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

/*
 * Copyright (c) 2000-2007 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 <ipc/ipc_types.h>
#include <ipc/ipc_port.h>

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

#include <vm/memory_object.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>

/*
 *      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);

extern void             vm_object_remove(
                                vm_object_t     object);

static vm_object_t      vm_object_cache_trim(
                                boolean_t called_from_vm_object_deallocate);

static void             vm_object_deactivate_all_pages(
                                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);

static 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;
vm_object_t                                             kernel_object;


/*
 *      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;

/*
 *      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;

/*
 *      Virtual memory objects that are not referenced by
 *      any address maps, but that are allowed to persist
 *      (an attribute specified by the associated memory manager),
 *      are kept in a queue (vm_object_cached_list).
 *
 *      When an object from this queue is referenced again,
 *      for example to make another address space mapping,
 *      it must be removed from the queue.  That is, the
 *      queue contains *only* objects with zero references.
 *
 *      The kernel may choose to terminate objects from this
 *      queue in order to reclaim storage.  The current policy
 *      is to permit a fixed maximum number of unreferenced
 *      objects (vm_object_cached_max).
 *
 *      A spin lock (accessed by routines
 *      vm_object_cache_{lock,lock_try,unlock}) governs the
 *      object cache.  It must be held when objects are
 *      added to or removed from the cache (in vm_object_terminate).
 *      The routines that acquire a reference to a virtual
 *      memory object based on one of the memory object ports
 *      must also lock the cache.
 *
 *      Ideally, the object cache should be more isolated
 *      from the reference mechanism, so that the lock need
 *      not be held to make simple references.
 */
static queue_head_t     vm_object_cached_list;
static int              vm_object_cached_count=0;
static int              vm_object_cached_high;  /* highest # cached objects */
static int              vm_object_cached_max = 512;     /* may be patched*/

static decl_mutex_data(,vm_object_cached_lock_data)

#define vm_object_cache_lock()          \
                mutex_lock(&vm_object_cached_lock_data)
#define vm_object_cache_lock_try()      \
                mutex_try(&vm_object_cached_lock_data)
#define vm_object_cache_unlock()        \
                mutex_unlock(&vm_object_cached_lock_data)

#define VM_OBJECT_HASH_COUNT            1024
static queue_head_t     vm_object_hashtable[VM_OBJECT_HASH_COUNT];
static struct zone              *vm_object_hash_zone;

struct vm_object_hash_entry {
        queue_chain_t           hash_link;      /* hash chain link */
        memory_object_t pager;          /* pager we represent */
        vm_object_t             object;         /* corresponding object */
        boolean_t               waiting;        /* someone waiting for
                                                 * termination */
};

typedef struct vm_object_hash_entry     *vm_object_hash_entry_t;
#define VM_OBJECT_HASH_ENTRY_NULL       ((vm_object_hash_entry_t) 0)

#define VM_OBJECT_HASH_SHIFT    8
#define vm_object_hash(pager) \
        ((((unsigned)pager) >> VM_OBJECT_HASH_SHIFT) % VM_OBJECT_HASH_COUNT)

void vm_object_hash_entry_free(
        vm_object_hash_entry_t  entry);

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

/*
 *      vm_object_hash_lookup looks up a pager in the hashtable
 *      and returns the corresponding entry, with optional removal.
 */

static vm_object_hash_entry_t
vm_object_hash_lookup(
        memory_object_t pager,
        boolean_t       remove_entry)
{
        register queue_t                bucket;
        register vm_object_hash_entry_t entry;

        bucket = &vm_object_hashtable[vm_object_hash(pager)];

        entry = (vm_object_hash_entry_t)queue_first(bucket);
        while (!queue_end(bucket, (queue_entry_t)entry)) {
                if (entry->pager == pager && !remove_entry)
                        return(entry);
                else if (entry->pager == pager) {
                        queue_remove(bucket, entry,
                                        vm_object_hash_entry_t, hash_link);
                        return(entry);
                }

                entry = (vm_object_hash_entry_t)queue_next(&entry->hash_link);
        }

        return(VM_OBJECT_HASH_ENTRY_NULL);
}

/*
 *      vm_object_hash_enter enters the specified
 *      pager / cache object association in the hashtable.
 */

static void
vm_object_hash_insert(
        vm_object_hash_entry_t  entry)
{
        register queue_t                bucket;

        bucket = &vm_object_hashtable[vm_object_hash(entry->pager)];

        queue_enter(bucket, entry, vm_object_hash_entry_t, hash_link);
}

static vm_object_hash_entry_t
vm_object_hash_entry_alloc(
        memory_object_t pager)
{
        vm_object_hash_entry_t  entry;

        entry = (vm_object_hash_entry_t)zalloc(vm_object_hash_zone);
        entry->pager = pager;
        entry->object = VM_OBJECT_NULL;
        entry->waiting = FALSE;

        return(entry);
}

void
vm_object_hash_entry_free(
        vm_object_hash_entry_t  entry)
{
        zfree(vm_object_hash_zone, entry);
}

/*
 *      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)
{
        XPR(XPR_VM_OBJECT,
                "vm_object_allocate, object 0x%X size 0x%X\n",
                (integer_t)object, size, 0,0,0);

        *object = vm_object_template;
        queue_init(&object->memq);
        queue_init(&object->msr_q);
#ifdef UPL_DEBUG
        queue_init(&object->uplq);
#endif /* UPL_DEBUG */
        vm_object_lock_init(object);
        object->size = size;
}

__private_extern__ vm_object_t
vm_object_allocate(
        vm_object_size_t        size)
{
        register 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_attr_t  vm_object_lck_grp_attr;
lck_attr_t      vm_object_lck_attr;
lck_attr_t      kernel_object_lck_attr;

/*
 *      vm_object_bootstrap:
 *
 *      Initialize the VM objects module.
 */
__private_extern__ void
vm_object_bootstrap(void)
{
        register int    i;

        vm_object_zone = zinit((vm_size_t) sizeof(struct vm_object),
                                round_page_32(512*1024),
                                round_page_32(12*1024),
                                "vm objects");

        queue_init(&vm_object_reaper_queue);
        queue_init(&vm_object_cached_list);
        mutex_init(&vm_object_cached_lock_data, 0);

        vm_object_hash_zone =
                        zinit((vm_size_t) sizeof (struct vm_object_hash_entry),
                              round_page_32(512*1024),
                              round_page_32(12*1024),
                              "vm object hash entries");

        for (i = 0; i < VM_OBJECT_HASH_COUNT; i++)
                queue_init(&vm_object_hashtable[i]);

        vm_object_init_lck_grp();

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

        /* memq; Lock; init after allocation */
        vm_object_template.memq.prev = NULL;
        vm_object_template.memq.next = NULL;
#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 allocate 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
        vm_object_template.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.copy = VM_OBJECT_NULL;
        vm_object_template.shadow = VM_OBJECT_NULL;
        vm_object_template.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;

        /* 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.temporary = 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.shadowed = FALSE;
        vm_object_template.silent_overwrite = FALSE;
        vm_object_template.advisory_pageout = 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.msr_q.prev = NULL;
        vm_object_template.msr_q.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;

#if     MACH_PAGEMAP
        vm_object_template.existence_map = VM_EXTERNAL_NULL;
#endif  /* MACH_PAGEMAP */
        vm_object_template.cow_hint = ~(vm_offset_t)0;
#if     MACH_ASSERT
        vm_object_template.paging_object = VM_OBJECT_NULL;
#endif  /* MACH_ASSERT */

        /* cache bitfields */
        vm_object_template.wimg_bits = VM_WIMG_DEFAULT;
        vm_object_template.code_signed = FALSE;
        vm_object_template.not_in_use = 0;
#ifdef 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;

        
        /*
         *      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.
 */

#ifdef ppc
        _vm_object_allocate((vm_last_addr - VM_MIN_KERNEL_ADDRESS) + 1,
                        kernel_object);
#else
        _vm_object_allocate((VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS) + 1,
                        kernel_object);
#endif
        kernel_object->copy_strategy = MEMORY_OBJECT_COPY_NONE;

        /*
         *      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;
#ifdef ppc
        _vm_object_allocate((vm_last_addr - VM_MIN_KERNEL_ADDRESS) + 1,
                        vm_submap_object);
#else
        _vm_object_allocate((VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS) + 1,
                        vm_submap_object);
#endif
        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);

#if     MACH_PAGEMAP
        vm_external_module_initialize();
#endif  /* MACH_PAGEMAP */
}

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_PREEMPT - 1,
                &thread);
        if (kr != KERN_SUCCESS) {
                panic("failed to launch vm_object_reaper_thread kr=0x%x", kr);
        }
        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_attr_setdefault(&vm_object_lck_attr);
        lck_attr_setdefault(&kernel_object_lck_attr);
        lck_attr_cleardebug(&kernel_object_lck_attr);
}


#define MIGHT_NOT_CACHE_SHADOWS         1
#if     MIGHT_NOT_CACHE_SHADOWS
static int cache_shadows = TRUE;
#endif  /* MIGHT_NOT_CACHE_SHADOWS */

/*
 *      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(
        register vm_object_t    object)
{
        boolean_t       retry_cache_trim = FALSE;
        vm_object_t     shadow = VM_OBJECT_NULL;
        uint32_t        try_failed_count = 0;
        
//      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) {
                vm_object_lock(kernel_object);
                kernel_object->ref_count--;
                if (kernel_object->ref_count == 0) {
                        panic("vm_object_deallocate: losing kernel_object\n");
                }
                vm_object_unlock(kernel_object);
                return;
        }

        if (object->ref_count > 2 ||
            (!object->named && object->ref_count > 1)) {
                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 && original_ref_count > 1)) {
                        atomic_swap = OSCompareAndSwap(
                                original_ref_count,
                                original_ref_count - 1,
                                (UInt32 *) &object->ref_count);
                        if (atomic_swap == FALSE) {
                                vm_object_deallocate_shared_swap_failures++;
                        }

                } else {
                        atomic_swap = FALSE;
                }
                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) {

                /*
                 *      The cache holds a reference (uncounted) to
                 *      the object; we must lock it before removing
                 *      the object.
                 */
                for (;;) {
                        vm_object_cache_lock();

                        /*
                         * if we try to take a regular lock here
                         * we risk deadlocking against someone
                         * holding a lock on this object while
                         * trying to vm_object_deallocate a different
                         * object
                         */
                        if (vm_object_lock_try(object))
                                break;
                        vm_object_cache_unlock();
                        try_failed_count++;

                        mutex_pause(try_failed_count);  /* wait a bit */
                }
                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_unlock(object);
                                vm_object_cache_unlock();
                                        
                                memory_object_unmap(pager);

                                try_failed_count = 0;
                                for (;;) {
                                        vm_object_cache_lock();

                                        /*
                                         * if we try to take a regular lock here
                                         * we risk deadlocking against someone
                                         * holding a lock on this object while
                                         * trying to vm_object_deallocate a different
                                         * object
                                         */
                                        if (vm_object_lock_try(object))
                                                break;
                                        vm_object_cache_unlock();
                                        try_failed_count++;

                                        mutex_pause(try_failed_count);  /* wait a bit */
                                }
                                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);
                        vm_object_cache_unlock();

                        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); 
                        if (retry_cache_trim &&
                            ((object = vm_object_cache_trim(TRUE)) !=
                             VM_OBJECT_NULL)) {
                                continue;
                        }
                        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);
                        vm_object_cache_unlock();
                        thread_block(THREAD_CONTINUE_NULL);
                        continue;
                }

                /*
                 *      If this object can persist, then enter it in
                 *      the cache. Otherwise, terminate it.
                 *
                 *      NOTE:  Only permanent objects are cached, and
                 *      permanent objects cannot have shadows.  This
                 *      affects the residence counting logic in a minor
                 *      way (can do it in-line, mostly).
                 */

                if ((object->can_persist) && (object->alive)) {
                        /*
                         *      Now it is safe to decrement reference count,
                         *      and to return if reference count is > 0.
                         */
                        vm_object_lock_assert_exclusive(object);
                        if (--object->ref_count > 0) {
                                vm_object_res_deallocate(object);
                                vm_object_unlock(object);
                                vm_object_cache_unlock();
                                if (retry_cache_trim &&
                                    ((object = vm_object_cache_trim(TRUE)) !=
                                     VM_OBJECT_NULL)) {
                                        continue;
                                }
                                return;
                        }

#if     MIGHT_NOT_CACHE_SHADOWS
                        /*
                         *      Remove shadow now if we don't
                         *      want to cache shadows.
                         */
                        if (! cache_shadows) {
                                shadow = object->shadow;
                                object->shadow = VM_OBJECT_NULL;
                        }
#endif  /* MIGHT_NOT_CACHE_SHADOWS */

                        /*
                         *      Enter the object onto the queue of
                         *      cached objects, and deactivate
                         *      all of its pages.
                         */
                        assert(object->shadow == VM_OBJECT_NULL);
                        VM_OBJ_RES_DECR(object);
                        XPR(XPR_VM_OBJECT,
                      "vm_o_deallocate: adding %x to cache, queue = (%x, %x)\n",
                                (integer_t)object,
                                (integer_t)vm_object_cached_list.next,
                                (integer_t)vm_object_cached_list.prev,0,0);

                        vm_object_cached_count++;
                        if (vm_object_cached_count > vm_object_cached_high)
                                vm_object_cached_high = vm_object_cached_count;
                        queue_enter(&vm_object_cached_list, object,
                                vm_object_t, cached_list);
                        vm_object_cache_unlock();
                        vm_object_deactivate_all_pages(object);
                        vm_object_unlock(object);

#if     MIGHT_NOT_CACHE_SHADOWS
                        /*
                         *      If we have a shadow that we need
                         *      to deallocate, do so now, remembering
                         *      to trim the cache later.
                         */
                        if (! cache_shadows && shadow != VM_OBJECT_NULL) {
                                object = shadow;
                                retry_cache_trim = TRUE;
                                continue;
                        }
#endif  /* MIGHT_NOT_CACHE_SHADOWS */

                        /*
                         *      Trim the cache. If the cache trim
                         *      returns with a shadow for us to deallocate,
                         *      then remember to retry the cache trim
                         *      when we are done deallocating the shadow.
                         *      Otherwise, we are done.
                         */

                        object = vm_object_cache_trim(TRUE);
                        if (object == VM_OBJECT_NULL) {
                                return;
                        }
                        retry_cache_trim = TRUE;

                } else {
                        /*
                         *      This object is not cachable; terminate it.
                         */
                        XPR(XPR_VM_OBJECT,
         "vm_o_deallocate: !cacheable 0x%X res %d paging_ops %d thread 0x%p ref %d\n",
                            (integer_t)object, object->resident_page_count,
                            object->paging_in_progress,
                            (void *)current_thread(),object->ref_count);

                        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;
                        }
                        if (retry_cache_trim &&
                            ((object = vm_object_cache_trim(TRUE)) !=
                             VM_OBJECT_NULL)) {
                                continue;
                        }
                        return;
                }
        }
        assert(! retry_cache_trim);
}

/*
 *      Check to see whether we really need to trim
 *      down the cache. If so, remove an object from
 *      the cache, terminate it, and repeat.
 *
 *      Called with, and returns with, cache lock unlocked.
 */
vm_object_t
vm_object_cache_trim(
        boolean_t called_from_vm_object_deallocate)
{
        register vm_object_t object = VM_OBJECT_NULL;
        vm_object_t shadow;

        for (;;) {

                /*
                 *      If we no longer need to trim the cache,
                 *      then we are done.
                 */

                vm_object_cache_lock();
                if (vm_object_cached_count <= vm_object_cached_max) {
                        vm_object_cache_unlock();
                        return VM_OBJECT_NULL;
                }

                /*
                 *      We must trim down the cache, so remove
                 *      the first object in the cache.
                 */
                XPR(XPR_VM_OBJECT,
                "vm_object_cache_trim: removing from front of cache (%x, %x)\n",
                        (integer_t)vm_object_cached_list.next,
                        (integer_t)vm_object_cached_list.prev, 0, 0, 0);

                object = (vm_object_t) queue_first(&vm_object_cached_list);
                if(object == (vm_object_t) &vm_object_cached_list) {
                        /* something's wrong with the calling parameter or */
                        /* the value of vm_object_cached_count, just fix   */
                        /* and return */
                        if(vm_object_cached_max < 0)
                                vm_object_cached_max = 0;
                        vm_object_cached_count = 0;
                        vm_object_cache_unlock();
                        return VM_OBJECT_NULL;
                }
                vm_object_lock(object);
                queue_remove(&vm_object_cached_list, object, vm_object_t,
                             cached_list);
                vm_object_cached_count--;

                /*
                 *      Since this object is in the cache, we know
                 *      that it is initialized and has no references.
                 *      Take a reference to avoid recursive deallocations.
                 */

                assert(object->pager_initialized);
                assert(object->ref_count == 0);
                vm_object_lock_assert_exclusive(object);
                object->ref_count++;

                /*
                 *      Terminate the object.
                 *      If the object had a shadow, we let vm_object_deallocate
                 *      deallocate it. "pageout" objects have a shadow, but
                 *      maintain a "paging reference" rather than a normal
                 *      reference.
                 *      (We are careful here to limit recursion.)
                 */
                shadow = object->pageout?VM_OBJECT_NULL:object->shadow;
                if(vm_object_terminate(object) != KERN_SUCCESS)
                        continue;
                if (shadow != VM_OBJECT_NULL) {
                        if (called_from_vm_object_deallocate) {
                                return shadow;
                        } else {
                                vm_object_deallocate(shadow);
                        }
                }
        }
}

#define VM_OBJ_TERM_STATS DEBUG
#if VM_OBJ_TERM_STATS
uint32_t vm_object_terminate_pages_freed = 0;
uint32_t vm_object_terminate_pages_removed = 0;
uint32_t vm_object_terminate_batches = 0;
uint32_t vm_object_terminate_biggest_batch = 0;
#endif /* VM_OBJ_TERM_STATS */

#define V_O_T_MAX_BATCH 256

/*
 *      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(
        register vm_object_t    object)
{
        register vm_page_t      p;
        vm_object_t             shadow_object;
        vm_page_t               local_free_q;
        int                     loop_count;
#if VM_OBJ_TERM_STATS
        uint32_t                local_free_count;
        uint32_t                pages_removed;
#endif /* VM_OBJ_TERM_STATS */

#if VM_OBJ_TERM_STATS
#define VM_OBJ_TERM_FREELIST_DEBUG(_pages_removed, _local_free_count)   \
        MACRO_BEGIN                                                     \
                if (_pages_removed) {                                   \
                        hw_atomic_add(&vm_object_terminate_batches, 1); \
                        hw_atomic_add(&vm_object_terminate_pages_removed, \
                                      _pages_removed);                  \
                        hw_atomic_add(&vm_object_terminate_pages_freed, \
                                      _local_free_count);               \
                        if (_local_free_count >                         \
                            vm_object_terminate_biggest_batch) {        \
                                vm_object_terminate_biggest_batch =     \
                                        _local_free_count;              \
                        }                                               \
                        _local_free_count = 0;                          \
                }                                                       \
        MACRO_END
#else /* VM_OBJ_TERM_STATS */
#define VM_OBJ_TERM_FREELIST_DEBUG(_pages_removed, _local_free_count)
#endif /* VM_OBJ_TERM_STATS */

#define VM_OBJ_TERM_FREELIST(_pages_removed, _local_free_count, _local_free_q) \
        MACRO_BEGIN                                                     \
                VM_OBJ_TERM_FREELIST_DEBUG(_pages_removed, _local_free_count); \
                if (_local_free_q) {                                    \
                        vm_page_free_list(_local_free_q);               \
                        _local_free_q = VM_PAGE_NULL;                   \
                }                                                       \
        MACRO_END



        XPR(XPR_VM_OBJECT, "vm_object_terminate, object 0x%X ref %d\n",
                (integer_t)object, object->ref_count, 0, 0, 0);

        local_free_q = VM_PAGE_NULL;
#if VM_OBJ_TERM_STATS
        local_free_count = 0;
        pages_removed = 0;
#endif /* VM_OBJ_TERM_STATS */

        if (!object->pageout && (!object->temporary || object->can_persist)
                        && (object->pager != NULL || object->shadow_severed)) {
           vm_object_cache_unlock();
           loop_count = V_O_T_MAX_BATCH;
           vm_page_lock_queues();
           while (!queue_empty(&object->memq)) {
                if (--loop_count == 0) {
                        /*
                         * Free the pages we've reclaimed so far and
                         * take a little break to avoid hogging
                         * the page queues lock too long.
                         */
                        VM_OBJ_TERM_FREELIST(pages_removed,
                                             local_free_count,
                                             local_free_q);
                        mutex_yield(&vm_page_queue_lock);
                        loop_count = V_O_T_MAX_BATCH;
                }
                /*
                 * 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;

                p = (vm_page_t) queue_first(&object->memq);

                VM_PAGE_CHECK(p);

                if (p->busy || p->cleaning) {
                        if(p->cleaning || p->absent) {
                                /* free the pages reclaimed so far */
                                VM_OBJ_TERM_FREELIST(pages_removed,
                                                     local_free_count,
                                                     local_free_q);
                                vm_page_unlock_queues();
                                vm_object_paging_wait(object, THREAD_UNINT);
                                vm_page_lock_queues();
                                continue;
                        } else {
                                panic("vm_object_terminate.3 %p %p", object, p);
                        }
                }

                p->busy = TRUE;
                VM_PAGE_QUEUES_REMOVE(p);
#if VM_OBJ_TERM_STATS
                pages_removed++;
#endif /* VM_OBJ_TERM_STATS */

                if (p->absent || p->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.
                         */

                        goto free_page;
                }

                if (p->fictitious) {
                        if (p->phys_page == vm_page_guard_addr) {
                                goto free_page;
                        }
                        panic("vm_object_terminate.4 %p %p", object, p);
                }

                if (!p->dirty && p->wpmapped)
                        p->dirty = pmap_is_modified(p->phys_page);

                if ((p->dirty || p->precious) && !p->error && object->alive) {
                        /* free the pages reclaimed so far */
                        VM_OBJ_TERM_FREELIST(pages_removed,
                                             local_free_count,
                                             local_free_q);
                        vm_page_unlock_queues();
                        vm_pageout_cluster(p); /* flush page */
                        vm_object_paging_wait(object, THREAD_UNINT);
                        XPR(XPR_VM_OBJECT,
                            "vm_object_terminate restart, object 0x%X ref %d\n",
                            (integer_t)object, object->ref_count, 0, 0, 0);
                        vm_page_lock_queues();
                } else {
                    free_page:
                        /*
                         * Add this page to our list of reclaimed pages,
                         * to be freed later.
                         */
                        vm_page_free_prepare(p);
                        p->pageq.next = (queue_entry_t) local_free_q;
                        local_free_q = p;
#if VM_OBJ_TERM_STATS
                        local_free_count++;
#endif /* VM_OBJ_TERM_STATS */
                }
           }

           /*
            * Free the remaining reclaimed pages.
            */
           VM_OBJ_TERM_FREELIST(pages_removed,
                                local_free_count,
                                local_free_q);
           vm_page_unlock_queues();
           vm_object_unlock(object);
           vm_object_cache_lock();
           vm_object_lock(object);
        }

        /*
         *      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_cache_unlock();
                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_cache_unlock();
                vm_object_unlock(object);
                return KERN_FAILURE;
        }

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

        object->terminating = TRUE;
        object->alive = FALSE;
        vm_object_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) {
                /*
                 * 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_cache_unlock();
                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;
        /* cache lock and object lock were 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 cache and the VM object must be locked by caller.
 * The locks 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_page_t               p;
        vm_page_t               local_free_q;
        int                     loop_count;
#if VM_OBJ_TERM_STATS
        uint32_t                local_free_count;
#endif /* VM_OBJ_TERM_STATS */

#if DEBUG
        mutex_assert(&vm_object_cached_lock_data, MA_OWNED);
#endif /* DEBUG */
        vm_object_lock_assert_exclusive(object);
        assert(object->paging_in_progress == 0);

        vm_object_reap_count++;

        local_free_q = VM_PAGE_NULL;
#if VM_OBJ_TERM_STATS
        local_free_count = 0;
#endif /* VM_OBJ_TERM_STATS */

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

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

        vm_object_lock_assert_exclusive(object);
        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->objq.next || object->objq.prev) {
                purgeable_q_t queue = vm_purgeable_object_remove(object);
                assert(queue);

                /* 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();
        }
    
        /*
         *      Clean or free the pages, as appropriate.
         *      It is possible for us to find busy/absent pages,
         *      if some faults on this object were aborted.
         */
        if (object->pageout) {
                assert(object->shadow != VM_OBJECT_NULL);

                vm_pageout_object_terminate(object);

        } else if ((object->temporary && !object->can_persist) ||
                   (pager == MEMORY_OBJECT_NULL)) {
                loop_count = V_O_T_MAX_BATCH;
                vm_page_lock_queues();
                while (!queue_empty(&object->memq)) {
                        if (--loop_count == 0) {
                                /*
                                 * Free the pages we reclaimed so far
                                 * and take a little break to avoid
                                 * hogging the page queue lock too long
                                 */
                                VM_OBJ_TERM_FREELIST(local_free_count,
                                                     local_free_count,
                                                     local_free_q);
                                mutex_yield(&vm_page_queue_lock);
                                loop_count = V_O_T_MAX_BATCH;
                        }
                        p = (vm_page_t) queue_first(&object->memq);

                        vm_page_free_prepare(p);

                        assert(p->pageq.next == NULL && p->pageq.prev == NULL);
                        p->pageq.next = (queue_entry_t) local_free_q;
                        local_free_q = p;
#if VM_OBJ_TERM_STATS
                        local_free_count++;
#endif /* VM_OBJ_TERM_STATS */
                }
                /*
                 * Free the remaining reclaimed pages
                 */
                VM_OBJ_TERM_FREELIST(local_free_count,
                                     local_free_count,
                                     local_free_q);
                vm_page_unlock_queues();
        } else if (!queue_empty(&object->memq)) {
                panic("vm_object_reap: queue just emptied isn't");
        }

        assert(object->paging_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);

#if     MACH_PAGEMAP
        vm_external_destroy(object->existence_map, object->size);
#endif  /* MACH_PAGEMAP */

        object->shadow = VM_OBJECT_NULL;

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

void
vm_object_reap_async(
        vm_object_t     object)
{
#if DEBUG
        mutex_assert(&vm_object_cached_lock_data, MA_OWNED);
#endif /* DEBUG */
        vm_object_lock_assert_exclusive(object);

        vm_object_reap_count_async++;

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

        while (!queue_empty(&vm_object_reaper_queue)) {
                queue_remove_first(&vm_object_reaper_queue,
                                   object,
                                   vm_object_t,
                                   cached_list);
                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) {
                        vm_object_cache_unlock();
                        vm_object_wait(object,
                                       VM_OBJECT_EVENT_PAGING_IN_PROGRESS,
                                       THREAD_UNINT);
                        vm_object_cache_lock();
                        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_cache_lock();
        }

        /* wait for more work... */
        assert_wait((event_t) &vm_object_reaper_queue, THREAD_UNINT);
        vm_object_cache_unlock();
        thread_block((thread_continue_t) vm_object_reaper_thread);
        /*NOTREACHED*/
}

/*
 *      Routine:        vm_object_pager_wakeup
 *      Purpose:        Wake up anyone waiting for termination of a pager.
 */

static void
vm_object_pager_wakeup(
        memory_object_t pager)
{
        vm_object_hash_entry_t  entry;
        boolean_t               waiting = FALSE;

        /*
         *      If anyone was waiting for the memory_object_terminate
         *      to be queued, wake them up now.
         */
        vm_object_cache_lock();
        entry = vm_object_hash_lookup(pager, TRUE);
        if (entry != VM_OBJECT_HASH_ENTRY_NULL)
                waiting = entry->waiting;
        vm_object_cache_unlock();
        if (entry != VM_OBJECT_HASH_ENTRY_NULL) {
                if (waiting)
                        thread_wakeup((event_t) pager);
                vm_object_hash_entry_free(entry);
        }
}

/*
 *      Routine:        vm_object_release_pager
 *      Purpose:        Terminate the pager and, upon completion,
 *                      release our last reference to it.
 *                      just like memory_object_terminate, except
 *                      that we wake up anyone blocked in vm_object_enter
 *                      waiting for termination message to be queued
 *                      before calling memory_object_init.
 */
static void
vm_object_release_pager(
        memory_object_t pager)
{

        /*
         *      Terminate the pager.
         */

        (void) memory_object_terminate(pager);

        /*
         *      Wakeup anyone waiting for this terminate
         */
        vm_object_pager_wakeup(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_cache_lock();
        vm_object_lock(object);
        object->can_persist = FALSE;
        object->named = FALSE;
        object->alive = FALSE;

        /*
         *      Rip out the pager from the vm_object now...
         */

        vm_object_remove(object);
        old_pager = object->pager;
        object->pager = MEMORY_OBJECT_NULL;
        if (old_pager != MEMORY_OBJECT_NULL)
                memory_object_control_disable(object->pager_control);
        vm_object_cache_unlock();

        /*
         * 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);
}

#define VM_OBJ_DEACT_ALL_STATS DEBUG
#if VM_OBJ_DEACT_ALL_STATS
uint32_t vm_object_deactivate_all_pages_batches = 0;
uint32_t vm_object_deactivate_all_pages_pages = 0;
#endif /* VM_OBJ_DEACT_ALL_STATS */
/*
 *      vm_object_deactivate_pages
 *
 *      Deactivate all pages in the specified object.  (Keep its pages
 *      in memory even though it is no longer referenced.)
 *
 *      The object must be locked.
 */
static void
vm_object_deactivate_all_pages(
        register vm_object_t    object)
{
        register vm_page_t      p;
        int                     loop_count;
#if VM_OBJ_DEACT_ALL_STATS
        int                     pages_count;
#endif /* VM_OBJ_DEACT_ALL_STATS */
#define V_O_D_A_P_MAX_BATCH     256

        loop_count = V_O_D_A_P_MAX_BATCH;
#if VM_OBJ_DEACT_ALL_STATS
        pages_count = 0;
#endif /* VM_OBJ_DEACT_ALL_STATS */
        vm_page_lock_queues();
        queue_iterate(&object->memq, p, vm_page_t, listq) {
                if (--loop_count == 0) {
#if VM_OBJ_DEACT_ALL_STATS
                        hw_atomic_add(&vm_object_deactivate_all_pages_batches,
                                      1);
                        hw_atomic_add(&vm_object_deactivate_all_pages_pages,
                                      pages_count);
                        pages_count = 0;
#endif /* VM_OBJ_DEACT_ALL_STATS */
                        mutex_yield(&vm_page_queue_lock);
                        loop_count = V_O_D_A_P_MAX_BATCH;
                }
                if (!p->busy && !p->throttled) {
#if VM_OBJ_DEACT_ALL_STATS
                        pages_count++;
#endif /* VM_OBJ_DEACT_ALL_STATS */
                        vm_page_deactivate(p);
                }
        }
#if VM_OBJ_DEACT_ALL_STATS
        if (pages_count) {
                hw_atomic_add(&vm_object_deactivate_all_pages_batches, 1);
                hw_atomic_add(&vm_object_deactivate_all_pages_pages,
                              pages_count);
                pages_count = 0;
        }
#endif /* VM_OBJ_DEACT_ALL_STATS */
        vm_page_unlock_queues();
}

__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)
{
        vm_object_t             orig_object;
        int pages_moved = 0;
        int pages_found = 0;

        /*
         * entered with object lock held, acquire a paging reference to
         * prevent the memory_object and control ports from
         * being destroyed.
         */
        orig_object = object;

        for (;;) {
                register vm_page_t      m;
                vm_object_offset_t      toffset;
                vm_object_size_t        tsize;

                vm_object_paging_begin(object);
                vm_page_lock_queues();

                for (tsize = size, toffset = offset; tsize; tsize -= PAGE_SIZE, toffset += PAGE_SIZE) {

                        if ((m = vm_page_lookup(object, toffset)) != VM_PAGE_NULL) {

                                pages_found++;

                                if ((m->wire_count == 0) && (!m->private) && (!m->gobbled) && (!m->busy)) {

                                        assert(!m->laundry);

                                        m->reference = FALSE;
                                        pmap_clear_reference(m->phys_page);

                                        if ((kill_page) && (object->internal)) {
                                                m->precious = FALSE;
                                                m->dirty = FALSE;
                                                pmap_clear_modify(m->phys_page);
#if     MACH_PAGEMAP
                                                vm_external_state_clr(object->existence_map, offset);
#endif  /* MACH_PAGEMAP */
                                        }

                                        if (!m->throttled) {
                                                VM_PAGE_QUEUES_REMOVE(m);

                                                assert(!m->laundry);
                                                assert(m->object != kernel_object);
                                                assert(m->pageq.next == NULL &&
                                                       m->pageq.prev == NULL);
                                        
                                                if(m->zero_fill) {
                                                        queue_enter_first(
                                                        &vm_page_queue_zf, 
                                                        m, vm_page_t, pageq);
                                                        vm_zf_queue_count++;
                                                } else {
                                                        queue_enter_first(
                                                                          &vm_page_queue_inactive, 
                                                                          m, vm_page_t, pageq);
                                                }

                                                m->inactive = TRUE;
                                                if (!m->fictitious) {
                                                        vm_page_inactive_count++;
                                                        token_new_pagecount++;
                                                } else {
                                                        assert(m->phys_page == vm_page_fictitious_addr);
                                                }

                                                pages_moved++;
                                        }
                                }
                        }
                }
                vm_page_unlock_queues();
                vm_object_paging_end(object);

                if (object->shadow) {
                        vm_object_t     tmp_object;

                        kill_page = 0;

                        offset += object->shadow_offset;

                        tmp_object = object->shadow;
                        vm_object_lock(tmp_object);

                        if (object != orig_object)
                                vm_object_unlock(object);
                        object = tmp_object;
                } else
                        break;
        }
        if (object != orig_object)
                vm_object_unlock(object);
}

/*
 *      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 temporary/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(
        register vm_object_t            object,
        register vm_object_offset_t     offset,
        vm_object_size_t                size,
        pmap_t                          pmap,
        vm_map_offset_t                 pmap_start,
        vm_prot_t                       prot)
{
        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(pmap, pmap_start, pmap_start + size, prot);
                } else {
                        vm_object_offset_t phys_start, phys_end, phys_addr;

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

                        for (phys_addr = phys_start;
                             phys_addr < phys_end;
                             phys_addr += PAGE_SIZE_64) {
                                pmap_page_protect(phys_addr >> 12, prot);
                        }
                }
                return;
        }

        assert(object->internal);

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

            /* 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;

                if (pmap != PMAP_NULL) {
                  queue_iterate(&object->memq, p, vm_page_t, listq) {
                    if (!p->fictitious &&
                        (offset <= p->offset) && (p->offset < end)) {
                        vm_map_offset_t start;

                        start = pmap_start + p->offset - offset;
                        pmap_protect(pmap, start, start + PAGE_SIZE_64, prot);
                    }
                  }
                } else {
                  queue_iterate(&object->memq, p, vm_page_t, listq) {
                    if (!p->fictitious &&
                        (offset <= p->offset) && (p->offset < end)) {

                        pmap_page_protect(p->phys_page, prot);
                    }
                  }
                }
           } else {
                vm_page_t               p;
                vm_object_offset_t      end;
                vm_object_offset_t      target_off;

                end = offset + size;

                if (pmap != PMAP_NULL) {
                        for(target_off = offset; 
                            target_off < end;
                            target_off += PAGE_SIZE) {
                                p = vm_page_lookup(object, target_off);
                                if (p != VM_PAGE_NULL) {
                                        vm_offset_t start;
                                        start = pmap_start + 
                                                (vm_offset_t)(p->offset - offset);
                                        pmap_protect(pmap, start, 
                                                        start + PAGE_SIZE, prot);
                                }
                        }
                } else {
                        for(target_off = offset; 
                                target_off < end; target_off += PAGE_SIZE) {
                                p = vm_page_lookup(object, target_off);
                                if (p != VM_PAGE_NULL) {
                                        pmap_page_protect(p->phys_page, prot);
                                }
                        }
                }
          }

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

                next_object = object->shadow;
                if (next_object != VM_OBJECT_NULL) {
                    offset += object->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);
}

/*
 *      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(
        register 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;

        XPR(XPR_VM_OBJECT, "v_o_c_slowly obj 0x%x off 0x%x size 0x%x\n",
            src_object, src_offset, size, 0, 0);

        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.user_tag  = 0;
        fault_info.lo_offset = src_offset;
        fault_info.hi_offset = src_offset + size;
        fault_info.no_cache  = FALSE;

        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;
                        register
                        vm_page_t       result_page;
                        kern_return_t   error_code;

                        vm_object_lock(src_object);
                        vm_object_paging_begin(src_object);

                        fault_info.cluster_size = size;

                        XPR(XPR_VM_FAULT,"vm_object_copy_slowly -> vm_fault_page",0,0,0,0,0);
                        result = vm_fault_page(src_object, src_offset,
                                VM_PROT_READ, FALSE,
                                &prot, &_result_page, &top_page,
                                (int *)0,
                                &error_code, FALSE, FALSE, &fault_info);

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

                                        /*
                                         *      We don't need to hold the object
                                         *      lock -- the busy page will be enough.
                                         *      [We don't care about picking up any
                                         *      new modifications.]
                                         *
                                         *      Copy the page to the new object.
                                         *
                                         *      POLICY DECISION:
                                         *              If result_page is clean,
                                         *              we could steal it instead
                                         *              of copying.
                                         */

                                        vm_object_unlock(result_page->object);
                                        vm_page_copy(result_page, new_page);

                                        /*
                                         *      Let go of both pages (make them
                                         *      not busy, perform wakeup, activate).
                                         */
                                        vm_object_lock(new_object);
                                        new_page->dirty = TRUE;
                                        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->active &&
                                            !result_page->inactive &&
                                            !result_page->throttled)
                                                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_FICTITIOUS_SHORTAGE:
                                        vm_page_more_fictitious();
                                        break;

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

                                case VM_FAULT_INTERRUPTED:
                                        vm_page_free(new_page);
                                        vm_object_deallocate(new_object);
                                        vm_object_deallocate(src_object);
                                        *_result_object = VM_OBJECT_NULL;
                                        return(MACH_SEND_INTERRUPTED);

                                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_page_lock_queues();
                                        vm_page_free(new_page);
                                        vm_page_unlock_queues();

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

        XPR(XPR_VM_OBJECT, "v_o_c_quickly obj 0x%x off 0x%x size 0x%x\n",
            *_object, offset, size, 0, 0);
        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->size < src_offset+size)
                copy->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;


        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.
         */

 Retry:
 
        /*
         * Wait for paging in progress.
         */
        if (!src_object->true_share && src_object->paging_in_progress) {
                if (src_object_shared == TRUE) {
                        vm_object_unlock(src_object);
                                
                        vm_object_lock(src_object);
                        src_object_shared = FALSE;
                }
                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->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++;

                                queue_iterate(&src_object->memq, p, vm_page_t, listq) {
                                        if (!p->fictitious && 
                                            p->offset >= old_copy->size && 
                                            p->offset < copy_size) {
                                                if (p->wire_count > 0) {
                                                        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 VM_OBJECT_NULL;
                                                } else {
                                                        pmap_page_protect(p->phys_page, 
                                                                          (VM_PROT_ALL & ~VM_PROT_WRITE));
                                                }
                                        }
                                }
                                old_copy->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->size > copy_size)
                        copy_size = old_copy->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->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->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++;

        queue_iterate(&src_object->memq, p, vm_page_t, listq) {
                if (!p->fictitious && p->offset < copy_size) {
                        if (p->wire_count > 0) {
                                if (old_copy)
                                        vm_object_unlock(old_copy);
                                vm_object_unlock(src_object);
                                vm_object_unlock(new_copy);
                                vm_object_deallocate(new_copy);
                                return VM_OBJECT_NULL;
                        } else {
                                pmap_page_protect(p->phys_page, 
                                                  (VM_PROT_ALL & ~VM_PROT_WRITE));
                        }
                }
        }
        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->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);

        XPR(XPR_VM_OBJECT,
                "vm_object_copy_delayed: used copy object %X for source %X\n",
                (integer_t)new_copy, (integer_t)src_object, 0, 0, 0);

        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(
        register 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:
                XPR(XPR_VM_OBJECT, "v_o_c_strategically obj 0x%x off 0x%x size 0x%x\n",(natural_t)src_object, src_offset, size, 0, 0);
                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 = FALSE;

__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)
{
        register vm_object_t    source;
        register vm_object_t    result;

        source = *object;
#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 (vm_object_shadow_check && source->ref_count == 1 &&
            (source->shadow == VM_OBJECT_NULL ||
             source->shadow->copy == VM_OBJECT_NULL))
        {
                source->shadowed = FALSE;
                return FALSE;
        }

        /*
         *      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->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_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.]
 *
 *      In addition to the lock on the object, the vm_object_cache_lock
 *      governs the associations.  References gained through the
 *      association require use of the cache lock.
 *
 *      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_enter
 *      Purpose:
 *              Find a VM object corresponding to the given
 *              pager; if no such object exists, create one,
 *              and initialize the pager.
 */
vm_object_t
vm_object_enter(
        memory_object_t         pager,
        vm_object_size_t        size,
        boolean_t               internal,
        boolean_t               init,
        boolean_t               named)
{
        register vm_object_t    object;
        vm_object_t             new_object;
        boolean_t               must_init;
        vm_object_hash_entry_t  entry, new_entry;
        uint32_t        try_failed_count = 0;

        if (pager == MEMORY_OBJECT_NULL)
                return(vm_object_allocate(size));

        new_object = VM_OBJECT_NULL;
        new_entry = VM_OBJECT_HASH_ENTRY_NULL;
        must_init = init;

        /*
         *      Look for an object associated with this port.
         */
Retry:
        vm_object_cache_lock();
        do {
                entry = vm_object_hash_lookup(pager, FALSE);

                if (entry == VM_OBJECT_HASH_ENTRY_NULL) {
                        if (new_object == VM_OBJECT_NULL) {
                                /*
                                 *      We must unlock to create a new object;
                                 *      if we do so, we must try the lookup again.
                                 */
                                vm_object_cache_unlock();
                                assert(new_entry == VM_OBJECT_HASH_ENTRY_NULL);
                                new_entry = vm_object_hash_entry_alloc(pager);
                                new_object = vm_object_allocate(size);
                                vm_object_cache_lock();
                        } else {
                                /*
                                 *      Lookup failed twice, and we have something
                                 *      to insert; set the object.
                                 */
                                vm_object_hash_insert(new_entry);
                                entry = new_entry;
                                entry->object = new_object;
                                new_entry = VM_OBJECT_HASH_ENTRY_NULL;
                                new_object = VM_OBJECT_NULL;
                                must_init = TRUE;
                        }
                } else if (entry->object == VM_OBJECT_NULL) {
                        /*
                         *      If a previous object is being terminated,
                         *      we must wait for the termination message
                         *      to be queued (and lookup the entry again).
                         */
                        entry->waiting = TRUE;
                        entry = VM_OBJECT_HASH_ENTRY_NULL;
                        assert_wait((event_t) pager, THREAD_UNINT);
                        vm_object_cache_unlock();
                        thread_block(THREAD_CONTINUE_NULL);
                        vm_object_cache_lock();
                }
        } while (entry == VM_OBJECT_HASH_ENTRY_NULL);

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

        if (!must_init) {
                if (!vm_object_lock_try(object)) {

                        vm_object_cache_unlock();

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

                        goto Retry;
                }
                assert(!internal || object->internal);
                if (named) {
                        assert(!object->named);
                        object->named = TRUE;
                }
                if (object->ref_count == 0) {
                        XPR(XPR_VM_OBJECT_CACHE,
                    "vm_object_enter: removing %x from cache, head (%x, %x)\n",
                                (integer_t)object,
                                (integer_t)vm_object_cached_list.next,
                                (integer_t)vm_object_cached_list.prev, 0,0);
                        queue_remove(&vm_object_cached_list, object,
                                     vm_object_t, cached_list);
                        vm_object_cached_count--;
                }
                vm_object_lock_assert_exclusive(object);
                object->ref_count++;
                vm_object_res_reference(object);
                vm_object_unlock(object);

                VM_STAT_INCR(hits);
        } 
        assert(object->ref_count > 0);

        VM_STAT_INCR(lookups);

        vm_object_cache_unlock();

        XPR(XPR_VM_OBJECT,
                "vm_o_enter: pager 0x%x obj 0x%x must_init %d\n",
                (integer_t)pager, (integer_t)object, must_init, 0, 0);

        /*
         *      If we raced to create a vm_object but lost, let's
         *      throw away ours.
         */

        if (new_object != VM_OBJECT_NULL)
                vm_object_deallocate(new_object);

        if (new_entry != VM_OBJECT_HASH_ENTRY_NULL)
                vm_object_hash_entry_free(new_entry);

        if (must_init) {
                memory_object_control_t control;

                /*
                 *      Allocate request port.
                 */

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

                vm_object_lock(object);
                assert(object != kernel_object);

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

                memory_object_reference(pager);
                object->pager_created = TRUE;
                object->pager = pager;
                object->internal = internal;
                object->pager_trusted = internal;
                if (!internal) {
                        /* copy strategy invalid until set by memory manager */
                        object->copy_strategy = MEMORY_OBJECT_COPY_INVALID;
                }
                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 (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);
        } else {
                vm_object_lock(object);
        }

        /*
         *      [At this point, the object must be locked]
         */

        /*
         *      Wait for the work above to be done by the first
         *      thread to map this object.
         */

        while (!object->pager_initialized) {
                vm_object_sleep(object,
                                VM_OBJECT_EVENT_INITIALIZED,
                                THREAD_UNINT);
        }
        vm_object_unlock(object);

        XPR(XPR_VM_OBJECT,
            "vm_object_enter: vm_object %x, memory_object %x, internal %d\n",
            (integer_t)object, (integer_t)object->pager, internal, 0,0);
        return(object);
}

/*
 *      Routine:        vm_object_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_pager_create on an object at
 *              a time.  Presumably, only the pageout
 *              daemon will be using this routine.
 */

void
vm_object_pager_create(
        register vm_object_t    object)
{
        memory_object_t         pager;
        vm_object_hash_entry_t  entry;
#if     MACH_PAGEMAP
        vm_object_size_t        size;
        vm_external_map_t       map;
#endif  /* MACH_PAGEMAP */

        XPR(XPR_VM_OBJECT, "vm_object_pager_create, object 0x%X\n",
                (integer_t)object, 0,0,0,0);

        assert(object != kernel_object);

        if (memory_manager_default_check() != KERN_SUCCESS)
                return;

        /*
         *      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;
        }

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

        object->pager_created = TRUE;
        object->paging_offset = 0;
                
#if     MACH_PAGEMAP
        size = object->size;
#endif  /* MACH_PAGEMAP */
        vm_object_unlock(object);

#if     MACH_PAGEMAP
        map = vm_external_create(size);
        vm_object_lock(object);
        assert(object->size == size);
        object->existence_map = map;
        vm_object_unlock(object);
#endif  /* MACH_PAGEMAP */

        /*
         *      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.
         */
        {
                memory_object_default_t         dmm;

                /* acquire a reference for the default memory manager */
                dmm = memory_manager_default_reference();

                assert(object->temporary);

                /* create our new memory object */
                (void) memory_object_create(dmm, object->size, &pager);

                memory_object_default_deallocate(dmm);
       }

        entry = vm_object_hash_entry_alloc(pager);

        vm_object_cache_lock();
        vm_object_hash_insert(entry);

        entry->object = object;
        vm_object_cache_unlock();

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

        if (vm_object_enter(pager, object->size, TRUE, TRUE, FALSE) != object)
                panic("vm_object_pager_create: mismatch");

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

        vm_object_lock(object);

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

/*
 *      Routine:        vm_object_remove
 *      Purpose:
 *              Eliminate the pager/object association
 *              for this pager.
 *      Conditions:
 *              The object cache must be locked.
 */
__private_extern__ void
vm_object_remove(
        vm_object_t     object)
{
        memory_object_t pager;

        if ((pager = object->pager) != MEMORY_OBJECT_NULL) {
                vm_object_hash_entry_t  entry;

                entry = vm_object_hash_lookup(pager, FALSE);
                if (entry != VM_OBJECT_HASH_ENTRY_NULL)
                        entry->object = VM_OBJECT_NULL;
        }

}

/*
 *      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;

#if MACH_PAGEMAP
static int      vm_external_discarded;
static int      vm_external_collapsed;
#endif

unsigned long vm_object_collapse_encrypted = 0;

/*
 *      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;

        backing_offset = object->shadow_offset;
        size = object->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 (!queue_empty(&backing_object->memq)) {
                
                p = (vm_page_t) queue_first(&backing_object->memq);
                
                new_offset = (p->offset - backing_offset);
                
                assert(!p->busy || p->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->offset < backing_offset || new_offset >= size) {
                        VM_PAGE_FREE(p);
                } else {
                        /*
                         * ENCRYPTED SWAP:
                         * The encryption key includes the "pager" and the
                         * "paging_offset".  These will not change during the 
                         * object collapse, so we can just move an encrypted
                         * page from one object to the other in this case.
                         * We can't decrypt the page here, since we can't drop
                         * the object lock.
                         */
                        if (p->encrypted) {
                                vm_object_collapse_encrypted++;
                        }
                        pp = vm_page_lookup(object, new_offset);
                        if (pp == VM_PAGE_NULL) {

                                /*
                                 *      Parent now has no page.
                                 *      Move the backing object's page up.
                                 */

                                vm_page_rename(p, object, new_offset, TRUE);
#if     MACH_PAGEMAP
                        } else if (pp->absent) {

                                /*
                                 *      Parent has an absent page...
                                 *      it's not being paged in, so
                                 *      it must really be missing from
                                 *      the parent.
                                 *
                                 *      Throw out the absent page...
                                 *      any faults looking for that
                                 *      page will restart with the new
                                 *      one.
                                 */

                                VM_PAGE_FREE(pp);
                                vm_page_rename(p, object, new_offset, TRUE);
#endif  /* MACH_PAGEMAP */
                        } else {
                                assert(! pp->absent);

                                /*
                                 *      Parent object has a real page.
                                 *      Throw away the backing object's
                                 *      page.
                                 */
                                VM_PAGE_FREE(p);
                        }
                }
        }
        
#if     !MACH_PAGEMAP
        assert((!object->pager_created && (object->pager == MEMORY_OBJECT_NULL))
                || (!backing_object->pager_created
                &&  (backing_object->pager == MEMORY_OBJECT_NULL)));
#else 
        assert(!object->pager_created && object->pager == MEMORY_OBJECT_NULL);
#endif  /* !MACH_PAGEMAP */

        if (backing_object->pager != MEMORY_OBJECT_NULL) {
                vm_object_hash_entry_t  entry;

                /*
                 *      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);
                object->pager = backing_object->pager;
                entry = vm_object_hash_lookup(object->pager, FALSE);
                assert(entry != VM_OBJECT_HASH_ENTRY_NULL);
                entry->object = object;
                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);
                }
        }

        vm_object_cache_unlock();

#if     MACH_PAGEMAP
        /*
         *      If the shadow offset is 0, the use the existence map from
         *      the backing object if there is one. If the shadow offset is
         *      not zero, toss it.
         *
         *      XXX - If the shadow offset is not 0 then a bit copy is needed
         *      if the map is to be salvaged.  For now, we just just toss the
         *      old map, giving the collapsed object no map. This means that
         *      the pager is invoked for zero fill pages.  If analysis shows
         *      that this happens frequently and is a performance hit, then
         *      this code should be fixed to salvage the map.
         */
        assert(object->existence_map == VM_EXTERNAL_NULL);
        if (backing_offset || (size != backing_object->size)) {
                vm_external_discarded++;
                vm_external_destroy(backing_object->existence_map,
                        backing_object->size);
        }
        else {
                vm_external_collapsed++;
                object->existence_map = backing_object->existence_map;
        }
        backing_object->existence_map = VM_EXTERNAL_NULL;
#endif  /* MACH_PAGEMAP */

        /*
         *      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->shadow_offset += backing_object->shadow_offset;
        } else {
                /* no shadow, therefore no shadow offset... */
                object->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.
         */
        
        assert((backing_object->ref_count == 1) &&
               (backing_object->resident_page_count == 0) &&
               (backing_object->paging_in_progress == 0));

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

        XPR(XPR_VM_OBJECT, "vm_object_collapse, collapsed 0x%X\n",
                (integer_t)backing_object, 0,0,0,0);

        vm_object_lock_destroy(backing_object);

        zfree(vm_object_zone, backing_object);
        
        object_collapses++;
}

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(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->shadow_offset += backing_object->shadow_offset;
        } else {
                /* no shadow, therefore no shadow offset... */
                object->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.
         *      [FBDP: that doesn't seem to be true any more]
         * 
         *      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 > 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_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);
        }
        
        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;
static unsigned long vm_object_collapse_delays = 0;
__private_extern__ void
vm_object_collapse(
        register vm_object_t                    object,
        register vm_object_offset_t             hint_offset,
        boolean_t                               can_bypass)
{
        register vm_object_t                    backing_object;
        register unsigned int                   rcount;
        register unsigned int                   size;
        vm_object_t                             original_object;

        vm_object_collapse_calls++;

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

        XPR(XPR_VM_OBJECT, "vm_object_collapse, obj 0x%X\n", 
                (integer_t)object, 0,0,0,0);

        if (object == VM_OBJECT_NULL)
                return;

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

                vm_object_lock(backing_object);

                /*
                 *      ...
                 *              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) {
                        /* try and collapse the rest of the shadow chain */
                        if (object != original_object) {
                                vm_object_unlock(object);
                        }
                        object = backing_object;
                        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;
                        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.
                 *
                 *      If MACH_PAGEMAP is defined:
                 *      The parent must not have a pager created for it,
                 *      since collapsing a backing_object dumps new pages
                 *      into the parent that its pager doesn't know about
                 *      (and the collapse code can't merge the existence
                 *      maps).
                 *      Otherwise:
                 *      As long as one of the objects is still not known
                 *      to the pager, we can collapse them.
                 */
                if (backing_object->ref_count == 1 &&
                    (!object->pager_created 
#if     !MACH_PAGEMAP
                     || !backing_object->pager_created
#endif  /*!MACH_PAGEMAP */
                    ) && vm_object_collapse_allowed) {

                        XPR(XPR_VM_OBJECT, 
                   "vm_object_collapse: %x to %x, pager %x, pager_control %x\n",
                                (integer_t)backing_object, (integer_t)object,
                                (integer_t)backing_object->pager, 
                                (integer_t)backing_object->pager_control, 0);

                        /*
                         *      We need the cache lock for collapsing,
                         *      but we must not deadlock.
                         */
                        
                        if (! vm_object_cache_lock_try()) {
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                vm_object_unlock(backing_object);
                                return;
                        }

                        /*
                         *      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;
                        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 = atop(object->size);
                rcount = object->resident_page_count;
                if (rcount != size) {
                        vm_object_offset_t      offset;
                        vm_object_offset_t      backing_offset;
                        unsigned int            backing_rcount;
                        unsigned int            lookups = 0;

                        /*
                         *      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
#if     MACH_PAGEMAP
                                && (backing_object->existence_map == VM_EXTERNAL_NULL)
#endif  /* MACH_PAGEMAP */
                                ) {
                                /* try and collapse the rest of the shadow chain */
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                object = backing_object;
                                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
#if     MACH_PAGEMAP
                                && (object->existence_map == VM_EXTERNAL_NULL)
#endif  /* MACH_PAGEMAP */
                                ) {
                                /* try and collapse the rest of the shadow chain */
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                object = backing_object;
                                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.
                         *
                         */

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

#if     MACH_PAGEMAP
#define EXISTS_IN_OBJECT(obj, off, rc) \
        (vm_external_state_get((obj)->existence_map, \
         (vm_offset_t)(off)) == VM_EXTERNAL_STATE_EXISTS || \
         ((rc) && ++lookups && vm_page_lookup((obj), (off)) != VM_PAGE_NULL && (rc)--))
#else
#define EXISTS_IN_OBJECT(obj, off, rc) \
        (((rc) && ++lookups && vm_page_lookup((obj), (off)) != VM_PAGE_NULL && (rc)--))
#endif  /* MACH_PAGEMAP */

                        /*
                         * 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;
                                /* try and collapse the rest of the shadow chain */
                                if (object != original_object) {
                                        vm_object_unlock(object);
                                }
                                object = backing_object;
                                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 
                         * resident.  So, we can't permanently decrement
                         * the rcount here because the second loop may
                         * find the same pages in the backing object'
                         * existence map that we found here and we would
                         * double-decrement the rcount.  We also may or
                         * may not have found the 
                         */
                        if (backing_rcount && 
#if     MACH_PAGEMAP
                            size > ((backing_object->existence_map) ?
                             backing_rcount : (backing_rcount >> 1))
#else
                            size > (backing_rcount >> 1)
#endif  /* MACH_PAGEMAP */
                                ) {
                                unsigned int rc = rcount;
                                vm_page_t p;

                                backing_rcount = backing_object->resident_page_count;
                                p = (vm_page_t)queue_first(&backing_object->memq);
                                do {
                                        /* Until we get more than one lookup lock */
                                        if (lookups > 256) {
                                                vm_object_collapse_delays++;
                                                lookups = 0;
                                                mutex_pause(0);
                                        }

                                        offset = (p->offset - backing_offset);
                                        if (offset < object->size &&
                                            offset != hint_offset &&
                                            !EXISTS_IN_OBJECT(object, offset, rc)) {
                                                /* found a dependency */
                                                object->cow_hint = (vm_offset_t)offset;
                                                break;
                                        }
                                        p = (vm_page_t) queue_next(&p->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;
                                        continue;
                                }
                        }

                        /*
                         * Walk through the offsets looking for pages in the
                         * backing object that show through to the object.
                         */
#if     MACH_PAGEMAP
                        if (backing_rcount || backing_object->existence_map) {
#else
                        if (backing_rcount) {
#endif  /* MACH_PAGEMAP */
                                offset = hint_offset;
                                
                                while((offset =
                                      (offset + PAGE_SIZE_64 < object->size) ?
                                      (offset + PAGE_SIZE_64) : 0) != hint_offset) {

                                        /* Until we get more than one lookup lock */
                                        if (lookups > 256) {
                                                vm_object_collapse_delays++;
                                                lookups = 0;
                                                mutex_pause(0);
                                        }

                                        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;
                                                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;
                                        continue;
                                }
                        }
                }

                /* 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;
        }

        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(
        register vm_object_t            object,
        register vm_object_offset_t     start,
        register vm_object_offset_t     end)
{
        register 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->cleaning && !p->pageout);
                                if (!p->fictitious && p->pmapped)
                                        pmap_disconnect(p->phys_page);
                                VM_PAGE_FREE(p);
                        }
                }
        } else {
                vm_object_page_remove_iterate++;

                p = (vm_page_t) queue_first(&object->memq);
                while (!queue_end(&object->memq, (queue_entry_t) p)) {
                        next = (vm_page_t) queue_next(&p->listq);
                        if ((start <= p->offset) && (p->offset < end)) {
                                assert(!p->cleaning && !p->pageout);
                                if (!p->fictitious && p->pmapped)
                                        pmap_disconnect(p->phys_page);
                                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(
        register 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);
        }

        XPR(XPR_VM_OBJECT,
       "vm_object_coalesce: 0x%X prev_off 0x%X prev_size 0x%X next_size 0x%X\n",
                (integer_t)prev_object, prev_offset, prev_size, next_size, 0);

        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)) {
                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->size) {
#if     MACH_PAGEMAP
                /*
                 *      We cannot extend an object that has existence info,
                 *      since the existence info might then fail to cover
                 *      the entire object.
                 *
                 *      This assertion must be true because the object
                 *      has no pager, and we only create existence info
                 *      for objects with pagers.
                 */
                assert(prev_object->existence_map == VM_EXTERNAL_NULL);
#endif  /* MACH_PAGEMAP */
                prev_object->size = newsize;
        }

        vm_object_unlock(prev_object);
        return(TRUE);
}

/*
 *      Attach a set of physical pages to an object, so that they can
 *      be mapped by mapping the object.  Typically used to map IO memory.
 *
 *      The mapping function and its private data are used to obtain the
 *      physical addresses for each page to be mapped.
 */
void
vm_object_page_map(
        vm_object_t             object,
        vm_object_offset_t      offset,
        vm_object_size_t        size,
        vm_object_offset_t      (*map_fn)(void *map_fn_data, 
                vm_object_offset_t offset),
                void            *map_fn_data)   /* private to map_fn */
{
        int     num_pages;
        int     i;
        vm_page_t       m;
        vm_page_t       old_page;
        vm_object_offset_t      addr;

        num_pages = atop_64(size);

        for (i = 0; i < num_pages; i++, offset += PAGE_SIZE_64) {

            addr = (*map_fn)(map_fn_data, offset);

            while ((m = vm_page_grab_fictitious()) == VM_PAGE_NULL)
                vm_page_more_fictitious();

            vm_object_lock(object);
            if ((old_page = vm_page_lookup(object, offset))
                        != VM_PAGE_NULL)
            {
                vm_page_lock_queues();
                vm_page_free(old_page);
                vm_page_unlock_queues();
            }

            vm_page_init(m, addr);
            /* private normally requires lock_queues but since we */
            /* are initializing the page, its not necessary here  */
            m->private = TRUE;          /* don`t free page */
            m->wire_count = 1;
            vm_page_insert(m, object, offset);

            PAGE_WAKEUP_DONE(m);
            vm_object_unlock(object);
        }
}

#include <mach_kdb.h>

#if     MACH_KDB
#include <ddb/db_output.h>
#include <vm/vm_print.h>

#define printf  kdbprintf

extern boolean_t        vm_object_cached(
                                vm_object_t object);

extern void             print_bitstring(
                                char byte);

boolean_t       vm_object_print_pages = FALSE;

void
print_bitstring(
        char byte)
{
        printf("%c%c%c%c%c%c%c%c",
               ((byte & (1 << 0)) ? '1' : '0'),
               ((byte & (1 << 1)) ? '1' : '0'),
               ((byte & (1 << 2)) ? '1' : '0'),
               ((byte & (1 << 3)) ? '1' : '0'),
               ((byte & (1 << 4)) ? '1' : '0'),
               ((byte & (1 << 5)) ? '1' : '0'),
               ((byte & (1 << 6)) ? '1' : '0'),
               ((byte & (1 << 7)) ? '1' : '0'));
}

boolean_t
vm_object_cached(
        register vm_object_t object)
{
        register vm_object_t o;

        queue_iterate(&vm_object_cached_list, o, vm_object_t, cached_list) {
                if (object == o) {
                        return TRUE;
                }
        }
        return FALSE;
}

#if     MACH_PAGEMAP
/*
 *      vm_external_print:      [ debug ]
 */
void
vm_external_print(
        vm_external_map_t       emap,
        vm_size_t               size)
{
        if (emap == VM_EXTERNAL_NULL) {
                printf("0  ");
        } else {
                vm_size_t existence_size = stob(size);
                printf("{ size=%d, map=[", existence_size);
                if (existence_size > 0) {
                        print_bitstring(emap[0]);
                }
                if (existence_size > 1) {
                        print_bitstring(emap[1]);
                }
                if (existence_size > 2) {
                        printf("...");
                        print_bitstring(emap[existence_size-1]);
                }
                printf("] }\n");
        }
        return;
}
#endif  /* MACH_PAGEMAP */

int
vm_follow_object(
        vm_object_t object)
{
        int count = 0;
        int orig_db_indent = db_indent;

        while (TRUE) {
                if (object == VM_OBJECT_NULL) {
                        db_indent = orig_db_indent;
                        return count;
                }

                count += 1;

                iprintf("object 0x%x", object);
                printf(", shadow=0x%x", object->shadow);
                printf(", copy=0x%x", object->copy);
                printf(", pager=0x%x", object->pager);
                printf(", ref=%d\n", object->ref_count);

                db_indent += 2;
                object = object->shadow;
        }

}

/*
 *      vm_object_print:        [ debug ]
 */
void
vm_object_print(db_expr_t db_addr, __unused boolean_t have_addr,
                __unused db_expr_t arg_count, __unused char *modif)
{
        vm_object_t     object;
        register vm_page_t p;
        const char *s;

        register int count;

        object = (vm_object_t) (long) db_addr;
        if (object == VM_OBJECT_NULL)
                return;

        iprintf("object 0x%x\n", object);

        db_indent += 2;

        iprintf("size=0x%x", object->size);
        printf(", memq_hint=%p", object->memq_hint);
        printf(", ref_count=%d\n", object->ref_count);
        iprintf("");
#if     TASK_SWAPPER
        printf("res_count=%d, ", object->res_count);
#endif  /* TASK_SWAPPER */
        printf("resident_page_count=%d\n", object->resident_page_count);

        iprintf("shadow=0x%x", object->shadow);
        if (object->shadow) {
                register int i = 0;
                vm_object_t shadow = object;
                while((shadow = shadow->shadow))
                        i++;
                printf(" (depth %d)", i);
        }
        printf(", copy=0x%x", object->copy);
        printf(", shadow_offset=0x%x", object->shadow_offset);
        printf(", last_alloc=0x%x\n", object->last_alloc);

        iprintf("pager=0x%x", object->pager);
        printf(", paging_offset=0x%x", object->paging_offset);
        printf(", pager_control=0x%x\n", object->pager_control);

        iprintf("copy_strategy=%d[", object->copy_strategy);
        switch (object->copy_strategy) {
                case MEMORY_OBJECT_COPY_NONE:
                printf("copy_none");
                break;

                case MEMORY_OBJECT_COPY_CALL:
                printf("copy_call");
                break;

                case MEMORY_OBJECT_COPY_DELAY:
                printf("copy_delay");
                break;

                case MEMORY_OBJECT_COPY_SYMMETRIC:
                printf("copy_symmetric");
                break;

                case MEMORY_OBJECT_COPY_INVALID:
                printf("copy_invalid");
                break;

                default:
                printf("?");
        }
        printf("]");

        iprintf("all_wanted=0x%x<", object->all_wanted);
        s = "";
        if (vm_object_wanted(object, VM_OBJECT_EVENT_INITIALIZED)) {
                printf("%sinit", s);
                s = ",";
        }
        if (vm_object_wanted(object, VM_OBJECT_EVENT_PAGER_READY)) {
                printf("%sready", s);
                s = ",";
        }
        if (vm_object_wanted(object, VM_OBJECT_EVENT_PAGING_IN_PROGRESS)) {
                printf("%spaging", s);
                s = ",";
        }
        if (vm_object_wanted(object, VM_OBJECT_EVENT_LOCK_IN_PROGRESS)) {
                printf("%slock", s);
                s = ",";
        }
        if (vm_object_wanted(object, VM_OBJECT_EVENT_UNCACHING)) {
                printf("%suncaching", s);
                s = ",";
        }
        if (vm_object_wanted(object, VM_OBJECT_EVENT_COPY_CALL)) {
                printf("%scopy_call", s);
                s = ",";
        }
        if (vm_object_wanted(object, VM_OBJECT_EVENT_CACHING)) {
                printf("%scaching", s);
                s = ",";
        }
        printf(">");
        printf(", paging_in_progress=%d\n", object->paging_in_progress);

        iprintf("%screated, %sinit, %sready, %spersist, %strusted, %spageout, %s, %s\n",
                (object->pager_created ? "" : "!"),
                (object->pager_initialized ? "" : "!"),
                (object->pager_ready ? "" : "!"),
                (object->can_persist ? "" : "!"),
                (object->pager_trusted ? "" : "!"),
                (object->pageout ? "" : "!"),
                (object->internal ? "internal" : "external"),
                (object->temporary ? "temporary" : "permanent"));
        iprintf("%salive, %spurgeable, %spurgeable_volatile, %spurgeable_empty, %sshadowed, %scached, %sprivate\n",
                (object->alive ? "" : "!"),
                ((object->purgable != VM_PURGABLE_DENY) ? "" : "!"),
                ((object->purgable == VM_PURGABLE_VOLATILE) ? "" : "!"),
                ((object->purgable == VM_PURGABLE_EMPTY) ? "" : "!"),
                (object->shadowed ? "" : "!"),
                (vm_object_cached(object) ? "" : "!"),
                (object->private ? "" : "!"));
        iprintf("%sadvisory_pageout, %ssilent_overwrite\n",
                (object->advisory_pageout ? "" : "!"),
                (object->silent_overwrite ? "" : "!"));

#if     MACH_PAGEMAP
        iprintf("existence_map=");
        vm_external_print(object->existence_map, object->size);
#endif  /* MACH_PAGEMAP */
#if     MACH_ASSERT
        iprintf("paging_object=0x%x\n", object->paging_object);
#endif  /* MACH_ASSERT */

        if (vm_object_print_pages) {
                count = 0;
                p = (vm_page_t) queue_first(&object->memq);
                while (!queue_end(&object->memq, (queue_entry_t) p)) {
                        if (count == 0) {
                                iprintf("memory:=");
                        } else if (count == 2) {
                                printf("\n");
                                iprintf(" ...");
                                count = 0;
                        } else {
                                printf(",");
                        }
                        count++;

                        printf("(off=0x%llX,page=%p)", p->offset, p);
                        p = (vm_page_t) queue_next(&p->listq);
                }
                if (count != 0) {
                        printf("\n");
                }
        }
        db_indent -= 2;
}


/*
 *      vm_object_find          [ debug ]
 *
 *      Find all tasks which reference the given vm_object.
 */

boolean_t vm_object_find(vm_object_t object);
boolean_t vm_object_print_verbose = FALSE;

boolean_t
vm_object_find(
        vm_object_t     object)
{
        task_t task;
        vm_map_t map;
        vm_map_entry_t entry;
        boolean_t found = FALSE;

        queue_iterate(&tasks, task, task_t, tasks) {
                map = task->map;
                for (entry = vm_map_first_entry(map);
                         entry && entry != vm_map_to_entry(map);
                         entry = entry->vme_next) {

                        vm_object_t obj;

                        /* 
                         * For the time being skip submaps,
                         * only the kernel can have submaps,
                         * and unless we are interested in 
                         * kernel objects, we can simply skip 
                         * submaps. See sb/dejan/nmk18b7/src/mach_kernel/vm
                         * for a full solution.
                         */
                        if (entry->is_sub_map)
                                continue;
                        if (entry) 
                                obj = entry->object.vm_object;
                        else 
                                continue;

                        while (obj != VM_OBJECT_NULL) {
                                if (obj == object) {
                                        if (!found) {
                                                printf("TASK\t\tMAP\t\tENTRY\n");
                                                found = TRUE;
                                        }
                                        printf("0x%x\t0x%x\t0x%x\n", 
                                                   task, map, entry);
                                }
                                obj = obj->shadow;
                        }
                }
        }

        return(found);
}

#endif  /* MACH_KDB */

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->fictitious) {
                                        if (m->phys_page !=
                                            vm_page_guard_addr) {
                                                vm_page_lockspin_queues();
                                                m->fictitious = FALSE;
                                                m->private = TRUE;
                                                m->phys_page = base_page;
                                                if(!m->busy) {
                                                        m->busy = TRUE;
                                                }
                                                if(!m->absent) {
                                                        m->absent = TRUE;
                                                }
                                                m->list_req_pending = TRUE;
                                                vm_page_unlock_queues();
                                        }
                                } else if (m->phys_page != base_page) {
                                        if (m->pmapped) {
                                                /*
                                                 * pmap call to clear old mapping
                                                 */
                                                pmap_disconnect(m->phys_page);
                                        }
                                        m->phys_page = base_page;
                                }

                                /*
                                 * ENCRYPTED SWAP:
                                 * We're not pointing to the same
                                 * physical page any longer and the
                                 * contents of the new one are not
                                 * supposed to be encrypted.
                                 * XXX What happens to the original
                                 * physical page. Is it lost ?
                                 */
                                m->encrypted = FALSE;

                        } else {
                                while ((m = vm_page_grab_fictitious()) 
                                                         == VM_PAGE_NULL)
                                        vm_page_more_fictitious();      
                                vm_page_lockspin_queues();
                                m->fictitious = FALSE;
                                m->private = TRUE;
                                m->phys_page = base_page;
                                m->list_req_pending = TRUE;
                                m->absent = TRUE;
                                m->unusual = TRUE;
                                vm_page_unlock_queues();
                                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->shadow_offset = (vm_object_offset_t)(phys_page << 12);
                object->size = size;
        }
        vm_object_unlock(object);
        return KERN_SUCCESS;
}

/*
 *      memory_object_free_from_cache:
 *
 *      Walk the vm_object cache list, removing and freeing vm_objects 
 *      which are backed by the pager identified by the caller, (pager_ops).  
 *      Remove up to "count" objects, if there are that may available
 *      in the cache.
 *
 *      Walk the list at most once, return the number of vm_objects
 *      actually freed.
 */

__private_extern__ kern_return_t
memory_object_free_from_cache(
        __unused host_t         host,
        memory_object_pager_ops_t pager_ops,
        int             *count)
{

        int     object_released = 0;

        register vm_object_t object = VM_OBJECT_NULL;
        vm_object_t shadow;

/*
        if(host == HOST_NULL)
                return(KERN_INVALID_ARGUMENT);
*/

 try_again:
        vm_object_cache_lock();

        queue_iterate(&vm_object_cached_list, object, 
                                        vm_object_t, cached_list) {
                if (object->pager &&
                    (pager_ops == object->pager->mo_pager_ops)) {
                        vm_object_lock(object);
                        queue_remove(&vm_object_cached_list, object, 
                                        vm_object_t, cached_list);
                        vm_object_cached_count--;

                        /*
                        *       Since this object is in the cache, we know
                        *       that it is initialized and has only a pager's
                        *       (implicit) reference. Take a reference to avoid
                        *       recursive deallocations.
                        */

                        assert(object->pager_initialized);
                        assert(object->ref_count == 0);
                        vm_object_lock_assert_exclusive(object);
                        object->ref_count++;

                        /*
                        *       Terminate the object.
                        *       If the object had a shadow, we let 
                        *       vm_object_deallocate deallocate it. 
                        *       "pageout" objects have a shadow, but
                        *       maintain a "paging reference" rather 
                        *       than a normal reference.
                        *       (We are careful here to limit recursion.)
                        */
                        shadow = object->pageout?VM_OBJECT_NULL:object->shadow;
                        if ((vm_object_terminate(object) == KERN_SUCCESS)
                                        && (shadow != VM_OBJECT_NULL)) {
                                vm_object_deallocate(shadow);
                        }
                
                        if(object_released++ == *count)
                                return KERN_SUCCESS;
                        goto try_again;
                }
        }
        vm_object_cache_unlock();
        *count  = object_released;
        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;
        vm_object_hash_entry_t  entry;

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

        vm_object_cache_lock();
        entry = vm_object_hash_lookup(pager, FALSE);
        if ((entry != VM_OBJECT_HASH_ENTRY_NULL) &&
                        (entry->object != VM_OBJECT_NULL)) {
                if (entry->object->named == TRUE)
                        panic("memory_object_create_named: caller already holds the right");    }

        vm_object_cache_unlock();
        if ((object = vm_object_enter(pager, size, FALSE, FALSE, TRUE))
            == 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;

        vm_object_cache_lock();
        object = memory_object_control_to_vm_object(control);
        if (object == VM_OBJECT_NULL) {
                vm_object_cache_unlock();
                return (KERN_INVALID_ARGUMENT);
        }

restart:
        vm_object_lock(object);

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

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

        if (object->named == TRUE) {
                vm_object_cache_unlock();
                vm_object_unlock(object);
                return KERN_SUCCESS;
        }

        if((object->ref_count == 0) && (!object->terminating)){
                queue_remove(&vm_object_cached_list, object,
                                     vm_object_t, cached_list);
                        vm_object_cached_count--;
                        XPR(XPR_VM_OBJECT_CACHE,
                       "memory_object_recover_named: removing %X, head (%X, %X)\n",
                            (integer_t)object, 
                            (integer_t)vm_object_cached_list.next,
                            (integer_t)vm_object_cached_list.prev, 0,0);
        }

        vm_object_cache_unlock();

        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) {

                /*
                 *      The cache holds a reference (uncounted) to
                 *      the object.  We must locke it before removing
                 *      the object.
                 *
                 */
                
                vm_object_cache_lock();
                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);
                        vm_object_cache_unlock();
                        thread_block(THREAD_CONTINUE_NULL);
                        continue;
                }

                if (((object->ref_count > 1)
                        && (flags & MEMORY_OBJECT_TERMINATE_IDLE))
                        || (object->terminating)) {
                        vm_object_unlock(object);
                        vm_object_cache_unlock();
                        return KERN_FAILURE;
                } else {
                        if (flags & MEMORY_OBJECT_RELEASE_NO_OP) {
                                vm_object_unlock(object);
                                vm_object_cache_unlock();
                                return KERN_SUCCESS;
                        }
                }
                
                if ((flags & MEMORY_OBJECT_RESPECT_CACHE) &&
                                        (object->ref_count == 1)) {
                        if(original_object)
                                object->named = FALSE;
                        vm_object_unlock(object);
                        vm_object_cache_unlock();
                        /* 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);
                        vm_object_cache_unlock();
                        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;

        XPR(XPR_MEMORY_OBJECT,
            "vm_o_lock_request, obj 0x%X off 0x%X size 0x%X flags %X prot %X\n",
            (integer_t)object, offset, size, 
            (((should_return&1)<<1)|should_flush), prot);

        /*
         *      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 and page queues are locked, the object must be a
 * purgeable object with no delayed copies pending.
 */
unsigned int
vm_object_purge(vm_object_t object)
{
        vm_page_t       p, next;
        unsigned int    num_purged_pages;
        vm_page_t       local_freeq;
        unsigned long   local_freed;
        int             purge_loop_quota;
/* free pages as soon as we gather PURGE_BATCH_FREE_LIMIT pages to free */
#define PURGE_BATCH_FREE_LIMIT  50
/* release page queues lock every PURGE_LOOP_QUOTA iterations */
#define PURGE_LOOP_QUOTA        100

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

        assert(object->purgable != VM_PURGABLE_NONVOLATILE);
        object->purgable = VM_PURGABLE_EMPTY;

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

        local_freeq = VM_PAGE_NULL;
        local_freed = 0;

        /*
         * Go through the object's resident pages and try and discard them.
         */
        next = (vm_page_t)queue_first(&object->memq);
        while (!queue_end(&object->memq, (queue_entry_t)next)) {
                p = next;
                next = (vm_page_t)queue_next(&next->listq);

                if (purge_loop_quota-- == 0) {
                        /*
                         * Avoid holding the page queues lock for too long.
                         * Let someone else take it for a while if needed.
                         * Keep holding the object's lock to guarantee that
                         * the object's page list doesn't change under us
                         * while we yield.
                         */
                        if (local_freeq != VM_PAGE_NULL) {
                                /*
                                 * Flush our queue of pages to free.
                                 */
                                vm_page_free_list(local_freeq);
                                local_freeq = VM_PAGE_NULL;
                                local_freed = 0;
                        }
                        mutex_yield(&vm_page_queue_lock);

                        /* resume with the current page and a new quota */
                        purge_loop_quota = PURGE_LOOP_QUOTA;
                }
                                
                       
                if (p->busy || p->cleaning || p->laundry ||
                    p->list_req_pending) {
                        /* page is being acted upon, so don't mess with it */
                        continue;
                }
                if (p->wire_count) {
                        /* don't discard a wired page */
                        continue;
                }

                assert(!p->laundry);
                assert(p->object != kernel_object);

                /* we can discard this page */

                /* advertize that this page is in a transition state */
                p->busy = TRUE;

                if (p->pmapped == TRUE) {
                        /* unmap the page */
                        int refmod_state;

                        refmod_state = pmap_disconnect(p->phys_page);
                        if (refmod_state & VM_MEM_MODIFIED) {
                                p->dirty = TRUE;
                        }
                }

                if (p->dirty || p->precious) {
                        /* we saved the cost of cleaning this page ! */
                        num_purged_pages++;
                        vm_page_purged_count++;
                }

                vm_page_free_prepare(p);

                /* ... and put it on our queue of pages to free */
                assert(p->pageq.next == NULL &&
                       p->pageq.prev == NULL);
                p->pageq.next = (queue_entry_t) local_freeq;
                local_freeq = p;
                if (++local_freed >= PURGE_BATCH_FREE_LIMIT) {
                        /* flush our queue of pages to free */
                        vm_page_free_list(local_freeq);
                        local_freeq = VM_PAGE_NULL;
                        local_freed = 0;
                }
        }

        /* flush our local queue of pages to free one last time */
        if (local_freeq != VM_PAGE_NULL) {
                vm_page_free_list(local_freeq);
                local_freeq = VM_PAGE_NULL;
                local_freed = 0;
        }

        return num_purged_pages;
}

/*
 * 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;
        }

        /*
         * 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;
        }

        new_state = *state & VM_PURGABLE_STATE_MASK;
        switch (new_state) {
        case VM_PURGABLE_DENY:
        case VM_PURGABLE_NONVOLATILE:
                object->purgable = new_state;

                if (old_state != VM_PURGABLE_NONVOLATILE) {
                        vm_page_lock_queues();
                        assert(vm_page_purgeable_count >=
                               object->resident_page_count);
                        vm_page_purgeable_count -= object->resident_page_count;

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

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

        case VM_PURGABLE_VOLATILE:

                if ((old_state != VM_PURGABLE_NONVOLATILE) && (old_state != VM_PURGABLE_VOLATILE))
                        break;
                purgeable_q_t queue;
        
                /* find the correct queue */
                if ((*state&VM_PURGABLE_ORDERING_MASK) == VM_PURGABLE_ORDERING_OBSOLETE)
                        queue = &purgeable_queues[PURGEABLE_Q_TYPE_FIFO];
                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) {
                        /* try to add token... this can fail */
                        vm_page_lock_queues();

                        kern_return_t result = vm_purgeable_token_add(queue);
                        if (result != KERN_SUCCESS) {
                                vm_page_unlock_queues();
                                return result;
                        }
                        vm_page_purgeable_count += object->resident_page_count;

                        vm_page_unlock_queues();

                        object->purgable = new_state;

                        /* object should not be on a queue */
                        assert(object->objq.next == NULL && object->objq.prev == NULL);
                }
                else if (old_state == VM_PURGABLE_VOLATILE) {
                        /*
                         * 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 */
            
                        purgeable_q_t old_queue=vm_purgeable_object_remove(object);
                        assert(old_queue);
            
                        if (old_queue != queue) {
                                kern_return_t result;

                                /* Changing queue. Have to move token. */
                                vm_page_lock_queues();
                                vm_purgeable_token_delete_first(old_queue);
                                result = vm_purgeable_token_add(queue);
                                vm_page_unlock_queues();

                                assert(result==KERN_SUCCESS);   /* this should never fail since we just freed a token */
                        }
                };
                vm_purgeable_object_add(object, queue, (*state&VM_VOLATILE_GROUP_MASK)>>VM_VOLATILE_GROUP_SHIFT );

                assert(queue->debug_count_objects>=0);
        
                break;


        case VM_PURGABLE_EMPTY:
                if (old_state != new_state) 
                {
                        assert(old_state==VM_PURGABLE_NONVOLATILE || old_state==VM_PURGABLE_VOLATILE);
                        if(old_state==VM_PURGABLE_VOLATILE) {
                                assert(object->objq.next != NULL && object->objq.prev != NULL); /* object should be on a queue */
                                purgeable_q_t old_queue=vm_purgeable_object_remove(object);
                                assert(old_queue);
                                vm_page_lock_queues();
                                vm_purgeable_token_delete_first(old_queue);
                        }

                        if (old_state==VM_PURGABLE_NONVOLATILE) {
                                vm_page_purgeable_count += object->resident_page_count;
                                vm_page_lock_queues();
                        }
                        (void) vm_object_purge(object);
                        vm_page_unlock_queues();
                }
                break;

        }
        *state = old_state;

        return KERN_SUCCESS;
}

#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(
        register 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);
}

#ifdef MACH_BSD
/*
 * Scale the vm_object_cache
 * This is required to make sure that the vm_object_cache is big
 * enough to effectively cache the mapped file.
 * This is really important with UBC as all the regular file vnodes
 * have memory object associated with them. Havving this cache too
 * small results in rapid reclaim of vnodes and hurts performance a LOT!
 *
 * This is also needed as number of vnodes can be dynamically scaled.
 */
kern_return_t
adjust_vm_object_cache(
        __unused vm_size_t oval,
        vm_size_t nval)
{
        vm_object_cached_max = nval;
        vm_object_cache_trim(FALSE);
        return (KERN_SUCCESS);
}
#endif /* MACH_BSD */


/*
 * 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.
 */
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;
        boolean_t               object1_paging, object2_paging;
        vm_page_t               page;
        vm_object_offset_t      page_offset;

        tmp_object = VM_OBJECT_NULL;
        object1_locked = FALSE; object2_locked = FALSE;
        object1_paging = FALSE; object2_paging = 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;
        }

        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;
        }
        /*
         * Since we're about to mess with the object's backing store,
         * mark it as "paging_in_progress".  Note that this is not 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").
         */
        vm_object_paging_begin(object1);
        object1_paging = TRUE;
        vm_object_unlock(object1);
        object1_locked = FALSE;

        /*
         * 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_begin(object2);
        object2_paging = TRUE;
        vm_object_unlock(object2);
        object2_locked = FALSE;

        /*
         * 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);
        vm_object_paging_begin(tmp_object);
        tmp_object->can_persist = FALSE;

        /*
         * 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) {
                vm_object_lock(object1);
                vm_object_lock(object2);
        } else {
                vm_object_lock(object2);
                vm_object_lock(object1);
        }
        object1_locked = TRUE;
        object2_locked = TRUE;

        if (object1->size != object2->size ||
            object1->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 || queue_empty(&object1->memq)) {
                /*
                 * No pages in object1, just transfer pages
                 * from object2 to object1.  No need to go through
                 * an intermediate object.
                 */
                while (!queue_empty(&object2->memq)) {
                        page = (vm_page_t) queue_first(&object2->memq);
                        vm_page_rename(page, object1, page->offset, FALSE);
                }
                assert(queue_empty(&object2->memq));
        } else if (object2->phys_contiguous || queue_empty(&object2->memq)) {
                /*
                 * No pages in object2, just transfer pages
                 * from object1 to object2.  No need to go through
                 * an intermediate object.
                 */
                while (!queue_empty(&object1->memq)) {
                        page = (vm_page_t) queue_first(&object1->memq);
                        vm_page_rename(page, object2, page->offset, FALSE);
                }
                assert(queue_empty(&object1->memq));
        } else {
                /* transfer object1's pages to tmp_object */
                vm_page_lock_queues();
                while (!queue_empty(&object1->memq)) {
                        page = (vm_page_t) queue_first(&object1->memq);
                        page_offset = page->offset;
                        vm_page_remove(page);
                        page->offset = page_offset;
                        queue_enter(&tmp_object->memq, page, vm_page_t, listq);
                }
                vm_page_unlock_queues();
                assert(queue_empty(&object1->memq));
                /* transfer object2's pages to object1 */
                while (!queue_empty(&object2->memq)) {
                        page = (vm_page_t) queue_first(&object2->memq);
                        vm_page_rename(page, object1, page->offset, FALSE);
                }
                assert(queue_empty(&object2->memq));
                /* transfer tmp_object's pages to object1 */
                while (!queue_empty(&tmp_object->memq)) {
                        page = (vm_page_t) queue_first(&tmp_object->memq);
                        queue_remove(&tmp_object->memq, page,
                                     vm_page_t, listq);
                        vm_page_insert(page, object2, page->offset);
                }
                assert(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

        /* "size" should be identical */
        assert(object1->size == object2->size);
        /* "Lock" refers to the object not its contents */
        /* "ref_count" refers to the object not its contents */
#if TASK_SWAPPER
        /* "res_count" refers to the object not its contents */
#endif
        /* "resident_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(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);
        /* "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(temporary);
        __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(silent_overwrite);
        __TRANSPOSE_FIELD(advisory_pageout);
        __TRANSPOSE_FIELD(true_share);
        /* "terminating" should not be set */
        assert(!object1->terminating);
        assert(!object2->terminating);
        __TRANSPOSE_FIELD(named);
        /* "shadow_severed" refers to the object not its contents */
        __TRANSPOSE_FIELD(phys_contiguous);
        __TRANSPOSE_FIELD(nophyscache);
        /* "cached_list" should be NULL */
        assert(object1->cached_list.prev == NULL);
        assert(object1->cached_list.next == NULL);
        assert(object2->cached_list.prev == NULL);
        assert(object2->cached_list.next == NULL);
        /* "msr_q" is linked to the object not its contents */
        assert(queue_empty(&object1->msr_q));
        assert(queue_empty(&object2->msr_q));
        __TRANSPOSE_FIELD(last_alloc);
        __TRANSPOSE_FIELD(sequential);
        __TRANSPOSE_FIELD(pages_created);
        __TRANSPOSE_FIELD(pages_used);
#if MACH_PAGEMAP
        __TRANSPOSE_FIELD(existence_map);
#endif
        __TRANSPOSE_FIELD(cow_hint);
#if MACH_ASSERT
        __TRANSPOSE_FIELD(paging_object);
#endif
        __TRANSPOSE_FIELD(wimg_bits);
        __TRANSPOSE_FIELD(code_signed);
        __TRANSPOSE_FIELD(not_in_use);
#ifdef UPL_DEBUG
        /* "uplq" refers to the object not its contents (see upl_transpose()) */
#endif

#undef __TRANSPOSE_FIELD

        retval = KERN_SUCCESS;

done:
        /*
         * Cleanup.
         */
        if (tmp_object != VM_OBJECT_NULL) {
                vm_object_paging_end(tmp_object);
                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;
        }
        if (object1_paging) {
                vm_object_lock(object1);
                vm_object_paging_end(object1);
                vm_object_unlock(object1);
                object1_paging = FALSE;
        }
        if (object2_paging) {
                vm_object_lock(object2);
                vm_object_paging_end(object2);
                vm_object_unlock(object2);
                object2_paging = FALSE;
        }

        return retval;
}


/*
 *      vm_object_build_cluster
 *
 *      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;

uint32_t pre_heat_scaling[MAX_UPL_TRANSFER];
uint32_t pre_heat_cluster[MAX_UPL_TRANSFER];

#define PRE_HEAT_MULTIPLIER 4

__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)
{
        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;
        int                     sequential_run;
        int                     sequential_behavior = VM_BEHAVIOR_SEQUENTIAL;

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

        if ( (max_length = *length) > (MAX_UPL_TRANSFER * PAGE_SIZE) ) 
                max_length = (MAX_UPL_TRANSFER * PAGE_SIZE);
        /*
         * we'll always return a cluster size of at least
         * 1 page, since the original fault must always
         * be processed
         */
        *length = PAGE_SIZE;

        if (speculative_reads_disabled || fault_info == NULL || max_length == 0) {
                /*
                 * no cluster... just fault the page in
                 */
                return;
        }
        orig_start = *start;
        target_start = orig_start;
        cluster_size = round_page_32(fault_info->cluster_size);
        behavior = fault_info->behavior;

        vm_object_lock(object);

        if (object->internal)
                object_size = object->size;
        else if (object->pager != MEMORY_OBJECT_NULL)
                vnode_pager_get_object_size(object->pager, &object_size);
        else
                goto out;       /* pager is gone for this object, nothing more to do */

        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 ((behavior = sequential_behavior) == VM_BEHAVIOR_SEQUENTIAL)
                                look_behind = FALSE;
                        else
                                look_ahead = FALSE;
                } else {
                        uint32_t        pages_unused;

                        if (object->pages_created < 32 * PRE_HEAT_MULTIPLIER) {
                                /*
                                 * prime the pump
                                 */
                                pre_heat_size = PAGE_SIZE * 8 * PRE_HEAT_MULTIPLIER;
                                break;
                        }
                        pages_unused = object->pages_created - object->pages_used;

                        if (pages_unused < (object->pages_created / 8)) {
                                pre_heat_size = PAGE_SIZE * 32 * PRE_HEAT_MULTIPLIER;
                        } else if (pages_unused < (object->pages_created / 4)) {
                                pre_heat_size = PAGE_SIZE * 16 * PRE_HEAT_MULTIPLIER;
                        } else if (pages_unused < (object->pages_created / 2)) {
                                pre_heat_size = PAGE_SIZE * 8 * PRE_HEAT_MULTIPLIER;
                        } else {
                                pre_heat_size = PAGE_SIZE * 4 * PRE_HEAT_MULTIPLIER;
                        }
                }
                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;

                break;

        case VM_BEHAVIOR_RSEQNTL:
                if ((pre_heat_size = cluster_size) == 0)
                        pre_heat_size = sequential_run + PAGE_SIZE;
                look_ahead = FALSE;

                break;

        }
        if (pre_heat_size > max_length)
                pre_heat_size = max_length;

        if (behavior == VM_BEHAVIOR_DEFAULT && vm_page_free_count < vm_page_free_target)
                pre_heat_size /= 2;

        if (look_ahead == TRUE) {
                if (look_behind == TRUE)
                        target_start &= ~(pre_heat_size - 1);

                if ((target_start + pre_heat_size) > object_size)
                        pre_heat_size = (vm_size_t)(trunc_page_64(object_size - target_start));

                tail_size = pre_heat_size - (orig_start - target_start) - PAGE_SIZE;
        } else {
                if (pre_heat_size > target_start)
                        pre_heat_size = target_start;
                tail_size = 0;
        }
        pre_heat_scaling[pre_heat_size / PAGE_SIZE]++;

        if (pre_heat_size <= PAGE_SIZE)
                goto out;

        if (look_behind == TRUE) {
                /*
                 * take a look at the pages before the original
                 * faulting offset 
                 */
                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 and internal objects w/o an existence map
                         * vm_externl_state_get will return VM_EXTERNAL_STATE_UNKNOWN
                         */
#if MACH_PAGEMAP
                        if (vm_external_state_get(object->existence_map, offset) == VM_EXTERNAL_STATE_ABSENT) {
                                /*
                                 * we know for a fact that the pager can't provide the page
                                 * so don't include it or any pages beyond it in this cluster
                                 */
                                break;
                        }
#endif
                        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;
                        /*
                         * for external objects and internal objects w/o an existence map
                         * vm_externl_state_get will return VM_EXTERNAL_STATE_UNKNOWN
                         */
#if MACH_PAGEMAP
                        if (vm_external_state_get(object->existence_map, offset) == VM_EXTERNAL_STATE_ABSENT) {
                                /*
                                 * we know for a fact that the pager can't provide the page
                                 * so don't include it or any pages beyond it in this cluster
                                 */
                                break;
                        }
#endif
                        if (vm_page_lookup(object, offset) != VM_PAGE_NULL) {
                                /*
                                 * don't bridge resident pages
                                 */
                                break;
                        }
                        *length += PAGE_SIZE;
                }
        }
out:
        pre_heat_cluster[*length / PAGE_SIZE]++;

        vm_object_unlock(object);
}


/*
 * 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->shadow_offset >> 12);
                        }
                        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->busy || dst_page->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->pmapped == TRUE)
                                pmap_disconnect(dst_page->phys_page);

                        vm_page_lock_queues();
                        vm_page_free(dst_page);
                        vm_page_unlock_queues();

                        break;
                }

                if (flags) {
                        *flags = 0;

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

                        if(dst_page->dirty) *flags |= UPL_POP_DIRTY;
                        if(dst_page->pageout) *flags |= UPL_POP_PAGEOUT;
                        if(dst_page->precious) *flags |= UPL_POP_PRECIOUS;
                        if(dst_page->absent) *flags |= UPL_POP_ABSENT;
                        if(dst_page->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->busy || (ops & UPL_POP_BUSY));
                        if (ops & UPL_POP_DIRTY) dst_page->dirty = TRUE;
                        if (ops & UPL_POP_PAGEOUT) dst_page->pageout = TRUE;
                        if (ops & UPL_POP_PRECIOUS) dst_page->precious = TRUE;
                        if (ops & UPL_POP_ABSENT) dst_page->absent = TRUE;
                        if (ops & UPL_POP_BUSY) dst_page->busy = TRUE;
                }

                if(ops & UPL_POP_CLR) {
                        assert(dst_page->busy);
                        if (ops & UPL_POP_DIRTY) dst_page->dirty = FALSE;
                        if (ops & UPL_POP_PAGEOUT) dst_page->pageout = FALSE;
                        if (ops & UPL_POP_PRECIOUS) dst_page->precious = FALSE;
                        if (ops & UPL_POP_ABSENT) dst_page->absent = FALSE;
                        if (ops & UPL_POP_BUSY) {
                                dst_page->busy = FALSE;
                                PAGE_WAKEUP(dst_page);
                        }
                }

                if (dst_page->encrypted) {
                        /*
                         * ENCRYPTED SWAP:
                         * We need to decrypt this encrypted page before the
                         * caller can access its contents.
                         * But if the caller really wants to access the page's
                         * contents, they have to keep the page "busy".
                         * Otherwise, the page could get recycled or re-encrypted
                         * at any time.
                         */
                        if ((ops & UPL_POP_SET) && (ops & UPL_POP_BUSY) &&
                            dst_page->busy) {
                                /*
                                 * The page is stable enough to be accessed by
                                 * the caller, so make sure its contents are
                                 * not encrypted.
                                 */
                                vm_page_decrypt(dst_page, 0);
                        } else {
                                /*
                                 * The page is not busy, so don't bother
                                 * decrypting it, since anything could
                                 * happen to it between now and when the
                                 * caller wants to access it.
                                 * We should not give the caller access
                                 * to this page.
                                 */
                                assert(!phys_entry);
                        }
                }

                if (phys_entry) {
                        /*
                         * The physical page number will remain valid
                         * only if the page is kept busy.
                         * ENCRYPTED SWAP: make sure we don't let the
                         * caller access an encrypted page.
                         */
                        assert(dst_page->busy);
                        assert(!dst_page->encrypted);
                        *phys_entry = dst_page->phys_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,
        int                     *range)
{
        vm_object_offset_t      offset;
        vm_page_t               dst_page;

        if (object->resident_page_count == 0) {
                if (range) {
                        if (ops & UPL_ROP_PRESENT)
                                *range = 0;
                        else
                                *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->busy || dst_page->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->pmapped == TRUE)
                                        pmap_disconnect(dst_page->phys_page);

                                vm_page_lock_queues();
                                vm_page_free(dst_page);
                                vm_page_unlock_queues();

                        } else if (ops & UPL_ROP_ABSENT)
                                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 = offset - offset_beg;
                else *range=0;
        }
        return KERN_SUCCESS;
}


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);
        }
        lck_rw_lock_exclusive(&object->Lock);
}

boolean_t
vm_object_lock_try(vm_object_t object)
{
        if (object == vm_pageout_scan_wants_object) {
                scan_object_collision++;
                mutex_pause(2);
        }
        return (lck_rw_try_lock_exclusive(&object->Lock));
}

void
vm_object_lock_shared(vm_object_t object)
{
        if (object == vm_pageout_scan_wants_object) {
                scan_object_collision++;
                mutex_pause(2);
        }
        lck_rw_lock_shared(&object->Lock);
}

boolean_t
vm_object_lock_try_shared(vm_object_t object)
{
        if (object == vm_pageout_scan_wants_object) {
                scan_object_collision++;
                mutex_pause(2);
        }
        return (lck_rw_try_lock_shared(&object->Lock));
}