE*) mis-usage, this triggers a
 * zero-fill as soon as a page is affected by a madvise(MADV_FREE*), to
 * simulate the loss of the page's contents as if the page had been
 * reclaimed and then re-faulted.
 */
#if DEVELOPMENT || DEBUG
int madvise_free_debug = 1;
#else /* DEBUG */
int madvise_free_debug = 0;
#endif /* DEBUG */

/*
 * Deactivate the pages in the specified object and range.  If kill_page is set, also discard any
 * page modified state from the pmap.  Update the chunk_state as we go along.  The caller must specify
 * a size that is less than or equal to the CHUNK_SIZE.
 */

static void
deactivate_pages_in_object(
        vm_object_t             object,
        vm_object_offset_t      offset,
        vm_object_size_t        size,
        boolean_t               kill_page,
        boolean_t               reusable_page,
        boolean_t               all_reusable,
        chunk_state_t           *chunk_state,
        pmap_flush_context      *pfc,
        struct pmap             *pmap,
        vm_map_offset_t         pmap_offset)
{
        vm_page_t       m;
        int             p;
        struct vm_page_delayed_work     dw_array[DEFAULT_DELAYED_WORK_LIMIT];
        struct vm_page_delayed_work     *dwp;
        int             dw_count;
        int             dw_limit;
        unsigned int    reusable = 0;

        /*
         * Examine each page in the chunk.  The variable 'p' is the page number relative to the start of the
         * chunk.  Since this routine is called once for each level in the shadow chain, the chunk_state may
         * have pages marked as having been processed already.  We stop the loop early if we find we've handled
         * all the pages in the chunk.
         */

        dwp = &dw_array[0];
        dw_count = 0;
        dw_limit = DELAYED_WORK_LIMIT(DEFAULT_DELAYED_WORK_LIMIT);

        for (p = 0; size && CHUNK_NOT_COMPLETE(*chunk_state); p++, size -= PAGE_SIZE_64, offset += PAGE_SIZE_64, pmap_offset += PAGE_SIZE_64) {
                /*
                 * If this offset has already been found and handled in a higher level object, then don't
                 * do anything with it in the current shadow object.
                 */

                if (PAGE_ALREADY_HANDLED(*chunk_state, p)) {
                        continue;
                }

                /*
                 * See if the page at this offset is around.  First check to see if the page is resident,
                 * then if not, check the existence map or with the pager.
                 */

                if ((m = vm_page_lookup(object, offset)) != VM_PAGE_NULL) {
                        /*
                         * We found a page we were looking for.  Mark it as "handled" now in the chunk_state
                         * so that we won't bother looking for a page at this offset again if there are more
                         * shadow objects.  Then deactivate the page.
                         */

                        MARK_PAGE_HANDLED(*chunk_state, p);

                        if ((!VM_PAGE_WIRED(m)) && (!m->vmp_private) && (!m->vmp_gobbled) && (!m->vmp_busy) &&
                            (!m->vmp_laundry) && (!m->vmp_cleaning) && !(m->vmp_free_when_done)) {
                                int     clear_refmod;
                                int     pmap_options;

                                dwp->dw_mask = 0;

                                pmap_options = 0;
                                clear_refmod = VM_MEM_REFERENCED;
                                dwp->dw_mask |= DW_clear_reference;

                                if ((kill_page) && (object->internal)) {
                                        if (madvise_free_debug) {
                                                /*
                                                 * zero-fill the page now
                                                 * to simulate it being
                                                 * reclaimed and re-faulted.
                                                 */
                                                pmap_zero_page(VM_PAGE_GET_PHYS_PAGE(m));
                                        }
                                        m->vmp_precious = FALSE;
                                        m->vmp_dirty = FALSE;

                                        clear_refmod |= VM_MEM_MODIFIED;
                                        if (m->vmp_q_state == VM_PAGE_ON_THROTTLED_Q) {
                                                /*
                                                 * This page is now clean and
                                                 * reclaimable.  Move it out
                                                 * of the throttled queue, so
                                                 * that vm_pageout_scan() can
                                                 * find it.
                                                 */
                                                dwp->dw_mask |= DW_move_page;
                                        }

                                        VM_COMPRESSOR_PAGER_STATE_CLR(object, offset);

                                        if (reusable_page && !m->vmp_reusable) {
                                                assert(!all_reusable);
                                                assert(!object->all_reusable);
                                                m->vmp_reusable = TRUE;
                                                object->reusable_page_count++;
                                                assert(object->resident_page_count >= object->reusable_page_count);
                                                reusable++;
                                                /*
                                                 * Tell pmap this page is now
                                                 * "reusable" (to update pmap
                                                 * stats for all mappings).
                                                 */
                                                pmap_options |= PMAP_OPTIONS_SET_REUSABLE;
                                        }
                                }
                                pmap_options |= PMAP_OPTIONS_NOFLUSH;
                                pmap_clear_refmod_options(VM_PAGE_GET_PHYS_PAGE(m),
                                    clear_refmod,
                                    pmap_options,
                                    (void *)pfc);

                                if ((m->vmp_q_state != VM_PAGE_ON_THROTTLED_Q) && !(reusable_page || all_reusable)) {
                                        dwp->dw_mask |= DW_move_page;
                                }

                                if (dwp->dw_mask) {
                                        VM_PAGE_ADD_DELAYED_WORK(dwp, m,
                                            dw_count);
                                }

                                if (dw_count >= dw_limit) {
                                        if (reusable) {
                                                OSAddAtomic(reusable,
                                                    &vm_page_stats_reusable.reusable_count);
                                                vm_page_stats_reusable.reusable += reusable;
                                                reusable = 0;
                                        }
                                        vm_page_do_delayed_work(object, VM_KERN_MEMORY_NONE, &dw_array[0], dw_count);

                                        dwp = &dw_array[0];
                                        dw_count = 0;
                                }
                        }
                } else {
                        /*
                         * The page at this offset isn't memory resident, check to see if it's
                         * been paged out.  If so, mark it as handled so we don't bother looking
                         * for it in the shadow chain.
                         */

                        if (page_is_paged_out(object, offset)) {
                                MARK_PAGE_HANDLED(*chunk_state, p);

                                /*
                                 * If we're killing a non-resident page, then clear the page in the existence
                                 * map so we don't bother paging it back in if it's touched again in the future.
                                 */

                                if ((kill_page) && (object->internal)) {
                                        VM_COMPRESSOR_PAGER_STATE_CLR(object, offset);

                                        if (pmap != PMAP_NULL) {
                                                /*
                                                 * Tell pmap that this page
                                                 * is no longer mapped, to
                                                 * adjust the footprint ledger
                                                 * because this page is no
                                                 * longer compressed.
                                                 */
                                                pmap_remove_options(
                                                        pmap,
                                                        pmap_offset,
                                                        (pmap_offset +
                                                        PAGE_SIZE),
                                                        PMAP_OPTIONS_REMOVE);
                                        }
                                }
                        }
                }
        }

        if (reusable) {
                OSAddAtomic(reusable, &vm_page_stats_reusable.reusable_count);
                vm_page_stats_reusable.reusable += reusable;
                reusable = 0;
        }

        if (dw_count) {
                vm_page_do_delayed_work(object, VM_KERN_MEMORY_NONE, &dw_array[0], dw_count);
        }
}


/*
 * Deactive a "chunk" of the given range of the object starting at offset.  A "chunk"
 * will always be less than or equal to the given size.  The total range is divided up
 * into chunks for efficiency and performance related to the locks and handling the shadow
 * chain.  This routine returns how much of the given "size" it actually processed.  It's
 * up to the caler to loop and keep calling this routine until the entire range they want
 * to process has been done.
 */

static vm_object_size_t
deactivate_a_chunk(
        vm_object_t             orig_object,
        vm_object_offset_t      offset,
        vm_object_size_t        size,
        boolean_t               kill_page,
        boolean_t               reusable_page,
        boolean_t               all_reusable,
        pmap_flush_context      *pfc,
        struct pmap             *pmap,
        vm_map_offset_t         pmap_offset)
{
        vm_object_t             object;
        vm_object_t             tmp_object;
        vm_object_size_t        length;
        chunk_state_t           chunk_state;


        /*
         * Get set to do a chunk.  We'll do up to CHUNK_SIZE, but no more than the
         * remaining size the caller asked for.
         */

        length = MIN(size, CHUNK_SIZE);

        /*
         * The chunk_state keeps track of which pages we've already processed if there's
         * a shadow chain on this object.  At this point, we haven't done anything with this
         * range of pages yet, so initialize the state to indicate no pages processed yet.
         */

        CHUNK_INIT(chunk_state, length);
        object = orig_object;

        /*
         * Start at the top level object and iterate around the loop once for each object
         * in the shadow chain.  We stop processing early if we've already found all the pages
         * in the range.  Otherwise we stop when we run out of shadow objects.
         */

        while (object && CHUNK_NOT_COMPLETE(chunk_state)) {
                vm_object_paging_begin(object);

                deactivate_pages_in_object(object, offset, length, kill_page, reusable_page, all_reusable, &chunk_state, pfc, pmap, pmap_offset);

                vm_object_paging_end(object);

                /*
                 * We've finished with this object, see if there's a shadow object.  If
                 * there is, update the offset and lock the new object.  We also turn off
                 * kill_page at this point since we only kill pages in the top most object.
                 */

                tmp_object = object->shadow;

                if (tmp_object) {
                        kill_page = FALSE;
                        reusable_page = FALSE;
                        all_reusable = FALSE;
                        offset += object->vo_shadow_offset;
                        vm_object_lock(tmp_object);
                }

                if (object != orig_object) {
                        vm_object_unlock(object);
                }

                object = tmp_object;
        }

        if (object && object != orig_object) {
                vm_object_unlock(object);
        }

        return length;
}



/*
 * Move any resident pages in the specified range to the inactive queue.  If kill_page is set,
 * we also clear the modified status of the page and "forget" any changes that have been made
 * to the page.
 */

__private_extern__ void
vm_object_deactivate_pages(
        vm_object_t             object,
        vm_object_offset_t      offset,
        vm_object_size_t        size,
        boolean_t               kill_page,
        boolean_t               reusable_page,
        struct pmap             *pmap,
        vm_map_offset_t         pmap_offset)
{
        vm_object_size_t        length;
        boolean_t               all_reusable;
        pmap_flush_context      pmap_flush_context_storage;

        /*
         * We break the range up into chunks and do one chunk at a time.  This is for
         * efficiency and performance while handling the shadow chains and the locks.
         * The deactivate_a_chunk() function returns how much of the range it processed.
         * We keep calling this routine until the given size is exhausted.
         */


        all_reusable = FALSE;
#if 11
        /*
         * For the sake of accurate "reusable" pmap stats, we need
         * to tell pmap about each page that is no longer "reusable",
         * so we can't do the "all_reusable" optimization.
         */
#else
        if (reusable_page &&
            object->internal &&
            object->vo_size != 0 &&
            object->vo_size == size &&
            object->reusable_page_count == 0) {
                all_reusable = TRUE;
                reusable_page = FALSE;
        }
#endif

        if ((reusable_page || all_reusable) && object->all_reusable) {
                /* This means MADV_FREE_REUSABLE has been called twice, which
                 * is probably illegal. */
                return;
        }

        pmap_flush_context_init(&pmap_flush_context_storage);

        while (size) {
                length = deactivate_a_chunk(object, offset, size, kill_page, reusable_page, all_reusable, &pmap_flush_context_storage, pmap, pmap_offset);

                size -= length;
                offset += length;
                pmap_offset += length;
        }
        pmap_flush(&pmap_flush_context_storage);

        if (all_reusable) {
                if (!object->all_reusable) {
                        unsigned int reusable;

                        object->all_reusable = TRUE;
                        assert(object->reusable_page_count == 0);
                        /* update global stats */
                        reusable = object->resident_page_count;
                        OSAddAtomic(reusable,
                            &vm_page_stats_reusable.reusable_count);
                        vm_page_stats_reusable.reusable += reusable;
                        vm_page_stats_reusable.all_reusable_calls++;
                }
        } else if (reusable_page) {
                vm_page_stats_reusable.partial_reusable_calls++;
        }
}

void
vm_object_reuse_pages(
        vm_object_t             object,
        vm_object_offset_t      start_offset,
        vm_object_offset_t      end_offset,
        boolean_t               allow_partial_reuse)
{
        vm_object_offset_t      cur_offset;
        vm_page_t               m;
        unsigned int            reused, reusable;

#define VM_OBJECT_REUSE_PAGE(object, m, reused)                         \
        MACRO_BEGIN                                                     \
                if ((m) != VM_PAGE_NULL &&                              \
                    (m)->vmp_reusable) {                                \
                        assert((object)->reusable_page_count <=         \
                               (object)->resident_page_count);          \
                        assert((object)->reusable_page_count > 0);      \
                        (object)->reusable_page_count--;                \
                        (m)->vmp_reusable = FALSE;                      \
                        (reused)++;                                     \
        /* \
         * Tell pmap that this page is no longer \
         * "reusable", to update the "reusable" stats \
         * for all the pmaps that have mapped this \
         * page. \
         */                                                             \
                        pmap_clear_refmod_options(VM_PAGE_GET_PHYS_PAGE((m)), \
                                                  0, /* refmod */       \
                                                  (PMAP_OPTIONS_CLEAR_REUSABLE \
                                                   | PMAP_OPTIONS_NOFLUSH), \
                                                  NULL);                \
                }                                                       \
        MACRO_END

        reused = 0;
        reusable = 0;

        vm_object_lock_assert_exclusive(object);

        if (object->all_reusable) {
                panic("object %p all_reusable: can't update pmap stats\n",
                    object);
                assert(object->reusable_page_count == 0);
                object->all_reusable = FALSE;
                if (end_offset - start_offset == object->vo_size ||
                    !allow_partial_reuse) {
                        vm_page_stats_reusable.all_reuse_calls++;
                        reused = object->resident_page_count;
                } else {
                        vm_page_stats_reusable.partial_reuse_calls++;
                        vm_page_queue_iterate(&object->memq, m, vmp_listq) {
                                if (m->vmp_offset < start_offset ||
                                    m->vmp_offset >= end_offset) {
                                        m->vmp_reusable = TRUE;
                                        object->reusable_page_count++;
                                        assert(object->resident_page_count >= object->reusable_page_count);
                                        continue;
                                } else {
                                        assert(!m->vmp_reusable);
                                        reused++;
                                }
                        }
                }
        } else if (object->resident_page_count >
            ((end_offset - start_offset) >> PAGE_SHIFT)) {
                vm_page_stats_reusable.partial_reuse_calls++;
                for (cur_offset = start_offset;
                    cur_offset < end_offset;
                    cur_offset += PAGE_SIZE_64) {
                        if (object->reusable_page_count == 0) {
                                break;
                        }
                        m = vm_page_lookup(object, cur_offset);
                        VM_OBJECT_REUSE_PAGE(object, m, reused);
                }
        } else {
                vm_page_stats_reusable.partial_reuse_calls++;
                vm_page_queue_iterate(&object->memq, m, vmp_listq) {
                        if (object->reusable_page_count == 0) {
                                break;
                        }
                        if (m->vmp_offset < start_offset ||
                            m->vmp_offset >= end_offset) {
                                continue;
                        }
                        VM_OBJECT_REUSE_PAGE(object, m, reused);
                }
        }

        /* update global stats */
        OSAddAtomic(reusable - reused, &vm_page_stats_reusable.reusable_count);
        vm_page_stats_reusable.reused += reused;
        vm_page_stats_reusable.reusable += reusable;
}

/*
 *      Routine:        vm_object_pmap_protect
 *
 *      Purpose:
 *              Reduces the permission for all physical
 *              pages in the specified object range.
 *
 *              If removing write permission only, it is
 *              sufficient to protect only the pages in
 *              the top-level object; only those pages may
 *              have write permission.
 *
 *              If removing all access, we must follow the
 *              shadow chain from the top-level object to
 *              remove access to all pages in shadowed objects.
 *
 *              The object must *not* be locked.  The object must
 *              be internal.
 *
 *              If pmap is not NULL, this routine assumes that
 *              the only mappings for the pages are in that
 *              pmap.
 */

__private_extern__ void
vm_object_pmap_protect(
        vm_object_t                     object,
        vm_object_offset_t              offset,
        vm_object_size_t                size,
        pmap_t                          pmap,
        vm_map_offset_t                 pmap_start,
        vm_prot_t                       prot)
{
        vm_object_pmap_protect_options(object, offset, size,
            pmap, pmap_start, prot, 0);
}

__private_extern__ void
vm_object_pmap_protect_options(
        vm_object_t                     object,
        vm_object_offset_t              offset,
        vm_object_size_t                size,
        pmap_t                          pmap,
        vm_map_offset_t                 pmap_start,
        vm_prot_t                       prot,
        int                             options)
{
        pmap_flush_context      pmap_flush_context_storage;
        boolean_t               delayed_pmap_flush = FALSE;

        if (object == VM_OBJECT_NULL) {
                return;
        }
        size = vm_object_round_page(size);
        offset = vm_object_trunc_page(offset);

        vm_object_lock(object);

        if (object->phys_contiguous) {
                if (pmap != NULL) {
                        vm_object_unlock(object);
                        pmap_protect_options(pmap,
                            pmap_start,
                            pmap_start + size,
                            prot,
                            options & ~PMAP_OPTIONS_NOFLUSH,
                            NULL);
                } else {
                        vm_object_offset_t phys_start, phys_end, phys_addr;

                        phys_start = object->vo_shadow_offset + offset;
                        phys_end = phys_start + size;
                        assert(phys_start <= phys_end);
                        assert(phys_end <= object->vo_shadow_offset + object->vo_size);
                        vm_object_unlock(object);

                        pmap_flush_context_init(&pmap_flush_context_storage);
                        delayed_pmap_flush = FALSE;

                        for (phys_addr = phys_start;
                            phys_addr < phys_end;
                            phys_addr += PAGE_SIZE_64) {
                                pmap_page_protect_options(
                                        (ppnum_t) (phys_addr >> PAGE_SHIFT),
                                        prot,
                                        options | PMAP_OPTIONS_NOFLUSH,
                                        (void *)&pmap_flush_context_storage);
                                delayed_pmap_flush = TRUE;
                        }
                        if (delayed_pmap_flush == TRUE) {
                                pmap_flush(&pmap_flush_context_storage);
                        }
                }
                return;
        }

        assert(object->internal);

        while (TRUE) {
                if (ptoa_64(object->resident_page_count) > size / 2 && pmap != PMAP_NULL) {
                        vm_object_unlock(object);
                        pmap_protect_options(pmap, pmap_start, pmap_start + size, prot,
                            options & ~PMAP_OPTIONS_NOFLUSH, NULL);
                        return;
                }

                pmap_flush_context_init(&pmap_flush_context_storage);
                delayed_pmap_flush = FALSE;

                /*
                 * if we are doing large ranges with respect to resident
                 * page count then we should interate over pages otherwise
                 * inverse page look-up will be faster
                 */
                if (ptoa_64(object->resident_page_count / 4) < size) {
                        vm_page_t               p;
                        vm_object_offset_t      end;

                        end = offset + size;

                        vm_page_queue_iterate(&object->memq, p, vmp_listq) {
                                if (!p->vmp_fictitious && (offset <= p->vmp_offset) && (p->vmp_offset < end)) {
                                        vm_map_offset_t start;

                                        start = pmap_start + p->vmp_offset - offset;

                                        if (pmap != PMAP_NULL) {
                                                pmap_protect_options(
                                                        pmap,
                                                        start,
                                                        start + PAGE_SIZE_64,
                                                        prot,
                                                        options | PMAP_OPTIONS_NOFLUSH,
                                                        &pmap_flush_context_storage);
                                        } else {
                                                pmap_page_protect_options(
                                                        VM_PAGE_GET_PHYS_PAGE(p),
                                                        prot,
                                                        options | PMAP_OPTIONS_NOFLUSH,
                                                        &pmap_flush_context_storage);
                                        }
                                        delayed_pmap_flush = TRUE;
                                }
                        }
                } else {
                        vm_page_t               p;
                        vm_object_offset_t      end;
                        vm_object_offset_t      target_off;

                        end = offset + size;

                        for (target_off = offset;
                            target_off < end; target_off += PAGE_SIZE) {
                                p = vm_page_lookup(object, target_off);

                                if (p != VM_PAGE_NULL) {
                                        vm_object_offset_t start;

                                        start = pmap_start + (p->vmp_offset - offset);

                                        if (pmap != PMAP_NULL) {
                                                pmap_protect_options(
                                                        pmap,
                                                        start,
                                                        start + PAGE_SIZE_64,
                                                        prot,
                                                        options | PMAP_OPTIONS_NOFLUSH,
                                                        &pmap_flush_context_storage);
                                        } else {
                                                pmap_page_protect_options(
                                                        VM_PAGE_GET_PHYS_PAGE(p),
                                                        prot,
                                                        options | PMAP_OPTIONS_NOFLUSH,
                                                        &pmap_flush_context_storage);
                                        }
                                        delayed_pmap_flush = TRUE;
                                }
                        }
                }
                if (delayed_pmap_flush == TRUE) {
                        pmap_flush(&pmap_flush_context_storage);
                }

                if (prot == VM_PROT_NONE) {
                        /*
                         * Must follow shadow chain to remove access
                         * to pages in shadowed objects.
                         */
                        vm_object_t     next_object;

                        next_object = object->shadow;
                        if (next_object != VM_OBJECT_NULL) {
                                offset += object->vo_shadow_offset;
                                vm_object_lock(next_object);
                                vm_object_unlock(object);
                                object = next_object;
                        } else {
                                /*
                                 * End of chain - we are done.
                                 */
                                break;
                        }
                } else {
                        /*
                         * Pages in shadowed objects may never have
                         * write permission - we may stop here.
                         */
                        break;
                }
        }

        vm_object_unlock(object);
}

uint32_t vm_page_busy_absent_skipped = 0;

/*
 *      Routine:        vm_object_copy_slowly
 *
 *      Description:
 *              Copy the specified range of the source
 *              virtual memory object without using
 *              protection-based optimizations (such
 *              as copy-on-write).  The pages in the
 *              region are actually copied.
 *
 *      In/out conditions:
 *              The caller must hold a reference and a lock
 *              for the source virtual memory object.  The source
 *              object will be returned *unlocked*.
 *
 *      Results:
 *              If the copy is completed successfully, KERN_SUCCESS is
 *              returned.  If the caller asserted the interruptible
 *              argument, and an interruption occurred while waiting
 *              for a user-generated event, MACH_SEND_INTERRUPTED is
 *              returned.  Other values may be returned to indicate
 *              hard errors during the copy operation.
 *
 *              A new virtual memory object is returned in a
 *              parameter (_result_object).  The contents of this
 *              new object, starting at a zero offset, are a copy
 *              of the source memory region.  In the event of
 *              an error, this parameter will contain the value
 *              VM_OBJECT_NULL.
 */
__private_extern__ kern_return_t
vm_object_copy_slowly(
        vm_object_t             src_object,
        vm_object_offset_t      src_offset,
        vm_object_size_t        size,
        boolean_t               interruptible,
        vm_object_t             *_result_object)        /* OUT */
{
        vm_object_t             new_object;
        vm_object_offset_t      new_offset;

        struct vm_object_fault_info fault_info = {};

        if (size == 0) {
                vm_object_unlock(src_object);
                *_result_object = VM_OBJECT_NULL;
                return KERN_INVALID_ARGUMENT;
        }

        /*
         *      Prevent destruction of the source object while we copy.
         */

        vm_object_reference_locked(src_object);
        vm_object_unlock(src_object);

        /*
         *      Create a new object to hold the copied pages.
         *      A few notes:
         *              We fill the new object starting at offset 0,
         *               regardless of the input offset.
         *              We don't bother to lock the new object within
         *               this routine, since we have the only reference.
         */

        new_object = vm_object_allocate(size);
        new_offset = 0;

        assert(size == trunc_page_64(size));    /* Will the loop terminate? */

        fault_info.interruptible = interruptible;
        fault_info.behavior  = VM_BEHAVIOR_SEQUENTIAL;
        fault_info.lo_offset = src_offset;
        fault_info.hi_offset = src_offset + size;
        fault_info.stealth = TRUE;

        for (;
            size != 0;
            src_offset += PAGE_SIZE_64,
            new_offset += PAGE_SIZE_64, size -= PAGE_SIZE_64
            ) {
                vm_page_t       new_page;
                vm_fault_return_t result;

                vm_object_lock(new_object);

                while ((new_page = vm_page_alloc(new_object, new_offset))
                    == VM_PAGE_NULL) {
                        vm_object_unlock(new_object);

                        if (!vm_page_wait(interruptible)) {
                                vm_object_deallocate(new_object);
                                vm_object_deallocate(src_object);
                                *_result_object = VM_OBJECT_NULL;
                                return MACH_SEND_INTERRUPTED;
                        }
                        vm_object_lock(new_object);
                }
                vm_object_unlock(new_object);

                do {
                        vm_prot_t       prot = VM_PROT_READ;
                        vm_page_t       _result_page;
                        vm_page_t       top_page;
                        vm_page_t       result_page;
                        kern_return_t   error_code;
                        vm_object_t     result_page_object;


                        vm_object_lock(src_object);

                        if (src_object->internal &&
                            src_object->shadow == VM_OBJECT_NULL &&
                            (src_object->pager == NULL ||
                            (VM_COMPRESSOR_PAGER_STATE_GET(src_object,
                            src_offset) ==
                            VM_EXTERNAL_STATE_ABSENT))) {
                                boolean_t can_skip_page;

                                _result_page = vm_page_lookup(src_object,
                                    src_offset);
                                if (_result_page == VM_PAGE_NULL) {
                                        /*
                                         * This page is neither resident nor
                                         * compressed and there's no shadow
                                         * object below "src_object", so this
                                         * page is really missing.
                                         * There's no need to zero-fill it just
                                         * to copy it:  let's leave it missing
                                         * in "new_object" and get zero-filled
                                         * on demand.
                                         */
                                        can_skip_page = TRUE;
                                } else if (workaround_41447923 &&
                                    src_object->pager == NULL &&
                                    _result_page != VM_PAGE_NULL &&
                                    _result_page->vmp_busy &&
                                    _result_page->vmp_absent &&
                                    src_object->purgable == VM_PURGABLE_DENY &&
                                    !src_object->blocked_access) {
                                        /*
                                         * This page is "busy" and "absent"
                                         * but not because we're waiting for
                                         * it to be decompressed.  It must
                                         * be because it's a "no zero fill"
                                         * page that is currently not
                                         * accessible until it gets overwritten
                                         * by a device driver.
                                         * Since its initial state would have
                                         * been "zero-filled", let's leave the
                                         * copy page missing and get zero-filled
                                         * on demand.
                                         */
                                        assert(src_object->internal);
                                        assert(src_object->shadow == NULL);
                                        assert(src_object->pager == NULL);
                                        can_skip_page = TRUE;
                                        vm_page_busy_absent_skipped++;
                                } else {
                                        can_skip_page = FALSE;
                                }
                                if (can_skip_page) {
                                        vm_object_unlock(src_object);
                                        /* free the unused "new_page"... */
                                        vm_object_lock(new_object);
                                        VM_PAGE_FREE(new_page);
                                        new_page = VM_PAGE_NULL;
                                        vm_object_unlock(new_object);
                                        /* ...and go to next page in "src_object" */
                                        result = VM_FAULT_SUCCESS;
                                        break;
                                }
                        }

                        vm_object_paging_begin(src_object);

                        /* cap size at maximum UPL size */
                        upl_size_t cluster_size;
                        if (os_convert_overflow(size, &cluster_size)) {
                                cluster_size = 0 - (upl_size_t)PAGE_SIZE;
                        }
                        fault_info.cluster_size = cluster_size;

                        _result_page = VM_PAGE_NULL;
                        result = vm_fault_page(src_object, src_offset,
                            VM_PROT_READ, FALSE,
                            FALSE,     /* page not looked up */
                            &prot, &_result_page, &top_page,
                            (int *)0,
                            &error_code, FALSE, FALSE, &fault_info);

                        switch (result) {
                        case VM_FAULT_SUCCESS:
                                result_page = _result_page;
                                result_page_object = VM_PAGE_OBJECT(result_page);

                                /*
                                 *      Copy the page to the new object.
                                 *
                                 *      POLICY DECISION:
                                 *              If result_page is clean,
                                 *              we could steal it instead
                                 *              of copying.
                                 */

                                vm_page_copy(result_page, new_page);
                                vm_object_unlock(result_page_object);

                                /*
                                 *      Let go of both pages (make them
                                 *      not busy, perform wakeup, activate).
                                 */
                                vm_object_lock(new_object);
                                SET_PAGE_DIRTY(new_page, FALSE);
                                PAGE_WAKEUP_DONE(new_page);
                                vm_object_unlock(new_object);

                                vm_object_lock(result_page_object);
                                PAGE_WAKEUP_DONE(result_page);

                                vm_page_lockspin_queues();
                                if ((result_page->vmp_q_state == VM_PAGE_ON_SPECULATIVE_Q) ||
                                    (result_page->vmp_q_state == VM_PAGE_NOT_ON_Q)) {
                                        vm_page_activate(result_page);
                                }
                                vm_page_activate(new_page);
                                vm_page_unlock_queues();

                                /*
                                 *      Release paging references and
                                 *      top-level placeholder page, if any.
                                 */

                                vm_fault_cleanup(result_page_object,
                                    top_page);

                                break;

                        case VM_FAULT_RETRY:
                                break;

                        case VM_FAULT_MEMORY_SHORTAGE:
                                if (vm_page_wait(interruptible)) {
                                        break;
                                }
                        /* fall thru */

                        case VM_FAULT_INTERRUPTED:
                                vm_object_lock(new_object);
                                VM_PAGE_FREE(new_page);
                                vm_object_unlock(new_object);

                                vm_object_deallocate(new_object);
                                vm_object_deallocate(src_object);
                                *_result_object = VM_OBJECT_NULL;
                                return MACH_SEND_INTERRUPTED;

                        case VM_FAULT_SUCCESS_NO_VM_PAGE:
                                /* success but no VM page: fail */
                                vm_object_paging_end(src_object);
                                vm_object_unlock(src_object);
                        /*FALLTHROUGH*/
                        case VM_FAULT_MEMORY_ERROR:
                                /*
                                 * A policy choice:
                                 *      (a) ignore pages that we can't
                                 *          copy
                                 *      (b) return the null object if
                                 *          any page fails [chosen]
                                 */

                                vm_object_lock(new_object);
                                VM_PAGE_FREE(new_page);
                                vm_object_unlock(new_object);

                                vm_object_deallocate(new_object);
                                vm_object_deallocate(src_object);
                                *_result_object = VM_OBJECT_NULL;
                                return error_code ? error_code:
                                       KERN_MEMORY_ERROR;

                        default:
                                panic("vm_object_copy_slowly: unexpected error"
                                    " 0x%x from vm_fault_page()\n", result);
                        }
                } while (result != VM_FAULT_SUCCESS);
        }

        /*
         *      Lose the extra reference, and return our object.
         */
        vm_object_deallocate(src_object);
        *_result_object = new_object;
        return KERN_SUCCESS;
}

/*
 *      Routine:        vm_object_copy_quickly
 *
 *      Purpose:
 *              Copy the specified range of the source virtual
 *              memory object, if it can be done without waiting
 *              for user-generated events.
 *
 *      Results:
 *              If the copy is successful, the copy is returned in
 *              the arguments; otherwise, the arguments are not
 *              affected.
 *
 *      In/out conditions:
 *              The object should be unlocked on entry and exit.
 */

/*ARGSUSED*/
__private_extern__ boolean_t
vm_object_copy_quickly(
        vm_object_t             *_object,               /* INOUT */
        __unused vm_object_offset_t     offset, /* IN */
        __unused vm_object_size_t       size,   /* IN */
        boolean_t               *_src_needs_copy,       /* OUT */
        boolean_t               *_dst_needs_copy)       /* OUT */
{
        vm_object_t     object = *_object;
        memory_object_copy_strategy_t copy_strategy;

        if (object == VM_OBJECT_NULL) {
                *_src_needs_copy = FALSE;
                *_dst_needs_copy = FALSE;
                return TRUE;
        }

        vm_object_lock(object);

        copy_strategy = object->copy_strategy;

        switch (copy_strategy) {
        case MEMORY_OBJECT_COPY_SYMMETRIC:

                /*
                 *      Symmetric copy strategy.
                 *      Make another reference to the object.
                 *      Leave object/offset unchanged.
                 */

                vm_object_reference_locked(object);
                object->shadowed = TRUE;
                vm_object_unlock(object);

                /*
                 *      Both source and destination must make
                 *      shadows, and the source must be made
                 *      read-only if not already.
                 */

                *_src_needs_copy = TRUE;
                *_dst_needs_copy = TRUE;

                break;

        case MEMORY_OBJECT_COPY_DELAY:
                vm_object_unlock(object);
                return FALSE;

        default:
                vm_object_unlock(object);
                return FALSE;
        }
        return TRUE;
}

static int copy_call_count = 0;
static int copy_call_sleep_count = 0;
static int copy_call_restart_count = 0;

/*
 *      Routine:        vm_object_copy_call [internal]
 *
 *      Description:
 *              Copy the source object (src_object), using the
 *              user-managed copy algorithm.
 *
 *      In/out conditions:
 *              The source object must be locked on entry.  It
 *              will be *unlocked* on exit.
 *
 *      Results:
 *              If the copy is successful, KERN_SUCCESS is returned.
 *              A new object that represents the copied virtual
 *              memory is returned in a parameter (*_result_object).
 *              If the return value indicates an error, this parameter
 *              is not valid.
 */
static kern_return_t
vm_object_copy_call(
        vm_object_t             src_object,
        vm_object_offset_t      src_offset,
        vm_object_size_t        size,
        vm_object_t             *_result_object)        /* OUT */
{
        kern_return_t   kr;
        vm_object_t     copy;
        boolean_t       check_ready = FALSE;
        uint32_t        try_failed_count = 0;

        /*
         *      If a copy is already in progress, wait and retry.
         *
         *      XXX
         *      Consider making this call interruptable, as Mike
         *      intended it to be.
         *
         *      XXXO
         *      Need a counter or version or something to allow
         *      us to use the copy that the currently requesting
         *      thread is obtaining -- is it worth adding to the
         *      vm object structure? Depends how common this case it.
         */
        copy_call_count++;
        while (vm_object_wanted(src_object, VM_OBJECT_EVENT_COPY_CALL)) {
                vm_object_sleep(src_object, VM_OBJECT_EVENT_COPY_CALL,
                    THREAD_UNINT);
                copy_call_restart_count++;
        }

        /*
         *      Indicate (for the benefit of memory_object_create_copy)
         *      that we want a copy for src_object. (Note that we cannot
         *      do a real assert_wait before calling memory_object_copy,
         *      so we simply set the flag.)
         */

        vm_object_set_wanted(src_object, VM_OBJECT_EVENT_COPY_CALL);
        vm_object_unlock(src_object);

        /*
         *      Ask the memory manager to give us a memory object
         *      which represents a copy of the src object.
         *      The memory manager may give us a memory object
         *      which we already have, or it may give us a
         *      new memory object. This memory object will arrive
         *      via memory_object_create_copy.
         */

        kr = KERN_FAILURE;      /* XXX need to change memory_object.defs */
        if (kr != KERN_SUCCESS) {
                return kr;
        }

        /*
         *      Wait for the copy to arrive.
         */
        vm_object_lock(src_object);
        while (vm_object_wanted(src_object, VM_OBJECT_EVENT_COPY_CALL)) {
                vm_object_sleep(src_object, VM_OBJECT_EVENT_COPY_CALL,
                    THREAD_UNINT);
                copy_call_sleep_count++;
        }
Retry:
        assert(src_object->copy != VM_OBJECT_NULL);
        copy = src_object->copy;
        if (!vm_object_lock_try(copy)) {
                vm_object_unlock(src_object);

                try_failed_count++;
                mutex_pause(try_failed_count);  /* wait a bit */

                vm_object_lock(src_object);
                goto Retry;
        }
        if (copy->vo_size < src_offset + size) {
                copy->vo_size = src_offset + size;
        }

        if (!copy->pager_ready) {
                check_ready = TRUE;
        }

        /*
         *      Return the copy.
         */
        *_result_object = copy;
        vm_object_unlock(copy);
        vm_object_unlock(src_object);

        /* Wait for the copy to be ready. */
        if (check_ready == TRUE) {
                vm_object_lock(copy);
                while (!copy->pager_ready) {
                        vm_object_sleep(copy, VM_OBJECT_EVENT_PAGER_READY, THREAD_UNINT);
                }
                vm_object_unlock(copy);
        }

        return KERN_SUCCESS;
}

static int copy_delayed_lock_collisions = 0;
static int copy_delayed_max_collisions = 0;
static int copy_delayed_lock_contention = 0;
static int copy_delayed_protect_iterate = 0;

/*
 *      Routine:        vm_object_copy_delayed [internal]
 *
 *      Description:
 *              Copy the specified virtual memory object, using
 *              the asymmetric copy-on-write algorithm.
 *
 *      In/out conditions:
 *              The src_object must be locked on entry.  It will be unlocked
 *              on exit - so the caller must also hold a reference to it.
 *
 *              This routine will not block waiting for user-generated
 *              events.  It is not interruptible.
 */
__private_extern__ vm_object_t
vm_object_copy_delayed(
        vm_object_t             src_object,
        vm_object_offset_t      src_offset,
        vm_object_size_t        size,
        boolean_t               src_object_shared)
{
        vm_object_t             new_copy = VM_OBJECT_NULL;
        vm_object_t             old_copy;
        vm_page_t               p;
        vm_object_size_t        copy_size = src_offset + size;
        pmap_flush_context      pmap_flush_context_storage;
        boolean_t               delayed_pmap_flush = FALSE;


        int collisions = 0;
        /*
         *      The user-level memory manager wants to see all of the changes
         *      to this object, but it has promised not to make any changes on
         *      its own.
         *
         *      Perform an asymmetric copy-on-write, as follows:
         *              Create a new object, called a "copy object" to hold
         *               pages modified by the new mapping  (i.e., the copy,
         *               not the original mapping).
         *              Record the original object as the backing object for
         *               the copy object.  If the original mapping does not
         *               change a page, it may be used read-only by the copy.
         *              Record the copy object in the original object.
         *               When the original mapping causes a page to be modified,
         *               it must be copied to a new page that is "pushed" to
         *               the copy object.
         *              Mark the new mapping (the copy object) copy-on-write.
         *               This makes the copy object itself read-only, allowing
         *               it to be reused if the original mapping makes no
         *               changes, and simplifying the synchronization required
         *               in the "push" operation described above.
         *
         *      The copy-on-write is said to be assymetric because the original
         *      object is *not* marked copy-on-write. A copied page is pushed
         *      to the copy object, regardless which party attempted to modify
         *      the page.
         *
         *      Repeated asymmetric copy operations may be done. If the
         *      original object has not been changed since the last copy, its
         *      copy object can be reused. Otherwise, a new copy object can be
         *      inserted between the original object and its previous copy
         *      object.  Since any copy object is read-only, this cannot affect
         *      affect the contents of the previous copy object.
         *
         *      Note that a copy object is higher in the object tree than the
         *      original object; therefore, use of the copy object recorded in
         *      the original object must be done carefully, to avoid deadlock.
         */

        copy_size = vm_object_round_page(copy_size);
Retry:

        /*
         * Wait for paging in progress.
         */
        if (!src_object->true_share &&
            (src_object->paging_in_progress != 0 ||
            src_object->activity_in_progress != 0)) {
                if (src_object_shared == TRUE) {
                        vm_object_unlock(src_object);
                        vm_object_lock(src_object);
                        src_object_shared = FALSE;
                        goto Retry;
                }
                vm_object_paging_wait(src_object, THREAD_UNINT);
        }
        /*
         *      See whether we can reuse the result of a previous
         *      copy operation.
         */

        old_copy = src_object->copy;
        if (old_copy != VM_OBJECT_NULL) {
                int lock_granted;

                /*
                 *      Try to get the locks (out of order)
                 */
                if (src_object_shared == TRUE) {
                        lock_granted = vm_object_lock_try_shared(old_copy);
                } else {
                        lock_granted = vm_object_lock_try(old_copy);
                }

                if (!lock_granted) {
                        vm_object_unlock(src_object);

                        if (collisions++ == 0) {
                                copy_delayed_lock_contention++;
                        }
                        mutex_pause(collisions);

                        /* Heisenberg Rules */
                        copy_delayed_lock_collisions++;

                        if (collisions > copy_delayed_max_collisions) {
                                copy_delayed_max_collisions = collisions;
                        }

                        if (src_object_shared == TRUE) {
                                vm_object_lock_shared(src_object);
                        } else {
                                vm_object_lock(src_object);
                        }

                        goto Retry;
                }

                /*
                 *      Determine whether the old copy object has
                 *      been modified.
                 */

                if (old_copy->resident_page_count == 0 &&
                    !old_copy->pager_created) {
                        /*
                         *      It has not been modified.
                         *
                         *      Return another reference to
                         *      the existing copy-object if
                         *      we can safely grow it (if
                         *      needed).
                         */

                        if (old_copy->vo_size < copy_size) {
                                if (src_object_shared == TRUE) {
                                        vm_object_unlock(old_copy);
                                        vm_object_unlock(src_object);

                                        vm_object_lock(src_object);
                                        src_object_shared = FALSE;
                                        goto Retry;
                                }
                                /*
                                 * We can't perform a delayed copy if any of the
                                 * pages in the extended range are wired (because
                                 * we can't safely take write permission away from
                                 * wired pages).  If the pages aren't wired, then
                                 * go ahead and protect them.
                                 */
                                copy_delayed_protect_iterate++;

                                pmap_flush_context_init(&pmap_flush_context_storage);
                                delayed_pmap_flush = FALSE;

                                vm_page_queue_iterate(&src_object->memq, p, vmp_listq) {
                                        if (!p->vmp_fictitious &&
                                            p->vmp_offset >= old_copy->vo_size &&
                                            p->vmp_offset < copy_size) {
                                                if (VM_PAGE_WIRED(p)) {
                                                        vm_object_unlock(old_copy);
                                                        vm_object_unlock(src_object);

                                                        if (new_copy != VM_OBJECT_NULL) {
                                                                vm_object_unlock(new_copy);
                                                                vm_object_deallocate(new_copy);
                                                        }
                                                        if (delayed_pmap_flush == TRUE) {
                                                                pmap_flush(&pmap_flush_context_storage);
                                                        }

                                                        return VM_OBJECT_NULL;
                                                } else {
                                                        pmap_page_protect_options(VM_PAGE_GET_PHYS_PAGE(p), (VM_PROT_ALL & ~VM_PROT_WRITE),
                                                            PMAP_OPTIONS_NOFLUSH, (void *)&pmap_flush_context_storage);
                                                        delayed_pmap_flush = TRUE;
                                                }
                                        }
                                }
                                if (delayed_pmap_flush == TRUE) {
                                        pmap_flush(&pmap_flush_context_storage);
                                }

                                old_copy->vo_size = copy_size;
                        }
                        if (src_object_shared == TRUE) {
                                vm_object_reference_shared(old_copy);
                        } else {
                                vm_object_reference_locked(old_copy);
                        }
                        vm_object_unlock(old_copy);
                        vm_object_unlock(src_object);

                        if (new_copy != VM_OBJECT_NULL) {
                                vm_object_unlock(new_copy);
                                vm_object_deallocate(new_copy);
                        }
                        return old_copy;
                }



                /*
                 * Adjust the size argument so that the newly-created
                 * copy object will be large enough to back either the
                 * old copy object or the new mapping.
                 */
                if (old_copy->vo_size > copy_size) {
                        copy_size = old_copy->vo_size;
                }

                if (new_copy == VM_OBJECT_NULL) {
                        vm_object_unlock(old_copy);
                        vm_object_unlock(src_object);
                        new_copy = vm_object_allocate(copy_size);
                        vm_object_lock(src_object);
                        vm_object_lock(new_copy);

                        src_object_shared = FALSE;
                        goto Retry;
                }
                new_copy->vo_size = copy_size;

                /*
                 *      The copy-object is always made large enough to
                 *      completely shadow the original object, since
                 *      it may have several users who want to shadow
                 *      the original object at different points.
                 */

                assert((old_copy->shadow == src_object) &&
                    (old_copy->vo_shadow_offset == (vm_object_offset_t) 0));
        } else if (new_copy == VM_OBJECT_NULL) {
                vm_object_unlock(src_object);
                new_copy = vm_object_allocate(copy_size);
                vm_object_lock(src_object);
                vm_object_lock(new_copy);

                src_object_shared = FALSE;
                goto Retry;
        }

        /*
         * We now have the src object locked, and the new copy object
         * allocated and locked (and potentially the old copy locked).
         * Before we go any further, make sure we can still perform
         * a delayed copy, as the situation may have changed.
         *
         * Specifically, we can't perform a delayed copy if any of the
         * pages in the range are wired (because we can't safely take
         * write permission away from wired pages).  If the pages aren't
         * wired, then go ahead and protect them.
         */
        copy_delayed_protect_iterate++;

        pmap_flush_context_init(&pmap_flush_context_storage);
        delayed_pmap_flush = FALSE;

        vm_page_queue_iterate(&src_object->memq, p, vmp_listq) {
                if (!p->vmp_fictitious && p->vmp_offset < copy_size) {
                        if (VM_PAGE_WIRED(p)) {
                                if (old_copy) {
                                        vm_object_unlock(old_copy);
                                }
                                vm_object_unlock(src_object);
                                vm_object_unlock(new_copy);
                                vm_object_deallocate(new_copy);

                                if (delayed_pmap_flush == TRUE) {
                                        pmap_flush(&pmap_flush_context_storage);
                                }

                                return VM_OBJECT_NULL;
                        } else {
                                pmap_page_protect_options(VM_PAGE_GET_PHYS_PAGE(p), (VM_PROT_ALL & ~VM_PROT_WRITE),
                                    PMAP_OPTIONS_NOFLUSH, (void *)&pmap_flush_context_storage);
                                delayed_pmap_flush = TRUE;
                        }
                }
        }
        if (delayed_pmap_flush == TRUE) {
                pmap_flush(&pmap_flush_context_storage);
        }

        if (old_copy != VM_OBJECT_NULL) {
                /*
                 *      Make the old copy-object shadow the new one.
                 *      It will receive no more pages from the original
                 *      object.
                 */

                /* remove ref. from old_copy */
                vm_object_lock_assert_exclusive(src_object);
                src_object->ref_count--;
                assert(src_object->ref_count > 0);
                vm_object_lock_assert_exclusive(old_copy);
                old_copy->shadow = new_copy;
                vm_object_lock_assert_exclusive(new_copy);
                assert(new_copy->ref_count > 0);
                new_copy->ref_count++;          /* for old_copy->shadow ref. */

#if TASK_SWAPPER
                if (old_copy->res_count) {
                        VM_OBJ_RES_INCR(new_copy);
                        VM_OBJ_RES_DECR(src_object);
                }
#endif

                vm_object_unlock(old_copy);     /* done with old_copy */
        }

        /*
         *      Point the new copy at the existing object.
         */
        vm_object_lock_assert_exclusive(new_copy);
        new_copy->shadow = src_object;
        new_copy->vo_shadow_offset = 0;
        new_copy->shadowed = TRUE;      /* caller must set needs_copy */

        vm_object_lock_assert_exclusive(src_object);
        vm_object_reference_locked(src_object);
        src_object->copy = new_copy;
        vm_object_unlock(src_object);
        vm_object_unlock(new_copy);

        return new_copy;
}

/*
 *      Routine:        vm_object_copy_strategically
 *
 *      Purpose:
 *              Perform a copy according to the source object's
 *              declared strategy.  This operation may block,
 *              and may be interrupted.
 */
__private_extern__ kern_return_t
vm_object_copy_strategically(
        vm_object_t             src_object,
        vm_object_offset_t      src_offset,
        vm_object_size_t        size,
        vm_object_t             *dst_object,    /* OUT */
        vm_object_offset_t      *dst_offset,    /* OUT */
        boolean_t               *dst_needs_copy) /* OUT */
{
        boolean_t       result;
        boolean_t       interruptible = THREAD_ABORTSAFE; /* XXX */
        boolean_t       object_lock_shared = FALSE;
        memory_object_copy_strategy_t copy_strategy;

        assert(src_object != VM_OBJECT_NULL);

        copy_strategy = src_object->copy_strategy;

        if (copy_strategy == MEMORY_OBJECT_COPY_DELAY) {
                vm_object_lock_shared(src_object);
                object_lock_shared = TRUE;
        } else {
                vm_object_lock(src_object);
        }

        /*
         *      The copy strategy is only valid if the memory manager
         *      is "ready". Internal objects are always ready.
         */

        while (!src_object->internal && !src_object->pager_ready) {
                wait_result_t wait_result;

                if (object_lock_shared == TRUE) {
                        vm_object_unlock(src_object);
                        vm_object_lock(src_object);
                        object_lock_shared = FALSE;
                        continue;
                }
                wait_result = vm_object_sleep(  src_object,
                    VM_OBJECT_EVENT_PAGER_READY,
                    interruptible);
                if (wait_result != THREAD_AWAKENED) {
                        vm_object_unlock(src_object);
                        *dst_object = VM_OBJECT_NULL;
                        *dst_offset = 0;
                        *dst_needs_copy = FALSE;
                        return MACH_SEND_INTERRUPTED;
                }
        }

        /*
         *      Use the appropriate copy strategy.
         */

        switch (copy_strategy) {
        case MEMORY_OBJECT_COPY_DELAY:
                *dst_object = vm_object_copy_delayed(src_object,
                    src_offset, size, object_lock_shared);
                if (*dst_object != VM_OBJECT_NULL) {
                        *dst_offset = src_offset;
                        *dst_needs_copy = TRUE;
                        result = KERN_SUCCESS;
                        break;
                }
                vm_object_lock(src_object);
        /* fall thru when delayed copy not allowed */

        case MEMORY_OBJECT_COPY_NONE:
                result = vm_object_copy_slowly(src_object, src_offset, size,
                    interruptible, dst_object);
                if (result == KERN_SUCCESS) {
                        *dst_offset = 0;
                        *dst_needs_copy = FALSE;
                }
                break;

        case MEMORY_OBJECT_COPY_CALL:
                result = vm_object_copy_call(src_object, src_offset, size,
                    dst_object);
                if (result == KERN_SUCCESS) {
                        *dst_offset = src_offset;
                        *dst_needs_copy = TRUE;
                }
                break;

        case MEMORY_OBJECT_COPY_SYMMETRIC:
                vm_object_unlock(src_object);
                result = KERN_MEMORY_RESTART_COPY;
                break;

        default:
                panic("copy_strategically: bad strategy");
                result = KERN_INVALID_ARGUMENT;
        }
        return result;
}

/*
 *      vm_object_shadow:
 *
 *      Create a new object which is backed by the
 *      specified existing object range.  The source
 *      object reference is deallocated.
 *
 *      The new object and offset into that object
 *      are returned in the source parameters.
 */
boolean_t vm_object_shadow_check = TRUE;

__private_extern__ boolean_t
vm_object_shadow(
        vm_object_t             *object,        /* IN/OUT */
        vm_object_offset_t      *offset,        /* IN/OUT */
        vm_object_size_t        length)
{
        vm_object_t     source;
        vm_object_t     result;

        source = *object;
        assert(source != VM_OBJECT_NULL);
        if (source == VM_OBJECT_NULL) {
                return FALSE;
        }

#if 0
        /*
         * XXX FBDP
         * This assertion is valid but it gets triggered by Rosetta for example
         * due to a combination of vm_remap() that changes a VM object's
         * copy_strategy from SYMMETRIC to DELAY and vm_protect(VM_PROT_COPY)
         * that then sets "needs_copy" on its map entry.  This creates a
         * mapping situation that VM should never see and doesn't know how to
         * handle.
         * It's not clear if this can create any real problem but we should
         * look into fixing this, probably by having vm_protect(VM_PROT_COPY)
         * do more than just set "needs_copy" to handle the copy-on-write...
         * In the meantime, let's disable the assertion.
         */
        assert(source->copy_strategy == MEMORY_OBJECT_COPY_SYMMETRIC);
#endif

        /*
         *      Determine if we really need a shadow.
         *
         *      If the source object is larger than what we are trying
         *      to create, then force the shadow creation even if the
         *      ref count is 1.  This will allow us to [potentially]
         *      collapse the underlying object away in the future
         *      (freeing up the extra data it might contain and that
         *      we don't need).
         */

        assert(source->copy_strategy != MEMORY_OBJECT_COPY_NONE); /* Purgeable objects shouldn't have shadow objects. */

        if (vm_object_shadow_check &&
            source->vo_size == length &&
            source->ref_count == 1) {
                /*
                 * Lock the object and check again.
                 * We also check to see if there's
                 * a shadow or copy object involved.
                 * We can't do that earlier because
                 * without the object locked, there
                 * could be a collapse and the chain
                 * gets modified leaving us with an
                 * invalid pointer.
                 */
                vm_object_lock(source);
                if (source->vo_size == length &&
                    source->ref_count == 1 &&
                    (source->shadow == VM_OBJECT_NULL ||
                    source->shadow->copy == VM_OBJECT_NULL)) {
                        source->shadowed = FALSE;
                        vm_object_unlock(source);
                        return FALSE;
                }
                /* things changed while we were locking "source"... */
                vm_object_unlock(source);
        }

        /*
         *      Allocate a new object with the given length
         */

        if ((result = vm_object_allocate(length)) == VM_OBJECT_NULL) {
                panic("vm_object_shadow: no object for shadowing");
        }

        /*
         *      The new object shadows the source object, adding
         *      a reference to it.  Our caller changes his reference
         *      to point to the new object, removing a reference to
         *      the source object.  Net result: no change of reference
         *      count.
         */
        result->shadow = source;

        /*
         *      Store the offset into the source object,
         *      and fix up the offset into the new object.
         */

        result->vo_shadow_offset = *offset;

        /*
         *      Return the new things
         */

        *offset = 0;
        *object = result;
        return TRUE;
}

/*
 *      The relationship between vm_object structures and
 *      the memory_object requires careful synchronization.
 *
 *      All associations are created by memory_object_create_named
 *  for external pagers and vm_object_compressor_pager_create for internal
 *  objects as follows:
 *
 *              pager:  the memory_object itself, supplied by
 *                      the user requesting a mapping (or the kernel,
 *                      when initializing internal objects); the
 *                      kernel simulates holding send rights by keeping
 *                      a port reference;
 *
 *              pager_request:
 *                      the memory object control port,
 *                      created by the kernel; the kernel holds
 *                      receive (and ownership) rights to this
 *                      port, but no other references.
 *
 *      When initialization is complete, the "initialized" field
 *      is asserted.  Other mappings using a particular memory object,
 *      and any references to the vm_object gained through the
 *      port association must wait for this initialization to occur.
 *
 *      In order to allow the memory manager to set attributes before
 *      requests (notably virtual copy operations, but also data or
 *      unlock requests) are made, a "ready" attribute is made available.
 *      Only the memory manager may affect the value of this attribute.
 *      Its value does not affect critical kernel functions, such as
 *      internal object initialization or destruction.  [Furthermore,
 *      memory objects created by the kernel are assumed to be ready
 *      immediately; the default memory manager need not explicitly
 *      set the "ready" attribute.]
 *
 *      [Both the "initialized" and "ready" attribute wait conditions
 *      use the "pager" field as the wait event.]
 *
 *      The port associations can be broken down by any of the
 *      following routines:
 *              vm_object_terminate:
 *                      No references to the vm_object remain, and
 *                      the object cannot (or will not) be cached.
 *                      This is the normal case, and is done even
 *                      though one of the other cases has already been
 *                      done.
 *              memory_object_destroy:
 *                      The memory manager has requested that the
 *                      kernel relinquish references to the memory
 *                      object. [The memory manager may not want to
 *                      destroy the memory object, but may wish to
 *                      refuse or tear down existing memory mappings.]
 *
 *      Each routine that breaks an association must break all of
 *      them at once.  At some later time, that routine must clear
 *      the pager field and release the memory object references.
 *      [Furthermore, each routine must cope with the simultaneous
 *      or previous operations of the others.]
 *
 *      Because the pager field may be cleared spontaneously, it
 *      cannot be used to determine whether a memory object has
 *      ever been associated with a particular vm_object.  [This
 *      knowledge is important to the shadow object mechanism.]
 *      For this reason, an additional "created" attribute is
 *      provided.
 *
 *      During various paging operations, the pager reference found in the
 *      vm_object must be valid.  To prevent this from being released,
 *      (other than being removed, i.e., made null), routines may use
 *      the vm_object_paging_begin/end routines [actually, macros].
 *      The implementation uses the "paging_in_progress" and "wanted" fields.
 *      [Operations that alter the validity of the pager values include the
 *      termination routines and vm_object_collapse.]
 */


/*
 *      Routine:        vm_object_memory_object_associate
 *      Purpose:
 *              Associate a VM object to the given pager.
 *              If a VM object is not provided, create one.
 *              Initialize the pager.
 */
vm_object_t
vm_object_memory_object_associate(
        memory_object_t         pager,
        vm_object_t             object,
        vm_object_size_t        size,
        boolean_t               named)
{
        memory_object_control_t control;

        assert(pager != MEMORY_OBJECT_NULL);

        if (object != VM_OBJECT_NULL) {
                assert(object->internal);
                assert(object->pager_created);
                assert(!object->pager_initialized);
                assert(!object->pager_ready);
                assert(object->pager_trusted);
        } else {
                object = vm_object_allocate(size);
                assert(object != VM_OBJECT_NULL);
                object->internal = FALSE;
                object->pager_trusted = FALSE;
                /* copy strategy invalid until set by memory manager */
                object->copy_strategy = MEMORY_OBJECT_COPY_INVALID;
        }

        /*
         *      Allocate request port.
         */

        control = memory_object_control_allocate(object);
        assert(control != MEMORY_OBJECT_CONTROL_NULL);

        vm_object_lock(object);

        assert(!object->pager_ready);
        assert(!object->pager_initialized);
        assert(object->pager == NULL);
        assert(object->pager_control == NULL);

        /*
         *      Copy the reference we were given.
         */

        memory_object_reference(pager);
        object->pager_created = TRUE;
        object->pager = pager;
        object->pager_control = control;
        object->pager_ready = FALSE;

        vm_object_unlock(object);

        /*
         *      Let the pager know we're using it.
         */

        (void) memory_object_init(pager,
            object->pager_control,
            PAGE_SIZE);

        vm_object_lock(object);
        if (named) {
                object->named = TRUE;
        }
        if (object->internal) {
                object->pager_ready = TRUE;
                vm_object_wakeup(object, VM_OBJECT_EVENT_PAGER_READY);
        }

        object->pager_initialized = TRUE;
        vm_object_wakeup(object, VM_OBJECT_EVENT_INITIALIZED);

        vm_object_unlock(object);

        return object;
}

/*
 *      Routine:        vm_object_compressor_pager_create
 *      Purpose:
 *              Create a memory object for an internal object.
 *      In/out conditions:
 *              The object is locked on entry and exit;
 *              it may be unlocked within this call.
 *      Limitations:
 *              Only one thread may be performing a
 *              vm_object_compressor_pager_create on an object at
 *              a time.  Presumably, only the pageout
 *              daemon will be using this routine.
 */

void
vm_object_compressor_pager_create(
        vm_object_t     object)
{
        memory_object_t         pager;
        vm_object_t             pager_object = VM_OBJECT_NULL;

        assert(object != kernel_object);

        /*
         *      Prevent collapse or termination by holding a paging reference
         */

        vm_object_paging_begin(object);
        if (object->pager_created) {
                /*
                 *      Someone else got to it first...
                 *      wait for them to finish initializing the ports
                 */
                while (!object->pager_initialized) {
                        vm_object_sleep(object,
                            VM_OBJECT_EVENT_INITIALIZED,
                            THREAD_UNINT);
                }
                vm_object_paging_end(object);
                return;
        }

        if ((uint32_t) (object->vo_size / PAGE_SIZE) !=
            (object->vo_size / PAGE_SIZE)) {
#if DEVELOPMENT || DEBUG
                printf("vm_object_compressor_pager_create(%p): "
                    "object size 0x%llx >= 0x%llx\n",
                    object,
                    (uint64_t) object->vo_size,
                    0x0FFFFFFFFULL * PAGE_SIZE);
#endif /* DEVELOPMENT || DEBUG */
                vm_object_paging_end(object);
                return;
        }

        /*
         *      Indicate that a memory object has been assigned
         *      before dropping the lock, to prevent a race.
         */

        object->pager_created = TRUE;
        object->pager_trusted = TRUE;
        object->paging_offset = 0;

        vm_object_unlock(object);

        /*
         *      Create the [internal] pager, and associate it with this object.
         *
         *      We make the association here so that vm_object_enter()
         *      can look up the object to complete initializing it.  No
         *      user will ever map this object.
         */
        {
                /* create our new memory object */
                assert((uint32_t) (object->vo_size / PAGE_SIZE) ==
                    (object->vo_size / PAGE_SIZE));
                (void) compressor_memory_object_create(
                        (memory_object_size_t) object->vo_size,
                        &pager);
                if (pager == NULL) {
                        panic("vm_object_compressor_pager_create(): "
                            "no pager for object %p size 0x%llx\n",
                            object, (uint64_t) object->vo_size);
                }
        }

        /*
         *      A reference was returned by
         *      memory_object_create(), and it is
         *      copied by vm_object_memory_object_associate().
         */

        pager_object = vm_object_memory_object_associate(pager,
            object,
            object->vo_size,
            FALSE);
        if (pager_object != object) {
                panic("vm_object_compressor_pager_create: mismatch (pager: %p, pager_object: %p, orig_object: %p, orig_object size: 0x%llx)\n", pager, pager_object, object, (uint64_t) object->vo_size);
        }

        /*
         *      Drop the reference we were passed.
         */
        memory_object_deallocate(pager);

        vm_object_lock(object);

        /*
         *      Release the paging reference
         */
        vm_object_paging_end(object);
}

/*
 *      Global variables for vm_object_collapse():
 *
 *              Counts for normal collapses and bypasses.
 *              Debugging variables, to watch or disable collapse.
 */
static long     object_collapses = 0;
static long     object_bypasses  = 0;

static boolean_t        vm_object_collapse_allowed = TRUE;
static boolean_t        vm_object_bypass_allowed = TRUE;

void vm_object_do_collapse_compressor(vm_object_t object,
    vm_object_t backing_object);
void
vm_object_do_collapse_compressor(
        vm_object_t object,
        vm_object_t backing_object)
{
        vm_object_offset_t new_offset, backing_offset;
        vm_object_size_t size;

        vm_counters.do_collapse_compressor++;

        vm_object_lock_assert_exclusive(object);
        vm_object_lock_assert_exclusive(backing_object);

        size = object->vo_size;

        /*
         *      Move all compressed pages from backing_object
         *      to the parent.
         */

        for (backing_offset = object->vo_shadow_offset;
            backing_offset < object->vo_shadow_offset + object->vo_size;
            backing_offset += PAGE_SIZE) {
                memory_object_offset_t backing_pager_offset;

                /* find the next compressed page at or after this offset */
                backing_pager_offset = (backing_offset +
                    backing_object->paging_offset);
                backing_pager_offset = vm_compressor_pager_next_compressed(
                        backing_object->pager,
                        backing_pager_offset);
                if (backing_pager_offset == (memory_object_offset_t) -1) {
                        /* no more compressed pages */
                        break;
                }
                backing_offset = (backing_pager_offset -
                    backing_object->paging_offset);

                new_offset = backing_offset - object->vo_shadow_offset;

                if (new_offset >= object->vo_size) {
                        /* we're out of the scope of "object": done */
                        break;
                }

                if ((vm_page_lookup(object, new_offset) != VM_PAGE_NULL) ||
                    (vm_compressor_pager_state_get(object->pager,
                    (new_offset +
                    object->paging_offset)) ==
                    VM_EXTERNAL_STATE_EXISTS)) {
                        /*
                         * This page already exists in object, resident or
                         * compressed.
                         * We don't need this compressed page in backing_object
                         * and it will be reclaimed when we release
                         * backing_object.
                         */
                        continue;
                }

                /*
                 * backing_object has this page in the VM compressor and
                 * we need to transfer it to object.
                 */
                vm_counters.do_collapse_compressor_pages++;
                vm_compressor_pager_transfer(
                        /* destination: */
                        object->pager,
                        (new_offset + object->paging_offset),
                        /* source: */
                        backing_object->pager,
                        (backing_offset + backing_object->paging_offset));
        }
}

/*
 *      Routine:        vm_object_do_collapse
 *      Purpose:
 *              Collapse an object with the object backing it.
 *              Pages in the backing object are moved into the
 *              parent, and the backing object is deallocated.
 *      Conditions:
 *              Both objects and the cache are locked; the page
 *              queues are unlocked.
 *
 */
static void
vm_object_do_collapse(
        vm_object_t object,
        vm_object_t backing_object)
{
        vm_page_t p, pp;
        vm_object_offset_t new_offset, backing_offset;
        vm_object_size_t size;

        vm_object_lock_assert_exclusive(object);
        vm_object_lock_assert_exclusive(backing_object);

        assert(object->purgable == VM_PURGABLE_DENY);
        assert(backing_object->purgable == VM_PURGABLE_DENY);

        backing_offset = object->vo_shadow_offset;
        size = object->vo_size;

        /*
         *      Move all in-memory pages from backing_object
         *      to the parent.  Pages that have been paged out
         *      will be overwritten by any of the parent's
         *      pages that shadow them.
         */

        while (!vm_page_queue_empty(&backing_object->memq)) {
                p = (vm_page_t) vm_page_queue_first(&backing_object->memq);

                new_offset = (p->vmp_offset - backing_offset);

                assert(!p->vmp_busy || p->vmp_absent);

                /*
                 *      If the parent has a page here, or if
                 *      this page falls outside the parent,
                 *      dispose of it.
                 *
                 *      Otherwise, move it as planned.
                 */

                if (p->vmp_offset < backing_offset || new_offset >= size) {
                        VM_PAGE_FREE(p);
                } else {
                        pp = vm_page_lookup(object, new_offset);
                        if (pp == VM_PAGE_NULL) {
                                if (VM_COMPRESSOR_PAGER_STATE_GET(object,
                                    new_offset)
                                    == VM_EXTERNAL_STATE_EXISTS) {
                                        /*
                                         * Parent object has this page
                                         * in the VM compressor.
                                         * Throw away the backing
                                         * object's page.
                                         */
                                        VM_PAGE_FREE(p);
                                } else {
                                        /*
                                         *      Parent now has no page.
                                         *      Move the backing object's page
                                         *      up.
                                         */
                                        vm_page_rename(p, object, new_offset);
                                }
                        } else {
                                assert(!pp->vmp_absent);

                                /*
                                 *      Parent object has a real page.
                                 *      Throw away the backing object's
                                 *      page.
                                 */
                                VM_PAGE_FREE(p);
                        }
                }
        }

        if (vm_object_collapse_compressor_allowed &&
            object->pager != MEMORY_OBJECT_NULL &&
            backing_object->pager != MEMORY_OBJECT_NULL) {
                /* move compressed pages from backing_object to object */
                vm_object_do_collapse_compressor(object, backing_object);
        } else if (backing_object->pager != MEMORY_OBJECT_NULL) {
                assert((!object->pager_created &&
                    (object->pager == MEMORY_OBJECT_NULL)) ||
                    (!backing_object->pager_created &&
                    (backing_object->pager == MEMORY_OBJECT_NULL)));
                /*
                 *      Move the pager from backing_object to object.
                 *
                 *      XXX We're only using part of the paging space
                 *      for keeps now... we ought to discard the
                 *      unused portion.
                 */

                assert(!object->paging_in_progress);
                assert(!object->activity_in_progress);
                assert(!object->pager_created);
                assert(object->pager == NULL);
                object->pager = backing_object->pager;

                object->pager_created = backing_object->pager_created;
                object->pager_control = backing_object->pager_control;
                object->pager_ready = backing_object->pager_ready;
                object->pager_initialized = backing_object->pager_initialized;
                object->paging_offset =
                    backing_object->paging_offset + backing_offset;
                if (object->pager_control != MEMORY_OBJECT_CONTROL_NULL) {
                        memory_object_control_collapse(object->pager_control,
                            object);
                }
                /* the backing_object has lost its pager: reset all fields */
                backing_object->pager_created = FALSE;
                backing_object->pager_control = NULL;
                backing_object->pager_ready = FALSE;
                backing_object->paging_offset = 0;
                backing_object->pager = NULL;
        }
        /*
         *      Object now shadows whatever backing_object did.
         *      Note that the reference to backing_object->shadow
         *      moves from within backing_object to within object.
         */

        assert(!object->phys_contiguous);
        assert(!backing_object->phys_contiguous);
        object->shadow = backing_object->shadow;
        if (object->shadow) {
                object->vo_shadow_offset += backing_object->vo_shadow_offset;
                /* "backing_object" gave its shadow to "object" */
                backing_object->shadow = VM_OBJECT_NULL;
                backing_object->vo_shadow_offset = 0;
        } else {
                /* no shadow, therefore no shadow offset... */
                object->vo_shadow_offset = 0;
        }
        assert((object->shadow == VM_OBJECT_NULL) ||
            (object->shadow->copy != backing_object));

        /*
         *      Discard backing_object.
         *
         *      Since the backing object has no pages, no
         *      pager left, and no object references within it,
         *      all that is necessary is to dispose of it.
         */
        object_collapses++;

        assert(backing_object->ref_count == 1);
        assert(backing_object->resident_page_count == 0);
        assert(backing_object->paging_in_progress == 0);
        assert(backing_object->activity_in_progress == 0);
        assert(backing_object->shadow == VM_OBJECT_NULL);
        assert(backing_object->vo_shadow_offset == 0);

        if (backing_object->pager != MEMORY_OBJECT_NULL) {
                /* ... unless it has a pager; need to terminate pager too */
                vm_counters.do_collapse_terminate++;
                if (vm_object_terminate(backing_object) != KERN_SUCCESS) {
                        vm_counters.do_collapse_terminate_failure++;
                }
                return;
        }

        assert(backing_object->pager == NULL);

        backing_object->alive = FALSE;
        vm_object_unlock(backing_object);

#if VM_OBJECT_TRACKING
        if (vm_object_tracking_inited) {
                btlog_remove_entries_for_element(vm_object_tracking_btlog,
                    backing_object);
        }
#endif /* VM_OBJECT_TRACKING */

        vm_object_lock_destroy(backing_object);

        zfree(vm_object_zone, backing_object);
}

static void
vm_object_do_bypass(
        vm_object_t object,
        vm_object_t backing_object)
{
        /*
         *      Make the parent shadow the next object
         *      in the chain.
         */

        vm_object_lock_assert_exclusive(object);
        vm_object_lock_assert_exclusive(backing_object);

#if     TASK_SWAPPER
        /*
         *      Do object reference in-line to
         *      conditionally increment shadow's
         *      residence count.  If object is not
         *      resident, leave residence count
         *      on shadow alone.
         */
        if (backing_object->shadow != VM_OBJECT_NULL) {
                vm_object_lock(backing_object->shadow);
                vm_object_lock_assert_exclusive(backing_object->shadow);
                backing_object->shadow->ref_count++;
                if (object->res_count != 0) {
                        vm_object_res_reference(backing_object->shadow);
                }
                vm_object_unlock(backing_object->shadow);
        }
#else   /* TASK_SWAPPER */
        vm_object_reference(backing_object->shadow);
#endif  /* TASK_SWAPPER */

        assert(!object->phys_contiguous);
        assert(!backing_object->phys_contiguous);
        object->shadow = backing_object->shadow;
        if (object->shadow) {
                object->vo_shadow_offset += backing_object->vo_shadow_offset;
        } else {
                /* no shadow, therefore no shadow offset... */
                object->vo_shadow_offset = 0;
        }

        /*
         *      Backing object might have had a copy pointer
         *      to us.  If it did, clear it.
         */
        if (backing_object->copy == object) {
                backing_object->copy = VM_OBJECT_NULL;
        }

        /*
         *      Drop the reference count on backing_object.
         #if    TASK_SWAPPER
         *      Since its ref_count was at least 2, it
         *      will not vanish; so we don't need to call
         *      vm_object_deallocate.
         *      [with a caveat for "named" objects]
         *
         *      The res_count on the backing object is
         *      conditionally decremented.  It's possible
         *      (via vm_pageout_scan) to get here with
         *      a "swapped" object, which has a 0 res_count,
         *      in which case, the backing object res_count
         *      is already down by one.
         #else
         *      Don't call vm_object_deallocate unless
         *      ref_count drops to zero.
         *
         *      The ref_count can drop to zero here if the
         *      backing object could be bypassed but not
         *      collapsed, such as when the backing object
         *      is temporary and cachable.
         #endif
         */
        if (backing_object->ref_count > 2 ||
            (!backing_object->named && backing_object->ref_count > 1)) {
                vm_object_lock_assert_exclusive(backing_object);
                backing_object->ref_count--;
#if     TASK_SWAPPER
                if (object->res_count != 0) {
                        vm_object_res_deallocate(backing_object);
                }
                assert(backing_object->ref_count > 0);
#endif  /* TASK_SWAPPER */
                vm_object_unlock(backing_object);
        } else {
                /*
                 *      Drop locks so that we can deallocate
                 *      the backing object.
                 */

#if     TASK_SWAPPER
                if (object->res_count == 0) {
                        /* XXX get a reference for the deallocate below */
                        vm_object_res_reference(backing_object);
                }
#endif  /* TASK_SWAPPER */
                /*
                 * vm_object_collapse (the caller of this function) is
                 * now called from contexts that may not guarantee that a
                 * valid reference is held on the object... w/o a valid
                 * reference, it is unsafe and unwise (you will definitely
                 * regret it) to unlock the object and then retake the lock
                 * since the object may be terminated and recycled in between.
                 * The "activity_in_progress" reference will keep the object
                 * 'stable'.
                 */
                vm_object_activity_begin(object);
                vm_object_unlock(object);

                vm_object_unlock(backing_object);
                vm_object_deallocate(backing_object);

                /*
                 *      Relock object. We don't have to reverify
                 *      its state since vm_object_collapse will
                 *      do that for us as it starts at the
                 *      top of its loop.
                 */

                vm_object_lock(object);
                vm_object_activity_end(object);
        }

        object_bypasses++;
}


/*
 *      vm_object_collapse:
 *
 *      Perform an object collapse or an object bypass if appropriate.
 *      The real work of collapsing and bypassing is performed in
 *      the routines vm_object_do_collapse and vm_object_do_bypass.
 *
 *      Requires that the object be locked and the page queues be unlocked.
 *
 */
static unsigned long vm_object_collapse_calls = 0;
static unsigned long vm_object_collapse_objects = 0;
static unsigned long vm_object_collapse_do_collapse = 0;
static unsigned long vm_object_collapse_do_bypass = 0;

__private_extern__ void
vm_object_collapse(
        vm_object_t                             object,
        vm_object_offset_t                      hint_offset,
        boolean_t                               can_bypass)
{
        vm_object_t                             backing_object;
        unsigned int                            rcount;
        unsigned int                            size;
        vm_object_t                             original_object;
        int                                     object_lock_type;
        int                                     backing_object_lock_type;

        vm_object_collapse_calls++;

        if (!vm_object_collapse_allowed &&
            !(can_bypass && vm_object_bypass_allowed)) {
                return;
        }

        if (object == VM_OBJECT_NULL) {
                return;
        }

        original_object = object;

        /*
         * The top object was locked "exclusive" by the caller.
         * In the first pass, to determine if we can collapse the shadow chain,
         * take a "shared" lock on the shadow objects.  If we can collapse,
         * we'll have to go down the chain again with exclusive locks.
         */
        object_lock_type = OBJECT_LOCK_EXCLUSIVE;
        backing_object_lock_type = OBJECT_LOCK_SHARED;

retry:
        object = original_object;
        vm_object_lock_assert_exclusive(object);

        while (TRUE) {
                vm_object_collapse_objects++;
                /*
                 *      Verify that the conditions are right for either
                 *      collapse or bypass:
                 */

                /*
                 *      There is a backing object, and
                 */

                backing_object = object->shadow;
                if (backing_object == VM_OBJECT_NULL) {
                        if (object != original_object) {
                                vm_object_unlock(object);
                        }
                        return;
                }
                if (backing_object_lock_type == OBJECT_LOCK_SHARED) {
                        vm_object_lock_shared(backing_object);
                } else {
                        vm_object_lock(backing_object);
                }

                /*
                 *      No pages in the object are currently
                 *      being paged out, and
                 */
                if (object->paging_in_progress != 0 ||
                    object->activity_in_progress != 0) {
                        /* try and collapse the rest of the shadow chain */
                        if (object != original_object) {
                                vm_object_unlock(object);
                        }
                        object = backing_object;
                        object_lock_type = backing_object_lock_type;
                        continue;
                }

                /*
                 *      ...
                 *              The backing object is not read_only,
                 *              and no pages in the backing object are
                 *              currently being paged out.
                 *              The backing object is internal.
                 *
                 */

                if (!backing_object->internal ||
                    backing_object->paging_in_progress != 0 ||
                    backing_object->activity_in_progress != 0) {
                        /* try and collapse the rest of the shadow chain */
                        if (object != original_object) {
                                vm_object_unlock(object);
                        }
                        object = backing_object;
                        object_lock_type = backing_object_lock_type;
                        continue;
                }

                /*
                 * Purgeable objects are not supposed to engage in
                 * copy-on-write activities, so should not have
                 * any shadow objects or be a shadow object to another
                 * object.
                 * Collapsing a purgeable object would require some
                 * updates to the purgeable compressed ledgers.
                 */
                if (object->purgable != VM_PURGABLE_DENY ||
                    backing_object->purgable != VM_PURGABLE_DENY) {
                        panic("vm_object_collapse() attempting to collapse "
                            "purgeable object: %p(%d) %p(%d)\n",
                            object, object->purgable,
                            backing_object, backing_object->purgable);
                        /* try and collapse the rest of the shadow chain */
                        if (object != original_object) {
                                vm_object_unlock(object);
                        }
                        object = backing_object;
                        object_lock_type = backing_object_lock_type;
                        continue;
                }

                /*
                 *      The backing object can't be a copy-object:
                 *      the shadow_offset for the copy-object must stay
                 *      as 0.  Furthermore (for the 'we have all the
                 *      pages' case), if we bypass backing_object and
                 *      just shadow the next object in the chain, old
                 *      pages from that object would then have to be copied
                 *      BOTH into the (former) backing_object and into the
                 *      parent object.
                 */
                if (backing_object->shadow != VM_OBJECT_NULL &&
                    backing_object->shadow->copy == backing_object) {
                        /* try and collapse the rest of the shadow chain */
                        if (object != original_object) {
                                vm_object_unlock(object);
                        }
                        object = backing_object;
                        object_lock_type = backing_object_lock_type;
                        continue;
                }

                /*
                 *      We can now try to either collapse the backing
                 *      object (if the parent is the only reference to
                 *      it) or (perhaps) remove the parent's reference
                 *      to it.
                 *
                 *      If there is exactly one reference to the backing
                 *      object, we may be able to collapse it into the
                 *      parent.
                 *
                 *      As long as one of the objects is still not known
                 *      to the pager, we can collapse them.
                 */
                if (backing_object->ref_count == 1 &&
                    (vm_object_collapse_compressor_allowed ||
                    !object->pager_created
                    || (!backing_object->pager_created)
                    ) && vm_object_collapse_allowed) {
                        /*
                         * We need the exclusive lock on the VM objects.
                         */
                        if (backing_object_lock_type != OBJECT_LOCK_EXCLUSIVE) {
                                /*
                                 * We have an object and its shadow locked
                                 * "shared".  We can't just upgrade the locks
                                 * to "exclusive", as some other thread might
                                 * also have these objects locked "shared" and
                                 * attempt to upgrade one or the other to
                                 * "exclusive".  The upgrades would block
                                 * forever waiting for the other "shared" locks
                                 * to get released.
                                 * So we have to release the locks and go
                                 * down the shadow chain again (since it could
                                 * have changed) with "exclusive" locking.
                                 */
                                vm_object_unlock(backing_object);
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                object_lock_type = OBJECT_LOCK_EXCLUSIVE;
                                backing_object_lock_type = OBJECT_LOCK_EXCLUSIVE;
                                goto retry;
                        }

                        /*
                         *      Collapse the object with its backing
                         *      object, and try again with the object's
                         *      new backing object.
                         */

                        vm_object_do_collapse(object, backing_object);
                        vm_object_collapse_do_collapse++;
                        continue;
                }

                /*
                 *      Collapsing the backing object was not possible
                 *      or permitted, so let's try bypassing it.
                 */

                if (!(can_bypass && vm_object_bypass_allowed)) {
                        /* try and collapse the rest of the shadow chain */
                        if (object != original_object) {
                                vm_object_unlock(object);
                        }
                        object = backing_object;
                        object_lock_type = backing_object_lock_type;
                        continue;
                }


                /*
                 *      If the object doesn't have all its pages present,
                 *      we have to make sure no pages in the backing object
                 *      "show through" before bypassing it.
                 */
                size = (unsigned int)atop(object->vo_size);
                rcount = object->resident_page_count;

                if (rcount != size) {
                        vm_object_offset_t      offset;
                        vm_object_offset_t      backing_offset;
                        unsigned int            backing_rcount;

                        /*
                         *      If the backing object has a pager but no pagemap,
                         *      then we cannot bypass it, because we don't know
                         *      what pages it has.
                         */
                        if (backing_object->pager_created) {
                                /* try and collapse the rest of the shadow chain */
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                object = backing_object;
                                object_lock_type = backing_object_lock_type;
                                continue;
                        }

                        /*
                         *      If the object has a pager but no pagemap,
                         *      then we cannot bypass it, because we don't know
                         *      what pages it has.
                         */
                        if (object->pager_created) {
                                /* try and collapse the rest of the shadow chain */
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                object = backing_object;
                                object_lock_type = backing_object_lock_type;
                                continue;
                        }

                        backing_offset = object->vo_shadow_offset;
                        backing_rcount = backing_object->resident_page_count;

                        if ((int)backing_rcount - (int)(atop(backing_object->vo_size) - size) > (int)rcount) {
                                /*
                                 * we have enough pages in the backing object to guarantee that
                                 * at least 1 of them must be 'uncovered' by a resident page
                                 * in the object we're evaluating, so move on and
                                 * try to collapse the rest of the shadow chain
                                 */
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                object = backing_object;
                                object_lock_type = backing_object_lock_type;
                                continue;
                        }

                        /*
                         *      If all of the pages in the backing object are
                         *      shadowed by the parent object, the parent
                         *      object no longer has to shadow the backing
                         *      object; it can shadow the next one in the
                         *      chain.
                         *
                         *      If the backing object has existence info,
                         *      we must check examine its existence info
                         *      as well.
                         *
                         */

#define EXISTS_IN_OBJECT(obj, off, rc)                  \
        ((VM_COMPRESSOR_PAGER_STATE_GET((obj), (off))   \
          == VM_EXTERNAL_STATE_EXISTS) ||               \
         ((rc) && vm_page_lookup((obj), (off)) != VM_PAGE_NULL && (rc)--))

                        /*
                         * Check the hint location first
                         * (since it is often the quickest way out of here).
                         */
                        if (object->cow_hint != ~(vm_offset_t)0) {
                                hint_offset = (vm_object_offset_t)object->cow_hint;
                        } else {
                                hint_offset = (hint_offset > 8 * PAGE_SIZE_64) ?
                                    (hint_offset - 8 * PAGE_SIZE_64) : 0;
                        }

                        if (EXISTS_IN_OBJECT(backing_object, hint_offset +
                            backing_offset, backing_rcount) &&
                            !EXISTS_IN_OBJECT(object, hint_offset, rcount)) {
                                /* dependency right at the hint */
                                object->cow_hint = (vm_offset_t) hint_offset; /* atomic */
                                /* try and collapse the rest of the shadow chain */
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                object = backing_object;
                                object_lock_type = backing_object_lock_type;
                                continue;
                        }

                        /*
                         * If the object's window onto the backing_object
                         * is large compared to the number of resident
                         * pages in the backing object, it makes sense to
                         * walk the backing_object's resident pages first.
                         *
                         * NOTE: Pages may be in both the existence map and/or
                         * resident, so if we don't find a dependency while
                         * walking the backing object's resident page list
                         * directly, and there is an existence map, we'll have
                         * to run the offset based 2nd pass.  Because we may
                         * have to run both passes, we need to be careful
                         * not to decrement 'rcount' in the 1st pass
                         */
                        if (backing_rcount && backing_rcount < (size / 8)) {
                                unsigned int rc = rcount;
                                vm_page_t p;

                                backing_rcount = backing_object->resident_page_count;
                                p = (vm_page_t)vm_page_queue_first(&backing_object->memq);
                                do {
                                        offset = (p->vmp_offset - backing_offset);

                                        if (offset < object->vo_size &&
                                            offset != hint_offset &&
                                            !EXISTS_IN_OBJECT(object, offset, rc)) {
                                                /* found a dependency */
                                                object->cow_hint = (vm_offset_t) offset; /* atomic */

                                                break;
                                        }
                                        p = (vm_page_t) vm_page_queue_next(&p->vmp_listq);
                                } while (--backing_rcount);
                                if (backing_rcount != 0) {
                                        /* try and collapse the rest of the shadow chain */
                                        if (object != original_object) {
                                                vm_object_unlock(object);
                                        }
                                        object = backing_object;
                                        object_lock_type = backing_object_lock_type;
                                        continue;
                                }
                        }

                        /*
                         * Walk through the offsets looking for pages in the
                         * backing object that show through to the object.
                         */
                        if (backing_rcount) {
                                offset = hint_offset;

                                while ((offset =
                                    (offset + PAGE_SIZE_64 < object->vo_size) ?
                                    (offset + PAGE_SIZE_64) : 0) != hint_offset) {
                                        if (EXISTS_IN_OBJECT(backing_object, offset +
                                            backing_offset, backing_rcount) &&
                                            !EXISTS_IN_OBJECT(object, offset, rcount)) {
                                                /* found a dependency */
                                                object->cow_hint = (vm_offset_t) offset; /* atomic */
                                                break;
                                        }
                                }
                                if (offset != hint_offset) {
                                        /* try and collapse the rest of the shadow chain */
                                        if (object != original_object) {
                                                vm_object_unlock(object);
                                        }
                                        object = backing_object;
                                        object_lock_type = backing_object_lock_type;
                                        continue;
                                }
                        }
                }

                /*
                 * We need "exclusive" locks on the 2 VM objects.
                 */
                if (backing_object_lock_type != OBJECT_LOCK_EXCLUSIVE) {
                        vm_object_unlock(backing_object);
                        if (object != original_object) {
                                vm_object_unlock(object);
                        }
                        object_lock_type = OBJECT_LOCK_EXCLUSIVE;
                        backing_object_lock_type = OBJECT_LOCK_EXCLUSIVE;
                        goto retry;
                }

                /* reset the offset hint for any objects deeper in the chain */
                object->cow_hint = (vm_offset_t)0;

                /*
                 *      All interesting pages in the backing object
                 *      already live in the parent or its pager.
                 *      Thus we can bypass the backing object.
                 */

                vm_object_do_bypass(object, backing_object);
                vm_object_collapse_do_bypass++;

                /*
                 *      Try again with this object's new backing object.
                 */

                continue;
        }

        /* NOT REACHED */
        /*
         *  if (object != original_object) {
         *       vm_object_unlock(object);
         *  }
         */
}

/*
 *      Routine:        vm_object_page_remove: [internal]
 *      Purpose:
 *              Removes all physical pages in the specified
 *              object range from the object's list of pages.
 *
 *      In/out conditions:
 *              The object must be locked.
 *              The object must not have paging_in_progress, usually
 *              guaranteed by not having a pager.
 */
unsigned int vm_object_page_remove_lookup = 0;
unsigned int vm_object_page_remove_iterate = 0;

__private_extern__ void
vm_object_page_remove(
        vm_object_t             object,
        vm_object_offset_t      start,
        vm_object_offset_t      end)
{
        vm_page_t       p, next;

        /*
         *      One and two page removals are most popular.
         *      The factor of 16 here is somewhat arbitrary.
         *      It balances vm_object_lookup vs iteration.
         */

        if (atop_64(end - start) < (unsigned)object->resident_page_count / 16) {
                vm_object_page_remove_lookup++;

                for (; start < end; start += PAGE_SIZE_64) {
                        p = vm_page_lookup(object, start);
                        if (p != VM_PAGE_NULL) {
                                assert(!p->vmp_cleaning && !p->vmp_laundry);
                                if (!p->vmp_fictitious && p->vmp_pmapped) {
                                        pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(p));
                                }
                                VM_PAGE_FREE(p);
                        }
                }
        } else {
                vm_object_page_remove_iterate++;

                p = (vm_page_t) vm_page_queue_first(&object->memq);
                while (!vm_page_queue_end(&object->memq, (vm_page_queue_entry_t) p)) {
                        next = (vm_page_t) vm_page_queue_next(&p->vmp_listq);
                        if ((start <= p->vmp_offset) && (p->vmp_offset < end)) {
                                assert(!p->vmp_cleaning && !p->vmp_laundry);
                                if (!p->vmp_fictitious && p->vmp_pmapped) {
                                        pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(p));
                                }
                                VM_PAGE_FREE(p);
                        }
                        p = next;
                }
        }
}


/*
 *      Routine:        vm_object_coalesce
 *      Function:       Coalesces two objects backing up adjoining
 *                      regions of memory into a single object.
 *
 *      returns TRUE if objects were combined.
 *
 *      NOTE:   Only works at the moment if the second object is NULL -
 *              if it's not, which object do we lock first?
 *
 *      Parameters:
 *              prev_object     First object to coalesce
 *              prev_offset     Offset into prev_object
 *              next_object     Second object into coalesce
 *              next_offset     Offset into next_object
 *
 *              prev_size       Size of reference to prev_object
 *              next_size       Size of reference to next_object
 *
 *      Conditions:
 *      The object(s) must *not* be locked. The map must be locked
 *      to preserve the reference to the object(s).
 */
static int vm_object_coalesce_count = 0;

__private_extern__ boolean_t
vm_object_coalesce(
        vm_object_t                     prev_object,
        vm_object_t                     next_object,
        vm_object_offset_t              prev_offset,
        __unused vm_object_offset_t next_offset,
        vm_object_size_t                prev_size,
        vm_object_size_t                next_size)
{
        vm_object_size_t        newsize;

#ifdef  lint
        next_offset++;
#endif  /* lint */

        if (next_object != VM_OBJECT_NULL) {
                return FALSE;
        }

        if (prev_object == VM_OBJECT_NULL) {
                return TRUE;
        }

        vm_object_lock(prev_object);

        /*
         *      Try to collapse the object first
         */
        vm_object_collapse(prev_object, prev_offset, TRUE);

        /*
         *      Can't coalesce if pages not mapped to
         *      prev_entry may be in use any way:
         *      . more than one reference
         *      . paged out
         *      . shadows another object
         *      . has a copy elsewhere
         *      . is purgeable
         *      . paging references (pages might be in page-list)
         */

        if ((prev_object->ref_count > 1) ||
            prev_object->pager_created ||
            (prev_object->shadow != VM_OBJECT_NULL) ||
            (prev_object->copy != VM_OBJECT_NULL) ||
            (prev_object->true_share != FALSE) ||
            (prev_object->purgable != VM_PURGABLE_DENY) ||
            (prev_object->paging_in_progress != 0) ||
            (prev_object->activity_in_progress != 0)) {
                vm_object_unlock(prev_object);
                return FALSE;
        }

        vm_object_coalesce_count++;

        /*
         *      Remove any pages that may still be in the object from
         *      a previous deallocation.
         */
        vm_object_page_remove(prev_object,
            prev_offset + prev_size,
            prev_offset + prev_size + next_size);

        /*
         *      Extend the object if necessary.
         */
        newsize = prev_offset + prev_size + next_size;
        if (newsize > prev_object->vo_size) {
                prev_object->vo_size = newsize;
        }

        vm_object_unlock(prev_object);
        return TRUE;
}

kern_return_t
vm_object_populate_with_private(
        vm_object_t             object,
        vm_object_offset_t      offset,
        ppnum_t                 phys_page,
        vm_size_t               size)
{
        ppnum_t                 base_page;
        vm_object_offset_t      base_offset;


        if (!object->private) {
                return KERN_FAILURE;
        }

        base_page = phys_page;

        vm_object_lock(object);

        if (!object->phys_contiguous) {
                vm_page_t       m;

                if ((base_offset = trunc_page_64(offset)) != offset) {
                        vm_object_unlock(object);
                        return KERN_FAILURE;
                }
                base_offset += object->paging_offset;

                while (size) {
                        m = vm_page_lookup(object, base_offset);

                        if (m != VM_PAGE_NULL) {
                                if (m->vmp_fictitious) {
                                        if (VM_PAGE_GET_PHYS_PAGE(m) != vm_page_guard_addr) {
                                                vm_page_lockspin_queues();
                                                m->vmp_private = TRUE;
                                                vm_page_unlock_queues();

                                                m->vmp_fictitious = FALSE;
                                                VM_PAGE_SET_PHYS_PAGE(m, base_page);
                                        }
                                } else if (VM_PAGE_GET_PHYS_PAGE(m) != base_page) {
                                        if (!m->vmp_private) {
                                                /*
                                                 * we'd leak a real page... that can't be right
                                                 */
                                                panic("vm_object_populate_with_private - %p not private", m);
                                        }
                                        if (m->vmp_pmapped) {
                                                /*
                                                 * pmap call to clear old mapping
                                                 */
                                                pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(m));
                                        }
                                        VM_PAGE_SET_PHYS_PAGE(m, base_page);
                                }
                        } else {
                                while ((m = vm_page_grab_fictitious()) == VM_PAGE_NULL) {
                                        vm_page_more_fictitious();
                                }

                                /*
                                 * private normally requires lock_queues but since we
                                 * are initializing the page, its not necessary here
                                 */
                                m->vmp_private = TRUE;
                                m->vmp_fictitious = FALSE;
                                VM_PAGE_SET_PHYS_PAGE(m, base_page);
                                m->vmp_unusual = TRUE;
                                m->vmp_busy = FALSE;

                                vm_page_insert(m, object, base_offset);
                        }
                        base_page++;                                                                    /* Go to the next physical page */
                        base_offset += PAGE_SIZE;
                        size -= PAGE_SIZE;
                }
        } else {
                /* NOTE: we should check the original settings here */
                /* if we have a size > zero a pmap call should be made */
                /* to disable the range */

                /* pmap_? */

                /* shadows on contiguous memory are not allowed */
                /* we therefore can use the offset field */
                object->vo_shadow_offset = (vm_object_offset_t)phys_page << PAGE_SHIFT;
                object->vo_size = size;
        }
        vm_object_unlock(object);

        return KERN_SUCCESS;
}


kern_return_t
memory_object_create_named(
        memory_object_t pager,
        memory_object_offset_t  size,
        memory_object_control_t         *control)
{
        vm_object_t             object;

        *control = MEMORY_OBJECT_CONTROL_NULL;
        if (pager == MEMORY_OBJECT_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        object = vm_object_memory_object_associate(pager,
            VM_OBJECT_NULL,
            size,
            TRUE);
        if (object == VM_OBJECT_NULL) {
                return KERN_INVALID_OBJECT;
        }

        /* wait for object (if any) to be ready */
        if (object != VM_OBJECT_NULL) {
                vm_object_lock(object);
                object->named = TRUE;
                while (!object->pager_ready) {
                        vm_object_sleep(object,
                            VM_OBJECT_EVENT_PAGER_READY,
                            THREAD_UNINT);
                }
                *control = object->pager_control;
                vm_object_unlock(object);
        }
        return KERN_SUCCESS;
}


/*
 *      Routine:        memory_object_recover_named [user interface]
 *      Purpose:
 *              Attempt to recover a named reference for a VM object.
 *              VM will verify that the object has not already started
 *              down the termination path, and if it has, will optionally
 *              wait for that to finish.
 *      Returns:
 *              KERN_SUCCESS - we recovered a named reference on the object
 *              KERN_FAILURE - we could not recover a reference (object dead)
 *              KERN_INVALID_ARGUMENT - bad memory object control
 */
kern_return_t
memory_object_recover_named(
        memory_object_control_t control,
        boolean_t               wait_on_terminating)
{
        vm_object_t             object;

        object = memory_object_control_to_vm_object(control);
        if (object == VM_OBJECT_NULL) {
                return KERN_INVALID_ARGUMENT;
        }
restart:
        vm_object_lock(object);

        if (object->terminating && wait_on_terminating) {
                vm_object_wait(object,
                    VM_OBJECT_EVENT_PAGING_IN_PROGRESS,
                    THREAD_UNINT);
                goto restart;
        }

        if (!object->alive) {
                vm_object_unlock(object);
                return KERN_FAILURE;
        }

        if (object->named == TRUE) {
                vm_object_unlock(object);
                return KERN_SUCCESS;
        }
        object->named = TRUE;
        vm_object_lock_assert_exclusive(object);
        object->ref_count++;
        vm_object_res_reference(object);
        while (!object->pager_ready) {
                vm_object_sleep(object,
                    VM_OBJECT_EVENT_PAGER_READY,
                    THREAD_UNINT);
        }
        vm_object_unlock(object);
        return KERN_SUCCESS;
}


/*
 *      vm_object_release_name:
 *
 *      Enforces name semantic on memory_object reference count decrement
 *      This routine should not be called unless the caller holds a name
 *      reference gained through the memory_object_create_named.
 *
 *      If the TERMINATE_IDLE flag is set, the call will return if the
 *      reference count is not 1. i.e. idle with the only remaining reference
 *      being the name.
 *      If the decision is made to proceed the name field flag is set to
 *      false and the reference count is decremented.  If the RESPECT_CACHE
 *      flag is set and the reference count has gone to zero, the
 *      memory_object is checked to see if it is cacheable otherwise when
 *      the reference count is zero, it is simply terminated.
 */

__private_extern__ kern_return_t
vm_object_release_name(
        vm_object_t     object,
        int             flags)
{
        vm_object_t     shadow;
        boolean_t       original_object = TRUE;

        while (object != VM_OBJECT_NULL) {
                vm_object_lock(object);

                assert(object->alive);
                if (original_object) {
                        assert(object->named);
                }
                assert(object->ref_count > 0);

                /*
                 *      We have to wait for initialization before
                 *      destroying or caching the object.
                 */

                if (object->pager_created && !object->pager_initialized) {
                        assert(!object->can_persist);
                        vm_object_assert_wait(object,
                            VM_OBJECT_EVENT_INITIALIZED,
                            THREAD_UNINT);
                        vm_object_unlock(object);
                        thread_block(THREAD_CONTINUE_NULL);
                        continue;
                }

                if (((object->ref_count > 1)
                    && (flags & MEMORY_OBJECT_TERMINATE_IDLE))
                    || (object->terminating)) {
                        vm_object_unlock(object);
                        return KERN_FAILURE;
                } else {
                        if (flags & MEMORY_OBJECT_RELEASE_NO_OP) {
                                vm_object_unlock(object);
                                return KERN_SUCCESS;
                        }
                }

                if ((flags & MEMORY_OBJECT_RESPECT_CACHE) &&
                    (object->ref_count == 1)) {
                        if (original_object) {
                                object->named = FALSE;
                        }
                        vm_object_unlock(object);
                        /* let vm_object_deallocate push this thing into */
                        /* the cache, if that it is where it is bound */
                        vm_object_deallocate(object);
                        return KERN_SUCCESS;
                }
                VM_OBJ_RES_DECR(object);
                shadow = object->pageout?VM_OBJECT_NULL:object->shadow;

                if (object->ref_count == 1) {
                        if (vm_object_terminate(object) != KERN_SUCCESS) {
                                if (original_object) {
                                        return KERN_FAILURE;
                                } else {
                                        return KERN_SUCCESS;
                                }
                        }
                        if (shadow != VM_OBJECT_NULL) {
                                original_object = FALSE;
                                object = shadow;
                                continue;
                        }
                        return KERN_SUCCESS;
                } else {
                        vm_object_lock_assert_exclusive(object);
                        object->ref_count--;
                        assert(object->ref_count > 0);
                        if (original_object) {
                                object->named = FALSE;
                        }
                        vm_object_unlock(object);
                        return KERN_SUCCESS;
                }
        }
        /*NOTREACHED*/
        assert(0);
        return KERN_FAILURE;
}


__private_extern__ kern_return_t
vm_object_lock_request(
        vm_object_t                     object,
        vm_object_offset_t              offset,
        vm_object_size_t                size,
        memory_object_return_t          should_return,
        int                             flags,
        vm_prot_t                       prot)
{
        __unused boolean_t      should_flush;

        should_flush = flags & MEMORY_OBJECT_DATA_FLUSH;

        /*
         *      Check for bogus arguments.
         */
        if (object == VM_OBJECT_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        if ((prot & ~VM_PROT_ALL) != 0 && prot != VM_PROT_NO_CHANGE) {
                return KERN_INVALID_ARGUMENT;
        }

        size = round_page_64(size);

        /*
         *      Lock the object, and acquire a paging reference to
         *      prevent the memory_object reference from being released.
         */
        vm_object_lock(object);
        vm_object_paging_begin(object);

        (void)vm_object_update(object,
            offset, size, NULL, NULL, should_return, flags, prot);

        vm_object_paging_end(object);
        vm_object_unlock(object);

        return KERN_SUCCESS;
}

/*
 * Empty a purgeable object by grabbing the physical pages assigned to it and
 * putting them on the free queue without writing them to backing store, etc.
 * When the pages are next touched they will be demand zero-fill pages.  We
 * skip pages which are busy, being paged in/out, wired, etc.  We do _not_
 * skip referenced/dirty pages, pages on the active queue, etc.  We're more
 * than happy to grab these since this is a purgeable object.  We mark the
 * object as "empty" after reaping its pages.
 *
 * On entry the object must be locked and it must be
 * purgeable with no delayed copies pending.
 */
uint64_t
vm_object_purge(vm_object_t object, int flags)
{
        unsigned int    object_page_count = 0, pgcount = 0;
        uint64_t        total_purged_pgcount = 0;
        boolean_t       skipped_object = FALSE;

        vm_object_lock_assert_exclusive(object);

        if (object->purgable == VM_PURGABLE_DENY) {
                return 0;
        }

        assert(object->copy == VM_OBJECT_NULL);
        assert(object->copy_strategy == MEMORY_OBJECT_COPY_NONE);

        /*
         * We need to set the object's state to VM_PURGABLE_EMPTY *before*
         * reaping its pages.  We update vm_page_purgeable_count in bulk
         * and we don't want vm_page_remove() to update it again for each
         * page we reap later.
         *
         * For the purgeable ledgers, pages from VOLATILE and EMPTY objects
         * are all accounted for in the "volatile" ledgers, so this does not
         * make any difference.
         * If we transitioned directly from NONVOLATILE to EMPTY,
         * vm_page_purgeable_count must have been updated when the object
         * was dequeued from its volatile queue and the purgeable ledgers
         * must have also been updated accordingly at that time (in
         * vm_object_purgable_control()).
         */
        if (object->purgable == VM_PURGABLE_VOLATILE) {
                unsigned int delta;
                assert(object->resident_page_count >=
                    object->wired_page_count);
                delta = (object->resident_page_count -
                    object->wired_page_count);
                if (delta != 0) {
                        assert(vm_page_purgeable_count >=
                            delta);
                        OSAddAtomic(-delta,
                            (SInt32 *)&vm_page_purgeable_count);
                }
                if (object->wired_page_count != 0) {
                        assert(vm_page_purgeable_wired_count >=
                            object->wired_page_count);
                        OSAddAtomic(-object->wired_page_count,
                            (SInt32 *)&vm_page_purgeable_wired_count);
                }
                object->purgable = VM_PURGABLE_EMPTY;
        }
        assert(object->purgable == VM_PURGABLE_EMPTY);

        object_page_count = object->resident_page_count;

        vm_object_reap_pages(object, REAP_PURGEABLE);

        if (object->resident_page_count >= object_page_count) {
                total_purged_pgcount = 0;
        } else {
                total_purged_pgcount = object_page_count - object->resident_page_count;
        }

        if (object->pager != NULL) {
                assert(VM_CONFIG_COMPRESSOR_IS_PRESENT);

                if (object->activity_in_progress == 0 &&
                    object->paging_in_progress == 0) {
                        /*
                         * Also reap any memory coming from this object
                         * in the VM compressor.
                         *
                         * There are no operations in progress on the VM object
                         * and no operation can start while we're holding the
                         * VM object lock, so it's safe to reap the compressed
                         * pages and update the page counts.
                         */
                        pgcount = vm_compressor_pager_get_count(object->pager);
                        if (pgcount) {
                                pgcount = vm_compressor_pager_reap_pages(object->pager, flags);
                                vm_compressor_pager_count(object->pager,
                                    -pgcount,
                                    FALSE,                       /* shared */
                                    object);
                                vm_object_owner_compressed_update(object,
                                    -pgcount);
                        }
                        if (!(flags & C_DONT_BLOCK)) {
                                assert(vm_compressor_pager_get_count(object->pager)
                                    == 0);
                        }
                } else {
                        /*
                         * There's some kind of paging activity in progress
                         * for this object, which could result in a page
                         * being compressed or decompressed, possibly while
                         * the VM object is not locked, so it could race
                         * with us.
                         *
                         * We can't really synchronize this without possibly
                         * causing a deadlock when the compressor needs to
                         * allocate or free memory while compressing or
                         * decompressing a page from a purgeable object
                         * mapped in the kernel_map...
                         *
                         * So let's not attempt to purge the compressor
                         * pager if there's any kind of operation in
                         * progress on the VM object.
                         */
                        skipped_object = TRUE;
                }
        }

        vm_object_lock_assert_exclusive(object);

        total_purged_pgcount += pgcount;

        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE, (MACHDBG_CODE(DBG_MACH_VM, OBJECT_PURGE_ONE)),
            VM_KERNEL_UNSLIDE_OR_PERM(object),                   /* purged object */
            object_page_count,
            total_purged_pgcount,
            skipped_object,
            0);

        return total_purged_pgcount;
}


/*
 * vm_object_purgeable_control() allows the caller to control and investigate the
 * state of a purgeable object.  A purgeable object is created via a call to
 * vm_allocate() with VM_FLAGS_PURGABLE specified.  A purgeable object will
 * never be coalesced with any other object -- even other purgeable objects --
 * and will thus always remain a distinct object.  A purgeable object has
 * special semantics when its reference count is exactly 1.  If its reference
 * count is greater than 1, then a purgeable object will behave like a normal
 * object and attempts to use this interface will result in an error return
 * of KERN_INVALID_ARGUMENT.
 *
 * A purgeable object may be put into a "volatile" state which will make the
 * object's pages elligable for being reclaimed without paging to backing
 * store if the system runs low on memory.  If the pages in a volatile
 * purgeable object are reclaimed, the purgeable object is said to have been
 * "emptied."  When a purgeable object is emptied the system will reclaim as
 * many pages from the object as it can in a convenient manner (pages already
 * en route to backing store or busy for other reasons are left as is).  When
 * a purgeable object is made volatile, its pages will generally be reclaimed
 * before other pages in the application's working set.  This semantic is
 * generally used by applications which can recreate the data in the object
 * faster than it can be paged in.  One such example might be media assets
 * which can be reread from a much faster RAID volume.
 *
 * A purgeable object may be designated as "non-volatile" which means it will
 * behave like all other objects in the system with pages being written to and
 * read from backing store as needed to satisfy system memory needs.  If the
 * object was emptied before the object was made non-volatile, that fact will
 * be returned as the old state of the purgeable object (see
 * VM_PURGABLE_SET_STATE below).  In this case, any pages of the object which
 * were reclaimed as part of emptying the object will be refaulted in as
 * zero-fill on demand.  It is up to the application to note that an object
 * was emptied and recreate the objects contents if necessary.  When a
 * purgeable object is made non-volatile, its pages will generally not be paged
 * out to backing store in the immediate future.  A purgeable object may also
 * be manually emptied.
 *
 * Finally, the current state (non-volatile, volatile, volatile & empty) of a
 * volatile purgeable object may be queried at any time.  This information may
 * be used as a control input to let the application know when the system is
 * experiencing memory pressure and is reclaiming memory.
 *
 * The specified address may be any address within the purgeable object.  If
 * the specified address does not represent any object in the target task's
 * virtual address space, then KERN_INVALID_ADDRESS will be returned.  If the
 * object containing the specified address is not a purgeable object, then
 * KERN_INVALID_ARGUMENT will be returned.  Otherwise, KERN_SUCCESS will be
 * returned.
 *
 * The control parameter may be any one of VM_PURGABLE_SET_STATE or
 * VM_PURGABLE_GET_STATE.  For VM_PURGABLE_SET_STATE, the in/out parameter
 * state is used to set the new state of the purgeable object and return its
 * old state.  For VM_PURGABLE_GET_STATE, the current state of the purgeable
 * object is returned in the parameter state.
 *
 * The in/out parameter state may be one of VM_PURGABLE_NONVOLATILE,
 * VM_PURGABLE_VOLATILE or VM_PURGABLE_EMPTY.  These, respectively, represent
 * the non-volatile, volatile and volatile/empty states described above.
 * Setting the state of a purgeable object to VM_PURGABLE_EMPTY will
 * immediately reclaim as many pages in the object as can be conveniently
 * collected (some may have already been written to backing store or be
 * otherwise busy).
 *
 * The process of making a purgeable object non-volatile and determining its
 * previous state is atomic.  Thus, if a purgeable object is made
 * VM_PURGABLE_NONVOLATILE and the old state is returned as
 * VM_PURGABLE_VOLATILE, then the purgeable object's previous contents are
 * completely intact and will remain so until the object is made volatile
 * again.  If the old state is returned as VM_PURGABLE_EMPTY then the object
 * was reclaimed while it was in a volatile state and its previous contents
 * have been lost.
 */
/*
 * The object must be locked.
 */
kern_return_t
vm_object_purgable_control(
        vm_object_t     object,
        vm_purgable_t   control,
        int             *state)
{
        int             old_state;
        int             new_state;

        if (object == VM_OBJECT_NULL) {
                /*
                 * Object must already be present or it can't be purgeable.
                 */
                return KERN_INVALID_ARGUMENT;
        }

        vm_object_lock_assert_exclusive(object);

        /*
         * Get current state of the purgeable object.
         */
        old_state = object->purgable;
        if (old_state == VM_PURGABLE_DENY) {
                return KERN_INVALID_ARGUMENT;
        }

        /* purgeable cant have delayed copies - now or in the future */
        assert(object->copy == VM_OBJECT_NULL);
        assert(object->copy_strategy == MEMORY_OBJECT_COPY_NONE);

        /*
         * Execute the desired operation.
         */
        if (control == VM_PURGABLE_GET_STATE) {
                *state = old_state;
                return KERN_SUCCESS;
        }

        if (control == VM_PURGABLE_SET_STATE &&
            object->purgeable_only_by_kernel) {
                return KERN_PROTECTION_FAILURE;
        }

        if (control != VM_PURGABLE_SET_STATE &&
            control != VM_PURGABLE_SET_STATE_FROM_KERNEL) {
                return KERN_INVALID_ARGUMENT;
        }

        if ((*state) & VM_PURGABLE_DEBUG_EMPTY) {
                object->volatile_empty = TRUE;
        }
        if ((*state) & VM_PURGABLE_DEBUG_FAULT) {
                object->volatile_fault = TRUE;
        }

        new_state = *state & VM_PURGABLE_STATE_MASK;
        if (new_state == VM_PURGABLE_VOLATILE) {
                if (old_state == VM_PURGABLE_EMPTY) {
                        /* what's been emptied must stay empty */
                        new_state = VM_PURGABLE_EMPTY;
                }
                if (object->volatile_empty) {
                        /* debugging mode: go straight to empty */
                        new_state = VM_PURGABLE_EMPTY;
                }
        }

        switch (new_state) {
        case VM_PURGABLE_DENY:
                /*
                 * Attempting to convert purgeable memory to non-purgeable:
                 * not allowed.
                 */
                return KERN_INVALID_ARGUMENT;
        case VM_PURGABLE_NONVOLATILE:
                object->purgable = new_state;

                if (old_state == VM_PURGABLE_VOLATILE) {
                        unsigned int delta;

                        assert(object->resident_page_count >=
                            object->wired_page_count);
                        delta = (object->resident_page_count -
                            object->wired_page_count);

                        assert(vm_page_purgeable_count >= delta);

                        if (delta != 0) {
                                OSAddAtomic(-delta,
                                    (SInt32 *)&vm_page_purgeable_count);
                        }
                        if (object->wired_page_count != 0) {
                                assert(vm_page_purgeable_wired_count >=
                                    object->wired_page_count);
                                OSAddAtomic(-object->wired_page_count,
                                    (SInt32 *)&vm_page_purgeable_wired_count);
                        }

                        vm_page_lock_queues();

                        /* object should be on a queue */
                        assert(object->objq.next != NULL &&
                            object->objq.prev != NULL);
                        purgeable_q_t queue;

                        /*
                         * Move object from its volatile queue to the
                         * non-volatile queue...
                         */
                        queue = vm_purgeable_object_remove(object);
                        assert(queue);

                        if (object->purgeable_when_ripe) {
                                vm_purgeable_token_delete_last(queue);
                        }
                        assert(queue->debug_count_objects >= 0);

                        vm_page_unlock_queues();
                }
                if (old_state == VM_PURGABLE_VOLATILE ||
                    old_state == VM_PURGABLE_EMPTY) {
                        /*
                         * Transfer the object's pages from the volatile to
                         * non-volatile ledgers.
                         */
                        vm_purgeable_accounting(object, VM_PURGABLE_VOLATILE);
                }

                break;

        case VM_PURGABLE_VOLATILE:
                if (object->volatile_fault) {
                        vm_page_t       p;
                        int             refmod;

                        vm_page_queue_iterate(&object->memq, p, vmp_listq) {
                                if (p->vmp_busy ||
                                    VM_PAGE_WIRED(p) ||
                                    p->vmp_fictitious) {
                                        continue;
                                }
                                refmod = pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(p));
                                if ((refmod & VM_MEM_MODIFIED) &&
                                    !p->vmp_dirty) {
                                        SET_PAGE_DIRTY(p, FALSE);
                                }
                        }
                }

                assert(old_state != VM_PURGABLE_EMPTY);

                purgeable_q_t queue;

                /* find the correct queue */
                if ((*state & VM_PURGABLE_ORDERING_MASK) == VM_PURGABLE_ORDERING_OBSOLETE) {
                        queue = &purgeable_queues[PURGEABLE_Q_TYPE_OBSOLETE];
                } else {
                        if ((*state & VM_PURGABLE_BEHAVIOR_MASK) == VM_PURGABLE_BEHAVIOR_FIFO) {
                                queue = &purgeable_queues[PURGEABLE_Q_TYPE_FIFO];
                        } else {
                                queue = &purgeable_queues[PURGEABLE_Q_TYPE_LIFO];
                        }
                }

                if (old_state == VM_PURGABLE_NONVOLATILE ||
                    old_state == VM_PURGABLE_EMPTY) {
                        unsigned int delta;

                        if ((*state & VM_PURGABLE_NO_AGING_MASK) ==
                            VM_PURGABLE_NO_AGING) {
                                object->purgeable_when_ripe = FALSE;
                        } else {
                                object->purgeable_when_ripe = TRUE;
                        }

                        if (object->purgeable_when_ripe) {
                                kern_return_t result;

                                /* try to add token... this can fail */
                                vm_page_lock_queues();

                                result = vm_purgeable_token_add(queue);
                                if (result != KERN_SUCCESS) {
                                        vm_page_unlock_queues();
                                        return result;
                                }
                                vm_page_unlock_queues();
                        }

                        assert(object->resident_page_count >=
                            object->wired_page_count);
                        delta = (object->resident_page_count -
                            object->wired_page_count);

                        if (delta != 0) {
                                OSAddAtomic(delta,
                                    &vm_page_purgeable_count);
                        }
                        if (object->wired_page_count != 0) {
                                OSAddAtomic(object->wired_page_count,
                                    &vm_page_purgeable_wired_count);
                        }

                        object->purgable = new_state;

                        /* object should be on "non-volatile" queue */
                        assert(object->objq.next != NULL);
                        assert(object->objq.prev != NULL);
                } else if (old_state == VM_PURGABLE_VOLATILE) {
                        purgeable_q_t   old_queue;
                        boolean_t       purgeable_when_ripe;

                        /*
                         * if reassigning priorities / purgeable groups, we don't change the
                         * token queue. So moving priorities will not make pages stay around longer.
                         * Reasoning is that the algorithm gives most priority to the most important
                         * object. If a new token is added, the most important object' priority is boosted.
                         * This biases the system already for purgeable queues that move a lot.
                         * It doesn't seem more biasing is neccessary in this case, where no new object is added.
                         */
                        assert(object->objq.next != NULL && object->objq.prev != NULL); /* object should be on a queue */

                        old_queue = vm_purgeable_object_remove(object);
                        assert(old_queue);

                        if ((*state & VM_PURGABLE_NO_AGING_MASK) ==
                            VM_PURGABLE_NO_AGING) {
                                purgeable_when_ripe = FALSE;
                        } else {
                                purgeable_when_ripe = TRUE;
                        }

                        if (old_queue != queue ||
                            (purgeable_when_ripe !=
                            object->purgeable_when_ripe)) {
                                kern_return_t result;

                                /* Changing queue. Have to move token. */
                                vm_page_lock_queues();
                                if (object->purgeable_when_ripe) {
                                        vm_purgeable_token_delete_last(old_queue);
                                }
                                object->purgeable_when_ripe = purgeable_when_ripe;
                                if (object->purgeable_when_ripe) {
                                        result = vm_purgeable_token_add(queue);
                                        assert(result == KERN_SUCCESS);   /* this should never fail since we just freed a token */
                                }
                                vm_page_unlock_queues();
                        }
                }
                ;
                vm_purgeable_object_add(object, queue, (*state & VM_VOLATILE_GROUP_MASK) >> VM_VOLATILE_GROUP_SHIFT );
                if (old_state == VM_PURGABLE_NONVOLATILE) {
                        vm_purgeable_accounting(object,
                            VM_PURGABLE_NONVOLATILE);
                }

                assert(queue->debug_count_objects >= 0);

                break;


        case VM_PURGABLE_EMPTY:
                if (object->volatile_fault) {
                        vm_page_t       p;
                        int             refmod;

                        vm_page_queue_iterate(&object->memq, p, vmp_listq) {
                                if (p->vmp_busy ||
                                    VM_PAGE_WIRED(p) ||
                                    p->vmp_fictitious) {
                                        continue;
                                }
                                refmod = pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(p));
                                if ((refmod & VM_MEM_MODIFIED) &&
                                    !p->vmp_dirty) {
                                        SET_PAGE_DIRTY(p, FALSE);
                                }
                        }
                }

                if (old_state == VM_PURGABLE_VOLATILE) {
                        purgeable_q_t old_queue;

                        /* object should be on a queue */
                        assert(object->objq.next != NULL &&
                            object->objq.prev != NULL);

                        old_queue = vm_purgeable_object_remove(object);
                        assert(old_queue);
                        if (object->purgeable_when_ripe) {
                                vm_page_lock_queues();
                                vm_purgeable_token_delete_first(old_queue);
                                vm_page_unlock_queues();
                        }
                }

                if (old_state == VM_PURGABLE_NONVOLATILE) {
                        /*
                         * This object's pages were previously accounted as
                         * "non-volatile" and now need to be accounted as
                         * "volatile".
                         */
                        vm_purgeable_accounting(object,
                            VM_PURGABLE_NONVOLATILE);
                        /*
                         * Set to VM_PURGABLE_EMPTY because the pages are no
                         * longer accounted in the "non-volatile" ledger
                         * and are also not accounted for in
                         * "vm_page_purgeable_count".
                         */
                        object->purgable = VM_PURGABLE_EMPTY;
                }

                (void) vm_object_purge(object, 0);
                assert(object->purgable == VM_PURGABLE_EMPTY);

                break;
        }

        *state = old_state;

        vm_object_lock_assert_exclusive(object);

        return KERN_SUCCESS;
}

kern_return_t
vm_object_get_page_counts(
        vm_object_t             object,
        vm_object_offset_t      offset,
        vm_object_size_t        size,
        unsigned int            *resident_page_count,
        unsigned int            *dirty_page_count)
{
        kern_return_t           kr = KERN_SUCCESS;
        boolean_t               count_dirty_pages = FALSE;
        vm_page_t               p = VM_PAGE_NULL;
        unsigned int            local_resident_count = 0;
        unsigned int            local_dirty_count = 0;
        vm_object_offset_t      cur_offset = 0;
        vm_object_offset_t      end_offset = 0;

        if (object == VM_OBJECT_NULL) {
                return KERN_INVALID_ARGUMENT;
        }


        cur_offset = offset;

        end_offset = offset + size;

        vm_object_lock_assert_exclusive(object);

        if (dirty_page_count != NULL) {
                count_dirty_pages = TRUE;
        }

        if (resident_page_count != NULL && count_dirty_pages == FALSE) {
                /*
                 * Fast path when:
                 * - we only want the resident page count, and,
                 * - the entire object is exactly covered by the request.
                 */
                if (offset == 0 && (object->vo_size == size)) {
                        *resident_page_count = object->resident_page_count;
                        goto out;
                }
        }

        if (object->resident_page_count <= (size >> PAGE_SHIFT)) {
                vm_page_queue_iterate(&object->memq, p, vmp_listq) {
                        if (p->vmp_offset >= cur_offset && p->vmp_offset < end_offset) {
                                local_resident_count++;

                                if (count_dirty_pages) {
                                        if (p->vmp_dirty || (p->vmp_wpmapped && pmap_is_modified(VM_PAGE_GET_PHYS_PAGE(p)))) {
                                                local_dirty_count++;
                                        }
                                }
                        }
                }
        } else {
                for (cur_offset = offset; cur_offset < end_offset; cur_offset += PAGE_SIZE_64) {
                        p = vm_page_lookup(object, cur_offset);

                        if (p != VM_PAGE_NULL) {
                                local_resident_count++;

                                if (count_dirty_pages) {
                                        if (p->vmp_dirty || (p->vmp_wpmapped && pmap_is_modified(VM_PAGE_GET_PHYS_PAGE(p)))) {
                                                local_dirty_count++;
                                        }
                                }
                        }
                }
        }

        if (resident_page_count != NULL) {
                *resident_page_count = local_resident_count;
        }

        if (dirty_page_count != NULL) {
                *dirty_page_count = local_dirty_count;
        }

out:
        return kr;
}


#if     TASK_SWAPPER
/*
 * vm_object_res_deallocate
 *
 * (recursively) decrement residence counts on vm objects and their shadows.
 * Called from vm_object_deallocate and when swapping out an object.
 *
 * The object is locked, and remains locked throughout the function,
 * even as we iterate down the shadow chain.  Locks on intermediate objects
 * will be dropped, but not the original object.
 *
 * NOTE: this function used to use recursion, rather than iteration.
 */

__private_extern__ void
vm_object_res_deallocate(
        vm_object_t     object)
{
        vm_object_t orig_object = object;
        /*
         * Object is locked so it can be called directly
         * from vm_object_deallocate.  Original object is never
         * unlocked.
         */
        assert(object->res_count > 0);
        while (--object->res_count == 0) {
                assert(object->ref_count >= object->res_count);
                vm_object_deactivate_all_pages(object);
                /* iterate on shadow, if present */
                if (object->shadow != VM_OBJECT_NULL) {
                        vm_object_t tmp_object = object->shadow;
                        vm_object_lock(tmp_object);
                        if (object != orig_object) {
                                vm_object_unlock(object);
                        }
                        object = tmp_object;
                        assert(object->res_count > 0);
                } else {
                        break;
                }
        }
        if (object != orig_object) {
                vm_object_unlock(object);
        }
}

/*
 * vm_object_res_reference
 *
 * Internal function to increment residence count on a vm object
 * and its shadows.  It is called only from vm_object_reference, and
 * when swapping in a vm object, via vm_map_swap.
 *
 * The object is locked, and remains locked throughout the function,
 * even as we iterate down the shadow chain.  Locks on intermediate objects
 * will be dropped, but not the original object.
 *
 * NOTE: this function used to use recursion, rather than iteration.
 */

__private_extern__ void
vm_object_res_reference(
        vm_object_t     object)
{
        vm_object_t orig_object = object;
        /*
         * Object is locked, so this can be called directly
         * from vm_object_reference.  This lock is never released.
         */
        while ((++object->res_count == 1) &&
            (object->shadow != VM_OBJECT_NULL)) {
                vm_object_t tmp_object = object->shadow;

                assert(object->ref_count >= object->res_count);
                vm_object_lock(tmp_object);
                if (object != orig_object) {
                        vm_object_unlock(object);
                }
                object = tmp_object;
        }
        if (object != orig_object) {
                vm_object_unlock(object);
        }
        assert(orig_object->ref_count >= orig_object->res_count);
}
#endif  /* TASK_SWAPPER */

/*
 *      vm_object_reference:
 *
 *      Gets another reference to the given object.
 */
#ifdef vm_object_reference
#undef vm_object_reference
#endif
__private_extern__ void
vm_object_reference(
        vm_object_t     object)
{
        if (object == VM_OBJECT_NULL) {
                return;
        }

        vm_object_lock(object);
        assert(object->ref_count > 0);
        vm_object_reference_locked(object);
        vm_object_unlock(object);
}

/*
 * vm_object_transpose
 *
 * This routine takes two VM objects of the same size and exchanges
 * their backing store.
 * The objects should be "quiesced" via a UPL operation with UPL_SET_IO_WIRE
 * and UPL_BLOCK_ACCESS if they are referenced anywhere.
 *
 * The VM objects must not be locked by caller.
 */
unsigned int vm_object_transpose_count = 0;
kern_return_t
vm_object_transpose(
        vm_object_t             object1,
        vm_object_t             object2,
        vm_object_size_t        transpose_size)
{
        vm_object_t             tmp_object;
        kern_return_t           retval;
        boolean_t               object1_locked, object2_locked;
        vm_page_t               page;
        vm_object_offset_t      page_offset;

        tmp_object = VM_OBJECT_NULL;
        object1_locked = FALSE; object2_locked = FALSE;

        if (object1 == object2 ||
            object1 == VM_OBJECT_NULL ||
            object2 == VM_OBJECT_NULL) {
                /*
                 * If the 2 VM objects are the same, there's
                 * no point in exchanging their backing store.
                 */
                retval = KERN_INVALID_VALUE;
                goto done;
        }

        /*
         * Since we need to lock both objects at the same time,
         * make sure we always lock them in the same order to
         * avoid deadlocks.
         */
        if (object1 > object2) {
                tmp_object = object1;
                object1 = object2;
                object2 = tmp_object;
        }

        /*
         * Allocate a temporary VM object to hold object1's contents
         * while we copy object2 to object1.
         */
        tmp_object = vm_object_allocate(transpose_size);
        vm_object_lock(tmp_object);
        tmp_object->can_persist = FALSE;


        /*
         * Grab control of the 1st VM object.
         */
        vm_object_lock(object1);
        object1_locked = TRUE;
        if (!object1->alive || object1->terminating ||
            object1->copy || object1->shadow || object1->shadowed ||
            object1->purgable != VM_PURGABLE_DENY) {
                /*
                 * We don't deal with copy or shadow objects (yet).
                 */
                retval = KERN_INVALID_VALUE;
                goto done;
        }
        /*
         * We're about to mess with the object's backing store and
         * taking a "paging_in_progress" reference wouldn't be enough
         * to prevent any paging activity on this object, so the caller should
         * have "quiesced" the objects beforehand, via a UPL operation with
         * UPL_SET_IO_WIRE (to make sure all the pages are there and wired)
         * and UPL_BLOCK_ACCESS (to mark the pages "busy").
         *
         * Wait for any paging operation to complete (but only paging, not
         * other kind of activities not linked to the pager).  After we're
         * statisfied that there's no more paging in progress, we keep the
         * object locked, to guarantee that no one tries to access its pager.
         */
        vm_object_paging_only_wait(object1, THREAD_UNINT);

        /*
         * Same as above for the 2nd object...
         */
        vm_object_lock(object2);
        object2_locked = TRUE;
        if (!object2->alive || object2->terminating ||
            object2->copy || object2->shadow || object2->shadowed ||
            object2->purgable != VM_PURGABLE_DENY) {
                retval = KERN_INVALID_VALUE;
                goto done;
        }
        vm_object_paging_only_wait(object2, THREAD_UNINT);


        if (object1->vo_size != object2->vo_size ||
            object1->vo_size != transpose_size) {
                /*
                 * If the 2 objects don't have the same size, we can't
                 * exchange their backing stores or one would overflow.
                 * If their size doesn't match the caller's
                 * "transpose_size", we can't do it either because the
                 * transpose operation will affect the entire span of
                 * the objects.
                 */
                retval = KERN_INVALID_VALUE;
                goto done;
        }


        /*
         * Transpose the lists of resident pages.
         * This also updates the resident_page_count and the memq_hint.
         */
        if (object1->phys_contiguous || vm_page_queue_empty(&object1->memq)) {
                /*
                 * No pages in object1, just transfer pages
                 * from object2 to object1.  No need to go through
                 * an intermediate object.
                 */
                while (!vm_page_queue_empty(&object2->memq)) {
                        page = (vm_page_t) vm_page_queue_first(&object2->memq);
                        vm_page_rename(page, object1, page->vmp_offset);
                }
                assert(vm_page_queue_empty(&object2->memq));
        } else if (object2->phys_contiguous || vm_page_queue_empty(&object2->memq)) {
                /*
                 * No pages in object2, just transfer pages
                 * from object1 to object2.  No need to go through
                 * an intermediate object.
                 */
                while (!vm_page_queue_empty(&object1->memq)) {
                        page = (vm_page_t) vm_page_queue_first(&object1->memq);
                        vm_page_rename(page, object2, page->vmp_offset);
                }
                assert(vm_page_queue_empty(&object1->memq));
        } else {
                /* transfer object1's pages to tmp_object */
                while (!vm_page_queue_empty(&object1->memq)) {
                        page = (vm_page_t) vm_page_queue_first(&object1->memq);
                        page_offset = page->vmp_offset;
                        vm_page_remove(page, TRUE);
                        page->vmp_offset = page_offset;
                        vm_page_queue_enter(&tmp_object->memq, page, vmp_listq);
                }
                assert(vm_page_queue_empty(&object1->memq));
                /* transfer object2's pages to object1 */
                while (!vm_page_queue_empty(&object2->memq)) {
                        page = (vm_page_t) vm_page_queue_first(&object2->memq);
                        vm_page_rename(page, object1, page->vmp_offset);
                }
                assert(vm_page_queue_empty(&object2->memq));
                /* transfer tmp_object's pages to object2 */
                while (!vm_page_queue_empty(&tmp_object->memq)) {
                        page = (vm_page_t) vm_page_queue_first(&tmp_object->memq);
                        vm_page_queue_remove(&tmp_object->memq, page, vmp_listq);
                        vm_page_insert(page, object2, page->vmp_offset);
                }
                assert(vm_page_queue_empty(&tmp_object->memq));
        }

#define __TRANSPOSE_FIELD(field)                                \
MACRO_BEGIN                                                     \
        tmp_object->field = object1->field;                     \
        object1->field = object2->field;                        \
        object2->field = tmp_object->field;                     \
MACRO_END

        /* "Lock" refers to the object not its contents */
        /* "size" should be identical */
        assert(object1->vo_size == object2->vo_size);
        /* "memq_hint" was updated above when transposing pages */
        /* "ref_count" refers to the object not its contents */
        assert(object1->ref_count >= 1);
        assert(object2->ref_count >= 1);
#if TASK_SWAPPER
        /* "res_count" refers to the object not its contents */
#endif
        /* "resident_page_count" was updated above when transposing pages */
        /* "wired_page_count" was updated above when transposing pages */
#if !VM_TAG_ACTIVE_UPDATE
        /* "wired_objq" was dealt with along with "wired_page_count" */
#endif /* ! VM_TAG_ACTIVE_UPDATE */
        /* "reusable_page_count" was updated above when transposing pages */
        /* there should be no "copy" */
        assert(!object1->copy);
        assert(!object2->copy);
        /* there should be no "shadow" */
        assert(!object1->shadow);
        assert(!object2->shadow);
        __TRANSPOSE_FIELD(vo_shadow_offset); /* used by phys_contiguous objects */
        __TRANSPOSE_FIELD(pager);
        __TRANSPOSE_FIELD(paging_offset);
        __TRANSPOSE_FIELD(pager_control);
        /* update the memory_objects' pointers back to the VM objects */
        if (object1->pager_control != MEMORY_OBJECT_CONTROL_NULL) {
                memory_object_control_collapse(object1->pager_control,
                    object1);
        }
        if (object2->pager_control != MEMORY_OBJECT_CONTROL_NULL) {
                memory_object_control_collapse(object2->pager_control,
                    object2);
        }
        __TRANSPOSE_FIELD(copy_strategy);
        /* "paging_in_progress" refers to the object not its contents */
        assert(!object1->paging_in_progress);
        assert(!object2->paging_in_progress);
        assert(object1->activity_in_progress);
        assert(object2->activity_in_progress);
        /* "all_wanted" refers to the object not its contents */
        __TRANSPOSE_FIELD(pager_created);
        __TRANSPOSE_FIELD(pager_initialized);
        __TRANSPOSE_FIELD(pager_ready);
        __TRANSPOSE_FIELD(pager_trusted);
        __TRANSPOSE_FIELD(can_persist);
        __TRANSPOSE_FIELD(internal);
        __TRANSPOSE_FIELD(private);
        __TRANSPOSE_FIELD(pageout);
        /* "alive" should be set */
        assert(object1->alive);
        assert(object2->alive);
        /* "purgeable" should be non-purgeable */
        assert(object1->purgable == VM_PURGABLE_DENY);
        assert(object2->purgable == VM_PURGABLE_DENY);
        /* "shadowed" refers to the the object not its contents */
        __TRANSPOSE_FIELD(purgeable_when_ripe);
        __TRANSPOSE_FIELD(true_share);
        /* "terminating" should not be set */
        assert(!object1->terminating);
        assert(!object2->terminating);
        /* transfer "named" reference if needed */
        if (object1->named && !object2->named) {
                assert(object1->ref_count >= 2);
                assert(object2->ref_count >= 1);
                object1->ref_count--;
                object2->ref_count++;
        } else if (!object1->named && object2->named) {
                assert(object1->ref_count >= 1);
                assert(object2->ref_count >= 2);
                object1->ref_count++;
                object2->ref_count--;
        }
        __TRANSPOSE_FIELD(named);
        /* "shadow_severed" refers to the object not its contents */
        __TRANSPOSE_FIELD(phys_contiguous);
        __TRANSPOSE_FIELD(nophyscache);
        /* "cached_list.next" points to transposed object */
        object1->cached_list.next = (queue_entry_t) object2;
        object2->cached_list.next = (queue_entry_t) object1;
        /* "cached_list.prev" should be NULL */
        assert(object1->cached_list.prev == NULL);
        assert(object2->cached_list.prev == NULL);
        __TRANSPOSE_FIELD(last_alloc);
        __TRANSPOSE_FIELD(sequential);
        __TRANSPOSE_FIELD(pages_created);
        __TRANSPOSE_FIELD(pages_used);
        __TRANSPOSE_FIELD(scan_collisions);
        __TRANSPOSE_FIELD(cow_hint);
        __TRANSPOSE_FIELD(wimg_bits);
        __TRANSPOSE_FIELD(set_cache_attr);
        __TRANSPOSE_FIELD(code_signed);
        object1->transposed = TRUE;
        object2->transposed = TRUE;
        __TRANSPOSE_FIELD(mapping_in_progress);
        __TRANSPOSE_FIELD(volatile_empty);
        __TRANSPOSE_FIELD(volatile_fault);
        __TRANSPOSE_FIELD(all_reusable);
        assert(object1->blocked_access);
        assert(object2->blocked_access);
        __TRANSPOSE_FIELD(set_cache_attr);
        assert(!object1->object_is_shared_cache);
        assert(!object2->object_is_shared_cache);
        /* ignore purgeable_queue_type and purgeable_queue_group */
        assert(!object1->io_tracking);
        assert(!object2->io_tracking);
#if VM_OBJECT_ACCESS_TRACKING
        assert(!object1->access_tracking);
        assert(!object2->access_tracking);
#endif /* VM_OBJECT_ACCESS_TRACKING */
        __TRANSPOSE_FIELD(no_tag_update);
#if CONFIG_SECLUDED_MEMORY
        assert(!object1->eligible_for_secluded);
        assert(!object2->eligible_for_secluded);
        assert(!object1->can_grab_secluded);
        assert(!object2->can_grab_secluded);
#else /* CONFIG_SECLUDED_MEMORY */
        assert(object1->__object3_unused_bits == 0);
        assert(object2->__object3_unused_bits == 0);
#endif /* CONFIG_SECLUDED_MEMORY */
#if UPL_DEBUG
        /* "uplq" refers to the object not its contents (see upl_transpose()) */
#endif
        assert((object1->purgable == VM_PURGABLE_DENY) || (object1->objq.next == NULL));
        assert((object1->purgable == VM_PURGABLE_DENY) || (object1->objq.prev == NULL));
        assert((object2->purgable == VM_PURGABLE_DENY) || (object2->objq.next == NULL));
        assert((object2->purgable == VM_PURGABLE_DENY) || (object2->objq.prev == NULL));

#undef __TRANSPOSE_FIELD

        retval = KERN_SUCCESS;

done:
        /*
         * Cleanup.
         */
        if (tmp_object != VM_OBJECT_NULL) {
                vm_object_unlock(tmp_object);
                /*
                 * Re-initialize the temporary object to avoid
                 * deallocating a real pager.
                 */
                _vm_object_allocate(transpose_size, tmp_object);
                vm_object_deallocate(tmp_object);
                tmp_object = VM_OBJECT_NULL;
        }

        if (object1_locked) {
                vm_object_unlock(object1);
                object1_locked = FALSE;
        }
        if (object2_locked) {
                vm_object_unlock(object2);
                object2_locked = FALSE;
        }

        vm_object_transpose_count++;

        return retval;
}


/*
 *      vm_object_cluster_size
 *
 *      Determine how big a cluster we should issue an I/O for...
 *
 *      Inputs:   *start == offset of page needed
 *                *length == maximum cluster pager can handle
 *      Outputs:  *start == beginning offset of cluster
 *                *length == length of cluster to try
 *
 *      The original *start will be encompassed by the cluster
 *
 */
extern int speculative_reads_disabled;

/*
 * Try to always keep these values an even multiple of PAGE_SIZE. We use these values
 * to derive min_ph_bytes and max_ph_bytes (IMP: bytes not # of pages) and expect those values to
 * always be page-aligned. The derivation could involve operations (e.g. division)
 * that could give us non-page-size aligned values if we start out with values that
 * are odd multiples of PAGE_SIZE.
 */
#if CONFIG_EMBEDDED
unsigned int preheat_max_bytes = (1024 * 512);
#else /* CONFIG_EMBEDDED */
unsigned int preheat_max_bytes = MAX_UPL_TRANSFER_BYTES;
#endif /* CONFIG_EMBEDDED */
unsigned int preheat_min_bytes = (1024 * 32);


__private_extern__ void
vm_object_cluster_size(vm_object_t object, vm_object_offset_t *start,
    vm_size_t *length, vm_object_fault_info_t fault_info, uint32_t *io_streaming)
{
        vm_size_t               pre_heat_size;
        vm_size_t               tail_size;
        vm_size_t               head_size;
        vm_size_t               max_length;
        vm_size_t               cluster_size;
        vm_object_offset_t      object_size;
        vm_object_offset_t      orig_start;
        vm_object_offset_t      target_start;
        vm_object_offset_t      offset;
        vm_behavior_t           behavior;
        boolean_t               look_behind = TRUE;
        boolean_t               look_ahead  = TRUE;
        boolean_t               isSSD = FALSE;
        uint32_t                throttle_limit;
        int                     sequential_run;
        int                     sequential_behavior = VM_BEHAVIOR_SEQUENTIAL;
        vm_size_t               max_ph_size;
        vm_size_t               min_ph_size;

        assert( !(*length & PAGE_MASK));
        assert( !(*start & PAGE_MASK_64));

        /*
         * remember maxiumum length of run requested
         */
        max_length = *length;
        /*
         * we'll always return a cluster size of at least
         * 1 page, since the original fault must always
         * be processed
         */
        *length = PAGE_SIZE;
        *io_streaming = 0;

        if (speculative_reads_disabled || fault_info == NULL) {
                /*
                 * no cluster... just fault the page in
                 */
                return;
        }
        orig_start = *start;
        target_start = orig_start;
        cluster_size = round_page(fault_info->cluster_size);
        behavior = fault_info->behavior;

        vm_object_lock(object);

        if (object->pager == MEMORY_OBJECT_NULL) {
                goto out;       /* pager is gone for this object, nothing more to do */
        }
        vnode_pager_get_isSSD(object->pager, &isSSD);

        min_ph_size = round_page(preheat_min_bytes);
        max_ph_size = round_page(preheat_max_bytes);

#if !CONFIG_EMBEDDED
        if (isSSD) {
                min_ph_size /= 2;
                max_ph_size /= 8;

                if (min_ph_size & PAGE_MASK_64) {
                        min_ph_size = trunc_page(min_ph_size);
                }

                if (max_ph_size & PAGE_MASK_64) {
                        max_ph_size = trunc_page(max_ph_size);
                }
        }
#endif /* !CONFIG_EMBEDDED */

        if (min_ph_size < PAGE_SIZE) {
                min_ph_size = PAGE_SIZE;
        }

        if (max_ph_size < PAGE_SIZE) {
                max_ph_size = PAGE_SIZE;
        } else if (max_ph_size > MAX_UPL_TRANSFER_BYTES) {
                max_ph_size = MAX_UPL_TRANSFER_BYTES;
        }

        if (max_length > max_ph_size) {
                max_length = max_ph_size;
        }

        if (max_length <= PAGE_SIZE) {
                goto out;
        }

        if (object->internal) {
                object_size = object->vo_size;
        } else {
                vnode_pager_get_object_size(object->pager, &object_size);
        }

        object_size = round_page_64(object_size);

        if (orig_start >= object_size) {
                /*
                 * fault occurred beyond the EOF...
                 * we need to punt w/o changing the
                 * starting offset
                 */
                goto out;
        }
        if (object->pages_used > object->pages_created) {
                /*
                 * must have wrapped our 32 bit counters
                 * so reset
                 */
                object->pages_used = object->pages_created = 0;
        }
        if ((sequential_run = object->sequential)) {
                if (sequential_run < 0) {
                        sequential_behavior = VM_BEHAVIOR_RSEQNTL;
                        sequential_run = 0 - sequential_run;
                } else {
                        sequential_behavior = VM_BEHAVIOR_SEQUENTIAL;
                }
        }
        switch (behavior) {
        default:
                behavior = VM_BEHAVIOR_DEFAULT;

        case VM_BEHAVIOR_DEFAULT:
                if (object->internal && fault_info->user_tag == VM_MEMORY_STACK) {
                        goto out;
                }

                if (sequential_run >= (3 * PAGE_SIZE)) {
                        pre_heat_size = sequential_run + PAGE_SIZE;

                        if (sequential_behavior == VM_BEHAVIOR_SEQUENTIAL) {
                                look_behind = FALSE;
                        } else {
                                look_ahead = FALSE;
                        }

                        *io_streaming = 1;
                } else {
                        if (object->pages_created < (20 * (min_ph_size >> PAGE_SHIFT))) {
                                /*
                                 * prime the pump
                                 */
                                pre_heat_size = min_ph_size;
                        } else {
                                /*
                                 * Linear growth in PH size: The maximum size is max_length...
                                 * this cacluation will result in a size that is neither a
                                 * power of 2 nor a multiple of PAGE_SIZE... so round
                                 * it up to the nearest PAGE_SIZE boundary
                                 */
                                pre_heat_size = (max_length * (uint64_t)object->pages_used) / object->pages_created;

                                if (pre_heat_size < min_ph_size) {
                                        pre_heat_size = min_ph_size;
                                } else {
                                        pre_heat_size = round_page(pre_heat_size);
                                }
                        }
                }
                break;

        case VM_BEHAVIOR_RANDOM:
                if ((pre_heat_size = cluster_size) <= PAGE_SIZE) {
                        goto out;
                }
                break;

        case VM_BEHAVIOR_SEQUENTIAL:
                if ((pre_heat_size = cluster_size) == 0) {
                        pre_heat_size = sequential_run + PAGE_SIZE;
                }
                look_behind = FALSE;
                *io_streaming = 1;

                break;

        case VM_BEHAVIOR_RSEQNTL:
                if ((pre_heat_size = cluster_size) == 0) {
                        pre_heat_size = sequential_run + PAGE_SIZE;
                }
                look_ahead = FALSE;
                *io_streaming = 1;

                break;
        }
        throttle_limit = (uint32_t) max_length;
        assert(throttle_limit == max_length);

        if (vnode_pager_get_throttle_io_limit(object->pager, &throttle_limit) == KERN_SUCCESS) {
                if (max_length > throttle_limit) {
                        max_length = throttle_limit;
                }
        }
        if (pre_heat_size > max_length) {
                pre_heat_size = max_length;
        }

        if (behavior == VM_BEHAVIOR_DEFAULT && (pre_heat_size > min_ph_size)) {
                unsigned int consider_free = vm_page_free_count + vm_page_cleaned_count;

                if (consider_free < vm_page_throttle_limit) {
                        pre_heat_size = trunc_page(pre_heat_size / 16);
                } else if (consider_free < vm_page_free_target) {
                        pre_heat_size = trunc_page(pre_heat_size / 4);
                }

                if (pre_heat_size < min_ph_size) {
                        pre_heat_size = min_ph_size;
                }
        }
        if (look_ahead == TRUE) {
                if (look_behind == TRUE) {
                        /*
                         * if we get here its due to a random access...
                         * so we want to center the original fault address
                         * within the cluster we will issue... make sure
                         * to calculate 'head_size' as a multiple of PAGE_SIZE...
                         * 'pre_heat_size' is a multiple of PAGE_SIZE but not
                         * necessarily an even number of pages so we need to truncate
                         * the result to a PAGE_SIZE boundary
                         */
                        head_size = trunc_page(pre_heat_size / 2);

                        if (target_start > head_size) {
                                target_start -= head_size;
                        } else {
                                target_start = 0;
                        }

                        /*
                         * 'target_start' at this point represents the beginning offset
                         * of the cluster we are considering... 'orig_start' will be in
                         * the center of this cluster if we didn't have to clip the start
                         * due to running into the start of the file
                         */
                }
                if ((target_start + pre_heat_size) > object_size) {
                        pre_heat_size = (vm_size_t)(round_page_64(object_size - target_start));
                }
                /*
                 * at this point caclulate the number of pages beyond the original fault
                 * address that we want to consider... this is guaranteed not to extend beyond
                 * the current EOF...
                 */
                assert((vm_size_t)(orig_start - target_start) == (orig_start - target_start));
                tail_size = pre_heat_size - (vm_size_t)(orig_start - target_start) - PAGE_SIZE;
        } else {
                if (pre_heat_size > target_start) {
                        /*
                         * since pre_heat_size is always smaller then 2^32,
                         * if it is larger then target_start (a 64 bit value)
                         * it is safe to clip target_start to 32 bits
                         */
                        pre_heat_size = (vm_size_t) target_start;
                }
                tail_size = 0;
        }
        assert( !(target_start & PAGE_MASK_64));
        assert( !(pre_heat_size & PAGE_MASK_64));

        if (pre_heat_size <= PAGE_SIZE) {
                goto out;
        }

        if (look_behind == TRUE) {
                /*
                 * take a look at the pages before the original
                 * faulting offset... recalculate this in case
                 * we had to clip 'pre_heat_size' above to keep
                 * from running past the EOF.
                 */
                head_size = pre_heat_size - tail_size - PAGE_SIZE;

                for (offset = orig_start - PAGE_SIZE_64; head_size; offset -= PAGE_SIZE_64, head_size -= PAGE_SIZE) {
                        /*
                         * don't poke below the lowest offset
                         */
                        if (offset < fault_info->lo_offset) {
                                break;
                        }
                        /*
                         * for external objects or internal objects w/o a pager,
                         * VM_COMPRESSOR_PAGER_STATE_GET will return VM_EXTERNAL_STATE_UNKNOWN
                         */
                        if (VM_COMPRESSOR_PAGER_STATE_GET(object, offset) == VM_EXTERNAL_STATE_ABSENT) {
                                break;
                        }
                        if (vm_page_lookup(object, offset) != VM_PAGE_NULL) {
                                /*
                                 * don't bridge resident pages
                                 */
                                break;
                        }
                        *start = offset;
                        *length += PAGE_SIZE;
                }
        }
        if (look_ahead == TRUE) {
                for (offset = orig_start + PAGE_SIZE_64; tail_size; offset += PAGE_SIZE_64, tail_size -= PAGE_SIZE) {
                        /*
                         * don't poke above the highest offset
                         */
                        if (offset >= fault_info->hi_offset) {
                                break;
                        }
                        assert(offset < object_size);

                        /*
                         * for external objects or internal objects w/o a pager,
                         * VM_COMPRESSOR_PAGER_STATE_GET will return VM_EXTERNAL_STATE_UNKNOWN
                         */
                        if (VM_COMPRESSOR_PAGER_STATE_GET(object, offset) == VM_EXTERNAL_STATE_ABSENT) {
                                break;
                        }
                        if (vm_page_lookup(object, offset) != VM_PAGE_NULL) {
                                /*
                                 * don't bridge resident pages
                                 */
                                break;
                        }
                        *length += PAGE_SIZE;
                }
        }
out:
        if (*length > max_length) {
                *length = max_length;
        }

        vm_object_unlock(object);

        DTRACE_VM1(clustersize, vm_size_t, *length);
}


/*
 * Allow manipulation of individual page state.  This is actually part of
 * the UPL regimen but takes place on the VM object rather than on a UPL
 */

kern_return_t
vm_object_page_op(
        vm_object_t             object,
        vm_object_offset_t      offset,
        int                     ops,
        ppnum_t                 *phys_entry,
        int                     *flags)
{
        vm_page_t               dst_page;

        vm_object_lock(object);

        if (ops & UPL_POP_PHYSICAL) {
                if (object->phys_contiguous) {
                        if (phys_entry) {
                                *phys_entry = (ppnum_t)
                                    (object->vo_shadow_offset >> PAGE_SHIFT);
                        }
                        vm_object_unlock(object);
                        return KERN_SUCCESS;
                } else {
                        vm_object_unlock(object);
                        return KERN_INVALID_OBJECT;
                }
        }
        if (object->phys_contiguous) {
                vm_object_unlock(object);
                return KERN_INVALID_OBJECT;
        }

        while (TRUE) {
                if ((dst_page = vm_page_lookup(object, offset)) == VM_PAGE_NULL) {
                        vm_object_unlock(object);
                        return KERN_FAILURE;
                }

                /* Sync up on getting the busy bit */
                if ((dst_page->vmp_busy || dst_page->vmp_cleaning) &&
                    (((ops & UPL_POP_SET) &&
                    (ops & UPL_POP_BUSY)) || (ops & UPL_POP_DUMP))) {
                        /* someone else is playing with the page, we will */
                        /* have to wait */
                        PAGE_SLEEP(object, dst_page, THREAD_UNINT);
                        continue;
                }

                if (ops & UPL_POP_DUMP) {
                        if (dst_page->vmp_pmapped == TRUE) {
                                pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(dst_page));
                        }

                        VM_PAGE_FREE(dst_page);
                        break;
                }

                if (flags) {
                        *flags = 0;

                        /* Get the condition of flags before requested ops */
                        /* are undertaken */

                        if (dst_page->vmp_dirty) {
                                *flags |= UPL_POP_DIRTY;
                        }
                        if (dst_page->vmp_free_when_done) {
                                *flags |= UPL_POP_PAGEOUT;
                        }
                        if (dst_page->vmp_precious) {
                                *flags |= UPL_POP_PRECIOUS;
                        }
                        if (dst_page->vmp_absent) {
                                *flags |= UPL_POP_ABSENT;
                        }
                        if (dst_page->vmp_busy) {
                                *flags |= UPL_POP_BUSY;
                        }
                }

                /* The caller should have made a call either contingent with */
                /* or prior to this call to set UPL_POP_BUSY */
                if (ops & UPL_POP_SET) {
                        /* The protection granted with this assert will */
                        /* not be complete.  If the caller violates the */
                        /* convention and attempts to change page state */
                        /* without first setting busy we may not see it */
                        /* because the page may already be busy.  However */
                        /* if such violations occur we will assert sooner */
                        /* or later. */
                        assert(dst_page->vmp_busy || (ops & UPL_POP_BUSY));
                        if (ops & UPL_POP_DIRTY) {
                                SET_PAGE_DIRTY(dst_page, FALSE);
                        }
                        if (ops & UPL_POP_PAGEOUT) {
                                dst_page->vmp_free_when_done = TRUE;
                        }
                        if (ops & UPL_POP_PRECIOUS) {
                                dst_page->vmp_precious = TRUE;
                        }
                        if (ops & UPL_POP_ABSENT) {
                                dst_page->vmp_absent = TRUE;
                        }
                        if (ops & UPL_POP_BUSY) {
                                dst_page->vmp_busy = TRUE;
                        }
                }

                if (ops & UPL_POP_CLR) {
                        assert(dst_page->vmp_busy);
                        if (ops & UPL_POP_DIRTY) {
                                dst_page->vmp_dirty = FALSE;
                        }
                        if (ops & UPL_POP_PAGEOUT) {
                                dst_page->vmp_free_when_done = FALSE;
                        }
                        if (ops & UPL_POP_PRECIOUS) {
                                dst_page->vmp_precious = FALSE;
                        }
                        if (ops & UPL_POP_ABSENT) {
                                dst_page->vmp_absent = FALSE;
                        }
                        if (ops & UPL_POP_BUSY) {
                                dst_page->vmp_busy = FALSE;
                                PAGE_WAKEUP(dst_page);
                        }
                }
                if (phys_entry) {
                        /*
                         * The physical page number will remain valid
                         * only if the page is kept busy.
                         */
                        assert(dst_page->vmp_busy);
                        *phys_entry = VM_PAGE_GET_PHYS_PAGE(dst_page);
                }

                break;
        }

        vm_object_unlock(object);
        return KERN_SUCCESS;
}

/*
 * vm_object_range_op offers performance enhancement over
 * vm_object_page_op for page_op functions which do not require page
 * level state to be returned from the call.  Page_op was created to provide
 * a low-cost alternative to page manipulation via UPLs when only a single
 * page was involved.  The range_op call establishes the ability in the _op
 * family of functions to work on multiple pages where the lack of page level
 * state handling allows the caller to avoid the overhead of the upl structures.
 */

kern_return_t
vm_object_range_op(
        vm_object_t             object,
        vm_object_offset_t      offset_beg,
        vm_object_offset_t      offset_end,
        int                     ops,
        uint32_t                *range)
{
        vm_object_offset_t      offset;
        vm_page_t               dst_page;

        if (offset_end - offset_beg > (uint32_t) -1) {
                /* range is too big and would overflow "*range" */
                return KERN_INVALID_ARGUMENT;
        }
        if (object->resident_page_count == 0) {
                if (range) {
                        if (ops & UPL_ROP_PRESENT) {
                                *range = 0;
                        } else {
                                *range = (uint32_t) (offset_end - offset_beg);
                                assert(*range == (offset_end - offset_beg));
                        }
                }
                return KERN_SUCCESS;
        }
        vm_object_lock(object);

        if (object->phys_contiguous) {
                vm_object_unlock(object);
                return KERN_INVALID_OBJECT;
        }

        offset = offset_beg & ~PAGE_MASK_64;

        while (offset < offset_end) {
                dst_page = vm_page_lookup(object, offset);
                if (dst_page != VM_PAGE_NULL) {
                        if (ops & UPL_ROP_DUMP) {
                                if (dst_page->vmp_busy || dst_page->vmp_cleaning) {
                                        /*
                                         * someone else is playing with the
                                         * page, we will have to wait
                                         */
                                        PAGE_SLEEP(object, dst_page, THREAD_UNINT);
                                        /*
                                         * need to relook the page up since it's
                                         * state may have changed while we slept
                                         * it might even belong to a different object
                                         * at this point
                                         */
                                        continue;
                                }
                                if (dst_page->vmp_laundry) {
                                        vm_pageout_steal_laundry(dst_page, FALSE);
                                }

                                if (dst_page->vmp_pmapped == TRUE) {
                                        pmap_disconnect(VM_PAGE_GET_PHYS_PAGE(dst_page));
                                }

                                VM_PAGE_FREE(dst_page);
                        } else if ((ops & UPL_ROP_ABSENT)
                            && (!dst_page->vmp_absent || dst_page->vmp_busy)) {
                                break;
                        }
                } else if (ops & UPL_ROP_PRESENT) {
                        break;
                }

                offset += PAGE_SIZE;
        }
        vm_object_unlock(object);

        if (range) {
                if (offset > offset_end) {
                        offset = offset_end;
                }
                if (offset > offset_beg) {
                        *range = (uint32_t) (offset - offset_beg);
                        assert(*range == (offset - offset_beg));
                } else {
                        *range = 0;
                }
        }
        return KERN_SUCCESS;
}

/*
 * Used to point a pager directly to a range of memory (when the pager may be associated
 *   with a non-device vnode).  Takes a virtual address, an offset, and a size.  We currently
 *   expect that the virtual address will denote the start of a range that is physically contiguous.
 */
kern_return_t
pager_map_to_phys_contiguous(
        memory_object_control_t object,
        memory_object_offset_t  offset,
        addr64_t                base_vaddr,
        vm_size_t               size)
{
        ppnum_t page_num;
        boolean_t clobbered_private;
        kern_return_t retval;
        vm_object_t pager_object;

        page_num = pmap_find_phys(kernel_pmap, base_vaddr);

        if (!page_num) {
                retval = KERN_FAILURE;
                goto out;
        }

        pager_object = memory_object_control_to_vm_object(object);

        if (!pager_object) {
                retval = KERN_FAILURE;
                goto out;
        }

        clobbered_private = pager_object->private;
        if (pager_object->private != TRUE) {
                vm_object_lock(pager_object);
                pager_object->private = TRUE;
                vm_object_unlock(pager_object);
        }
        retval = vm_object_populate_with_private(pager_object, offset, page_num, size);

        if (retval != KERN_SUCCESS) {
                if (pager_object->private != clobbered_private) {
                        vm_object_lock(pager_object);
                        pager_object->private = clobbered_private;
                        vm_object_unlock(pager_object);
                }
        }

out:
        return retval;
}

uint32_t scan_object_collision = 0;

void
vm_object_lock(vm_object_t object)
{
        if (object == vm_pageout_scan_wants_object) {
                scan_object_collision++;
                mutex_pause(2);
        }
        DTRACE_VM(vm_object_lock_w);
        lck_rw_lock_exclusive(&object->Lock);
#if DEVELOPMENT || DEBUG
        object->Lock_owner = current_thread();
#endif
}

boolean_t
vm_object_lock_avoid(vm_object_t object)
{
        if (object == vm_pageout_scan_wants_object) {
                scan_object_collision++;
                return TRUE;
        }
        return FALSE;
}

boolean_t
_vm_object_lock_try(vm_object_t object)
{
        boolean_t       retval;

        retval = lck_rw_try_lock_exclusive(&object->Lock);
#if DEVELOPMENT || DEBUG
        if (retval == TRUE) {
                DTRACE_VM(vm_object_lock_w);
                object->Lock_owner = current_thread();
        }
#endif
        return retval;
}

boolean_t
vm_object_lock_try(vm_object_t object)
{
        /*
         * Called from hibernate path so check before blocking.
         */
        if (vm_object_lock_avoid(object) && ml_get_interrupts_enabled() && get_preemption_level() == 0) {
                mutex_pause(2);
        }
        return _vm_object_lock_try(object);
}

void
vm_object_lock_shared(vm_object_t object)
{
        if (vm_object_lock_avoid(object)) {
                mutex_pause(2);
        }
        DTRACE_VM(vm_object_lock_r);
        lck_rw_lock_shared(&object->Lock);
}

boolean_t
vm_object_lock_yield_shared(vm_object_t object)
{
        boolean_t retval = FALSE, force_yield = FALSE;;

        vm_object_lock_assert_shared(object);

        force_yield = vm_object_lock_avoid(object);

        retval = lck_rw_lock_yield_shared(&object->Lock, force_yield);
        if (retval) {
                DTRACE_VM(vm_object_lock_yield);
        }

        return retval;
}

boolean_t
vm_object_lock_try_shared(vm_object_t object)
{
        boolean_t retval;

        if (vm_object_lock_avoid(object)) {
                mutex_pause(2);
        }
        retval = lck_rw_try_lock_shared(&object->Lock);
        if (retval) {
                DTRACE_VM(vm_object_lock_r);
        }
        return retval;
}

boolean_t
vm_object_lock_upgrade(vm_object_t object)
{
        boolean_t       retval;

        retval = lck_rw_lock_shared_to_exclusive(&object->Lock);
#if DEVELOPMENT || DEBUG
        if (retval == TRUE) {
                DTRACE_VM(vm_object_lock_w);
                object->Lock_owner = current_thread();
        }
#endif
        return retval;
}

void
vm_object_unlock(vm_object_t object)
{
#if DEVELOPMENT || DEBUG
        if (object->Lock_owner) {
                if (object->Lock_owner != current_thread()) {
                        panic("vm_object_unlock: not owner - %p\n", object);
                }
                object->Lock_owner = 0;
                DTRACE_VM(vm_object_unlock);
        }
#endif
        lck_rw_done(&object->Lock);
}


unsigned int vm_object_change_wimg_mode_count = 0;

/*
 * The object must be locked
 */
void
vm_object_change_wimg_mode(vm_object_t object, unsigned int wimg_mode)
{
        vm_page_t p;

        vm_object_lock_assert_exclusive(object);

        vm_object_paging_wait(object, THREAD_UNINT);

        vm_page_queue_iterate(&object->memq, p, vmp_listq) {
                if (!p->vmp_fictitious) {
                        pmap_set_cache_attributes(VM_PAGE_GET_PHYS_PAGE(p), wimg_mode);
                }
        }
        if (wimg_mode == VM_WIMG_USE_DEFAULT) {
                object->set_cache_attr = FALSE;
        } else {
                object->set_cache_attr = TRUE;
        }

        object->wimg_bits = wimg_mode;

        vm_object_change_wimg_mode_count++;
}

#if CONFIG_FREEZE

/*
 * This routine does the "relocation" of previously
 * compressed pages belonging to this object that are
 * residing in a number of compressed segments into
 * a set of compressed segments dedicated to hold
 * compressed pages belonging to this object.
 */

extern void *freezer_chead;
extern char *freezer_compressor_scratch_buf;
extern int c_freezer_compression_count;
extern AbsoluteTime c_freezer_last_yield_ts;

#define MAX_FREE_BATCH  32
#define FREEZER_DUTY_CYCLE_ON_MS        5
#define FREEZER_DUTY_CYCLE_OFF_MS       5

static int c_freezer_should_yield(void);


static int
c_freezer_should_yield()
{
        AbsoluteTime    cur_time;
        uint64_t        nsecs;

        assert(c_freezer_last_yield_ts);
        clock_get_uptime(&cur_time);

        SUB_ABSOLUTETIME(&cur_time, &c_freezer_last_yield_ts);
        absolutetime_to_nanoseconds(cur_time, &nsecs);

        if (nsecs > 1000 * 1000 * FREEZER_DUTY_CYCLE_ON_MS) {
                return 1;
        }
        return 0;
}


void
vm_object_compressed_freezer_done()
{
        vm_compressor_finished_filling(&freezer_chead);
}


uint32_t
vm_object_compressed_freezer_pageout(
        vm_object_t object, uint32_t dirty_budget)
{
        vm_page_t                       p;
        vm_page_t                       local_freeq = NULL;
        int                             local_freed = 0;
        kern_return_t                   retval = KERN_SUCCESS;
        int                             obj_resident_page_count_snapshot = 0;
        uint32_t                        paged_out_count = 0;

        assert(object != VM_OBJECT_NULL);
        assert(object->internal);

        vm_object_lock(object);

        if (!object->pager_initialized || object->pager == MEMORY_OBJECT_NULL) {
                if (!object->pager_initialized) {
                        vm_object_collapse(object, (vm_object_offset_t) 0, TRUE);

                        if (!object->pager_initialized) {
                                vm_object_compressor_pager_create(object);
                        }
                }

                if (!object->pager_initialized || object->pager == MEMORY_OBJECT_NULL) {
                        vm_object_unlock(object);
                        return paged_out_count;
                }
        }

        if (VM_CONFIG_FREEZER_SWAP_IS_ACTIVE) {
                vm_object_offset_t      curr_offset = 0;

                /*
                 * Go through the object and make sure that any
                 * previously compressed pages are relocated into
                 * a compressed segment associated with our "freezer_chead".
                 */
                while (curr_offset < object->vo_size) {
                        curr_offset = vm_compressor_pager_next_compressed(object->pager, curr_offset);

                        if (curr_offset == (vm_object_offset_t) -1) {
                                break;
                        }

                        retval = vm_compressor_pager_relocate(object->pager, curr_offset, &freezer_chead);

                        if (retval != KERN_SUCCESS) {
                                break;
                        }

                        curr_offset += PAGE_SIZE_64;
                }
        }

        /*
         * We can't hold the object lock while heading down into the compressed pager
         * layer because we might need the kernel map lock down there to allocate new
         * compressor data structures. And if this same object is mapped in the kernel
         * and there's a fault on it, then that thread will want the object lock while
         * holding the kernel map lock.
         *
         * Since we are going to drop/grab the object lock repeatedly, we must make sure
         * we won't be stuck in an infinite loop if the same page(s) keep getting
         * decompressed. So we grab a snapshot of the number of pages in the object and
         * we won't process any more than that number of pages.
         */

        obj_resident_page_count_snapshot = object->resident_page_count;

        vm_object_activity_begin(object);

        while ((obj_resident_page_count_snapshot--) && !vm_page_queue_empty(&object->memq) && paged_out_count < dirty_budget) {
                p = (vm_page_t)vm_page_queue_first(&object->memq);

                KERNEL_DEBUG(0xe0430004 | DBG_FUNC_START, object, local_freed, 0, 0, 0);

                vm_page_lockspin_queues();

                if (p->vmp_cleaning || p->vmp_fictitious || p->vmp_busy || p->vmp_absent || p->vmp_unusual || p->vmp_error || VM_PAGE_WIRED(p)) {
                        vm_page_unlock_queues();

                        KERNEL_DEBUG(0xe0430004 | DBG_FUNC_END, object, local_freed, 1, 0, 0);

                        vm_page_queue_remove(&object->memq, p, vmp_listq);
                        vm_page_queue_enter(&object->memq, p, vmp_listq);

                        continue;
                }

                if (p->vmp_pmapped == TRUE) {
                        int refmod_state, pmap_flags;

                        if (p->vmp_dirty || p->vmp_precious) {
                                pmap_flags = PMAP_OPTIONS_COMPRESSOR;
                        } else {
                                pmap_flags = PMAP_OPTIONS_COMPRESSOR_IFF_MODIFIED;
                        }

                        refmod_state = pmap_disconnect_options(VM_PAGE_GET_PHYS_PAGE(p), pmap_flags, NULL);
                        if (refmod_state & VM_MEM_MODIFIED) {
                                SET_PAGE_DIRTY(p, FALSE);
                        }
                }

                if (p->vmp_dirty == FALSE && p->vmp_precious == FALSE) {
                        /*
                         * Clean and non-precious page.
                         */
                        vm_page_unlock_queues();
                        VM_PAGE_FREE(p);

                        KERNEL_DEBUG(0xe0430004 | DBG_FUNC_END, object, local_freed, 2, 0, 0);
                        continue;
                }

                if (p->vmp_laundry) {
                        vm_pageout_steal_laundry(p, TRUE);
                }

                vm_page_queues_remove(p, TRUE);

                vm_page_unlock_queues();


                /*
                 * In case the compressor fails to compress this page, we need it at
                 * the back of the object memq so that we don't keep trying to process it.
                 * Make the move here while we have the object lock held.
                 */

                vm_page_queue_remove(&object->memq, p, vmp_listq);
                vm_page_queue_enter(&object->memq, p, vmp_listq);

                /*
                 * Grab an activity_in_progress here for vm_pageout_compress_page() to consume.
                 *
                 * Mark the page busy so no one messes with it while we have the object lock dropped.
                 */
                p->vmp_busy = TRUE;

                vm_object_activity_begin(object);

                vm_object_unlock(object);

                if (vm_pageout_compress_page(&freezer_chead, freezer_compressor_scratch_buf, p) == KERN_SUCCESS) {
                        /*
                         * page has already been un-tabled from the object via 'vm_page_remove'
                         */
                        p->vmp_snext = local_freeq;
                        local_freeq = p;
                        local_freed++;
                        paged_out_count++;

                        if (local_freed >= MAX_FREE_BATCH) {
                                OSAddAtomic64(local_freed, &vm_pageout_vminfo.vm_pageout_compressions);

                                vm_page_free_list(local_freeq, TRUE);

                                local_freeq = NULL;
                                local_freed = 0;
                        }
                        c_freezer_compression_count++;
                }
                KERNEL_DEBUG(0xe0430004 | DBG_FUNC_END, object, local_freed, 0, 0, 0);

                if (local_freed == 0 && c_freezer_should_yield()) {
                        thread_yield_internal(FREEZER_DUTY_CYCLE_OFF_MS);
                        clock_get_uptime(&c_freezer_last_yield_ts);
                }

                vm_object_lock(object);
        }

        if (local_freeq) {
                OSAddAtomic64(local_freed, &vm_pageout_vminfo.vm_pageout_compressions);

                vm_page_free_list(local_freeq, TRUE);

                local_freeq = NULL;
                local_freed = 0;
        }

        vm_object_activity_end(object);

        vm_object_unlock(object);

        if (c_freezer_should_yield()) {
                thread_yield_internal(FREEZER_DUTY_CYCLE_OFF_MS);
                clock_get_uptime(&c_freezer_last_yield_ts);
        }
        return paged_out_count;
}

#endif /* CONFIG_FREEZE */


void
vm_object_pageout(
        vm_object_t object)
{
        vm_page_t                       p, next;
        struct  vm_pageout_queue        *iq;

        if (!VM_CONFIG_COMPRESSOR_IS_PRESENT) {
                return;
        }

        iq = &vm_pageout_queue_internal;

        assert(object != VM_OBJECT_NULL );

        vm_object_lock(object);

        if (!object->internal ||
            object->terminating ||
            !object->alive) {
                vm_object_unlock(object);
                return;
        }

        if (!object->pager_initialized || object->pager == MEMORY_OBJECT_NULL) {
                if (!object->pager_initialized) {
                        vm_object_collapse(object, (vm_object_offset_t) 0, TRUE);

                        if (!object->pager_initialized) {
                                vm_object_compressor_pager_create(object);
                        }
                }

                if (!object->pager_initialized || object->pager == MEMORY_OBJECT_NULL) {
                        vm_object_unlock(object);
                        return;
                }
        }

ReScan:
        next = (vm_page_t)vm_page_queue_first(&object->memq);

        while (!vm_page_queue_end(&object->memq, (vm_page_queue_entry_t)next)) {
                p = next;
                next = (vm_page_t)vm_page_queue_next(&next->vmp_listq);

                assert(p->vmp_q_state != VM_PAGE_ON_FREE_Q);

                if ((p->vmp_q_state == VM_PAGE_ON_THROTTLED_Q) ||
                    p->vmp_cleaning ||
                    p->vmp_laundry ||
                    p->vmp_busy ||
                    p->vmp_absent ||
                    p->vmp_error ||
                    p->vmp_fictitious ||
                    VM_PAGE_WIRED(p)) {
                        /*
                         * Page is already being cleaned or can't be cleaned.
                         */
                        continue;
                }
                if (vm_compressor_low_on_space()) {
                        break;
                }

                /* Throw to the pageout queue */

                vm_page_lockspin_queues();

                if (VM_PAGE_Q_THROTTLED(iq)) {
                        iq->pgo_draining = TRUE;

                        assert_wait((event_t) (&iq->pgo_laundry + 1),
                            THREAD_INTERRUPTIBLE);
                        vm_page_unlock_queues();
                        vm_object_unlock(object);

                        thread_block(THREAD_CONTINUE_NULL);

                        vm_object_lock(object);
                        goto ReScan;
                }

                assert(!p->vmp_fictitious);
                assert(!p->vmp_busy);
                assert(!p->vmp_absent);
                assert(!p->vmp_unusual);
                assert(!p->vmp_error);
                assert(!VM_PAGE_WIRED(p));
                assert(!p->vmp_cleaning);

                if (p->vmp_pmapped == TRUE) {
                        int refmod_state;
                        int pmap_options;

                        /*
                         * Tell pmap the page should be accounted
                         * for as "compressed" if it's been modified.
                         */
                        pmap_options =
                            PMAP_OPTIONS_COMPRESSOR_IFF_MODIFIED;
                        if (p->vmp_dirty || p->vmp_precious) {
                                /*
                                 * We already know it's been modified,
                                 * so tell pmap to account for it
                                 * as "compressed".
                                 */
                                pmap_options = PMAP_OPTIONS_COMPRESSOR;
                        }
                        refmod_state = pmap_disconnect_options(VM_PAGE_GET_PHYS_PAGE(p),
                            pmap_options,
                            NULL);
                        if (refmod_state & VM_MEM_MODIFIED) {
                                SET_PAGE_DIRTY(p, FALSE);
                        }
                }

                if (!p->vmp_dirty && !p->vmp_precious) {
                        vm_page_unlock_queues();
                        VM_PAGE_FREE(p);
                        continue;
                }
                vm_page_queues_remove(p, TRUE);

                vm_pageout_cluster(p);

                vm_page_unlock_queues();
        }
        vm_object_unlock(object);
}


#if CONFIG_IOSCHED
void
vm_page_request_reprioritize(vm_object_t o, uint64_t blkno, uint32_t len, int prio)
{
        io_reprioritize_req_t   req;
        struct vnode            *devvp = NULL;

        if (vnode_pager_get_object_devvp(o->pager, (uintptr_t *)&devvp) != KERN_SUCCESS) {
                return;
        }

        /*
         * Create the request for I/O reprioritization.
         * We use the noblock variant of zalloc because we're holding the object
         * lock here and we could cause a deadlock in low memory conditions.
         */
        req = (io_reprioritize_req_t)zalloc_noblock(io_reprioritize_req_zone);
        if (req == NULL) {
                return;
        }
        req->blkno = blkno;
        req->len = len;
        req->priority = prio;
        req->devvp = devvp;

        /* Insert request into the reprioritization list */
        IO_REPRIORITIZE_LIST_LOCK();
        queue_enter(&io_reprioritize_list, req, io_reprioritize_req_t, io_reprioritize_list);
        IO_REPRIORITIZE_LIST_UNLOCK();

        /* Wakeup reprioritize thread */
        IO_REPRIO_THREAD_WAKEUP();

        return;
}

void
vm_decmp_upl_reprioritize(upl_t upl, int prio)
{
        int offset;
        vm_object_t object;
        io_reprioritize_req_t   req;
        struct vnode            *devvp = NULL;
        uint64_t                blkno;
        uint32_t                len;
        upl_t                   io_upl;
        uint64_t                *io_upl_reprio_info;
        int                     io_upl_size;

        if ((upl->flags & UPL_TRACKED_BY_OBJECT) == 0 || (upl->flags & UPL_EXPEDITE_SUPPORTED) == 0) {
                return;
        }

        /*
         * We dont want to perform any allocations with the upl lock held since that might
         * result in a deadlock. If the system is low on memory, the pageout thread would
         * try to pageout stuff and might wait on this lock. If we are waiting for the memory to
         * be freed up by the pageout thread, it would be a deadlock.
         */


        /* First step is just to get the size of the upl to find out how big the reprio info is */
        if (!upl_try_lock(upl)) {
                return;
        }

        if (upl->decmp_io_upl == NULL) {
                /* The real I/O upl was destroyed by the time we came in here. Nothing to do. */
                upl_unlock(upl);
                return;
        }

        io_upl = upl->decmp_io_upl;
        assert((io_upl->flags & UPL_DECMP_REAL_IO) != 0);
        io_upl_size = io_upl->size;
        upl_unlock(upl);

        /* Now perform the allocation */
        io_upl_reprio_info = (uint64_t *)kalloc(sizeof(uint64_t) * (io_upl_size / PAGE_SIZE));
        if (io_upl_reprio_info == NULL) {
                return;
        }

        /* Now again take the lock, recheck the state and grab out the required info */
        if (!upl_try_lock(upl)) {
                goto out;
        }

        if (upl->decmp_io_upl == NULL || upl->decmp_io_upl != io_upl) {
                /* The real I/O upl was destroyed by the time we came in here. Nothing to do. */
                upl_unlock(upl);
                goto out;
        }
        memcpy(io_upl_reprio_info, io_upl->upl_reprio_info, sizeof(uint64_t) * (io_upl_size / PAGE_SIZE));

        /* Get the VM object for this UPL */
        if (io_upl->flags & UPL_SHADOWED) {
                object = io_upl->map_object->shadow;
        } else {
                object = io_upl->map_object;
        }

        /* Get the dev vnode ptr for this object */
        if (!object || !object->pager ||
            vnode_pager_get_object_devvp(object->pager, (uintptr_t *)&devvp) != KERN_SUCCESS) {
                upl_unlock(upl);
                goto out;
        }

        upl_unlock(upl);

        /* Now we have all the information needed to do the expedite */

        offset = 0;
        while (offset < io_upl_size) {
                blkno   = io_upl_reprio_info[(offset / PAGE_SIZE)] & UPL_REPRIO_INFO_MASK;
                len     = (io_upl_reprio_info[(offset / PAGE_SIZE)] >> UPL_REPRIO_INFO_SHIFT) & UPL_REPRIO_INFO_MASK;

                /*
                 * This implementation may cause some spurious expedites due to the
                 * fact that we dont cleanup the blkno & len from the upl_reprio_info
                 * even after the I/O is complete.
                 */

                if (blkno != 0 && len != 0) {
                        /* Create the request for I/O reprioritization */
                        req = (io_reprioritize_req_t)zalloc(io_reprioritize_req_zone);
                        assert(req != NULL);
                        req->blkno = blkno;
                        req->len = len;
                        req->priority = prio;
                        req->devvp = devvp;

                        /* Insert request into the reprioritization list */
                        IO_REPRIORITIZE_LIST_LOCK();
                        queue_enter(&io_reprioritize_list, req, io_reprioritize_req_t, io_reprioritize_list);
                        IO_REPRIORITIZE_LIST_UNLOCK();

                        offset += len;
                } else {
                        offset += PAGE_SIZE;
                }
        }

        /* Wakeup reprioritize thread */
        IO_REPRIO_THREAD_WAKEUP();

out:
        kfree(io_upl_reprio_info, sizeof(uint64_t) * (io_upl_size / PAGE_SIZE));
        return;
}

void
vm_page_handle_prio_inversion(vm_object_t o, vm_page_t m)
{
        upl_t upl;
        upl_page_info_t *pl;
        unsigned int i, num_pages;
        int cur_tier;

        cur_tier = proc_get_effective_thread_policy(current_thread(), TASK_POLICY_IO);

        /*
         *  Scan through all UPLs associated with the object to find the
         *  UPL containing the contended page.
         */
        queue_iterate(&o->uplq, upl, upl_t, uplq) {
                if (((upl->flags & UPL_EXPEDITE_SUPPORTED) == 0) || upl->upl_priority <= cur_tier) {
                        continue;
                }
                pl = UPL_GET_INTERNAL_PAGE_LIST(upl);
                num_pages = (upl->size / PAGE_SIZE);

                /*
                 *  For each page in the UPL page list, see if it matches the contended
                 *  page and was issued as a low prio I/O.
                 */
                for (i = 0; i < num_pages; i++) {
                        if (UPL_PAGE_PRESENT(pl, i) && VM_PAGE_GET_PHYS_PAGE(m) == pl[i].phys_addr) {
                                if ((upl->flags & UPL_DECMP_REQ) && upl->decmp_io_upl) {
                                        KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, VM_PAGE_EXPEDITE)) | DBG_FUNC_NONE, VM_KERNEL_UNSLIDE_OR_PERM(upl->upl_creator), VM_KERNEL_UNSLIDE_OR_PERM(m),
                                            VM_KERNEL_UNSLIDE_OR_PERM(upl), upl->upl_priority, 0);
                                        vm_decmp_upl_reprioritize(upl, cur_tier);
                                        break;
                                }
                                KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, VM_PAGE_EXPEDITE)) | DBG_FUNC_NONE, VM_KERNEL_UNSLIDE_OR_PERM(upl->upl_creator), VM_KERNEL_UNSLIDE_OR_PERM(m),
                                    upl->upl_reprio_info[i], upl->upl_priority, 0);
                                if (UPL_REPRIO_INFO_BLKNO(upl, i) != 0 && UPL_REPRIO_INFO_LEN(upl, i) != 0) {
                                        vm_page_request_reprioritize(o, UPL_REPRIO_INFO_BLKNO(upl, i), UPL_REPRIO_INFO_LEN(upl, i), cur_tier);
                                }
                                break;
                        }
                }
                /* Check if we found any hits */
                if (i != num_pages) {
                        break;
                }
        }

        return;
}

wait_result_t
vm_page_sleep(vm_object_t o, vm_page_t m, int interruptible)
{
        wait_result_t ret;

        KERNEL_DEBUG((MACHDBG_CODE(DBG_MACH_VM, VM_PAGE_SLEEP)) | DBG_FUNC_START, o, m, 0, 0, 0);

        if (o->io_tracking && ((m->vmp_busy == TRUE) || (m->vmp_cleaning == TRUE) || VM_PAGE_WIRED(m))) {
                /*
                 *  Indicates page is busy due to an I/O. Issue a reprioritize request if necessary.
                 */
                vm_page_handle_prio_inversion(o, m);
        }
        m->vmp_wanted = TRUE;
        ret = thread_sleep_vm_object(o, m, interruptible);
        KERNEL_DEBUG((MACHDBG_CODE(DBG_MACH_VM, VM_PAGE_SLEEP)) | DBG_FUNC_END, o, m, 0, 0, 0);
        return ret;
}

static void
io_reprioritize_thread(void *param __unused, wait_result_t wr __unused)
{
        io_reprioritize_req_t   req = NULL;

        while (1) {
                IO_REPRIORITIZE_LIST_LOCK();
                if (queue_empty(&io_reprioritize_list)) {
                        IO_REPRIORITIZE_LIST_UNLOCK();
                        break;
                }

                queue_remove_first(&io_reprioritize_list, req, io_reprioritize_req_t, io_reprioritize_list);
                IO_REPRIORITIZE_LIST_UNLOCK();

                vnode_pager_issue_reprioritize_io(req->devvp, req->blkno, req->len, req->priority);
                zfree(io_reprioritize_req_zone, req);
        }

        IO_REPRIO_THREAD_CONTINUATION();
}
#endif

#if VM_OBJECT_ACCESS_TRACKING
void
vm_object_access_tracking(
        vm_object_t     object,
        int             *access_tracking_p,
        uint32_t        *access_tracking_reads_p,
        uint32_t        *access_tracking_writes_p)
{
        int     access_tracking;

        access_tracking = !!*access_tracking_p;

        vm_object_lock(object);
        *access_tracking_p = object->access_tracking;
        if (access_tracking_reads_p) {
                *access_tracking_reads_p = object->access_tracking_reads;
        }
        if (access_tracking_writes_p) {
                *access_tracking_writes_p = object->access_tracking_writes;
        }
        object->access_tracking = access_tracking;
        object->access_tracking_reads = 0;
        object->access_tracking_writes = 0;
        vm_object_unlock(object);

        if (access_tracking) {
                vm_object_pmap_protect_options(object,
                    0,
                    object->vo_size,
                    PMAP_NULL,
                    0,
                    VM_PROT_NONE,
                    0);
        }
}
#endif /* VM_OBJECT_ACCESS_TRACKING */

void
vm_object_ledger_tag_ledgers(
        vm_object_t     object,
        int             *ledger_idx_volatile,
        int             *ledger_idx_nonvolatile,
        int             *ledger_idx_volatile_compressed,
        int             *ledger_idx_nonvolatile_compressed,
        boolean_t       *do_footprint)
{
        assert(object->shadow == VM_OBJECT_NULL);

        *do_footprint = !object->vo_no_footprint;

        switch (object->vo_ledger_tag) {
        case VM_LEDGER_TAG_NONE:
                /*
                 * Regular purgeable memory:
                 * counts in footprint only when nonvolatile.
                 */
                *do_footprint = TRUE;
                assert(object->purgable != VM_PURGABLE_DENY);
                *ledger_idx_volatile = task_ledgers.purgeable_volatile;
                *ledger_idx_nonvolatile = task_ledgers.purgeable_nonvolatile;
                *ledger_idx_volatile_compressed = task_ledgers.purgeable_volatile_compressed;
                *ledger_idx_nonvolatile_compressed = task_ledgers.purgeable_nonvolatile_compressed;
                break;
        case VM_LEDGER_TAG_DEFAULT:
                /*
                 * "default" tagged memory:
                 * counts in footprint only when nonvolatile and not marked
                 * as "no_footprint".
                 */
                *ledger_idx_volatile = task_ledgers.tagged_nofootprint;
                *ledger_idx_volatile_compressed = task_ledgers.tagged_nofootprint_compressed;
                if (*do_footprint) {
                        *ledger_idx_nonvolatile = task_ledgers.tagged_footprint;
                        *ledger_idx_nonvolatile_compressed = task_ledgers.tagged_footprint_compressed;
                } else {
                        *ledger_idx_nonvolatile = task_ledgers.tagged_nofootprint;
                        *ledger_idx_nonvolatile_compressed = task_ledgers.tagged_nofootprint_compressed;
                }
                break;
        case VM_LEDGER_TAG_NETWORK:
                /*
                 * "network" tagged memory:
                 * never counts in footprint.
                 */
                *do_footprint = FALSE;
                *ledger_idx_volatile = task_ledgers.network_volatile;
                *ledger_idx_volatile_compressed = task_ledgers.network_volatile_compressed;
                *ledger_idx_nonvolatile = task_ledgers.network_nonvolatile;
                *ledger_idx_nonvolatile_compressed = task_ledgers.network_nonvolatile_compressed;
                break;
        case VM_LEDGER_TAG_MEDIA:
                /*
                 * "media" tagged memory:
                 * counts in footprint only when nonvolatile and not marked
                 * as "no footprint".
                 */
                *ledger_idx_volatile = task_ledgers.media_nofootprint;
                *ledger_idx_volatile_compressed = task_ledgers.media_nofootprint_compressed;
                if (*do_footprint) {
                        *ledger_idx_nonvolatile = task_ledgers.media_footprint;
                        *ledger_idx_nonvolatile_compressed = task_ledgers.media_footprint_compressed;
                } else {
                        *ledger_idx_nonvolatile = task_ledgers.media_nofootprint;
                        *ledger_idx_nonvolatile_compressed = task_ledgers.media_nofootprint_compressed;
                }
                break;
        case VM_LEDGER_TAG_GRAPHICS:
                /*
                 * "graphics" tagged memory:
                 * counts in footprint only when nonvolatile and not marked
                 * as "no footprint".
                 */
                *ledger_idx_volatile = task_ledgers.graphics_nofootprint;
                *ledger_idx_volatile_compressed = task_ledgers.graphics_nofootprint_compressed;
                if (*do_footprint) {
                        *ledger_idx_nonvolatile = task_ledgers.graphics_footprint;
                        *ledger_idx_nonvolatile_compressed = task_ledgers.graphics_footprint_compressed;
                } else {
                        *ledger_idx_nonvolatile = task_ledgers.graphics_nofootprint;
                        *ledger_idx_nonvolatile_compressed = task_ledgers.graphics_nofootprint_compressed;
                }
                break;
        case VM_LEDGER_TAG_NEURAL:
                /*
                 * "neural" tagged memory:
                 * counts in footprint only when nonvolatile and not marked
                 * as "no footprint".
                 */
                *ledger_idx_volatile = task_ledgers.neural_nofootprint;
                *ledger_idx_volatile_compressed = task_ledgers.neural_nofootprint_compressed;
                if (*do_footprint) {
                        *ledger_idx_nonvolatile = task_ledgers.neural_footprint;
                        *ledger_idx_nonvolatile_compressed = task_ledgers.neural_footprint_compressed;
                } else {
                        *ledger_idx_nonvolatile = task_ledgers.neural_nofootprint;
                        *ledger_idx_nonvolatile_compressed = task_ledgers.neural_nofootprint_compressed;
                }
                break;
        default:
                panic("%s: object %p has unsupported ledger_tag %d\n",
                    __FUNCTION__, object, object->vo_ledger_tag);
        }
}

kern_return_t
vm_object_ownership_change(
        vm_object_t     object,
        int             new_ledger_tag,
        task_t          new_owner,
        int             new_ledger_flags,
        boolean_t       old_task_objq_locked)
{
        int             old_ledger_tag;
        task_t          old_owner;
        int             resident_count, wired_count;
        unsigned int    compressed_count;
        int             ledger_idx_volatile;
        int             ledger_idx_nonvolatile;
        int             ledger_idx_volatile_compressed;
        int             ledger_idx_nonvolatile_compressed;
        int             ledger_idx;
        int             ledger_idx_compressed;
        boolean_t       do_footprint, old_no_footprint, new_no_footprint;
        boolean_t       new_task_objq_locked;

        vm_object_lock_assert_exclusive(object);

        if (!object->internal) {
                return KERN_INVALID_ARGUMENT;
        }
        if (new_ledger_tag == VM_LEDGER_TAG_NONE &&
            object->purgable == VM_PURGABLE_DENY) {
                /* non-purgeable memory must have a valid non-zero ledger tag */
                return KERN_INVALID_ARGUMENT;
        }
        if (new_ledger_tag < 0 ||
            new_ledger_tag > VM_LEDGER_TAG_MAX) {
                return KERN_INVALID_ARGUMENT;
        }
        if (new_ledger_flags & ~VM_LEDGER_FLAGS) {
                return KERN_INVALID_ARGUMENT;
        }
        if (object->vo_ledger_tag == VM_LEDGER_TAG_NONE &&
            object->purgable == VM_PURGABLE_DENY) {
                /*
                 * This VM object is neither ledger-tagged nor purgeable.
                 * We can convert it to "ledger tag" ownership iff it
                 * has not been used at all yet (no resident pages and
                 * no pager) and it's going to be assigned to a valid task.
                 */
                if (object->resident_page_count != 0 ||
                    object->pager != NULL ||
                    object->pager_created ||
                    object->ref_count != 1 ||
                    object->vo_owner != TASK_NULL ||
                    object->copy_strategy != MEMORY_OBJECT_COPY_NONE ||
                    new_owner == TASK_NULL) {
                        return KERN_FAILURE;
                }
        }

        if (new_ledger_flags & VM_LEDGER_FLAG_NO_FOOTPRINT) {
                new_no_footprint = TRUE;
        } else {
                new_no_footprint = FALSE;
        }
#if __arm64__
        if (!new_no_footprint &&
            object->purgable != VM_PURGABLE_DENY &&
            new_owner != TASK_NULL &&
            new_owner != VM_OBJECT_OWNER_DISOWNED &&
            new_owner->task_legacy_footprint) {
                /*
                 * This task has been granted "legacy footprint" and should
                 * not be charged for its IOKit purgeable memory.  Since we
                 * might now change the accounting of such memory to the
                 * "graphics" ledger, for example, give it the "no footprint"
                 * option.
                 */
                new_no_footprint = TRUE;
        }
#endif /* __arm64__ */
        assert(object->copy_strategy == MEMORY_OBJECT_COPY_NONE);
        assert(object->shadow == VM_OBJECT_NULL);
        assert(object->copy == VM_OBJECT_NULL);

        old_ledger_tag = object->vo_ledger_tag;
        old_no_footprint = object->vo_no_footprint;
        old_owner = VM_OBJECT_OWNER(object);

        DTRACE_VM7(object_ownership_change,
            vm_object_t, object,
            task_t, old_owner,
            int, old_ledger_tag,
            int, old_no_footprint,
            task_t, new_owner,
            int, new_ledger_tag,
            int, new_no_footprint);

        assert(object->internal);
        resident_count = object->resident_page_count - object->wired_page_count;
        wired_count = object->wired_page_count;
        compressed_count = vm_compressor_pager_get_count(object->pager);

        /*
         * Deal with the old owner and/or ledger tag, if needed.
         */
        if (old_owner != TASK_NULL &&
            ((old_owner != new_owner)           /* new owner ... */
            ||                                  /* ... or ... */
            (old_no_footprint != new_no_footprint) /* new "no_footprint" */
            ||                                  /* ... or ... */
            old_ledger_tag != new_ledger_tag)) { /* ... new ledger */
                /*
                 * Take this object off of the old owner's ledgers.
                 */
                vm_object_ledger_tag_ledgers(object,
                    &ledger_idx_volatile,
                    &ledger_idx_nonvolatile,
                    &ledger_idx_volatile_compressed,
                    &ledger_idx_nonvolatile_compressed,
                    &do_footprint);
                if (object->purgable == VM_PURGABLE_VOLATILE ||
                    object->purgable == VM_PURGABLE_EMPTY) {
                        ledger_idx = ledger_idx_volatile;
                        ledger_idx_compressed = ledger_idx_volatile_compressed;
                } else {
                        ledger_idx = ledger_idx_nonvolatile;
                        ledger_idx_compressed = ledger_idx_nonvolatile_compressed;
                }
                if (resident_count) {
                        /*
                         * Adjust the appropriate old owners's ledgers by the
                         * number of resident pages.
                         */
                        ledger_debit(old_owner->ledger,
                            ledger_idx,
                            ptoa_64(resident_count));
                        /* adjust old owner's footprint */
                        if (do_footprint &&
                            object->purgable != VM_PURGABLE_VOLATILE &&
                            object->purgable != VM_PURGABLE_EMPTY) {
                                ledger_debit(old_owner->ledger,
                                    task_ledgers.phys_footprint,
                                    ptoa_64(resident_count));
                        }
                }
                if (wired_count) {
                        /* wired pages are always nonvolatile */
                        ledger_debit(old_owner->ledger,
                            ledger_idx_nonvolatile,
                            ptoa_64(wired_count));
                        if (do_footprint) {
                                ledger_debit(old_owner->ledger,
                                    task_ledgers.phys_footprint,
                                    ptoa_64(wired_count));
                        }
                }
                if (compressed_count) {
                        /*
                         * Adjust the appropriate old owner's ledgers
                         * by the number of compressed pages.
                         */
                        ledger_debit(old_owner->ledger,
                            ledger_idx_compressed,
                            ptoa_64(compressed_count));
                        if (do_footprint &&
                            object->purgable != VM_PURGABLE_VOLATILE &&
                            object->purgable != VM_PURGABLE_EMPTY) {
                                ledger_debit(old_owner->ledger,
                                    task_ledgers.phys_footprint,
                                    ptoa_64(compressed_count));
                        }
                }
                if (old_owner != new_owner) {
                        /* remove object from old_owner's list of owned objects */
                        DTRACE_VM2(object_owner_remove,
                            vm_object_t, object,
                            task_t, old_owner);
                        if (!old_task_objq_locked) {
                                task_objq_lock(old_owner);
                        }
                        old_owner->task_owned_objects--;
                        queue_remove(&old_owner->task_objq, object,
                            vm_object_t, task_objq);
                        switch (object->purgable) {
                        case VM_PURGABLE_NONVOLATILE:
                        case VM_PURGABLE_EMPTY:
                                vm_purgeable_nonvolatile_owner_update(old_owner,
                                    -1);
                                break;
                        case VM_PURGABLE_VOLATILE:
                                vm_purgeable_volatile_owner_update(old_owner,
                                    -1);
                                break;
                        default:
                                break;
                        }
                        if (!old_task_objq_locked) {
                                task_objq_unlock(old_owner);
                        }
                }
        }

        /*
         * Switch to new ledger tag and/or owner.
         */

        new_task_objq_locked = FALSE;
        if (new_owner != old_owner &&
            new_owner != TASK_NULL &&
            new_owner != VM_OBJECT_OWNER_DISOWNED) {
                /*
                 * If the new owner is not accepting new objects ("disowning"),
                 * the object becomes "disowned" and will be added to
                 * the kernel's task_objq.
                 *
                 * Check first without locking, to avoid blocking while the
                 * task is disowning its objects.
                 */
                if (new_owner->task_objects_disowning) {
                        new_owner = VM_OBJECT_OWNER_DISOWNED;
                } else {
                        task_objq_lock(new_owner);
                        /* check again now that we have the lock */
                        if (new_owner->task_objects_disowning) {
                                new_owner = VM_OBJECT_OWNER_DISOWNED;
                                task_objq_unlock(new_owner);
                        } else {
                                new_task_objq_locked = TRUE;
                        }
                }
        }

        object->vo_ledger_tag = new_ledger_tag;
        object->vo_owner = new_owner;
        object->vo_no_footprint = new_no_footprint;

        if (new_owner == VM_OBJECT_OWNER_DISOWNED) {
                /*
                 * Disowned objects are added to the kernel's task_objq but
                 * are marked as owned by "VM_OBJECT_OWNER_DISOWNED" to
                 * differentiate them from objects intentionally owned by
                 * the kernel.
                 */
                assert(old_owner != kernel_task);
                new_owner = kernel_task;
                assert(!new_task_objq_locked);
                task_objq_lock(new_owner);
                new_task_objq_locked = TRUE;
        }

        /*
         * Deal with the new owner and/or ledger tag, if needed.
         */
        if (new_owner != TASK_NULL &&
            ((new_owner != old_owner)           /* new owner ... */
            ||                                  /* ... or ... */
            (new_no_footprint != old_no_footprint) /* ... new "no_footprint" */
            ||                                  /* ... or ... */
            new_ledger_tag != old_ledger_tag)) { /* ... new ledger */
                /*
                 * Add this object to the new owner's ledgers.
                 */
                vm_object_ledger_tag_ledgers(object,
                    &ledger_idx_volatile,
                    &ledger_idx_nonvolatile,
                    &ledger_idx_volatile_compressed,
                    &ledger_idx_nonvolatile_compressed,
                    &do_footprint);
                if (object->purgable == VM_PURGABLE_VOLATILE ||
                    object->purgable == VM_PURGABLE_EMPTY) {
                        ledger_idx = ledger_idx_volatile;
                        ledger_idx_compressed = ledger_idx_volatile_compressed;
                } else {
                        ledger_idx = ledger_idx_nonvolatile;
                        ledger_idx_compressed = ledger_idx_nonvolatile_compressed;
                }
                if (resident_count) {
                        /*
                         * Adjust the appropriate new owners's ledgers by the
                         * number of resident pages.
                         */
                        ledger_credit(new_owner->ledger,
                            ledger_idx,
                            ptoa_64(resident_count));
                        /* adjust new owner's footprint */
                        if (do_footprint &&
                            object->purgable != VM_PURGABLE_VOLATILE &&
                            object->purgable != VM_PURGABLE_EMPTY) {
                                ledger_credit(new_owner->ledger,
                                    task_ledgers.phys_footprint,
                                    ptoa_64(resident_count));
                        }
                }
                if (wired_count) {
                        /* wired pages are always nonvolatile */
                        ledger_credit(new_owner->ledger,
                            ledger_idx_nonvolatile,
                            ptoa_64(wired_count));
                        if (do_footprint) {
                                ledger_credit(new_owner->ledger,
                                    task_ledgers.phys_footprint,
                                    ptoa_64(wired_count));
                        }
                }
                if (compressed_count) {
                        /*
                         * Adjust the new owner's ledgers by the number of
                         * compressed pages.
                         */
                        ledger_credit(new_owner->ledger,
                            ledger_idx_compressed,
                            ptoa_64(compressed_count));
                        if (do_footprint &&
                            object->purgable != VM_PURGABLE_VOLATILE &&
                            object->purgable != VM_PURGABLE_EMPTY) {
                                ledger_credit(new_owner->ledger,
                                    task_ledgers.phys_footprint,
                                    ptoa_64(compressed_count));
                        }
                }
                if (new_owner != old_owner) {
                        /* add object to new_owner's list of owned objects */
                        DTRACE_VM2(object_owner_add,
                            vm_object_t, object,
                            task_t, new_owner);
                        assert(new_task_objq_locked);
                        new_owner->task_owned_objects++;
                        queue_enter(&new_owner->task_objq, object,
                            vm_object_t, task_objq);
                        switch (object->purgable) {
                        case VM_PURGABLE_NONVOLATILE:
                        case VM_PURGABLE_EMPTY:
                                vm_purgeable_nonvolatile_owner_update(new_owner,
                                    +1);
                                break;
                        case VM_PURGABLE_VOLATILE:
                                vm_purgeable_volatile_owner_update(new_owner,
                                    +1);
                                break;
                        default:
                                break;
                        }
                }
        }

        if (new_task_objq_locked) {
                task_objq_unlock(new_owner);
        }

        return KERN_SUCCESS;
}

void
vm_owned_objects_disown(
        task_t  task)
{
        vm_object_t     next_object;
        vm_object_t     object;
        int             collisions;
        kern_return_t   kr;

        if (task == NULL) {
                return;
        }

        collisions = 0;

again:
        if (task->task_objects_disowned) {
                /* task has already disowned its owned objects */
                assert(task->task_volatile_objects == 0);
                assert(task->task_nonvolatile_objects == 0);
                assert(task->task_owned_objects == 0);
                return;
        }

        task_objq_lock(task);

        task->task_objects_disowning = TRUE;

        for (object = (vm_object_t) queue_first(&task->task_objq);
            !queue_end(&task->task_objq, (queue_entry_t) object);
            object = next_object) {
                if (task->task_nonvolatile_objects == 0 &&
                    task->task_volatile_objects == 0 &&
                    task->task_owned_objects == 0) {
                        /* no more objects owned by "task" */
                        break;
                }

                next_object = (vm_object_t) queue_next(&object->task_objq);

#if DEBUG
                assert(object->vo_purgeable_volatilizer == NULL);
#endif /* DEBUG */
                assert(object->vo_owner == task);
                if (!vm_object_lock_try(object)) {
                        task_objq_unlock(task);
                        mutex_pause(collisions++);
                        goto again;
                }
                /* transfer ownership to the kernel */
                assert(VM_OBJECT_OWNER(object) != kernel_task);
                kr = vm_object_ownership_change(
                        object,
                        object->vo_ledger_tag, /* unchanged */
                        VM_OBJECT_OWNER_DISOWNED, /* new owner */
                        0, /* new_ledger_flags */
                        TRUE);  /* old_owner->task_objq locked */
                assert(kr == KERN_SUCCESS);
                assert(object->vo_owner == VM_OBJECT_OWNER_DISOWNED);
                vm_object_unlock(object);
        }

        if (__improbable(task->task_volatile_objects != 0 ||
            task->task_nonvolatile_objects != 0 ||
            task->task_owned_objects != 0)) {
                panic("%s(%p): volatile=%d nonvolatile=%d owned=%d q=%p q_first=%p q_last=%p",
                    __FUNCTION__,
                    task,
                    task->task_volatile_objects,
                    task->task_nonvolatile_objects,
                    task->task_owned_objects,
                    &task->task_objq,
                    queue_first(&task->task_objq),
                    queue_last(&task->task_objq));
        }

        /* there shouldn't be any objects owned by task now */
        assert(task->task_volatile_objects == 0);
        assert(task->task_nonvolatile_objects == 0);
        assert(task->task_owned_objects == 0);
        assert(task->task_objects_disowning);

        /* and we don't need to try and disown again */
        task->task_objects_disowned = TRUE;

        task_objq_unlock(task);
}