xnu-2782.40.9.tar.gz

[apple/xnu.git] / osfmk / kern / zalloc.c

/*
 * Copyright (c) 2000-2014 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:   kern/zalloc.c
 *      Author: Avadis Tevanian, Jr.
 *
 *      Zone-based memory allocator.  A zone is a collection of fixed size
 *      data blocks for which quick allocation/deallocation is possible.
 */
#include <zone_debug.h>
#include <zone_alias_addr.h>

#include <mach/mach_types.h>
#include <mach/vm_param.h>
#include <mach/kern_return.h>
#include <mach/mach_host_server.h>
#include <mach/task_server.h>
#include <mach/machine/vm_types.h>
#include <mach_debug/zone_info.h>
#include <mach/vm_map.h>

#include <kern/kern_types.h>
#include <kern/assert.h>
#include <kern/host.h>
#include <kern/macro_help.h>
#include <kern/sched.h>
#include <kern/locks.h>
#include <kern/sched_prim.h>
#include <kern/misc_protos.h>
#include <kern/thread_call.h>
#include <kern/zalloc.h>
#include <kern/kalloc.h>
#include <kern/btlog.h>

#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_page.h>

#include <pexpert/pexpert.h>

#include <machine/machparam.h>
#include <machine/machine_routines.h>  /* ml_cpu_get_info */

#include <libkern/OSDebug.h>
#include <libkern/OSAtomic.h>
#include <sys/kdebug.h>

/*
 *  ZONE_ALIAS_ADDR
 *
 * With this option enabled, zones with alloc_size <= PAGE_SIZE allocate
 * a virtual page from the zone_map, but before zcram-ing the allocated memory
 * into the zone, the page is translated to use the alias address of the page
 * in the static kernel region. zone_gc reverses that translation when
 * scanning the freelist to collect free pages so that it can look up the page
 * in the zone_page_table, and free it to kmem_free.
 *
 * The static kernel region is a flat 1:1 mapping of physical memory passed
 * to xnu by the booter. It is mapped to the range:
 * [gVirtBase, gVirtBase + gPhysSize]
 *
 * Accessing memory via the static kernel region is faster due to the
 * entire region being mapped via large pages, cutting down
 * on TLB misses.
 *
 * zinit favors using PAGE_SIZE backing allocations for a zone unless it would
 * waste more than 10% space to use a single page, in order to take advantage
 * of the speed benefit for as many zones as possible.
 *
 * Zones with > PAGE_SIZE allocations can't take advantage of this
 * because kernel_memory_allocate doesn't give out physically contiguous pages.
 *
 * zone_virtual_addr()
 *  - translates an address from the static kernel region to the zone_map
 *  - returns the same address if it's not from the static kernel region
 * It relies on the fact that a physical page mapped to the
 * zone_map is not mapped anywhere else (except the static kernel region).
 *
 * zone_alias_addr()
 *  - translates a virtual memory address from the zone_map to the
 *    corresponding address in the static kernel region
 *
 */

#if     !ZONE_ALIAS_ADDR
#define from_zone_map(addr, size) \
        ((vm_offset_t)(addr)             >= zone_map_min_address && \
        ((vm_offset_t)(addr) + size - 1) <  zone_map_max_address )
#else
#define from_zone_map(addr, size) \
        ((vm_offset_t)(zone_virtual_addr((vm_map_address_t)(uintptr_t)addr))            >= zone_map_min_address && \
        ((vm_offset_t)(zone_virtual_addr((vm_map_address_t)(uintptr_t)addr)) + size -1) <  zone_map_max_address )
#endif

/*
 * Zone Corruption Debugging
 *
 * We use three techniques to detect modification of a zone element
 * after it's been freed.
 *
 * (1) Check the freelist next pointer for sanity.
 * (2) Store a backup of the next pointer at the end of the element,
 *     and compare it to the primary next pointer when the element is allocated
 *     to detect corruption of the freelist due to use-after-free bugs.
 *     The backup pointer is also XORed with a per-boot random cookie.
 * (3) Poison the freed element by overwriting it with 0xdeadbeef,
 *     and check for that value when the element is being reused to make sure
 *     no part of the element has been modified while it was on the freelist.
 *     This will also help catch read-after-frees, as code will now dereference
 *     0xdeadbeef instead of a valid but freed pointer.
 *
 * (1) and (2) occur for every allocation and free to a zone.
 * This is done to make it slightly more difficult for an attacker to
 * manipulate the freelist to behave in a specific way.
 *
 * Poisoning (3) occurs periodically for every N frees (counted per-zone)
 * and on every free for zones smaller than a cacheline.  If -zp
 * is passed as a boot arg, poisoning occurs for every free.
 *
 * Performance slowdown is inversely proportional to the frequency of poisoning,
 * with a 4-5% hit around N=1, down to ~0.3% at N=16 and just "noise" at N=32
 * and higher. You can expect to find a 100% reproducible bug in an average of
 * N tries, with a standard deviation of about N, but you will want to set
 * "-zp" to always poison every free if you are attempting to reproduce
 * a known bug.
 *
 * For a more heavyweight, but finer-grained method of detecting misuse
 * of zone memory, look up the "Guard mode" zone allocator in gzalloc.c.
 *
 * Zone Corruption Logging
 *
 * You can also track where corruptions come from by using the boot-arguments
 * "zlog=<zone name to log> -zc". Search for "Zone corruption logging" later
 * in this document for more implementation and usage information.
 *
 * Zone Leak Detection
 *
 * To debug leaks of zone memory, use the zone leak detection tool 'zleaks'
 * found later in this file via the showtopztrace and showz* macros in kgmacros,
 * or use zlog without the -zc argument.
 *
 */

/* Returns TRUE if we rolled over the counter at factor */
static inline boolean_t
sample_counter(volatile uint32_t * count_p, uint32_t factor)
{
        uint32_t old_count, new_count;
        boolean_t rolled_over;

        do {
                new_count = old_count = *count_p;

                if (++new_count >= factor) {
                        rolled_over = TRUE;
                        new_count = 0;
                } else {
                        rolled_over = FALSE;
                }

        } while (!OSCompareAndSwap(old_count, new_count, count_p));

        return rolled_over;
}

#if defined(__LP64__)
#define ZP_POISON       0xdeadbeefdeadbeef
#else
#define ZP_POISON       0xdeadbeef
#endif

#define ZP_DEFAULT_SAMPLING_FACTOR 16
#define ZP_DEFAULT_SCALE_FACTOR 4

/*
 *  A zp_factor of 0 indicates zone poisoning is disabled,
 *  however, we still poison zones smaller than zp_tiny_zone_limit (a cacheline).
 *  Passing the -no-zp boot-arg disables even this behavior.
 *  In all cases, we record and check the integrity of a backup pointer.
 */

/* set by zp-factor=N boot arg, zero indicates non-tiny poisoning disabled */
uint32_t        zp_factor               = 0;

/* set by zp-scale=N boot arg, scales zp_factor by zone size */
uint32_t        zp_scale                = 0;

/* set in zp_init, zero indicates -no-zp boot-arg */
vm_size_t       zp_tiny_zone_limit      = 0;

/* initialized to a per-boot random value in zp_init */
uintptr_t       zp_poisoned_cookie      = 0;
uintptr_t       zp_nopoison_cookie      = 0;


/*
 * initialize zone poisoning
 * called from zone_bootstrap before any allocations are made from zalloc
 */
static inline void
zp_init(void)
{
        char temp_buf[16];

        /*
         * Initialize backup pointer random cookie for poisoned elements
         * Try not to call early_random() back to back, it may return
         * the same value if mach_absolute_time doesn't have sufficient time
         * to tick over between calls.  <rdar://problem/11597395>
         * (This is only a problem on embedded devices)
         */
        zp_poisoned_cookie = (uintptr_t) early_random();

        /*
         * Always poison zones smaller than a cacheline,
         * because it's pretty close to free
         */
        ml_cpu_info_t cpu_info;
        ml_cpu_get_info(&cpu_info);
        zp_tiny_zone_limit = (vm_size_t) cpu_info.cache_line_size;

        zp_factor = ZP_DEFAULT_SAMPLING_FACTOR;
        zp_scale  = ZP_DEFAULT_SCALE_FACTOR;

        //TODO: Bigger permutation?
        /*
         * Permute the default factor +/- 1 to make it less predictable
         * This adds or subtracts ~4 poisoned objects per 1000 frees.
         */
        if (zp_factor != 0) {
                uint32_t rand_bits = early_random() & 0x3;

                if (rand_bits == 0x1)
                        zp_factor += 1;
                else if (rand_bits == 0x2)
                        zp_factor -= 1;
                /* if 0x0 or 0x3, leave it alone */
        }

        /* -zp: enable poisoning for every alloc and free */
        if (PE_parse_boot_argn("-zp", temp_buf, sizeof(temp_buf))) {
                zp_factor = 1;
        }

        /* -no-zp: disable poisoning completely even for tiny zones */
        if (PE_parse_boot_argn("-no-zp", temp_buf, sizeof(temp_buf))) {
                zp_factor          = 0;
                zp_tiny_zone_limit = 0;
                printf("Zone poisoning disabled\n");
        }

        /* zp-factor=XXXX: override how often to poison freed zone elements */
        if (PE_parse_boot_argn("zp-factor", &zp_factor, sizeof(zp_factor))) {
                printf("Zone poisoning factor override: %u\n", zp_factor);
        }

        /* zp-scale=XXXX: override how much zone size scales zp-factor by */
        if (PE_parse_boot_argn("zp-scale", &zp_scale, sizeof(zp_scale))) {
                printf("Zone poisoning scale factor override: %u\n", zp_scale);
        }

        /* Initialize backup pointer random cookie for unpoisoned elements */
        zp_nopoison_cookie = (uintptr_t) early_random();

#if MACH_ASSERT
        if (zp_poisoned_cookie == zp_nopoison_cookie)
                panic("early_random() is broken: %p and %p are not random\n",
                      (void *) zp_poisoned_cookie, (void *) zp_nopoison_cookie);
#endif

        /*
         * Use the last bit in the backup pointer to hint poisoning state
         * to backup_ptr_mismatch_panic. Valid zone pointers are aligned, so
         * the low bits are zero.
         */
        zp_poisoned_cookie |=   (uintptr_t)0x1ULL;
        zp_nopoison_cookie &= ~((uintptr_t)0x1ULL);

#if defined(__LP64__)
        /*
         * Make backup pointers more obvious in GDB for 64 bit
         * by making OxFFFFFF... ^ cookie = 0xFACADE...
         * (0xFACADE = 0xFFFFFF ^ 0x053521)
         * (0xC0FFEE = 0xFFFFFF ^ 0x3f0011)
         * The high 3 bytes of a zone pointer are always 0xFFFFFF, and are checked
         * by the sanity check, so it's OK for that part of the cookie to be predictable.
         *
         * TODO: Use #defines, xors, and shifts
         */

        zp_poisoned_cookie &= 0x000000FFFFFFFFFF;
        zp_poisoned_cookie |= 0x0535210000000000; /* 0xFACADE */

        zp_nopoison_cookie &= 0x000000FFFFFFFFFF;
        zp_nopoison_cookie |= 0x3f00110000000000; /* 0xC0FFEE */
#endif
}

/* zone_map page count for page table structure */
uint64_t zone_map_table_page_count = 0;

/*
 * These macros are used to keep track of the number
 * of pages being used by the zone currently. The
 * z->page_count is protected by the zone lock.
 */
#define ZONE_PAGE_COUNT_INCR(z, count)          \
{                                               \
        OSAddAtomic64(count, &(z->page_count)); \
}

#define ZONE_PAGE_COUNT_DECR(z, count)                  \
{                                                       \
        OSAddAtomic64(-count, &(z->page_count));        \
}

/* for is_sane_zone_element and garbage collection */

vm_offset_t     zone_map_min_address = 0;  /* initialized in zone_init */
vm_offset_t     zone_map_max_address = 0;

/* Helpful for walking through a zone's free element list. */
struct zone_free_element {
        struct zone_free_element *next;
        /* ... */
        /* void *backup_ptr; */
};

struct zone_page_metadata {
        queue_chain_t                           pages;
        struct zone_free_element        *elements;
        zone_t                                          zone;
        uint16_t                                        alloc_count;
        uint16_t                                        free_count;
};

/* The backup pointer is stored in the last pointer-sized location in an element. */
static inline vm_offset_t *
get_backup_ptr(vm_size_t  elem_size,
               vm_offset_t *element)
{
        return (vm_offset_t *) ((vm_offset_t)element + elem_size - sizeof(vm_offset_t));
}

static inline struct zone_page_metadata *
get_zone_page_metadata(struct zone_free_element *element)
{
        return (struct zone_page_metadata *)(trunc_page((vm_offset_t)element) + PAGE_SIZE - sizeof(struct zone_page_metadata));
}

/*
 * Zone checking helper function.
 * A pointer that satisfies these conditions is OK to be a freelist next pointer
 * A pointer that doesn't satisfy these conditions indicates corruption
 */
static inline boolean_t
is_sane_zone_ptr(zone_t         zone,
                 vm_offset_t    addr,
                 size_t         obj_size)
{
        /*  Must be aligned to pointer boundary */
        if (__improbable((addr & (sizeof(vm_offset_t) - 1)) != 0))
                return FALSE;

        /*  Must be a kernel address */
        if (__improbable(!pmap_kernel_va(addr)))
                return FALSE;

        /*  Must be from zone map if the zone only uses memory from the zone_map */
        /*
         *  TODO: Remove the zone->collectable check when every
         *  zone using foreign memory is properly tagged with allows_foreign
         */
        if (zone->collectable && !zone->allows_foreign) {
#if ZONE_ALIAS_ADDR
                /*
                 * If this address is in the static kernel region, it might be
                 * the alias address of a valid zone element.
                 * If we tried to find the zone_virtual_addr() of an invalid
                 * address in the static kernel region, it will panic, so don't 
                 * check addresses in this region.
                 *
                 * TODO: Use a safe variant of zone_virtual_addr to
                 *  make this check more accurate
                 *
                 * The static kernel region is mapped at:
                 * [gVirtBase, gVirtBase + gPhysSize]
                 */
                if ((addr - gVirtBase) < gPhysSize)
                        return TRUE;
#endif
                /*  check if addr is from zone map */
                if (addr                 >= zone_map_min_address &&
                   (addr + obj_size - 1) <  zone_map_max_address )
                        return TRUE;

                return FALSE;
        }

        return TRUE;
}

static inline boolean_t
is_sane_zone_page_metadata(zone_t       zone,
                           vm_offset_t  page_meta)
{
        /* NULL page metadata structures are invalid */
        if (page_meta == 0)
                return FALSE;
        return is_sane_zone_ptr(zone, page_meta, sizeof(struct zone_page_metadata));
}

static inline boolean_t
is_sane_zone_element(zone_t      zone,
                     vm_offset_t addr)
{
        /*  NULL is OK because it indicates the tail of the list */
        if (addr == 0)
                return TRUE;
        return is_sane_zone_ptr(zone, addr, zone->elem_size);
}
        
/* Someone wrote to freed memory. */
static inline void /* noreturn */
zone_element_was_modified_panic(zone_t        zone,
                                vm_offset_t   element,
                                vm_offset_t   found,
                                vm_offset_t   expected,
                                vm_offset_t   offset)
{
        panic("a freed zone element has been modified in zone %s: expected %p but found %p, bits changed %p, at offset %d of %d in element %p, cookies %p %p",
                         zone->zone_name,
              (void *)   expected,
              (void *)   found,
              (void *)   (expected ^ found),
              (uint32_t) offset,
              (uint32_t) zone->elem_size,
              (void *)   element,
              (void *)   zp_nopoison_cookie,
              (void *)   zp_poisoned_cookie);
}

/*
 * The primary and backup pointers don't match.
 * Determine which one was likely the corrupted pointer, find out what it
 * probably should have been, and panic.
 * I would like to mark this as noreturn, but panic() isn't marked noreturn.
 */
static void /* noreturn */
backup_ptr_mismatch_panic(zone_t        zone,
                          vm_offset_t   element,
                          vm_offset_t   primary,
                          vm_offset_t   backup)
{
        vm_offset_t likely_backup;

        boolean_t   sane_backup;
        boolean_t   sane_primary = is_sane_zone_element(zone, primary);
        boolean_t   element_was_poisoned = (backup & 0x1) ? TRUE : FALSE;

#if defined(__LP64__)
        /* We can inspect the tag in the upper bits for additional confirmation */
        if ((backup & 0xFFFFFF0000000000) == 0xFACADE0000000000)
                element_was_poisoned = TRUE;
        else if ((backup & 0xFFFFFF0000000000) == 0xC0FFEE0000000000)
                element_was_poisoned = FALSE;
#endif

        if (element_was_poisoned) {
                likely_backup = backup ^ zp_poisoned_cookie;
                sane_backup = is_sane_zone_element(zone, likely_backup);
        } else {
                likely_backup = backup ^ zp_nopoison_cookie;
                sane_backup = is_sane_zone_element(zone, likely_backup);
        }

        /* The primary is definitely the corrupted one */
        if (!sane_primary && sane_backup)
                zone_element_was_modified_panic(zone, element, primary, likely_backup, 0);

        /* The backup is definitely the corrupted one */
        if (sane_primary && !sane_backup)
                zone_element_was_modified_panic(zone, element, backup,
                                                (primary ^ (element_was_poisoned ? zp_poisoned_cookie : zp_nopoison_cookie)),
                                                zone->elem_size - sizeof(vm_offset_t));

        /*
         * Not sure which is the corrupted one.
         * It's less likely that the backup pointer was overwritten with
         * ( (sane address) ^ (valid cookie) ), so we'll guess that the
         * primary pointer has been overwritten with a sane but incorrect address.
         */
        if (sane_primary && sane_backup)
                zone_element_was_modified_panic(zone, element, primary, likely_backup, 0);

        /* Neither are sane, so just guess. */
        zone_element_was_modified_panic(zone, element, primary, likely_backup, 0);
}


/*
 * Sets the next element of tail to elem.
 * elem can be NULL.
 * Preserves the poisoning state of the element.
 */
static inline void
append_zone_element(zone_t                    zone,
                    struct zone_free_element *tail,
                    struct zone_free_element *elem)
{
        vm_offset_t *backup = get_backup_ptr(zone->elem_size, (vm_offset_t *) tail);

        vm_offset_t old_backup = *backup;

        vm_offset_t old_next = (vm_offset_t) tail->next;
        vm_offset_t new_next = (vm_offset_t) elem;

        if      (old_next == (old_backup ^ zp_nopoison_cookie))
                *backup = new_next ^ zp_nopoison_cookie;
        else if (old_next == (old_backup ^ zp_poisoned_cookie))
                *backup = new_next ^ zp_poisoned_cookie;
        else
                backup_ptr_mismatch_panic(zone,
                                          (vm_offset_t) tail,
                                          old_next,
                                          old_backup);

        tail->next = elem;
}


/*
 * Insert a linked list of elements (delineated by head and tail) at the head of
 * the zone free list. Every element in the list being added has already gone
 * through append_zone_element, so their backup pointers are already
 * set properly.
 * Precondition: There should be no elements after tail
 */
static inline void
add_list_to_zone(zone_t                    zone,
                 struct zone_free_element *head,
                 struct zone_free_element *tail)
{
        assert(tail->next == NULL);
        assert(!zone->use_page_list);

        append_zone_element(zone, tail, zone->free_elements);

        zone->free_elements = head;
}


/*
 * Adds the element to the head of the zone's free list
 * Keeps a backup next-pointer at the end of the element
 */
static inline void
free_to_zone(zone_t      zone,
             vm_offset_t element,
             boolean_t   poison)
{
        vm_offset_t old_head;
        struct zone_page_metadata *page_meta;

        vm_offset_t *primary  = (vm_offset_t *) element;
        vm_offset_t *backup   = get_backup_ptr(zone->elem_size, primary);

        if (zone->use_page_list) {
                page_meta = get_zone_page_metadata((struct zone_free_element *)element);
                assert(page_meta->zone == zone);
                old_head = (vm_offset_t)page_meta->elements;
        } else {
                old_head = (vm_offset_t)zone->free_elements;
        }

#if MACH_ASSERT
        if (__improbable(!is_sane_zone_element(zone, old_head)))
                panic("zfree: invalid head pointer %p for freelist of zone %s\n",
                      (void *) old_head, zone->zone_name);
#endif

        if (__improbable(!is_sane_zone_element(zone, element)))
                panic("zfree: freeing invalid pointer %p to zone %s\n",
                      (void *) element, zone->zone_name);

        /*
         * Always write a redundant next pointer
         * So that it is more difficult to forge, xor it with a random cookie
         * A poisoned element is indicated by using zp_poisoned_cookie
         * instead of zp_nopoison_cookie
         */

        *backup = old_head ^ (poison ? zp_poisoned_cookie : zp_nopoison_cookie);

        /* Insert this element at the head of the free list */
        *primary             = old_head;
        if (zone->use_page_list) {
                page_meta->elements = (struct zone_free_element *)element;
                page_meta->free_count++;
                if (zone->allows_foreign && !from_zone_map(element, zone->elem_size)) {
                        if (page_meta->free_count == 1) {
                                /* first foreign element freed on page, move from all_used */
                                remqueue((queue_entry_t)page_meta);
                                enqueue_tail(&zone->pages.any_free_foreign, (queue_entry_t)page_meta);
                        } else {
                                /* no other list transitions */
                        }
                } else if (page_meta->free_count == page_meta->alloc_count) {
                        /* whether the page was on the intermediate or all_used, queue, move it to free */
                        remqueue((queue_entry_t)page_meta);
                        enqueue_tail(&zone->pages.all_free, (queue_entry_t)page_meta);
                } else if (page_meta->free_count == 1) {
                        /* first free element on page, move from all_used */
                        remqueue((queue_entry_t)page_meta);
                        enqueue_tail(&zone->pages.intermediate, (queue_entry_t)page_meta);
                }
        } else {
                zone->free_elements = (struct zone_free_element *)element;
        }
        zone->count--;
        zone->countfree++;
}


/*
 * Removes an element from the zone's free list, returning 0 if the free list is empty.
 * Verifies that the next-pointer and backup next-pointer are intact,
 * and verifies that a poisoned element hasn't been modified.
 */
static inline vm_offset_t
try_alloc_from_zone(zone_t zone,
                    boolean_t* check_poison)
{
        vm_offset_t  element;
        struct zone_page_metadata *page_meta;

        *check_poison = FALSE;

        /* if zone is empty, bail */
        if (zone->use_page_list) {
                if (zone->allows_foreign && !queue_empty(&zone->pages.any_free_foreign))
                        page_meta = (struct zone_page_metadata *)queue_first(&zone->pages.any_free_foreign);
                else if (!queue_empty(&zone->pages.intermediate))
                        page_meta = (struct zone_page_metadata *)queue_first(&zone->pages.intermediate);
                else if (!queue_empty(&zone->pages.all_free))
                        page_meta = (struct zone_page_metadata *)queue_first(&zone->pages.all_free);
                else {
                        return 0;
                }

                /* Check if page_meta passes is_sane_zone_element */
                if (__improbable(!is_sane_zone_page_metadata(zone, (vm_offset_t)page_meta)))
                        panic("zalloc: invalid metadata structure %p for freelist of zone %s\n",
                                (void *) page_meta, zone->zone_name);
                assert(page_meta->zone == zone);
                element = (vm_offset_t)page_meta->elements;
        } else {
                if (zone->free_elements == NULL)
                        return 0;

                element = (vm_offset_t)zone->free_elements;
        }

#if MACH_ASSERT
        if (__improbable(!is_sane_zone_element(zone, element)))
                panic("zfree: invalid head pointer %p for freelist of zone %s\n",
                      (void *) element, zone->zone_name);
#endif

        vm_offset_t *primary = (vm_offset_t *) element;
        vm_offset_t *backup  = get_backup_ptr(zone->elem_size, primary);

        vm_offset_t  next_element          = *primary;
        vm_offset_t  next_element_backup   = *backup;

        /*
         * backup_ptr_mismatch_panic will determine what next_element
         * should have been, and print it appropriately
         */
        if (__improbable(!is_sane_zone_element(zone, next_element)))
                backup_ptr_mismatch_panic(zone, element, next_element, next_element_backup);

        /* Check the backup pointer for the regular cookie */
        if (__improbable(next_element != (next_element_backup ^ zp_nopoison_cookie))) {

                /* Check for the poisoned cookie instead */
                if (__improbable(next_element != (next_element_backup ^ zp_poisoned_cookie)))
                        /* Neither cookie is valid, corruption has occurred */
                        backup_ptr_mismatch_panic(zone, element, next_element, next_element_backup);

                /*
                 * Element was marked as poisoned, so check its integrity before using it.
                 */
                *check_poison = TRUE;
        }

        if (zone->use_page_list) {
                        
                /* Make sure the page_meta is at the correct offset from the start of page */
                if (__improbable(page_meta != get_zone_page_metadata((struct zone_free_element *)element)))
                        panic("zalloc: metadata located at incorrect location on page of zone %s\n",
                                zone->zone_name);

                /* Make sure next_element belongs to the same page as page_meta */
                if (next_element) {
                        if (__improbable(page_meta != get_zone_page_metadata((struct zone_free_element *)next_element)))
                                panic("zalloc: next element pointer %p for element %p points to invalid element for zone %s\n",
                                        (void *)next_element, (void *)element, zone->zone_name);
                }
        }

        /* Remove this element from the free list */
        if (zone->use_page_list) {

                page_meta->elements = (struct zone_free_element *)next_element;
                page_meta->free_count--;

                if (zone->allows_foreign && !from_zone_map(element, zone->elem_size)) {
                        if (page_meta->free_count == 0) {
                                /* move to all used */
                                remqueue((queue_entry_t)page_meta);
                                enqueue_tail(&zone->pages.all_used, (queue_entry_t)page_meta);
                        } else {
                                /* no other list transitions */
                        }
                } else if (page_meta->free_count == 0) {
                        /* remove from intermediate or free, move to all_used */
                        remqueue((queue_entry_t)page_meta);
                        enqueue_tail(&zone->pages.all_used, (queue_entry_t)page_meta);
                } else if (page_meta->alloc_count == page_meta->free_count + 1) {
                        /* remove from free, move to intermediate */
                        remqueue((queue_entry_t)page_meta);
                        enqueue_tail(&zone->pages.intermediate, (queue_entry_t)page_meta);
                }
        } else {
                zone->free_elements = (struct zone_free_element *)next_element;
        }
        zone->countfree--;
        zone->count++;
        zone->sum_count++;

        return element;
}


/*
 * End of zone poisoning
 */

/*
 * Fake zones for things that want to report via zprint but are not actually zones.
 */
struct fake_zone_info {
        const char* name;
        void (*init)(int);
        void (*query)(int *,
                     vm_size_t *, vm_size_t *, vm_size_t *, vm_size_t *,
                      uint64_t *, int *, int *, int *);
};

static const struct fake_zone_info fake_zones[] = {
        {
                .name = "kernel_stacks",
                .init = stack_fake_zone_init,
                .query = stack_fake_zone_info,
        },
        {
                .name = "page_tables",
                .init = pt_fake_zone_init,
                .query = pt_fake_zone_info,
        },
        {
                .name = "kalloc.large",
                .init = kalloc_fake_zone_init,
                .query = kalloc_fake_zone_info,
        },
};
static const unsigned int num_fake_zones =
        sizeof (fake_zones) / sizeof (fake_zones[0]);

/*
 * Zone info options
 */
boolean_t zinfo_per_task = FALSE;               /* enabled by -zinfop in boot-args */
#define ZINFO_SLOTS 200                         /* for now */
#define ZONES_MAX (ZINFO_SLOTS - num_fake_zones - 1)

/*
 * Support for garbage collection of unused zone pages
 *
 * The kernel virtually allocates the "zone map" submap of the kernel
 * map. When an individual zone needs more storage, memory is allocated
 * out of the zone map, and the two-level "zone_page_table" is
 * on-demand expanded so that it has entries for those pages.
 * zone_page_init()/zone_page_alloc() initialize "alloc_count"
 * to the number of zone elements that occupy the zone page (which may
 * be a minimum of 1, including if a zone element spans multiple
 * pages).
 *
 * Asynchronously, the zone_gc() logic attempts to walk zone free
 * lists to see if all the elements on a zone page are free. If
 * "collect_count" (which it increments during the scan) matches
 * "alloc_count", the zone page is a candidate for collection and the
 * physical page is returned to the VM system. During this process, the
 * first word of the zone page is re-used to maintain a linked list of
 * to-be-collected zone pages.
 */
typedef uint32_t zone_page_index_t;
#define ZONE_PAGE_INDEX_INVALID ((zone_page_index_t)0xFFFFFFFFU)

struct zone_page_table_entry {
        volatile        uint16_t        alloc_count;
        volatile        uint16_t        collect_count;
};

#define ZONE_PAGE_USED  0
#define ZONE_PAGE_UNUSED 0xffff

/* Forwards */
void            zone_page_init(
                                vm_offset_t     addr,
                                vm_size_t       size);

void            zone_page_alloc(
                                vm_offset_t     addr,
                                vm_size_t       size);

void            zone_page_free_element(
                                zone_page_index_t       *free_page_head,
                                zone_page_index_t       *free_page_tail,
                                vm_offset_t     addr,
                                vm_size_t       size);

void            zone_page_collect(
                                vm_offset_t     addr,
                                vm_size_t       size);

boolean_t       zone_page_collectable(
                                vm_offset_t     addr,
                                vm_size_t       size);

void            zone_page_keep(
                                vm_offset_t     addr,
                                vm_size_t       size);

void            zone_display_zprint(void);

zone_t          zone_find_largest(void);

/* 
 * Async allocation of zones 
 * This mechanism allows for bootstrapping an empty zone which is setup with 
 * non-blocking flags. The first call to zalloc_noblock() will kick off a thread_call
 * to zalloc_async. We perform a zalloc() (which may block) and then an immediate free. 
 * This will prime the zone for the next use.
 *
 * Currently the thread_callout function (zalloc_async) will loop through all zones
 * looking for any zone with async_pending set and do the work for it. 
 * 
 * NOTE: If the calling thread for zalloc_noblock is lower priority than thread_call,
 * then zalloc_noblock to an empty zone may succeed. 
 */
void            zalloc_async(
                                thread_call_param_t     p0,  
                                thread_call_param_t     p1);

static thread_call_data_t call_async_alloc;

vm_map_t        zone_map = VM_MAP_NULL;

zone_t          zone_zone = ZONE_NULL;  /* the zone containing other zones */

zone_t          zinfo_zone = ZONE_NULL; /* zone of per-task zone info */

/*
 *      The VM system gives us an initial chunk of memory.
 *      It has to be big enough to allocate the zone_zone
 *      all the way through the pmap zone.
 */

vm_offset_t     zdata;
vm_size_t       zdata_size;

#define zone_wakeup(zone) thread_wakeup((event_t)(zone))
#define zone_sleep(zone)                                \
        (void) lck_mtx_sleep(&(zone)->lock, LCK_SLEEP_SPIN, (event_t)(zone), THREAD_UNINT);

/*
 *      The zone_locks_grp allows for collecting lock statistics.
 *      All locks are associated to this group in zinit.
 *      Look at tools/lockstat for debugging lock contention.
 */

lck_grp_t       zone_locks_grp;
lck_grp_attr_t  zone_locks_grp_attr;

#define lock_zone_init(zone)                            \
MACRO_BEGIN                                             \
        lck_attr_setdefault(&(zone)->lock_attr);                        \
        lck_mtx_init_ext(&(zone)->lock, &(zone)->lock_ext,              \
            &zone_locks_grp, &(zone)->lock_attr);                       \
MACRO_END

#define lock_try_zone(zone)     lck_mtx_try_lock_spin(&zone->lock)

/*
 *      Garbage collection map information
 */
#define ZONE_PAGE_TABLE_FIRST_LEVEL_SIZE (32)
struct zone_page_table_entry * volatile zone_page_table[ZONE_PAGE_TABLE_FIRST_LEVEL_SIZE];
vm_size_t                       zone_page_table_used_size;
unsigned int                    zone_pages;
unsigned int                   zone_page_table_second_level_size;                      /* power of 2 */
unsigned int                   zone_page_table_second_level_shift_amount;

#define zone_page_table_first_level_slot(x)  ((x) >> zone_page_table_second_level_shift_amount)
#define zone_page_table_second_level_slot(x) ((x) & (zone_page_table_second_level_size - 1))

void   zone_page_table_expand(zone_page_index_t pindex);
struct zone_page_table_entry *zone_page_table_lookup(zone_page_index_t pindex);

/*
 *      Exclude more than one concurrent garbage collection
 */
decl_lck_mtx_data(, zone_gc_lock)

lck_attr_t      zone_gc_lck_attr;
lck_grp_t       zone_gc_lck_grp;
lck_grp_attr_t  zone_gc_lck_grp_attr;
lck_mtx_ext_t   zone_gc_lck_ext;

/*
 *      Protects first_zone, last_zone, num_zones,
 *      and the next_zone field of zones.
 */
decl_simple_lock_data(, all_zones_lock)
zone_t                  first_zone;
zone_t                  *last_zone;
unsigned int            num_zones;

boolean_t zone_gc_allowed = TRUE;
boolean_t zone_gc_forced = FALSE;
boolean_t panic_include_zprint = FALSE;
boolean_t zone_gc_allowed_by_time_throttle = TRUE;

#define ZALLOC_DEBUG_ZONEGC             0x00000001
#define ZALLOC_DEBUG_ZCRAM              0x00000002
uint32_t zalloc_debug = 0;

/*
 * Zone leak debugging code
 *
 * When enabled, this code keeps a log to track allocations to a particular zone that have not
 * yet been freed.  Examining this log will reveal the source of a zone leak.  The log is allocated
 * only when logging is enabled, so there is no effect on the system when it's turned off.  Logging is
 * off by default.
 *
 * Enable the logging via the boot-args. Add the parameter "zlog=<zone>" to boot-args where <zone>
 * is the name of the zone you wish to log.  
 *
 * This code only tracks one zone, so you need to identify which one is leaking first.
 * Generally, you'll know you have a leak when you get a "zalloc retry failed 3" panic from the zone
 * garbage collector.  Note that the zone name printed in the panic message is not necessarily the one
 * containing the leak.  So do a zprint from gdb and locate the zone with the bloated size.  This
 * is most likely the problem zone, so set zlog in boot-args to this zone name, reboot and re-run the test.  The
 * next time it panics with this message, examine the log using the kgmacros zstack, findoldest and countpcs.
 * See the help in the kgmacros for usage info.
 *
 *
 * Zone corruption logging
 *
 * Logging can also be used to help identify the source of a zone corruption.  First, identify the zone
 * that is being corrupted, then add "-zc zlog=<zone name>" to the boot-args.  When -zc is used in conjunction
 * with zlog, it changes the logging style to track both allocations and frees to the zone.  So when the
 * corruption is detected, examining the log will show you the stack traces of the callers who last allocated
 * and freed any particular element in the zone.  Use the findelem kgmacro with the address of the element that's been
 * corrupted to examine its history.  This should lead to the source of the corruption.
 */

static int log_records; /* size of the log, expressed in number of records */

#define MAX_ZONE_NAME   32      /* max length of a zone name we can take from the boot-args */

static char zone_name_to_log[MAX_ZONE_NAME] = "";       /* the zone name we're logging, if any */

/* Log allocations and frees to help debug a zone element corruption */
boolean_t       corruption_debug_flag    = FALSE;    /* enabled by "-zc" boot-arg */

/*
 * The number of records in the log is configurable via the zrecs parameter in boot-args.  Set this to 
 * the number of records you want in the log.  For example, "zrecs=1000" sets it to 1000 records.  Note
 * that the larger the size of the log, the slower the system will run due to linear searching in the log,
 * but one doesn't generally care about performance when tracking down a leak.  The log is capped at 8000
 * records since going much larger than this tends to make the system unresponsive and unbootable on small
 * memory configurations.  The default value is 4000 records.
 */

#if     defined(__LP64__)
#define ZRECORDS_MAX            128000          /* Max records allowed in the log */
#else
#define ZRECORDS_MAX            8000            /* Max records allowed in the log */
#endif
#define ZRECORDS_DEFAULT        4000            /* default records in log if zrecs is not specificed in boot-args */

/*
 * Each record in the log contains a pointer to the zone element it refers to,
 * and a small array to hold the pc's from the stack trace.  A
 * record is added to the log each time a zalloc() is done in the zone_of_interest.  For leak debugging,
 * the record is cleared when a zfree() is done.  For corruption debugging, the log tracks both allocs and frees.
 * If the log fills, old records are replaced as if it were a circular buffer.
 */


/*
 * Opcodes for the btlog operation field:
 */

#define ZOP_ALLOC       1
#define ZOP_FREE        0

/*
 * The allocation log and all the related variables are protected by the zone lock for the zone_of_interest
 */
static btlog_t *zlog_btlog;             /* the log itself, dynamically allocated when logging is enabled  */
static zone_t  zone_of_interest = NULL;         /* the zone being watched; corresponds to zone_name_to_log */

/*
 * Decide if we want to log this zone by doing a string compare between a zone name and the name
 * of the zone to log. Return true if the strings are equal, false otherwise.  Because it's not
 * possible to include spaces in strings passed in via the boot-args, a period in the logname will
 * match a space in the zone name.
 */

static int
log_this_zone(const char *zonename, const char *logname) 
{
        int len;
        const char *zc = zonename;
        const char *lc = logname;

        /*
         * Compare the strings.  We bound the compare by MAX_ZONE_NAME.
         */

        for (len = 1; len <= MAX_ZONE_NAME; zc++, lc++, len++) {

                /*
                 * If the current characters don't match, check for a space in
                 * in the zone name and a corresponding period in the log name.
                 * If that's not there, then the strings don't match.
                 */

                if (*zc != *lc && !(*zc == ' ' && *lc == '.')) 
                        break;

                /*
                 * The strings are equal so far.  If we're at the end, then it's a match.
                 */

                if (*zc == '\0')
                        return TRUE;
        }

        return FALSE;
}


/*
 * Test if we want to log this zalloc/zfree event.  We log if this is the zone we're interested in and
 * the buffer for the records has been allocated.
 */

#define DO_LOGGING(z)           (zlog_btlog && (z) == zone_of_interest)

extern boolean_t kmem_alloc_ready;

#if CONFIG_ZLEAKS
#pragma mark -
#pragma mark Zone Leak Detection

/* 
 * The zone leak detector, abbreviated 'zleak', keeps track of a subset of the currently outstanding
 * allocations made by the zone allocator.  Every zleak_sample_factor allocations in each zone, we capture a
 * backtrace.  Every free, we examine the table and determine if the allocation was being tracked, 
 * and stop tracking it if it was being tracked.
 *
 * We track the allocations in the zallocations hash table, which stores the address that was returned from 
 * the zone allocator.  Each stored entry in the zallocations table points to an entry in the ztraces table, which
 * stores the backtrace associated with that allocation.  This provides uniquing for the relatively large
 * backtraces - we don't store them more than once.
 *
 * Data collection begins when the zone map is 50% full, and only occurs for zones that are taking up
 * a large amount of virtual space.
 */
#define ZLEAK_STATE_ENABLED             0x01    /* Zone leak monitoring should be turned on if zone_map fills up. */
#define ZLEAK_STATE_ACTIVE              0x02    /* We are actively collecting traces. */
#define ZLEAK_STATE_ACTIVATING          0x04    /* Some thread is doing setup; others should move along. */
#define ZLEAK_STATE_FAILED              0x08    /* Attempt to allocate tables failed.  We will not try again. */
uint32_t        zleak_state = 0;                /* State of collection, as above */

boolean_t       panic_include_ztrace    = FALSE;        /* Enable zleak logging on panic */
vm_size_t       zleak_global_tracking_threshold;        /* Size of zone map at which to start collecting data */
vm_size_t       zleak_per_zone_tracking_threshold;      /* Size a zone will have before we will collect data on it */
unsigned int    zleak_sample_factor     = 1000;         /* Allocations per sample attempt */

/*
 * Counters for allocation statistics.
 */ 

/* Times two active records want to occupy the same spot */
unsigned int z_alloc_collisions = 0;
unsigned int z_trace_collisions = 0;

/* Times a new record lands on a spot previously occupied by a freed allocation */
unsigned int z_alloc_overwrites = 0;
unsigned int z_trace_overwrites = 0;

/* Times a new alloc or trace is put into the hash table */
unsigned int z_alloc_recorded   = 0;
unsigned int z_trace_recorded   = 0;

/* Times zleak_log returned false due to not being able to acquire the lock */
unsigned int z_total_conflicts  = 0;


#pragma mark struct zallocation
/*
 * Structure for keeping track of an allocation
 * An allocation bucket is in use if its element is not NULL
 */
struct zallocation {
        uintptr_t               za_element;             /* the element that was zalloc'ed or zfree'ed, NULL if bucket unused */
        vm_size_t               za_size;                        /* how much memory did this allocation take up? */
        uint32_t                za_trace_index; /* index into ztraces for backtrace associated with allocation */
        /* TODO: #if this out */
        uint32_t                za_hit_count;           /* for determining effectiveness of hash function */
};

/* Size must be a power of two for the zhash to be able to just mask off bits instead of mod */
uint32_t zleak_alloc_buckets = CONFIG_ZLEAK_ALLOCATION_MAP_NUM;
uint32_t zleak_trace_buckets = CONFIG_ZLEAK_TRACE_MAP_NUM;

vm_size_t zleak_max_zonemap_size;

/* Hashmaps of allocations and their corresponding traces */
static struct zallocation*      zallocations;
static struct ztrace*           ztraces;

/* not static so that panic can see this, see kern/debug.c */
struct ztrace*                          top_ztrace;

/* Lock to protect zallocations, ztraces, and top_ztrace from concurrent modification. */
static lck_spin_t                       zleak_lock;
static lck_attr_t                       zleak_lock_attr;
static lck_grp_t                        zleak_lock_grp;
static lck_grp_attr_t                   zleak_lock_grp_attr;

/*
 * Initializes the zone leak monitor.  Called from zone_init()
 */
static void 
zleak_init(vm_size_t max_zonemap_size) 
{
        char                    scratch_buf[16];
        boolean_t               zleak_enable_flag = FALSE;

        zleak_max_zonemap_size = max_zonemap_size;
        zleak_global_tracking_threshold = max_zonemap_size / 2; 
        zleak_per_zone_tracking_threshold = zleak_global_tracking_threshold / 8;

        /* -zleakoff (flag to disable zone leak monitor) */
        if (PE_parse_boot_argn("-zleakoff", scratch_buf, sizeof(scratch_buf))) {
                zleak_enable_flag = FALSE;
                printf("zone leak detection disabled\n");
        } else {
                zleak_enable_flag = TRUE;
                printf("zone leak detection enabled\n");
        }
        
        /* zfactor=XXXX (override how often to sample the zone allocator) */
        if (PE_parse_boot_argn("zfactor", &zleak_sample_factor, sizeof(zleak_sample_factor))) {
                printf("Zone leak factor override: %u\n", zleak_sample_factor);
        }

        /* zleak-allocs=XXXX (override number of buckets in zallocations) */
        if (PE_parse_boot_argn("zleak-allocs", &zleak_alloc_buckets, sizeof(zleak_alloc_buckets))) {
                printf("Zone leak alloc buckets override: %u\n", zleak_alloc_buckets);
                /* uses 'is power of 2' trick: (0x01000 & 0x00FFF == 0) */
                if (zleak_alloc_buckets == 0 || (zleak_alloc_buckets & (zleak_alloc_buckets-1))) {
                        printf("Override isn't a power of two, bad things might happen!\n");
                }
        }
        
        /* zleak-traces=XXXX (override number of buckets in ztraces) */
        if (PE_parse_boot_argn("zleak-traces", &zleak_trace_buckets, sizeof(zleak_trace_buckets))) {
                printf("Zone leak trace buckets override: %u\n", zleak_trace_buckets);
                /* uses 'is power of 2' trick: (0x01000 & 0x00FFF == 0) */
                if (zleak_trace_buckets == 0 || (zleak_trace_buckets & (zleak_trace_buckets-1))) {
                        printf("Override isn't a power of two, bad things might happen!\n");
                }
        }
        
        /* allocate the zleak_lock */
        lck_grp_attr_setdefault(&zleak_lock_grp_attr);
        lck_grp_init(&zleak_lock_grp, "zleak_lock", &zleak_lock_grp_attr);
        lck_attr_setdefault(&zleak_lock_attr);
        lck_spin_init(&zleak_lock, &zleak_lock_grp, &zleak_lock_attr);
        
        if (zleak_enable_flag) {
                zleak_state = ZLEAK_STATE_ENABLED;
        }
}

#if CONFIG_ZLEAKS

/*
 * Support for kern.zleak.active sysctl - a simplified
 * version of the zleak_state variable.
 */
int
get_zleak_state(void)
{
        if (zleak_state & ZLEAK_STATE_FAILED)
                return (-1);
        if (zleak_state & ZLEAK_STATE_ACTIVE)
                return (1);
        return (0);
}

#endif


kern_return_t
zleak_activate(void)
{
        kern_return_t retval;
        vm_size_t z_alloc_size = zleak_alloc_buckets * sizeof(struct zallocation);
        vm_size_t z_trace_size = zleak_trace_buckets * sizeof(struct ztrace);
        void *allocations_ptr = NULL;
        void *traces_ptr = NULL;

        /* Only one thread attempts to activate at a time */
        if (zleak_state & (ZLEAK_STATE_ACTIVE | ZLEAK_STATE_ACTIVATING | ZLEAK_STATE_FAILED)) {
                return KERN_SUCCESS;
        }

        /* Indicate that we're doing the setup */
        lck_spin_lock(&zleak_lock);
        if (zleak_state & (ZLEAK_STATE_ACTIVE | ZLEAK_STATE_ACTIVATING | ZLEAK_STATE_FAILED)) {
                lck_spin_unlock(&zleak_lock);
                return KERN_SUCCESS;
        }

        zleak_state |= ZLEAK_STATE_ACTIVATING;
        lck_spin_unlock(&zleak_lock);

        /* Allocate and zero tables */
        retval = kmem_alloc_kobject(kernel_map, (vm_offset_t*)&allocations_ptr, z_alloc_size);
        if (retval != KERN_SUCCESS) {
                goto fail;
        }

        retval = kmem_alloc_kobject(kernel_map, (vm_offset_t*)&traces_ptr, z_trace_size);
        if (retval != KERN_SUCCESS) {
                goto fail;
        }

        bzero(allocations_ptr, z_alloc_size);
        bzero(traces_ptr, z_trace_size);

        /* Everything's set.  Install tables, mark active. */
        zallocations = allocations_ptr;
        ztraces = traces_ptr;

        /*
         * Initialize the top_ztrace to the first entry in ztraces, 
         * so we don't have to check for null in zleak_log
         */
        top_ztrace = &ztraces[0];

        /*
         * Note that we do need a barrier between installing
         * the tables and setting the active flag, because the zfree()
         * path accesses the table without a lock if we're active.
         */
        lck_spin_lock(&zleak_lock);
        zleak_state |= ZLEAK_STATE_ACTIVE;
        zleak_state &= ~ZLEAK_STATE_ACTIVATING;
        lck_spin_unlock(&zleak_lock);
        
        return 0;

fail:   
        /*
         * If we fail to allocate memory, don't further tax
         * the system by trying again.
         */
        lck_spin_lock(&zleak_lock);
        zleak_state |= ZLEAK_STATE_FAILED;
        zleak_state &= ~ZLEAK_STATE_ACTIVATING;
        lck_spin_unlock(&zleak_lock);

        if (allocations_ptr != NULL) {
                kmem_free(kernel_map, (vm_offset_t)allocations_ptr, z_alloc_size);
        }

        if (traces_ptr != NULL) {
                kmem_free(kernel_map, (vm_offset_t)traces_ptr, z_trace_size);
        }

        return retval;
}

/*
 * TODO: What about allocations that never get deallocated, 
 * especially ones with unique backtraces? Should we wait to record
 * until after boot has completed?  
 * (How many persistent zallocs are there?)
 */

/*
 * This function records the allocation in the allocations table, 
 * and stores the associated backtrace in the traces table 
 * (or just increments the refcount if the trace is already recorded)
 * If the allocation slot is in use, the old allocation is replaced with the new allocation, and
 * the associated trace's refcount is decremented.
 * If the trace slot is in use, it returns.
 * The refcount is incremented by the amount of memory the allocation consumes.
 * The return value indicates whether to try again next time.
 */
static boolean_t
zleak_log(uintptr_t* bt,
                  uintptr_t addr,
                  uint32_t depth,
                  vm_size_t allocation_size) 
{
        /* Quit if there's someone else modifying the hash tables */
        if (!lck_spin_try_lock(&zleak_lock)) {
                z_total_conflicts++;
                return FALSE;
        }
        
        struct zallocation* allocation  = &zallocations[hashaddr(addr, zleak_alloc_buckets)];
        
        uint32_t trace_index = hashbacktrace(bt, depth, zleak_trace_buckets);
        struct ztrace* trace = &ztraces[trace_index];
        
        allocation->za_hit_count++;
        trace->zt_hit_count++;
        
        /* 
         * If the allocation bucket we want to be in is occupied, and if the occupier
         * has the same trace as us, just bail.  
         */
        if (allocation->za_element != (uintptr_t) 0 && trace_index == allocation->za_trace_index) {
                z_alloc_collisions++;
                
                lck_spin_unlock(&zleak_lock);
                return TRUE;
        }
        
        /* STEP 1: Store the backtrace in the traces array. */
        /* A size of zero indicates that the trace bucket is free. */
        
        if (trace->zt_size > 0 && bcmp(trace->zt_stack, bt, (depth * sizeof(uintptr_t))) != 0 ) {
                /* 
                 * Different unique trace with same hash!
                 * Just bail - if we're trying to record the leaker, hopefully the other trace will be deallocated
                 * and get out of the way for later chances
                 */
                trace->zt_collisions++;
                z_trace_collisions++;
                
                lck_spin_unlock(&zleak_lock);
                return TRUE;
        } else if (trace->zt_size > 0) {
                /* Same trace, already added, so increment refcount */
                trace->zt_size += allocation_size;
        } else {
                /* Found an unused trace bucket, record the trace here! */
                if (trace->zt_depth != 0) /* if this slot was previously used but not currently in use */
                        z_trace_overwrites++;
                
                z_trace_recorded++;
                trace->zt_size                  = allocation_size;
                memcpy(trace->zt_stack, bt, (depth * sizeof(uintptr_t)) );
                
                trace->zt_depth         = depth;
                trace->zt_collisions    = 0;
        }
        
        /* STEP 2: Store the allocation record in the allocations array. */
        
        if (allocation->za_element != (uintptr_t) 0) {
                /* 
                 * Straight up replace any allocation record that was there.  We don't want to do the work
                 * to preserve the allocation entries that were there, because we only record a subset of the 
                 * allocations anyways.
                 */
                
                z_alloc_collisions++;
                
                struct ztrace* associated_trace = &ztraces[allocation->za_trace_index];
                /* Knock off old allocation's size, not the new allocation */
                associated_trace->zt_size -= allocation->za_size;
        } else if (allocation->za_trace_index != 0) {
                /* Slot previously used but not currently in use */
                z_alloc_overwrites++;
        }

        allocation->za_element          = addr;
        allocation->za_trace_index      = trace_index;
        allocation->za_size             = allocation_size;
        
        z_alloc_recorded++;
        
        if (top_ztrace->zt_size < trace->zt_size)
                top_ztrace = trace;
        
        lck_spin_unlock(&zleak_lock);
        return TRUE;
}

/*
 * Free the allocation record and release the stacktrace.
 * This should be as fast as possible because it will be called for every free.
 */
static void
zleak_free(uintptr_t addr,
                   vm_size_t allocation_size) 
{
        if (addr == (uintptr_t) 0)
                return;
        
        struct zallocation* allocation = &zallocations[hashaddr(addr, zleak_alloc_buckets)];
        
        /* Double-checked locking: check to find out if we're interested, lock, check to make
         * sure it hasn't changed, then modify it, and release the lock.
         */
        
        if (allocation->za_element == addr && allocation->za_trace_index < zleak_trace_buckets) {
                /* if the allocation was the one, grab the lock, check again, then delete it */
                lck_spin_lock(&zleak_lock);
                
                if (allocation->za_element == addr && allocation->za_trace_index < zleak_trace_buckets) {
                        struct ztrace *trace;

                        /* allocation_size had better match what was passed into zleak_log - otherwise someone is freeing into the wrong zone! */
                        if (allocation->za_size != allocation_size) {
                                panic("Freeing as size %lu memory that was allocated with size %lu\n", 
                                                (uintptr_t)allocation_size, (uintptr_t)allocation->za_size);
                        }
                        
                        trace = &ztraces[allocation->za_trace_index];
                        
                        /* size of 0 indicates trace bucket is unused */
                        if (trace->zt_size > 0) {
                                trace->zt_size -= allocation_size;
                        }
                        
                        /* A NULL element means the allocation bucket is unused */
                        allocation->za_element = 0;
                }
                lck_spin_unlock(&zleak_lock);
        }
}

#endif /* CONFIG_ZLEAKS */

/*  These functions outside of CONFIG_ZLEAKS because they are also used in
 *  mbuf.c for mbuf leak-detection.  This is why they lack the z_ prefix.
 */

/*
 * This function captures a backtrace from the current stack and
 * returns the number of frames captured, limited by max_frames.
 * It's fast because it does no checking to make sure there isn't bad data.
 * Since it's only called from threads that we're going to keep executing,
 * if there's bad data we were going to die eventually.
 * If this function is inlined, it doesn't record the frame of the function it's inside.
 * (because there's no stack frame!)
 */

uint32_t
fastbacktrace(uintptr_t* bt, uint32_t max_frames)
{
        uintptr_t* frameptr = NULL, *frameptr_next = NULL;
        uintptr_t retaddr = 0;
        uint32_t frame_index = 0, frames = 0;
        uintptr_t kstackb, kstackt;
        thread_t cthread = current_thread();

        if (__improbable(cthread == NULL))
                return 0;

        kstackb = cthread->kernel_stack;
        kstackt = kstackb + kernel_stack_size;
        /* Load stack frame pointer (EBP on x86) into frameptr */
        frameptr = __builtin_frame_address(0);
        if (((uintptr_t)frameptr > kstackt) || ((uintptr_t)frameptr < kstackb))
                frameptr = NULL;

        while (frameptr != NULL && frame_index < max_frames ) {
                /* Next frame pointer is pointed to by the previous one */
                frameptr_next = (uintptr_t*) *frameptr;

                /* Bail if we see a zero in the stack frame, that means we've reached the top of the stack */
                /* That also means the return address is worthless, so don't record it */
                if (frameptr_next == NULL)
                        break;
                /* Verify thread stack bounds */
                if (((uintptr_t)frameptr_next > kstackt) || ((uintptr_t)frameptr_next < kstackb))
                        break;
                /* Pull return address from one spot above the frame pointer */
                retaddr = *(frameptr + 1);

                /* Store it in the backtrace array */
                bt[frame_index++] = retaddr;

                frameptr = frameptr_next;
        }

        /* Save the number of frames captured for return value */
        frames = frame_index;

        /* Fill in the rest of the backtrace with zeros */
        while (frame_index < max_frames)
                bt[frame_index++] = 0;

        return frames;
}

/* "Thomas Wang's 32/64 bit mix functions."  http://www.concentric.net/~Ttwang/tech/inthash.htm */
uintptr_t
hash_mix(uintptr_t x)
{
#ifndef __LP64__
        x += ~(x << 15);
        x ^=  (x >> 10);
        x +=  (x << 3 );
        x ^=  (x >> 6 );
        x += ~(x << 11);
        x ^=  (x >> 16);
#else
        x += ~(x << 32);
        x ^=  (x >> 22);
        x += ~(x << 13);
        x ^=  (x >> 8 );
        x +=  (x << 3 );
        x ^=  (x >> 15);
        x += ~(x << 27);
        x ^=  (x >> 31);
#endif
        return x;
}

uint32_t
hashbacktrace(uintptr_t* bt, uint32_t depth, uint32_t max_size)
{

        uintptr_t hash = 0;
        uintptr_t mask = max_size - 1;

        while (depth) {
                hash += bt[--depth];
        }

        hash = hash_mix(hash) & mask;

        assert(hash < max_size);

        return (uint32_t) hash;
}

/*
 *  TODO: Determine how well distributed this is
 *      max_size must be a power of 2. i.e 0x10000 because 0x10000-1 is 0x0FFFF which is a great bitmask
 */
uint32_t
hashaddr(uintptr_t pt, uint32_t max_size)
{
        uintptr_t hash = 0;
        uintptr_t mask = max_size - 1;

        hash = hash_mix(pt) & mask;

        assert(hash < max_size);

        return (uint32_t) hash;
}

/* End of all leak-detection code */
#pragma mark -

/*
 *      zinit initializes a new zone.  The zone data structures themselves
 *      are stored in a zone, which is initially a static structure that
 *      is initialized by zone_init.
 */
zone_t
zinit(
        vm_size_t       size,           /* the size of an element */
        vm_size_t       max,            /* maximum memory to use */
        vm_size_t       alloc,          /* allocation size */
        const char      *name)          /* a name for the zone */
{
        zone_t          z;
        boolean_t       use_page_list = FALSE;

        if (zone_zone == ZONE_NULL) {

                z = (struct zone *)zdata;
                /* special handling in zcram() because the first element is being used */
        } else
                z = (zone_t) zalloc(zone_zone);

        if (z == ZONE_NULL)
                return(ZONE_NULL);

        /* Zone elements must fit both a next pointer and a backup pointer */
        vm_size_t  minimum_element_size = sizeof(vm_offset_t) * 2;
        if (size < minimum_element_size)
                size = minimum_element_size;

        /*
         *  Round element size to a multiple of sizeof(pointer)
         *  This also enforces that allocations will be aligned on pointer boundaries
         */
        size = ((size-1) + sizeof(vm_offset_t)) -
               ((size-1) % sizeof(vm_offset_t));

        if (alloc == 0)
                alloc = PAGE_SIZE;

        alloc = round_page(alloc);
        max   = round_page(max);

        /*
         * we look for an allocation size with less than 1% waste
         * up to 5 pages in size...
         * otherwise, we look for an allocation size with least fragmentation
         * in the range of 1 - 5 pages
         * This size will be used unless
         * the user suggestion is larger AND has less fragmentation
         */
#if     ZONE_ALIAS_ADDR
        /* Favor PAGE_SIZE allocations unless we waste >10% space */
        if ((size < PAGE_SIZE) && (PAGE_SIZE % size <= PAGE_SIZE / 10))
                alloc = PAGE_SIZE;
        else
#endif
#if     defined(__LP64__)               
                if (((alloc % size) != 0) || (alloc > PAGE_SIZE * 8))
#endif
                {
                vm_size_t best, waste; unsigned int i;
                best  = PAGE_SIZE;
                waste = best % size;

                for (i = 1; i <= 5; i++) {
                        vm_size_t tsize, twaste;

                        tsize = i * PAGE_SIZE;

                        if ((tsize % size) < (tsize / 100)) {
                                alloc = tsize;
                                goto use_this_allocation;
                        }
                        twaste = tsize % size;
                        if (twaste < waste)
                                best = tsize, waste = twaste;
                }
                if (alloc <= best || (alloc % size >= waste))
                        alloc = best;
        }
use_this_allocation:
        if (max && (max < alloc))
                max = alloc;

        /*
         * Opt into page list tracking if we can reliably map an allocation
         * to its page_metadata, and if the wastage in the tail of
         * the allocation is not too large
         */
        if (alloc == PAGE_SIZE) {
                if ((PAGE_SIZE % size) >= sizeof(struct zone_page_metadata)) {
                        use_page_list = TRUE;
                } else if ((PAGE_SIZE - sizeof(struct zone_page_metadata)) % size <= PAGE_SIZE / 100) {
                        use_page_list = TRUE;
                }
        }

        z->free_elements = NULL;
        queue_init(&z->pages.any_free_foreign);
        queue_init(&z->pages.all_free);
        queue_init(&z->pages.intermediate);
        queue_init(&z->pages.all_used);
        z->cur_size = 0;
        z->page_count = 0;
        z->max_size = max;
        z->elem_size = size;
        z->alloc_size = alloc;
        z->zone_name = name;
        z->count = 0;
        z->countfree = 0;
        z->sum_count = 0LL;
        z->doing_alloc = FALSE;
        z->doing_gc = FALSE;
        z->exhaustible = FALSE;
        z->collectable = TRUE;
        z->allows_foreign = FALSE;
        z->expandable  = TRUE;
        z->waiting = FALSE;
        z->async_pending = FALSE;
        z->caller_acct = TRUE;
        z->noencrypt = FALSE;
        z->no_callout = FALSE;
        z->async_prio_refill = FALSE;
        z->gzalloc_exempt = FALSE;
        z->alignment_required = FALSE;
        z->use_page_list = use_page_list;
        z->prio_refill_watermark = 0;
        z->zone_replenish_thread = NULL;
        z->zp_count = 0;
#if CONFIG_ZLEAKS
        z->zleak_capture = 0;
        z->zleak_on = FALSE;
#endif /* CONFIG_ZLEAKS */

#if     ZONE_DEBUG
        z->active_zones.next = z->active_zones.prev = NULL;     
        zone_debug_enable(z);
#endif  /* ZONE_DEBUG */
        lock_zone_init(z);

        /*
         *      Add the zone to the all-zones list.
         *      If we are tracking zone info per task, and we have
         *      already used all the available stat slots, then keep
         *      using the overflow zone slot.
         */
        z->next_zone = ZONE_NULL;
        simple_lock(&all_zones_lock);
        *last_zone = z;
        last_zone = &z->next_zone;
        z->index = num_zones;
        if (zinfo_per_task) {
                if (num_zones > ZONES_MAX)
                        z->index = ZONES_MAX;
        }
        num_zones++;
        simple_unlock(&all_zones_lock);

        /*
         * Check if we should be logging this zone.  If so, remember the zone pointer.
         */
        if (log_this_zone(z->zone_name, zone_name_to_log)) {
                zone_of_interest = z;
        }

        /*
         * If we want to log a zone, see if we need to allocate buffer space for the log.  Some vm related zones are
         * zinit'ed before we can do a kmem_alloc, so we have to defer allocation in that case.  kmem_alloc_ready is set to
         * TRUE once enough of the VM system is up and running to allow a kmem_alloc to work.  If we want to log one
         * of the VM related zones that's set up early on, we will skip allocation of the log until zinit is called again
         * later on some other zone.  So note we may be allocating a buffer to log a zone other than the one being initialized
         * right now.
         */
        if (zone_of_interest != NULL && zlog_btlog == NULL && kmem_alloc_ready) {
                zlog_btlog = btlog_create(log_records, MAX_ZTRACE_DEPTH, NULL, NULL, NULL);
                if (zlog_btlog) {
                        printf("zone: logging started for zone %s\n", zone_of_interest->zone_name);
                } else {
                        printf("zone: couldn't allocate memory for zrecords, turning off zleak logging\n");
                        zone_of_interest = NULL;
                }
        }
#if     CONFIG_GZALLOC  
        gzalloc_zone_init(z);
#endif
        return(z);
}
unsigned        zone_replenish_loops, zone_replenish_wakeups, zone_replenish_wakeups_initiated, zone_replenish_throttle_count;

static void zone_replenish_thread(zone_t);

/* High priority VM privileged thread used to asynchronously refill a designated
 * zone, such as the reserved VM map entry zone.
 */
static void zone_replenish_thread(zone_t z) {
        vm_size_t free_size;
        current_thread()->options |= TH_OPT_VMPRIV;

        for (;;) {
                lock_zone(z);
                assert(z->prio_refill_watermark != 0);
                while ((free_size = (z->cur_size - (z->count * z->elem_size))) < (z->prio_refill_watermark * z->elem_size)) {
                        assert(z->doing_alloc == FALSE);
                        assert(z->async_prio_refill == TRUE);

                        unlock_zone(z);
                        int     zflags = KMA_KOBJECT|KMA_NOPAGEWAIT;
                        vm_offset_t space, alloc_size;
                        kern_return_t kr;
                                
                        if (vm_pool_low())
                                alloc_size = round_page(z->elem_size);
                        else
                                alloc_size = z->alloc_size;
                                
                        if (z->noencrypt)
                                zflags |= KMA_NOENCRYPT;
                                
                        kr = kernel_memory_allocate(zone_map, &space, alloc_size, 0, zflags);

                        if (kr == KERN_SUCCESS) {
#if     ZONE_ALIAS_ADDR
                                if (alloc_size == PAGE_SIZE)
                                        space = zone_alias_addr(space);
#endif
                                ZONE_PAGE_COUNT_INCR(z, (alloc_size / PAGE_SIZE));      
                                zcram(z, space, alloc_size);
                        } else if (kr == KERN_RESOURCE_SHORTAGE) {
                                VM_PAGE_WAIT();
                        } else if (kr == KERN_NO_SPACE) {
                                kr = kernel_memory_allocate(kernel_map, &space, alloc_size, 0, zflags);
                                if (kr == KERN_SUCCESS) {
#if     ZONE_ALIAS_ADDR
                                        if (alloc_size == PAGE_SIZE)
                                                space = zone_alias_addr(space);
#endif
                                        zcram(z, space, alloc_size);
                                } else {
                                        assert_wait_timeout(&z->zone_replenish_thread, THREAD_UNINT, 1, 100 * NSEC_PER_USEC);
                                        thread_block(THREAD_CONTINUE_NULL);
                                }
                        }

                        lock_zone(z);
                        zone_replenish_loops++;
                }

                unlock_zone(z);
                /* Signal any potential throttled consumers, terminating
                 * their timer-bounded waits.
                 */
                thread_wakeup(z);

                assert_wait(&z->zone_replenish_thread, THREAD_UNINT);
                thread_block(THREAD_CONTINUE_NULL);
                zone_replenish_wakeups++;
        }
}

void
zone_prio_refill_configure(zone_t z, vm_size_t low_water_mark) {
        z->prio_refill_watermark = low_water_mark;

        z->async_prio_refill = TRUE;
        OSMemoryBarrier();
        kern_return_t tres = kernel_thread_start_priority((thread_continue_t)zone_replenish_thread, z, MAXPRI_KERNEL, &z->zone_replenish_thread);

        if (tres != KERN_SUCCESS) {
                panic("zone_prio_refill_configure, thread create: 0x%x", tres);
        }

        thread_deallocate(z->zone_replenish_thread);
}

/*
 *      Cram the given memory into the specified zone.
 */
void
zcram(
        zone_t          zone,
        vm_offset_t                     newmem,
        vm_size_t               size)
{
        vm_size_t       elem_size;
        boolean_t   from_zm = FALSE;

        /* Basic sanity checks */
        assert(zone != ZONE_NULL && newmem != (vm_offset_t)0);
        assert(!zone->collectable || zone->allows_foreign
                || (from_zone_map(newmem, size)));

        elem_size = zone->elem_size;

        if (from_zone_map(newmem, size))
                from_zm = TRUE;

        if (zalloc_debug & ZALLOC_DEBUG_ZCRAM)
                kprintf("zcram(%p[%s], 0x%lx%s, 0x%lx)\n", zone, zone->zone_name,
                                (unsigned long)newmem, from_zm ? "" : "[F]", (unsigned long)size);

        if (from_zm && !zone->use_page_list)
                zone_page_init(newmem, size);

        lock_zone(zone);

        if (zone->use_page_list) {
                struct zone_page_metadata *page_metadata;

                assert((newmem & PAGE_MASK) == 0);
                assert((size & PAGE_MASK) == 0);
                for (; size > 0; newmem += PAGE_SIZE, size -= PAGE_SIZE) {

                        vm_size_t pos_in_page;
                        page_metadata = (struct zone_page_metadata *)(newmem + PAGE_SIZE - sizeof(struct zone_page_metadata));
                        
                        page_metadata->pages.next = NULL;
                        page_metadata->pages.prev = NULL;
                        page_metadata->elements = NULL;
                        page_metadata->zone = zone;
                        page_metadata->alloc_count = 0;
                        page_metadata->free_count = 0;

                        enqueue_tail(&zone->pages.all_used, (queue_entry_t)page_metadata);

                        for (pos_in_page = 0; (newmem + pos_in_page + elem_size) < (vm_offset_t)page_metadata; pos_in_page += elem_size) {
                                page_metadata->alloc_count++;
                                zone->count++;  /* compensate for free_to_zone */
                                if ((newmem + pos_in_page) == (vm_offset_t)zone) {
                                        /*
                                         * special case for the "zone_zone" zone, which is using the first
                                         * allocation of its pmap_steal_memory()-ed allocation for
                                         * the "zone_zone" variable already.
                                         */
                                } else {
                                        free_to_zone(zone, newmem + pos_in_page, FALSE);
                                }
                                zone->cur_size += elem_size;
                        }
                }
        } else {
                while (size >= elem_size) {
                        zone->count++;  /* compensate for free_to_zone */
                        if (newmem == (vm_offset_t)zone) {
                                /* Don't free zone_zone zone */
                        } else {
                                free_to_zone(zone, newmem, FALSE);
                        }
                        if (from_zm)
                                zone_page_alloc(newmem, elem_size);
                        size -= elem_size;
                        newmem += elem_size;
                        zone->cur_size += elem_size;
                }
        }
        unlock_zone(zone);
}


/*
 *      Steal memory for the zone package.  Called from
 *      vm_page_bootstrap().
 */
void
zone_steal_memory(void)
{
#if     CONFIG_GZALLOC
        gzalloc_configure();
#endif
        /* Request enough early memory to get to the pmap zone */
        zdata_size = 12 * sizeof(struct zone);
        zdata_size = round_page(zdata_size);
        zdata = (vm_offset_t)pmap_steal_memory(zdata_size);
}


/*
 * Fill a zone with enough memory to contain at least nelem elements.
 * Memory is obtained with kmem_alloc_kobject from the kernel_map.
 * Return the number of elements actually put into the zone, which may
 * be more than the caller asked for since the memory allocation is
 * rounded up to a full page.
 */
int
zfill(
        zone_t  zone,
        int     nelem)
{
        kern_return_t   kr;
        vm_size_t       size;
        vm_offset_t     memory;
        int             nalloc;

        assert(nelem > 0);
        if (nelem <= 0)
                return 0;
        size = nelem * zone->elem_size;
        size = round_page(size);
        kr = kmem_alloc_kobject(kernel_map, &memory, size);
        if (kr != KERN_SUCCESS)
                return 0;

        zone_change(zone, Z_FOREIGN, TRUE);
        ZONE_PAGE_COUNT_INCR(zone, (size / PAGE_SIZE));
        zcram(zone, memory, size);
        nalloc = (int)(size / zone->elem_size);
        assert(nalloc >= nelem);

        return nalloc;
}

/*
 *      Initialize the "zone of zones" which uses fixed memory allocated
 *      earlier in memory initialization.  zone_bootstrap is called
 *      before zone_init.
 */
void
zone_bootstrap(void)
{
        char temp_buf[16];

        if (PE_parse_boot_argn("-zinfop", temp_buf, sizeof(temp_buf))) {
                zinfo_per_task = TRUE;
        }

        if (!PE_parse_boot_argn("zalloc_debug", &zalloc_debug, sizeof(zalloc_debug)))
                zalloc_debug = 0;

        /* Set up zone element poisoning */
        zp_init();

        /* should zlog log to debug zone corruption instead of leaks? */
        if (PE_parse_boot_argn("-zc", temp_buf, sizeof(temp_buf))) {
                corruption_debug_flag = TRUE;
        }       

        /*
         * Check for and set up zone leak detection if requested via boot-args.  We recognized two
         * boot-args:
         *
         *      zlog=<zone_to_log>
         *      zrecs=<num_records_in_log>
         *
         * The zlog arg is used to specify the zone name that should be logged, and zrecs is used to
         * control the size of the log.  If zrecs is not specified, a default value is used.
         */

        if (PE_parse_boot_argn("zlog", zone_name_to_log, sizeof(zone_name_to_log)) == TRUE) {
                if (PE_parse_boot_argn("zrecs", &log_records, sizeof(log_records)) == TRUE) {

                        /*
                         * Don't allow more than ZRECORDS_MAX records even if the user asked for more.
                         * This prevents accidentally hogging too much kernel memory and making the system
                         * unusable.
                         */

                        log_records = MIN(ZRECORDS_MAX, log_records);

                } else {
                        log_records = ZRECORDS_DEFAULT;
                }
        }

        simple_lock_init(&all_zones_lock, 0);

        first_zone = ZONE_NULL;
        last_zone = &first_zone;
        num_zones = 0;
        thread_call_setup(&call_async_alloc, zalloc_async, NULL);

        /* assertion: nobody else called zinit before us */
        assert(zone_zone == ZONE_NULL);
        
        /* initializing global lock group for zones */
        lck_grp_attr_setdefault(&zone_locks_grp_attr);
        lck_grp_init(&zone_locks_grp, "zone_locks", &zone_locks_grp_attr);

        zone_zone = zinit(sizeof(struct zone), 128 * sizeof(struct zone),
                          sizeof(struct zone), "zones");
        zone_change(zone_zone, Z_COLLECT, FALSE);
        zone_change(zone_zone, Z_CALLERACCT, FALSE);
        zone_change(zone_zone, Z_NOENCRYPT, TRUE);

        zcram(zone_zone, zdata, zdata_size);

        /* initialize fake zones and zone info if tracking by task */
        if (zinfo_per_task) {
                vm_size_t zisize = sizeof(zinfo_usage_store_t) * ZINFO_SLOTS;
                unsigned int i;

                for (i = 0; i < num_fake_zones; i++)
                        fake_zones[i].init(ZINFO_SLOTS - num_fake_zones + i);
                zinfo_zone = zinit(zisize, zisize * CONFIG_TASK_MAX,
                                   zisize, "per task zinfo");
                zone_change(zinfo_zone, Z_CALLERACCT, FALSE);
        }
}

void
zinfo_task_init(task_t task)
{
        if (zinfo_per_task) {
                task->tkm_zinfo = zalloc(zinfo_zone);
                memset(task->tkm_zinfo, 0, sizeof(zinfo_usage_store_t) * ZINFO_SLOTS);
        } else {
                task->tkm_zinfo = NULL;
        }
}

void
zinfo_task_free(task_t task)
{
        assert(task != kernel_task);
        if (task->tkm_zinfo != NULL) {
                zfree(zinfo_zone, task->tkm_zinfo);
                task->tkm_zinfo = NULL;
        }
}
                
/* Global initialization of Zone Allocator.
 * Runs after zone_bootstrap.
 */
void
zone_init(
        vm_size_t max_zonemap_size)
{
        kern_return_t   retval;
        vm_offset_t     zone_min;
        vm_offset_t     zone_max;

        retval = kmem_suballoc(kernel_map, &zone_min, max_zonemap_size,
                               FALSE, VM_FLAGS_ANYWHERE | VM_FLAGS_PERMANENT,
                               &zone_map);

        if (retval != KERN_SUCCESS)
                panic("zone_init: kmem_suballoc failed");
        zone_max = zone_min + round_page(max_zonemap_size);
#if     CONFIG_GZALLOC
        gzalloc_init(max_zonemap_size);
#endif
        /*
         * Setup garbage collection information:
         */
        zone_map_min_address = zone_min;
        zone_map_max_address = zone_max;

#if defined(__LP64__)
        /*
         * ensure that any vm_page_t that gets created from
         * the vm_page zone can be packed properly (see vm_page.h
         * for the packing requirements
         */
        if (VM_PAGE_UNPACK_PTR(VM_PAGE_PACK_PTR(zone_map_min_address)) != (vm_page_t)zone_map_min_address)
                panic("VM_PAGE_PACK_PTR failed on zone_map_min_address - %p", (void *)zone_map_min_address);

        if (VM_PAGE_UNPACK_PTR(VM_PAGE_PACK_PTR(zone_map_max_address)) != (vm_page_t)zone_map_max_address)
                panic("VM_PAGE_PACK_PTR failed on zone_map_max_address - %p", (void *)zone_map_max_address);
#endif

        zone_pages = (unsigned int)atop_kernel(zone_max - zone_min);
        zone_page_table_used_size = sizeof(zone_page_table);

        zone_page_table_second_level_size = 1;
        zone_page_table_second_level_shift_amount = 0;
        
        /*
         * Find the power of 2 for the second level that allows
         * the first level to fit in ZONE_PAGE_TABLE_FIRST_LEVEL_SIZE
         * slots.
         */
        while ((zone_page_table_first_level_slot(zone_pages-1)) >= ZONE_PAGE_TABLE_FIRST_LEVEL_SIZE) {
                zone_page_table_second_level_size <<= 1;
                zone_page_table_second_level_shift_amount++;
        }
        
        lck_grp_attr_setdefault(&zone_gc_lck_grp_attr);
        lck_grp_init(&zone_gc_lck_grp, "zone_gc", &zone_gc_lck_grp_attr);
        lck_attr_setdefault(&zone_gc_lck_attr);
        lck_mtx_init_ext(&zone_gc_lock, &zone_gc_lck_ext, &zone_gc_lck_grp, &zone_gc_lck_attr);
        
#if CONFIG_ZLEAKS
        /*
         * Initialize the zone leak monitor
         */
        zleak_init(max_zonemap_size);
#endif /* CONFIG_ZLEAKS */
}

void
zone_page_table_expand(zone_page_index_t pindex)
{
        unsigned int first_index;
        struct zone_page_table_entry * volatile * first_level_ptr;

        assert(pindex < zone_pages);

        first_index = zone_page_table_first_level_slot(pindex);
        first_level_ptr = &zone_page_table[first_index];

        if (*first_level_ptr == NULL) {
                /*
                 * We were able to verify the old first-level slot
                 * had NULL, so attempt to populate it.
                 */

                vm_offset_t second_level_array = 0;
                vm_size_t second_level_size = round_page(zone_page_table_second_level_size * sizeof(struct zone_page_table_entry));
                zone_page_index_t i;
                struct zone_page_table_entry *entry_array;

                if (kmem_alloc_kobject(zone_map, &second_level_array,
                                                           second_level_size) != KERN_SUCCESS) {
                        panic("zone_page_table_expand");
                }
                zone_map_table_page_count += (second_level_size / PAGE_SIZE);

                /*
                 * zone_gc() may scan the "zone_page_table" directly,
                 * so make sure any slots have a valid unused state.
                 */
                entry_array = (struct zone_page_table_entry *)second_level_array;
                for (i=0; i < zone_page_table_second_level_size; i++) {
                        entry_array[i].alloc_count = ZONE_PAGE_UNUSED;
                        entry_array[i].collect_count = 0;
                }

                if (OSCompareAndSwapPtr(NULL, entry_array, first_level_ptr)) {
                        /* Old slot was NULL, replaced with expanded level */
                        OSAddAtomicLong(second_level_size, &zone_page_table_used_size);
                } else {
                        /* Old slot was not NULL, someone else expanded first */
                        kmem_free(zone_map, second_level_array, second_level_size);
                        zone_map_table_page_count -= (second_level_size / PAGE_SIZE);
                }
        } else {
                /* Old slot was not NULL, already been expanded */
        }
}

struct zone_page_table_entry *
zone_page_table_lookup(zone_page_index_t pindex)
{
        unsigned int first_index = zone_page_table_first_level_slot(pindex);
        struct zone_page_table_entry *second_level = zone_page_table[first_index];

        if (second_level) {
                return &second_level[zone_page_table_second_level_slot(pindex)];
        }

        return NULL;
}

extern volatile SInt32 kfree_nop_count;

#pragma mark -
#pragma mark zalloc_canblock

/*
 *      zalloc returns an element from the specified zone.
 */
static void *
zalloc_internal(
        zone_t  zone,
        boolean_t canblock,
        boolean_t nopagewait)
{
        vm_offset_t     addr = 0;
        kern_return_t   retval;
        uintptr_t       zbt[MAX_ZTRACE_DEPTH];  /* used in zone leak logging and zone leak detection */
        int             numsaved = 0;
        boolean_t       zone_replenish_wakeup = FALSE, zone_alloc_throttle = FALSE;
#if     CONFIG_GZALLOC || ZONE_DEBUG    
        boolean_t       did_gzalloc = FALSE;
#endif
        thread_t thr = current_thread();
        boolean_t       check_poison = FALSE;

#if CONFIG_ZLEAKS
        uint32_t        zleak_tracedepth = 0;  /* log this allocation if nonzero */
#endif /* CONFIG_ZLEAKS */

        assert(zone != ZONE_NULL);

#if     CONFIG_GZALLOC
        addr = gzalloc_alloc(zone, canblock);
        did_gzalloc = (addr != 0);
#endif

        /*
         * If zone logging is turned on and this is the zone we're tracking, grab a backtrace.
         */
        if (__improbable(DO_LOGGING(zone)))
                numsaved = OSBacktrace((void*) zbt, MAX_ZTRACE_DEPTH);

#if CONFIG_ZLEAKS
        /*
         * Zone leak detection: capture a backtrace every zleak_sample_factor
         * allocations in this zone.
         */
        if (__improbable(zone->zleak_on && sample_counter(&zone->zleak_capture, zleak_sample_factor) == TRUE)) {
                /* Avoid backtracing twice if zone logging is on */
                if (numsaved == 0)
                        zleak_tracedepth = fastbacktrace(zbt, MAX_ZTRACE_DEPTH);
                else
                        zleak_tracedepth = numsaved;
        }
#endif /* CONFIG_ZLEAKS */

        lock_zone(zone);

        if (zone->async_prio_refill && zone->zone_replenish_thread) {
                    do {
                            vm_size_t zfreec = (zone->cur_size - (zone->count * zone->elem_size));
                            vm_size_t zrefillwm = zone->prio_refill_watermark * zone->elem_size;
                            zone_replenish_wakeup = (zfreec < zrefillwm);
                            zone_alloc_throttle = (zfreec < (zrefillwm / 2)) && ((thr->options & TH_OPT_VMPRIV) == 0);

                            if (zone_replenish_wakeup) {
                                    zone_replenish_wakeups_initiated++;
                                    unlock_zone(zone);
                                    /* Signal the potentially waiting
                                     * refill thread.
                                     */
                                    thread_wakeup(&zone->zone_replenish_thread);

                                    /* Scheduling latencies etc. may prevent
                                     * the refill thread from keeping up
                                     * with demand. Throttle consumers
                                     * when we fall below half the
                                     * watermark, unless VM privileged
                                     */
                                    if (zone_alloc_throttle) {
                                            zone_replenish_throttle_count++;
                                            assert_wait_timeout(zone, THREAD_UNINT, 1, NSEC_PER_MSEC);
                                            thread_block(THREAD_CONTINUE_NULL);
                                    }
                                    lock_zone(zone);
                            }
                    } while (zone_alloc_throttle == TRUE);
        }
        
        if (__probable(addr == 0))
                addr = try_alloc_from_zone(zone, &check_poison);


        while ((addr == 0) && canblock) {
                /*
                 *      If nothing was there, try to get more
                 */
                if (zone->doing_alloc) {
                        /*
                         *      Someone is allocating memory for this zone.
                         *      Wait for it to show up, then try again.
                         */
                        zone->waiting = TRUE;
                        zone_sleep(zone);
                } else if (zone->doing_gc) {
                        /* zone_gc() is running. Since we need an element
                         * from the free list that is currently being
                         * collected, set the waiting bit and try to
                         * interrupt the GC process, and try again
                         * when we obtain the lock.
                         */
                        zone->waiting = TRUE;
                        zone_sleep(zone);
                } else {
                        vm_offset_t space;
                        vm_size_t alloc_size;
                        int retry = 0;

                        if ((zone->cur_size + zone->elem_size) >
                            zone->max_size) {
                                if (zone->exhaustible)
                                        break;
                                if (zone->expandable) {
                                        /*
                                         * We're willing to overflow certain
                                         * zones, but not without complaining.
                                         *
                                         * This is best used in conjunction
                                         * with the collectable flag. What we
                                         * want is an assurance we can get the
                                         * memory back, assuming there's no
                                         * leak. 
                                         */
                                        zone->max_size += (zone->max_size >> 1);
                                } else {
                                        unlock_zone(zone);

                                        panic_include_zprint = TRUE;
#if CONFIG_ZLEAKS
                                        if (zleak_state & ZLEAK_STATE_ACTIVE)
                                                panic_include_ztrace = TRUE;
#endif /* CONFIG_ZLEAKS */
                                        panic("zalloc: zone \"%s\" empty.", zone->zone_name);
                                }
                        }
                        zone->doing_alloc = TRUE;
                        unlock_zone(zone);

                        for (;;) {
                                int     zflags = KMA_KOBJECT|KMA_NOPAGEWAIT;

                                if (vm_pool_low() || retry >= 1)
                                        alloc_size = 
                                                round_page(zone->elem_size);
                                else
                                        alloc_size = zone->alloc_size;
                                
                                if (zone->noencrypt)
                                        zflags |= KMA_NOENCRYPT;
                                
                                retval = kernel_memory_allocate(zone_map, &space, alloc_size, 0, zflags);
                                if (retval == KERN_SUCCESS) {
#if     ZONE_ALIAS_ADDR
                                        if (alloc_size == PAGE_SIZE)
                                                space = zone_alias_addr(space);
#endif
                                        
#if CONFIG_ZLEAKS
                                        if ((zleak_state & (ZLEAK_STATE_ENABLED | ZLEAK_STATE_ACTIVE)) == ZLEAK_STATE_ENABLED) {
                                                if (zone_map->size >= zleak_global_tracking_threshold) {
                                                        kern_return_t kr;
                                                        
                                                        kr = zleak_activate();
                                                        if (kr != KERN_SUCCESS) {
                                                                printf("Failed to activate live zone leak debugging (%d).\n", kr);
                                                        }
                                                }
                                        }
                                        
                                        if ((zleak_state & ZLEAK_STATE_ACTIVE) && !(zone->zleak_on)) {
                                                if (zone->cur_size > zleak_per_zone_tracking_threshold) {
                                                        zone->zleak_on = TRUE;
                                                }       
                                        }
#endif /* CONFIG_ZLEAKS */
                                        ZONE_PAGE_COUNT_INCR(zone, (alloc_size / PAGE_SIZE));
                                        zcram(zone, space, alloc_size);
                                        
                                        break;
                                } else if (retval != KERN_RESOURCE_SHORTAGE) {
                                        retry++;
                                        
                                        if (retry == 2) {
                                                zone_gc(TRUE);
                                                printf("zalloc did gc\n");
                                                zone_display_zprint();
                                        }
                                        if (retry == 3) {
                                                panic_include_zprint = TRUE;
#if CONFIG_ZLEAKS
                                                if ((zleak_state & ZLEAK_STATE_ACTIVE)) {
                                                        panic_include_ztrace = TRUE;
                                                }
#endif /* CONFIG_ZLEAKS */              
                                                if (retval == KERN_NO_SPACE) {
                                                        zone_t zone_largest = zone_find_largest();
                                                        panic("zalloc: zone map exhausted while allocating from zone %s, likely due to memory leak in zone %s (%lu total bytes, %d elements allocated)",
                                                        zone->zone_name, zone_largest->zone_name,
                                                        (unsigned long)zone_largest->cur_size, zone_largest->count);

                                                }
                                                panic("zalloc: \"%s\" (%d elements) retry fail %d, kfree_nop_count: %d", zone->zone_name, zone->count, retval, (int)kfree_nop_count);
                                        }
                                } else {
                                        break;
                                }
                        }
                        lock_zone(zone);
                        zone->doing_alloc = FALSE; 
                        if (zone->waiting) {
                                zone->waiting = FALSE;
                                zone_wakeup(zone);
                        }
                        addr = try_alloc_from_zone(zone, &check_poison);
                        if (addr == 0 &&
                            retval == KERN_RESOURCE_SHORTAGE) {
                                if (nopagewait == TRUE)
                                        break;  /* out of the main while loop */
                                unlock_zone(zone);

                                VM_PAGE_WAIT();
                                lock_zone(zone);
                        }
                }
                if (addr == 0)
                        addr = try_alloc_from_zone(zone, &check_poison);
        }

#if CONFIG_ZLEAKS
        /* Zone leak detection:
         * If we're sampling this allocation, add it to the zleaks hash table. 
         */
        if (addr && zleak_tracedepth > 0)  {
                /* Sampling can fail if another sample is happening at the same time in a different zone. */
                if (!zleak_log(zbt, addr, zleak_tracedepth, zone->elem_size)) {
                        /* If it failed, roll back the counter so we sample the next allocation instead. */
                        zone->zleak_capture = zleak_sample_factor;
                }
        }
#endif /* CONFIG_ZLEAKS */                      
                        
                        
        if ((addr == 0) && (!canblock || nopagewait) && (zone->async_pending == FALSE) && (zone->no_callout == FALSE) && (zone->exhaustible == FALSE) && (!vm_pool_low())) {
                zone->async_pending = TRUE;
                unlock_zone(zone);
                thread_call_enter(&call_async_alloc);
                lock_zone(zone);
                addr = try_alloc_from_zone(zone, &check_poison);
        }

        /*
         * See if we should be logging allocations in this zone.  Logging is rarely done except when a leak is
         * suspected, so this code rarely executes.  We need to do this code while still holding the zone lock
         * since it protects the various log related data structures.
         */

        if (__improbable(DO_LOGGING(zone) && addr)) {
                btlog_add_entry(zlog_btlog, (void *)addr, ZOP_ALLOC, (void **)zbt, numsaved);
        }

        vm_offset_t     inner_size = zone->elem_size;
        
#if     ZONE_DEBUG
        if (!did_gzalloc && addr && zone_debug_enabled(zone)) {
                enqueue_tail(&zone->active_zones, (queue_entry_t)addr);
                addr += ZONE_DEBUG_OFFSET;
                inner_size -= ZONE_DEBUG_OFFSET;
        }
#endif

        unlock_zone(zone);

        if (__improbable(check_poison && addr)) {
                vm_offset_t *element_cursor  = ((vm_offset_t *) addr) + 1;
                vm_offset_t *backup  = get_backup_ptr(inner_size, (vm_offset_t *) addr);

                for ( ; element_cursor < backup ; element_cursor++)
                        if (__improbable(*element_cursor != ZP_POISON))
                                zone_element_was_modified_panic(zone,
                                                                addr,
                                                                *element_cursor,
                                                                ZP_POISON,
                                                                ((vm_offset_t)element_cursor) - addr);
        }

        if (addr) {
                /*
                 * Clear out the old next pointer and backup to avoid leaking the cookie
                 * and so that only values on the freelist have a valid cookie
                 */

                vm_offset_t *primary  = (vm_offset_t *) addr;
                vm_offset_t *backup   = get_backup_ptr(inner_size, primary);

                *primary = ZP_POISON;
                *backup  = ZP_POISON;
        }

        TRACE_MACHLEAKS(ZALLOC_CODE, ZALLOC_CODE_2, zone->elem_size, addr);

        if (addr) {
                task_t task;
                zinfo_usage_t zinfo;
                vm_size_t sz = zone->elem_size;

                if (zone->caller_acct)
                        ledger_credit(thr->t_ledger, task_ledgers.tkm_private, sz);
                else
                        ledger_credit(thr->t_ledger, task_ledgers.tkm_shared, sz);

                if ((task = thr->task) != NULL && (zinfo = task->tkm_zinfo) != NULL)
                        OSAddAtomic64(sz, (int64_t *)&zinfo[zone->index].alloc);
        }
        return((void *)addr);
}


void *
zalloc(zone_t zone)
{
        return (zalloc_internal(zone, TRUE, FALSE));
}

void *
zalloc_noblock(zone_t zone)
{
        return (zalloc_internal(zone, FALSE, FALSE));
}

void *
zalloc_nopagewait(zone_t zone)
{
        return (zalloc_internal(zone, TRUE, TRUE));
}

void *
zalloc_canblock(zone_t zone, boolean_t canblock)
{
        return (zalloc_internal(zone, canblock, FALSE));
}


void
zalloc_async(
        __unused thread_call_param_t          p0,
        __unused thread_call_param_t p1)
{
        zone_t current_z = NULL, head_z;
        unsigned int max_zones, i;
        void *elt = NULL;
        boolean_t pending = FALSE;
        
        simple_lock(&all_zones_lock);
        head_z = first_zone;
        max_zones = num_zones;
        simple_unlock(&all_zones_lock);
        current_z = head_z;
        for (i = 0; i < max_zones; i++) {
                lock_zone(current_z);
                if (current_z->async_pending == TRUE) {
                        current_z->async_pending = FALSE;
                        pending = TRUE;
                }
                unlock_zone(current_z);

                if (pending == TRUE) {
                        elt = zalloc_canblock(current_z, TRUE);
                        zfree(current_z, elt);
                        pending = FALSE;
                }
                /*
                 * This is based on assumption that zones never get
                 * freed once allocated and linked. 
                 * Hence a read outside of lock is OK.
                 */
                current_z = current_z->next_zone;
        }
}

/*
 *      zget returns an element from the specified zone
 *      and immediately returns nothing if there is nothing there.
 *
 *      This form should be used when you can not block (like when
 *      processing an interrupt).
 *
 *      XXX: It seems like only vm_page_grab_fictitious_common uses this, and its
 *  friend vm_page_more_fictitious can block, so it doesn't seem like 
 *  this is used for interrupts any more....
 */
void *
zget(
        register zone_t zone)
{
        vm_offset_t     addr;
        boolean_t       check_poison = FALSE;
        
#if CONFIG_ZLEAKS
        uintptr_t       zbt[MAX_ZTRACE_DEPTH];          /* used for zone leak detection */
        uint32_t        zleak_tracedepth = 0;  /* log this allocation if nonzero */
#endif /* CONFIG_ZLEAKS */

        assert( zone != ZONE_NULL );

#if CONFIG_ZLEAKS
        /*
         * Zone leak detection: capture a backtrace
         */
        if (__improbable(zone->zleak_on && sample_counter(&zone->zleak_capture, zleak_sample_factor) == TRUE)) {
                zleak_tracedepth = fastbacktrace(zbt, MAX_ZTRACE_DEPTH);
        }
#endif /* CONFIG_ZLEAKS */

        if (!lock_try_zone(zone))
                return NULL;
        
        addr = try_alloc_from_zone(zone, &check_poison);

        vm_offset_t     inner_size = zone->elem_size;
        
#if     ZONE_DEBUG
        if (addr && zone_debug_enabled(zone)) {
                enqueue_tail(&zone->active_zones, (queue_entry_t)addr);
                addr += ZONE_DEBUG_OFFSET;
                inner_size -= ZONE_DEBUG_OFFSET;
        }
#endif  /* ZONE_DEBUG */
        
#if CONFIG_ZLEAKS
        /*
         * Zone leak detection: record the allocation 
         */
        if (zone->zleak_on && zleak_tracedepth > 0 && addr) {
                /* Sampling can fail if another sample is happening at the same time in a different zone. */
                if (!zleak_log(zbt, addr, zleak_tracedepth, zone->elem_size)) {
                        /* If it failed, roll back the counter so we sample the next allocation instead. */
                        zone->zleak_capture = zleak_sample_factor;
                }
        }
#endif /* CONFIG_ZLEAKS */
        
        unlock_zone(zone);

        if (__improbable(check_poison && addr)) {
                vm_offset_t *element_cursor  = ((vm_offset_t *) addr) + 1;
                vm_offset_t *backup  = get_backup_ptr(inner_size, (vm_offset_t *) addr);

                for ( ; element_cursor < backup ; element_cursor++)
                        if (__improbable(*element_cursor != ZP_POISON))
                                zone_element_was_modified_panic(zone,
                                                                addr,
                                                                *element_cursor,
                                                                ZP_POISON,
                                                                ((vm_offset_t)element_cursor) - addr);
        }

        if (addr) {
                /*
                 * Clear out the old next pointer and backup to avoid leaking the cookie
                 * and so that only values on the freelist have a valid cookie
                 */
                vm_offset_t *primary  = (vm_offset_t *) addr;
                vm_offset_t *backup   = get_backup_ptr(inner_size, primary);

                *primary = ZP_POISON;
                *backup  = ZP_POISON;
        }

        return((void *) addr);
}

/* Keep this FALSE by default.  Large memory machine run orders of magnitude
   slower in debug mode when true.  Use debugger to enable if needed */
/* static */ boolean_t zone_check = FALSE;

static void zone_check_freelist(zone_t zone, vm_offset_t elem)
{
        struct zone_free_element *this;
        struct zone_page_metadata *thispage;

        if (zone->use_page_list) {
                if (zone->allows_foreign) {
                        for (thispage = (struct zone_page_metadata *)queue_first(&zone->pages.any_free_foreign);
                                 !queue_end(&zone->pages.any_free_foreign, (queue_entry_t)thispage);
                                 thispage = (struct zone_page_metadata *)queue_next((queue_chain_t *)thispage)) {
                                for (this = thispage->elements;
                                         this != NULL;
                                         this = this->next) {
                                        if (!is_sane_zone_element(zone, (vm_address_t)this) || (vm_address_t)this == elem)
                                                panic("zone_check_freelist");
                                }
                        }
                }
                for (thispage = (struct zone_page_metadata *)queue_first(&zone->pages.all_free);
                         !queue_end(&zone->pages.all_free, (queue_entry_t)thispage);
                         thispage = (struct zone_page_metadata *)queue_next((queue_chain_t *)thispage)) {
                        for (this = thispage->elements;
                                 this != NULL;
                                 this = this->next) {
                                if (!is_sane_zone_element(zone, (vm_address_t)this) || (vm_address_t)this == elem)
                                        panic("zone_check_freelist");
                        }
                }
                for (thispage = (struct zone_page_metadata *)queue_first(&zone->pages.intermediate);
                         !queue_end(&zone->pages.intermediate, (queue_entry_t)thispage);
                         thispage = (struct zone_page_metadata *)queue_next((queue_chain_t *)thispage)) {
                        for (this = thispage->elements;
                                 this != NULL;
                                 this = this->next) {
                                if (!is_sane_zone_element(zone, (vm_address_t)this) || (vm_address_t)this == elem)
                                        panic("zone_check_freelist");
                        }
                }
        } else {
                for (this = zone->free_elements;
                         this != NULL;
                         this = this->next) {
                        if (!is_sane_zone_element(zone, (vm_address_t)this) || (vm_address_t)this == elem)
                                panic("zone_check_freelist");
                }
        }
}

static zone_t zone_last_bogus_zone = ZONE_NULL;
static vm_offset_t zone_last_bogus_elem = 0;

void
zfree(
        register zone_t zone,
        void            *addr)
{
        vm_offset_t     elem = (vm_offset_t) addr;
        uintptr_t       zbt[MAX_ZTRACE_DEPTH];                  /* only used if zone logging is enabled via boot-args */
        int             numsaved = 0;
        boolean_t       gzfreed = FALSE;
        boolean_t       poison = FALSE;

        assert(zone != ZONE_NULL);

#if 1
        if (zone->use_page_list) {
                struct zone_page_metadata *page_meta = get_zone_page_metadata((struct zone_free_element *)addr);
                if (zone != page_meta->zone) {
                        /*
                         * Something bad has happened. Someone tried to zfree a pointer but the metadata says it is from
                         * a different zone (or maybe it's from a zone that doesn't use page free lists at all). We can repair
                         * some cases of this, if:
                         * 1) The specified zone had use_page_list, and the true zone also has use_page_list set. In that case
                         *    we can swap the zone_t
                         * 2) The specified zone had use_page_list, but the true zone does not. In this case page_meta is garbage,
                         *    and dereferencing page_meta->zone might panic.
                         * To distinguish the two, we enumerate the zone list to match it up.
                         * We do not handle the case where an incorrect zone is passed that does not have use_page_list set,
                         * even if the true zone did have this set.
                         */
                        zone_t fixed_zone = NULL;
                        int fixed_i, max_zones;

                        simple_lock(&all_zones_lock);
                        max_zones = num_zones;
                        fixed_zone = first_zone;
                        simple_unlock(&all_zones_lock);

                        for (fixed_i=0; fixed_i < max_zones; fixed_i++, fixed_zone = fixed_zone->next_zone) {
                                if (fixed_zone == page_meta->zone && fixed_zone->use_page_list) {
                                        /* we can fix this */
                                        printf("Fixing incorrect zfree from zone %s to zone %s\n", zone->zone_name, fixed_zone->zone_name);
                                        zone = fixed_zone;
                                        break;
                                }
                        }
                }
        }
#endif

        /*
         * If zone logging is turned on and this is the zone we're tracking, grab a backtrace.
         */

        if (__improbable(DO_LOGGING(zone) && corruption_debug_flag))
                numsaved = OSBacktrace((void *)zbt, MAX_ZTRACE_DEPTH);

#if MACH_ASSERT
        /* Basic sanity checks */
        if (zone == ZONE_NULL || elem == (vm_offset_t)0)
                panic("zfree: NULL");
        /* zone_gc assumes zones are never freed */
        if (zone == zone_zone)
                panic("zfree: freeing to zone_zone breaks zone_gc!");
#endif

#if     CONFIG_GZALLOC  
        gzfreed = gzalloc_free(zone, addr);
#endif

        TRACE_MACHLEAKS(ZFREE_CODE, ZFREE_CODE_2, zone->elem_size, (uintptr_t)addr);

        if (__improbable(!gzfreed && zone->collectable && !zone->allows_foreign &&
                !from_zone_map(elem, zone->elem_size))) {
#if MACH_ASSERT
                panic("zfree: non-allocated memory in collectable zone!");
#endif
                zone_last_bogus_zone = zone;
                zone_last_bogus_elem = elem;
                return;
        }

        if ((zp_factor != 0 || zp_tiny_zone_limit != 0) && !gzfreed) {
                /*
                 * Poison the memory before it ends up on the freelist to catch
                 * use-after-free and use of uninitialized memory
                 *
                 * Always poison tiny zones' elements (limit is 0 if -no-zp is set)
                 * Also poison larger elements periodically
                 */

                vm_offset_t     inner_size = zone->elem_size;

#if     ZONE_DEBUG
                if (!gzfreed && zone_debug_enabled(zone)) {
                        inner_size -= ZONE_DEBUG_OFFSET;
                }
#endif
                uint32_t sample_factor = zp_factor + (((uint32_t)inner_size) >> zp_scale);

                if (inner_size <= zp_tiny_zone_limit)
                        poison = TRUE;
                else if (zp_factor != 0 && sample_counter(&zone->zp_count, sample_factor) == TRUE)
                        poison = TRUE;

                if (__improbable(poison)) {

                        /* memset_pattern{4|8} could help make this faster: <rdar://problem/4662004> */
                        /* Poison everything but primary and backup */
                        vm_offset_t *element_cursor  = ((vm_offset_t *) elem) + 1;
                        vm_offset_t *backup   = get_backup_ptr(inner_size, (vm_offset_t *)elem);

                        for ( ; element_cursor < backup; element_cursor++)
                                *element_cursor = ZP_POISON;
                }
        }

        lock_zone(zone);

        /*
         * See if we're doing logging on this zone.  There are two styles of logging used depending on
         * whether we're trying to catch a leak or corruption.  See comments above in zalloc for details.
         */

        if (__improbable(DO_LOGGING(zone))) {
                if (corruption_debug_flag) {
                        /*
                         * We're logging to catch a corruption.  Add a record of this zfree operation
                         * to log.
                         */
                        btlog_add_entry(zlog_btlog, (void *)addr, ZOP_FREE, (void **)zbt, numsaved);
                } else {
                        /*
                         * We're logging to catch a leak. Remove any record we might have for this
                         * element since it's being freed.  Note that we may not find it if the buffer
                         * overflowed and that's OK.  Since the log is of a limited size, old records
                         * get overwritten if there are more zallocs than zfrees.
                         */
                        btlog_remove_entries_for_element(zlog_btlog, (void *)addr);
                }
        }

#if     ZONE_DEBUG
        if (!gzfreed && zone_debug_enabled(zone)) {
                queue_t tmp_elem;

                elem -= ZONE_DEBUG_OFFSET;
                if (zone_check) {
                        /* check the zone's consistency */

                        for (tmp_elem = queue_first(&zone->active_zones);
                             !queue_end(tmp_elem, &zone->active_zones);
                             tmp_elem = queue_next(tmp_elem))
                                if (elem == (vm_offset_t)tmp_elem)
                                        break;
                        if (elem != (vm_offset_t)tmp_elem)
                                panic("zfree()ing element from wrong zone");
                }
                remqueue((queue_t) elem);
        }
#endif  /* ZONE_DEBUG */
        if (zone_check) {
                zone_check_freelist(zone, elem);
        }

        if (__probable(!gzfreed))
                free_to_zone(zone, elem, poison);

#if MACH_ASSERT
        if (zone->count < 0)
                panic("zfree: zone count underflow in zone %s while freeing element %p, possible cause: double frees or freeing memory that did not come from this zone",
                zone->zone_name, addr);
#endif
        

#if CONFIG_ZLEAKS
        /*
         * Zone leak detection: un-track the allocation 
         */
        if (zone->zleak_on) {
                zleak_free(elem, zone->elem_size);
        }
#endif /* CONFIG_ZLEAKS */
        
        /*
         * If elements have one or more pages, and memory is low,
         * request to run the garbage collection in the zone  the next 
         * time the pageout thread runs.
         */
        if (zone->elem_size >= PAGE_SIZE && 
            vm_pool_low()){
                zone_gc_forced = TRUE;
        }
        unlock_zone(zone);

        {
                thread_t thr = current_thread();
                task_t task;
                zinfo_usage_t zinfo;
                vm_size_t sz = zone->elem_size;

                if (zone->caller_acct)
                        ledger_debit(thr->t_ledger, task_ledgers.tkm_private, sz);
                else
                        ledger_debit(thr->t_ledger, task_ledgers.tkm_shared, sz);

                if ((task = thr->task) != NULL && (zinfo = task->tkm_zinfo) != NULL)
                        OSAddAtomic64(sz, (int64_t *)&zinfo[zone->index].free);
        }
}


/*      Change a zone's flags.
 *      This routine must be called immediately after zinit.
 */
void
zone_change(
        zone_t          zone,
        unsigned int    item,
        boolean_t       value)
{
        assert( zone != ZONE_NULL );
        assert( value == TRUE || value == FALSE );

        switch(item){
                case Z_NOENCRYPT:
                        zone->noencrypt = value;
                        break;
                case Z_EXHAUST:
                        zone->exhaustible = value;
                        break;
                case Z_COLLECT:
                        zone->collectable = value;
                        break;
                case Z_EXPAND:
                        zone->expandable = value;
                        break;
                case Z_FOREIGN:
                        zone->allows_foreign = value;
                        break;
                case Z_CALLERACCT:
                        zone->caller_acct = value;
                        break;
                case Z_NOCALLOUT:
                        zone->no_callout = value;
                        break;
                case Z_GZALLOC_EXEMPT:
                        zone->gzalloc_exempt = value;
#if     CONFIG_GZALLOC
                        gzalloc_reconfigure(zone);
#endif
                        break;
                case Z_ALIGNMENT_REQUIRED:
                        zone->alignment_required = value;
#if     ZONE_DEBUG                      
                        zone_debug_disable(zone);
#endif
#if     CONFIG_GZALLOC
                        gzalloc_reconfigure(zone);
#endif
                        break;
                default:
                        panic("Zone_change: Wrong Item Type!");
                        /* break; */
        }
}

/*
 * Return the expected number of free elements in the zone.
 * This calculation will be incorrect if items are zfree'd that
 * were never zalloc'd/zget'd. The correct way to stuff memory
 * into a zone is by zcram.
 */

integer_t
zone_free_count(zone_t zone)
{
        integer_t free_count;

        lock_zone(zone);
        free_count = zone->countfree;
        unlock_zone(zone);

        assert(free_count >= 0);

        return(free_count);
}

/*
 *  Zone garbage collection subroutines
 */

boolean_t
zone_page_collectable(
        vm_offset_t     addr,
        vm_size_t       size)
{
        struct zone_page_table_entry    *zp;
        zone_page_index_t i, j;

#if     ZONE_ALIAS_ADDR
        addr = zone_virtual_addr(addr);
#endif
#if MACH_ASSERT
        if (!from_zone_map(addr, size))
                panic("zone_page_collectable");
#endif

        i = (zone_page_index_t)atop_kernel(addr-zone_map_min_address);
        j = (zone_page_index_t)atop_kernel((addr+size-1) - zone_map_min_address);

        for (; i <= j; i++) {
                zp = zone_page_table_lookup(i);
                if (zp->collect_count == zp->alloc_count)
                        return (TRUE);
        }

        return (FALSE);
}

void
zone_page_keep(
        vm_offset_t     addr,
        vm_size_t       size)
{
        struct zone_page_table_entry    *zp;
        zone_page_index_t i, j;

#if     ZONE_ALIAS_ADDR
        addr = zone_virtual_addr(addr);
#endif
#if MACH_ASSERT
        if (!from_zone_map(addr, size))
                panic("zone_page_keep");
#endif

        i = (zone_page_index_t)atop_kernel(addr-zone_map_min_address);
        j = (zone_page_index_t)atop_kernel((addr+size-1) - zone_map_min_address);

        for (; i <= j; i++) {
                zp = zone_page_table_lookup(i);
                zp->collect_count = 0;
        }
}

void
zone_page_collect(
        vm_offset_t     addr,
        vm_size_t       size)
{
        struct zone_page_table_entry    *zp;
        zone_page_index_t i, j;

#if     ZONE_ALIAS_ADDR
        addr = zone_virtual_addr(addr);
#endif
#if MACH_ASSERT
        if (!from_zone_map(addr, size))
                panic("zone_page_collect");
#endif

        i = (zone_page_index_t)atop_kernel(addr-zone_map_min_address);
        j = (zone_page_index_t)atop_kernel((addr+size-1) - zone_map_min_address);

        for (; i <= j; i++) {
                zp = zone_page_table_lookup(i);
                ++zp->collect_count;
        }
}

void
zone_page_init(
        vm_offset_t     addr,
        vm_size_t       size)
{
        struct zone_page_table_entry    *zp;
        zone_page_index_t i, j;

#if     ZONE_ALIAS_ADDR
        addr = zone_virtual_addr(addr);
#endif
#if MACH_ASSERT
        if (!from_zone_map(addr, size))
                panic("zone_page_init");
#endif

        i = (zone_page_index_t)atop_kernel(addr-zone_map_min_address);
        j = (zone_page_index_t)atop_kernel((addr+size-1) - zone_map_min_address);

        for (; i <= j; i++) {
                /* make sure entry exists before marking unused */
                zone_page_table_expand(i);

                zp = zone_page_table_lookup(i);
                assert(zp);
                zp->alloc_count = ZONE_PAGE_UNUSED;
                zp->collect_count = 0;
        }
}

void
zone_page_alloc(
        vm_offset_t     addr,
        vm_size_t       size)
{
        struct zone_page_table_entry    *zp;
        zone_page_index_t i, j;

#if     ZONE_ALIAS_ADDR
        addr = zone_virtual_addr(addr);
#endif
#if MACH_ASSERT
        if (!from_zone_map(addr, size))
                panic("zone_page_alloc");
#endif

        i = (zone_page_index_t)atop_kernel(addr-zone_map_min_address);
        j = (zone_page_index_t)atop_kernel((addr+size-1) - zone_map_min_address);

        for (; i <= j; i++) {
                zp = zone_page_table_lookup(i);
                assert(zp);

                /*
                 * Set alloc_count to ZONE_PAGE_USED if
                 * it was previously set to ZONE_PAGE_UNUSED.
                 */
                if (zp->alloc_count == ZONE_PAGE_UNUSED)
                        zp->alloc_count = ZONE_PAGE_USED;

                ++zp->alloc_count;
        }
}

void
zone_page_free_element(
        zone_page_index_t       *free_page_head,
        zone_page_index_t       *free_page_tail,
        vm_offset_t     addr,
        vm_size_t       size)
{
        struct zone_page_table_entry    *zp;
        zone_page_index_t i, j;

#if     ZONE_ALIAS_ADDR
        addr = zone_virtual_addr(addr);
#endif
#if MACH_ASSERT
        if (!from_zone_map(addr, size))
                panic("zone_page_free_element");
#endif

        /* Clear out the old next and backup pointers */
        vm_offset_t *primary  = (vm_offset_t *) addr;
        vm_offset_t *backup   = get_backup_ptr(size, primary);

        *primary = ZP_POISON;
        *backup  = ZP_POISON;

        i = (zone_page_index_t)atop_kernel(addr-zone_map_min_address);
        j = (zone_page_index_t)atop_kernel((addr+size-1) - zone_map_min_address);

        for (; i <= j; i++) {
                zp = zone_page_table_lookup(i);

                if (zp->collect_count > 0)
                        --zp->collect_count;
                if (--zp->alloc_count == 0) {
                        vm_address_t        free_page_address;
                        vm_address_t        prev_free_page_address;

                        zp->alloc_count  = ZONE_PAGE_UNUSED;
                        zp->collect_count = 0;


                        /*
                         * This element was the last one on this page, re-use the page's
                         * storage for a page freelist
                         */
                        free_page_address = zone_map_min_address + PAGE_SIZE * ((vm_size_t)i);
                        *(zone_page_index_t *)free_page_address = ZONE_PAGE_INDEX_INVALID;

                        if (*free_page_head == ZONE_PAGE_INDEX_INVALID) {
                                *free_page_head = i;
                                *free_page_tail = i;
                        } else {
                                prev_free_page_address = zone_map_min_address + PAGE_SIZE * ((vm_size_t)(*free_page_tail));
                                *(zone_page_index_t *)prev_free_page_address = i;
                                *free_page_tail = i;
                        }
                }
        }
}




struct {
        uint64_t        zgc_invoked;
        uint64_t        zgc_bailed;
        uint32_t        pgs_freed;

        uint32_t        elems_collected,
                                elems_freed,
                                elems_kept;
} zgc_stats;

/*      Zone garbage collection
 *
 *      zone_gc will walk through all the free elements in all the
 *      zones that are marked collectable looking for reclaimable
 *      pages.  zone_gc is called by consider_zone_gc when the system
 *      begins to run out of memory.
 */
void
zone_gc(boolean_t all_zones)
{
        unsigned int    max_zones;
        zone_t                  z;
        unsigned int    i;
        uint32_t        old_pgs_freed;
        zone_page_index_t zone_free_page_head;
        zone_page_index_t zone_free_page_tail;
        thread_t        mythread = current_thread();

        lck_mtx_lock(&zone_gc_lock);

        zgc_stats.zgc_invoked++;
        old_pgs_freed = zgc_stats.pgs_freed;

        simple_lock(&all_zones_lock);
        max_zones = num_zones;
        z = first_zone;
        simple_unlock(&all_zones_lock);

        if (zalloc_debug & ZALLOC_DEBUG_ZONEGC)
                kprintf("zone_gc(all_zones=%s) starting...\n", all_zones ? "TRUE" : "FALSE");

        /*
         * it's ok to allow eager kernel preemption while
         * while holding a zone lock since it's taken
         * as a spin lock (which prevents preemption)
         */
        thread_set_eager_preempt(mythread);

#if MACH_ASSERT
        for (i = 0; i < zone_pages; i++) {
                struct zone_page_table_entry    *zp;
        
                zp = zone_page_table_lookup(i);
                assert(!zp || (zp->collect_count == 0));
        }
#endif /* MACH_ASSERT */

        for (i = 0; i < max_zones; i++, z = z->next_zone) {
                unsigned int                    n, m;
                vm_size_t                       elt_size, size_freed;
                struct zone_free_element        *elt, *base_elt, *base_prev, *prev, *scan, *keep, *tail;
                int                             kmem_frees = 0, total_freed_pages = 0;
                struct zone_page_metadata               *page_meta;
                queue_head_t    page_meta_head;

                assert(z != ZONE_NULL);

                if (!z->collectable)
                        continue;

                if (all_zones == FALSE && z->elem_size < PAGE_SIZE && !z->use_page_list)
                        continue;

                lock_zone(z);

                elt_size = z->elem_size;

                /*
                 * Do a quick feasibility check before we scan the zone: 
                 * skip unless there is likelihood of getting pages back
                 * (i.e we need a whole allocation block's worth of free
                 * elements before we can garbage collect) and
                 * the zone has more than 10 percent of it's elements free
                 * or the element size is a multiple of the PAGE_SIZE 
                 */
                if ((elt_size & PAGE_MASK) && 
                    !z->use_page_list &&
                     (((z->cur_size - z->count * elt_size) <= (2 * z->alloc_size)) ||
                      ((z->cur_size - z->count * elt_size) <= (z->cur_size / 10)))) {
                        unlock_zone(z);         
                        continue;
                }

                z->doing_gc = TRUE;

                /*
                 * Snatch all of the free elements away from the zone.
                 */

                if (z->use_page_list) {
                        queue_new_head(&z->pages.all_free, &page_meta_head, struct zone_page_metadata *, pages);
                        queue_init(&z->pages.all_free);
                } else {
                        scan = (void *)z->free_elements;
                        z->free_elements = 0;
                }

                unlock_zone(z);

                if (z->use_page_list) {
                        /*
                         * For zones that maintain page lists (which in turn
                         * track free elements on those pages), zone_gc()
                         * is incredibly easy, and we bypass all the logic
                         * for scanning elements and mapping them to
                         * collectable pages
                         */

                        size_freed = 0;

                        queue_iterate(&page_meta_head, page_meta, struct zone_page_metadata *, pages) {
                                assert(from_zone_map((vm_address_t)page_meta, sizeof(*page_meta))); /* foreign elements should be in any_free_foreign */

                                zgc_stats.elems_freed += page_meta->free_count;
                                size_freed += elt_size * page_meta->free_count;
                                zgc_stats.elems_collected += page_meta->free_count;
                        }
                        
                        lock_zone(z);

                        if (size_freed > 0) {
                                z->cur_size -= size_freed;
                                z->countfree -= size_freed/elt_size;
                        }

                        z->doing_gc = FALSE;
                        if (z->waiting) {
                                z->waiting = FALSE;
                                zone_wakeup(z);
                        }

                        unlock_zone(z);

                        if (queue_empty(&page_meta_head))
                                continue;

                        thread_clear_eager_preempt(mythread);

                        while ((page_meta = (struct zone_page_metadata *)dequeue_head(&page_meta_head)) != NULL) {
                                vm_address_t            free_page_address;

                                free_page_address = trunc_page((vm_address_t)page_meta);
#if     ZONE_ALIAS_ADDR
                                free_page_address = zone_virtual_addr(free_page_address);
#endif
                                kmem_free(zone_map, free_page_address, PAGE_SIZE);
                                ZONE_PAGE_COUNT_DECR(z, 1);
                                total_freed_pages++;
                                zgc_stats.pgs_freed += 1;
                                
                                if (++kmem_frees == 32) {
                                        thread_yield_internal(1);
                                        kmem_frees = 0;
                                }
                        }

                        if (zalloc_debug & ZALLOC_DEBUG_ZONEGC)
                                kprintf("zone_gc() of zone %s freed %lu elements, %d pages\n", z->zone_name, (unsigned long)size_freed/elt_size, total_freed_pages);

                        thread_set_eager_preempt(mythread);
                        continue; /* go to next zone */
                }

                /*
                 * Pass 1:
                 *
                 * Determine which elements we can attempt to collect
                 * and count them up in the page table.  Foreign elements
                 * are returned to the zone.
                 */

                prev = (void *)&scan;
                elt = scan;
                n = 0; tail = keep = NULL;

                zone_free_page_head = ZONE_PAGE_INDEX_INVALID;
                zone_free_page_tail = ZONE_PAGE_INDEX_INVALID;


                while (elt != NULL) {
                        if (from_zone_map(elt, elt_size)) {
                                zone_page_collect((vm_offset_t)elt, elt_size);

                                prev = elt;
                                elt = elt->next;

                                ++zgc_stats.elems_collected;
                        }
                        else {
                                if (keep == NULL)
                                        keep = tail = elt;
                                else {
                                        append_zone_element(z, tail, elt);
                                        tail = elt;
                                }

                                append_zone_element(z, prev, elt->next);
                                elt = elt->next;
                                append_zone_element(z, tail, NULL);
                        }

                        /*
                         * Dribble back the elements we are keeping.
                         * If there are none, give some elements that we haven't looked at yet
                         * back to the freelist so that others waiting on the zone don't get stuck
                         * for too long.  This might prevent us from recovering some memory,
                         * but allows us to avoid having to allocate new memory to serve requests
                         * while zone_gc has all the free memory tied up.
                         * <rdar://problem/3893406>
                         */

                        if (++n >= 50) {
                                if (z->waiting == TRUE) {
                                        /* z->waiting checked without lock held, rechecked below after locking */
                                        lock_zone(z);

                                        if (keep != NULL) {
                                                add_list_to_zone(z, keep, tail);
                                                tail = keep = NULL;
                                        } else {
                                                m =0;
                                                base_elt = elt;
                                                base_prev = prev;
                                                while ((elt != NULL) && (++m < 50)) { 
                                                        prev = elt;
                                                        elt = elt->next;
                                                }
                                                if (m !=0 ) {
                                                        /* Extract the elements from the list and
                                                         * give them back */
                                                        append_zone_element(z, prev, NULL);
                                                        add_list_to_zone(z, base_elt, prev);
                                                        append_zone_element(z, base_prev, elt);
                                                        prev = base_prev;
                                                }
                                        }

                                        if (z->waiting) {
                                                z->waiting = FALSE;
                                                zone_wakeup(z);
                                        }

                                        unlock_zone(z);
                                }
                                n =0;
                        }
                }

                /*
                 * Return any remaining elements.
                 */

                if (keep != NULL) {
                        lock_zone(z);

                        add_list_to_zone(z, keep, tail);

                        if (z->waiting) {
                                z->waiting = FALSE;
                                zone_wakeup(z);
                        }

                        unlock_zone(z);
                }

                /*
                 * Pass 2:
                 *
                 * Determine which pages we can reclaim and
                 * free those elements.
                 */

                size_freed = 0;
                elt = scan;
                n = 0; tail = keep = NULL;

                while (elt != NULL) {
                        if (zone_page_collectable((vm_offset_t)elt, elt_size)) {
                                struct zone_free_element *next_elt = elt->next;

                                size_freed += elt_size;

                                /*
                                 * If this is the last allocation on the page(s),
                                 * we may use their storage to maintain the linked
                                 * list of free-able pages. So store elt->next because
                                 * "elt" may be scribbled over.
                                 */
                                zone_page_free_element(&zone_free_page_head, &zone_free_page_tail, (vm_offset_t)elt, elt_size);

                                elt = next_elt;

                                ++zgc_stats.elems_freed;
                        }
                        else {
                                zone_page_keep((vm_offset_t)elt, elt_size);

                                if (keep == NULL)
                                        keep = tail = elt;
                                else {
                                        append_zone_element(z, tail, elt);
                                        tail = elt;
                                }

                                elt = elt->next;
                                append_zone_element(z, tail, NULL);

                                ++zgc_stats.elems_kept;
                        }

                        /*
                         * Dribble back the elements we are keeping,
                         * and update the zone size info.
                         */

                        if (++n >= 50) {
                                lock_zone(z);

                                z->cur_size -= size_freed;
                                z->countfree -= size_freed/elt_size;
                                size_freed = 0;

                                if (keep != NULL) {
                                        add_list_to_zone(z, keep, tail);
                                }

                                if (z->waiting) {
                                        z->waiting = FALSE;
                                        zone_wakeup(z);
                                }

                                unlock_zone(z);

                                n = 0; tail = keep = NULL;
                        }
                }

                /*
                 * Return any remaining elements, and update
                 * the zone size info.
                 */

                lock_zone(z);

                if (size_freed > 0 || keep != NULL) {

                        z->cur_size -= size_freed;
                        z->countfree -= size_freed/elt_size;

                        if (keep != NULL) {
                                add_list_to_zone(z, keep, tail);
                        }

                }

                z->doing_gc = FALSE;
                if (z->waiting) {
                        z->waiting = FALSE;
                        zone_wakeup(z);
                }
                unlock_zone(z);

                if (zone_free_page_head == ZONE_PAGE_INDEX_INVALID)
                        continue;

                /*
                 * we don't want to allow eager kernel preemption while holding the
                 * various locks taken in the kmem_free path of execution
                 */
                thread_clear_eager_preempt(mythread);


                /*
                 * This loop counts the number of pages that should be freed by the
                 * next loop that tries to coalesce the kmem_frees()
                 */
                uint32_t pages_to_free_count = 0;
                vm_address_t            fpa;
                zone_page_index_t index;
                for (index = zone_free_page_head; index != ZONE_PAGE_INDEX_INVALID;) {
                        pages_to_free_count++;
                        fpa = zone_map_min_address + PAGE_SIZE * ((vm_size_t)index);
                        index = *(zone_page_index_t *)fpa;
                }

                /*
                 * Reclaim the pages we are freeing.
                 */
                while (zone_free_page_head != ZONE_PAGE_INDEX_INVALID) {
                        zone_page_index_t       zind = zone_free_page_head;
                        vm_address_t            free_page_address;
                        int                     page_count;

                        /*
                         * Use the first word of the page about to be freed to find the next free page
                         */
                        free_page_address = zone_map_min_address + PAGE_SIZE * ((vm_size_t)zind);
                        zone_free_page_head = *(zone_page_index_t *)free_page_address;

                        page_count = 1;
                        total_freed_pages++;

                        while (zone_free_page_head != ZONE_PAGE_INDEX_INVALID) {
                                zone_page_index_t       next_zind = zone_free_page_head;
                                vm_address_t            next_free_page_address;

                                next_free_page_address = zone_map_min_address + PAGE_SIZE * ((vm_size_t)next_zind);

                                if (next_free_page_address == (free_page_address - PAGE_SIZE)) {
                                        free_page_address = next_free_page_address;
                                } else if (next_free_page_address != (free_page_address + (PAGE_SIZE * page_count)))
                                        break;

                                zone_free_page_head = *(zone_page_index_t *)next_free_page_address;
                                page_count++;
                                total_freed_pages++;
                        }
                        kmem_free(zone_map, free_page_address, page_count * PAGE_SIZE);
                        ZONE_PAGE_COUNT_DECR(z, page_count);
                        zgc_stats.pgs_freed += page_count;
                        pages_to_free_count -= page_count;

                        if (++kmem_frees == 32) {
                                thread_yield_internal(1);
                                kmem_frees = 0;
                        }
                }

                /* Check that we actually free the exact number of pages we were supposed to */
                assert(pages_to_free_count == 0);

                if (zalloc_debug & ZALLOC_DEBUG_ZONEGC)
                        kprintf("zone_gc() of zone %s freed %lu elements, %d pages\n", z->zone_name, (unsigned long)size_freed/elt_size, total_freed_pages);

                thread_set_eager_preempt(mythread);
        }

        if (old_pgs_freed == zgc_stats.pgs_freed)
                zgc_stats.zgc_bailed++;

        thread_clear_eager_preempt(mythread);

        lck_mtx_unlock(&zone_gc_lock);

}

extern vm_offset_t kmapoff_kaddr;
extern unsigned int kmapoff_pgcnt;

/*
 *      consider_zone_gc:
 *
 *      Called by the pageout daemon when the system needs more free pages.
 */

void
consider_zone_gc(boolean_t force)
{
        boolean_t all_zones = FALSE;

        if (kmapoff_kaddr != 0) {
                /*
                 * One-time reclaim of kernel_map resources we allocated in
                 * early boot.
                 */
                (void) vm_deallocate(kernel_map,
                    kmapoff_kaddr, kmapoff_pgcnt * PAGE_SIZE_64);
                kmapoff_kaddr = 0;
        }

        if (zone_gc_allowed &&
            (zone_gc_allowed_by_time_throttle ||
             zone_gc_forced ||
             force)) {
                if (zone_gc_allowed_by_time_throttle == TRUE) {
                        zone_gc_allowed_by_time_throttle = FALSE;
                        all_zones = TRUE;
                }
                zone_gc_forced = FALSE;

                zone_gc(all_zones);
        }
}

/*
 *      By default, don't attempt zone GC more frequently
 *      than once / 1 minutes.
 */
void
compute_zone_gc_throttle(void *arg __unused)
{
        zone_gc_allowed_by_time_throttle = TRUE;
}


#if CONFIG_TASK_ZONE_INFO

kern_return_t
task_zone_info(
        task_t                  task,
        mach_zone_name_array_t  *namesp,
        mach_msg_type_number_t  *namesCntp,
        task_zone_info_array_t  *infop,
        mach_msg_type_number_t  *infoCntp)
{
        mach_zone_name_t        *names;
        vm_offset_t             names_addr;
        vm_size_t               names_size;
        task_zone_info_t        *info;
        vm_offset_t             info_addr;
        vm_size_t               info_size;
        unsigned int            max_zones, i;
        zone_t                  z;
        mach_zone_name_t        *zn;
        task_zone_info_t        *zi;
        kern_return_t           kr;

        vm_size_t               used;
        vm_map_copy_t           copy;


        if (task == TASK_NULL)
                return KERN_INVALID_TASK;

        /*
         *      We assume that zones aren't freed once allocated.
         *      We won't pick up any zones that are allocated later.
         */

        simple_lock(&all_zones_lock);
        max_zones = (unsigned int)(num_zones + num_fake_zones);
        z = first_zone;
        simple_unlock(&all_zones_lock);

        names_size = round_page(max_zones * sizeof *names);
        kr = kmem_alloc_pageable(ipc_kernel_map,
                                 &names_addr, names_size);
        if (kr != KERN_SUCCESS)
                return kr;
        names = (mach_zone_name_t *) names_addr;

        info_size = round_page(max_zones * sizeof *info);
        kr = kmem_alloc_pageable(ipc_kernel_map,
                                 &info_addr, info_size);
        if (kr != KERN_SUCCESS) {
                kmem_free(ipc_kernel_map,
                          names_addr, names_size);
                return kr;
        }

        info = (task_zone_info_t *) info_addr;

        zn = &names[0];
        zi = &info[0];

        for (i = 0; i < max_zones - num_fake_zones; i++) {
                struct zone zcopy;

                assert(z != ZONE_NULL);

                lock_zone(z);
                zcopy = *z;
                unlock_zone(z);

                simple_lock(&all_zones_lock);
                z = z->next_zone;
                simple_unlock(&all_zones_lock);

                /* assuming here the name data is static */
                (void) strncpy(zn->mzn_name, zcopy.zone_name,
                               sizeof zn->mzn_name);
                zn->mzn_name[sizeof zn->mzn_name - 1] = '\0';

                zi->tzi_count = (uint64_t)zcopy.count;
                zi->tzi_cur_size = (uint64_t)zcopy.cur_size;
                zi->tzi_max_size = (uint64_t)zcopy.max_size;
                zi->tzi_elem_size = (uint64_t)zcopy.elem_size;
                zi->tzi_alloc_size = (uint64_t)zcopy.alloc_size;
                zi->tzi_sum_size = zcopy.sum_count * zcopy.elem_size;
                zi->tzi_exhaustible = (uint64_t)zcopy.exhaustible;
                zi->tzi_collectable = (uint64_t)zcopy.collectable;
                zi->tzi_caller_acct = (uint64_t)zcopy.caller_acct;
                if (task->tkm_zinfo != NULL) {
                        zi->tzi_task_alloc = task->tkm_zinfo[zcopy.index].alloc;
                        zi->tzi_task_free = task->tkm_zinfo[zcopy.index].free;
                } else {
                        zi->tzi_task_alloc = 0;
                        zi->tzi_task_free = 0;
                }
                zn++;
                zi++;
        }

        /*
         * loop through the fake zones and fill them using the specialized
         * functions
         */
        for (i = 0; i < num_fake_zones; i++) {
                int count, collectable, exhaustible, caller_acct, index;
                vm_size_t cur_size, max_size, elem_size, alloc_size;
                uint64_t sum_size;

                strncpy(zn->mzn_name, fake_zones[i].name, sizeof zn->mzn_name);
                zn->mzn_name[sizeof zn->mzn_name - 1] = '\0';
                fake_zones[i].query(&count, &cur_size,
                                    &max_size, &elem_size,
                                    &alloc_size, &sum_size,
                                    &collectable, &exhaustible, &caller_acct);
                zi->tzi_count = (uint64_t)count;
                zi->tzi_cur_size = (uint64_t)cur_size;
                zi->tzi_max_size = (uint64_t)max_size;
                zi->tzi_elem_size = (uint64_t)elem_size;
                zi->tzi_alloc_size = (uint64_t)alloc_size;
                zi->tzi_sum_size = sum_size;
                zi->tzi_collectable = (uint64_t)collectable;
                zi->tzi_exhaustible = (uint64_t)exhaustible;
                zi->tzi_caller_acct = (uint64_t)caller_acct;
                if (task->tkm_zinfo != NULL) {
                        index = ZINFO_SLOTS - num_fake_zones + i;
                        zi->tzi_task_alloc = task->tkm_zinfo[index].alloc;
                        zi->tzi_task_free = task->tkm_zinfo[index].free;
                } else {
                        zi->tzi_task_alloc = 0;
                        zi->tzi_task_free = 0;
                }
                zn++;
                zi++;
        }

        used = max_zones * sizeof *names;
        if (used != names_size)
                bzero((char *) (names_addr + used), names_size - used);

        kr = vm_map_copyin(ipc_kernel_map, (vm_map_address_t)names_addr,
                           (vm_map_size_t)names_size, TRUE, &copy);
        assert(kr == KERN_SUCCESS);

        *namesp = (mach_zone_name_t *) copy;
        *namesCntp = max_zones;

        used = max_zones * sizeof *info;

        if (used != info_size)
                bzero((char *) (info_addr + used), info_size - used);

        kr = vm_map_copyin(ipc_kernel_map, (vm_map_address_t)info_addr,
                           (vm_map_size_t)info_size, TRUE, &copy);
        assert(kr == KERN_SUCCESS);

        *infop = (task_zone_info_t *) copy;
        *infoCntp = max_zones;

        return KERN_SUCCESS;
}

#else   /* CONFIG_TASK_ZONE_INFO */

kern_return_t
task_zone_info(
        __unused task_t         task,
        __unused mach_zone_name_array_t *namesp,
        __unused mach_msg_type_number_t *namesCntp,
        __unused task_zone_info_array_t *infop,
        __unused mach_msg_type_number_t *infoCntp)
{
        return KERN_FAILURE;
}

#endif  /* CONFIG_TASK_ZONE_INFO */

kern_return_t
mach_zone_info(
        host_priv_t             host,
        mach_zone_name_array_t  *namesp,
        mach_msg_type_number_t  *namesCntp,
        mach_zone_info_array_t  *infop,
        mach_msg_type_number_t  *infoCntp)
{
        mach_zone_name_t        *names;
        vm_offset_t             names_addr;
        vm_size_t               names_size;
        mach_zone_info_t        *info;
        vm_offset_t             info_addr;
        vm_size_t               info_size;
        unsigned int            max_zones, i;
        zone_t                  z;
        mach_zone_name_t        *zn;
        mach_zone_info_t        *zi;
        kern_return_t           kr;
        
        vm_size_t               used;
        vm_map_copy_t           copy;


        if (host == HOST_NULL)
                return KERN_INVALID_HOST;
#if CONFIG_DEBUGGER_FOR_ZONE_INFO
        if (!PE_i_can_has_debugger(NULL))
                return KERN_INVALID_HOST;
#endif

        /*
         *      We assume that zones aren't freed once allocated.
         *      We won't pick up any zones that are allocated later.
         */

        simple_lock(&all_zones_lock);
        max_zones = (unsigned int)(num_zones + num_fake_zones);
        z = first_zone;
        simple_unlock(&all_zones_lock);

        names_size = round_page(max_zones * sizeof *names);
        kr = kmem_alloc_pageable(ipc_kernel_map,
                                 &names_addr, names_size);
        if (kr != KERN_SUCCESS)
                return kr;
        names = (mach_zone_name_t *) names_addr;

        info_size = round_page(max_zones * sizeof *info);
        kr = kmem_alloc_pageable(ipc_kernel_map,
                                 &info_addr, info_size);
        if (kr != KERN_SUCCESS) {
                kmem_free(ipc_kernel_map,
                          names_addr, names_size);
                return kr;
        }

        info = (mach_zone_info_t *) info_addr;

        zn = &names[0];
        zi = &info[0];

        for (i = 0; i < max_zones - num_fake_zones; i++) {
                struct zone zcopy;

                assert(z != ZONE_NULL);

                lock_zone(z);
                zcopy = *z;
                unlock_zone(z);

                simple_lock(&all_zones_lock);
                z = z->next_zone;
                simple_unlock(&all_zones_lock);

                /* assuming here the name data is static */
                (void) strncpy(zn->mzn_name, zcopy.zone_name,
                               sizeof zn->mzn_name);
                zn->mzn_name[sizeof zn->mzn_name - 1] = '\0';

                zi->mzi_count = (uint64_t)zcopy.count;
                zi->mzi_cur_size = (uint64_t)zcopy.cur_size;
                zi->mzi_max_size = (uint64_t)zcopy.max_size;
                zi->mzi_elem_size = (uint64_t)zcopy.elem_size;
                zi->mzi_alloc_size = (uint64_t)zcopy.alloc_size;
                zi->mzi_sum_size = zcopy.sum_count * zcopy.elem_size;
                zi->mzi_exhaustible = (uint64_t)zcopy.exhaustible;
                zi->mzi_collectable = (uint64_t)zcopy.collectable;
                zn++;
                zi++;
        }

        /*
         * loop through the fake zones and fill them using the specialized
         * functions
         */
        for (i = 0; i < num_fake_zones; i++) {
                int count, collectable, exhaustible, caller_acct;
                vm_size_t cur_size, max_size, elem_size, alloc_size;
                uint64_t sum_size;

                strncpy(zn->mzn_name, fake_zones[i].name, sizeof zn->mzn_name);
                zn->mzn_name[sizeof zn->mzn_name - 1] = '\0';
                fake_zones[i].query(&count, &cur_size,
                                    &max_size, &elem_size,
                                    &alloc_size, &sum_size,
                                    &collectable, &exhaustible, &caller_acct);
                zi->mzi_count = (uint64_t)count;
                zi->mzi_cur_size = (uint64_t)cur_size;
                zi->mzi_max_size = (uint64_t)max_size;
                zi->mzi_elem_size = (uint64_t)elem_size;
                zi->mzi_alloc_size = (uint64_t)alloc_size;
                zi->mzi_sum_size = sum_size;
                zi->mzi_collectable = (uint64_t)collectable;
                zi->mzi_exhaustible = (uint64_t)exhaustible;

                zn++;
                zi++;
        }

        used = max_zones * sizeof *names;
        if (used != names_size)
                bzero((char *) (names_addr + used), names_size - used);

        kr = vm_map_copyin(ipc_kernel_map, (vm_map_address_t)names_addr,
                           (vm_map_size_t)names_size, TRUE, &copy);
        assert(kr == KERN_SUCCESS);

        *namesp = (mach_zone_name_t *) copy;
        *namesCntp = max_zones;

        used = max_zones * sizeof *info;

        if (used != info_size)
                bzero((char *) (info_addr + used), info_size - used);

        kr = vm_map_copyin(ipc_kernel_map, (vm_map_address_t)info_addr,
                           (vm_map_size_t)info_size, TRUE, &copy);
        assert(kr == KERN_SUCCESS);

        *infop = (mach_zone_info_t *) copy;
        *infoCntp = max_zones;

        return KERN_SUCCESS;
}

/*
 * host_zone_info - LEGACY user interface for Mach zone information
 *                  Should use mach_zone_info() instead!
 */
kern_return_t
host_zone_info(
        host_priv_t             host,
        zone_name_array_t       *namesp,
        mach_msg_type_number_t  *namesCntp,
        zone_info_array_t       *infop,
        mach_msg_type_number_t  *infoCntp)
{
        zone_name_t     *names;
        vm_offset_t     names_addr;
        vm_size_t       names_size;
        zone_info_t     *info;
        vm_offset_t     info_addr;
        vm_size_t       info_size;
        unsigned int    max_zones, i;
        zone_t          z;
        zone_name_t    *zn;
        zone_info_t    *zi;
        kern_return_t   kr;

        vm_size_t       used;
        vm_map_copy_t   copy;


        if (host == HOST_NULL)
                return KERN_INVALID_HOST;
#if CONFIG_DEBUGGER_FOR_ZONE_INFO
        if (!PE_i_can_has_debugger(NULL))
                return KERN_INVALID_HOST;
#endif

#if defined(__LP64__)
        if (!thread_is_64bit(current_thread()))
                return KERN_NOT_SUPPORTED;
#else
        if (thread_is_64bit(current_thread()))
                return KERN_NOT_SUPPORTED;
#endif

        /*
         *      We assume that zones aren't freed once allocated.
         *      We won't pick up any zones that are allocated later.
         */

        simple_lock(&all_zones_lock);
        max_zones = (unsigned int)(num_zones + num_fake_zones);
        z = first_zone;
        simple_unlock(&all_zones_lock);

        names_size = round_page(max_zones * sizeof *names);
        kr = kmem_alloc_pageable(ipc_kernel_map,
                                 &names_addr, names_size);
        if (kr != KERN_SUCCESS)
                return kr;
        names = (zone_name_t *) names_addr;

        info_size = round_page(max_zones * sizeof *info);
        kr = kmem_alloc_pageable(ipc_kernel_map,
                                 &info_addr, info_size);
        if (kr != KERN_SUCCESS) {
                kmem_free(ipc_kernel_map,
                          names_addr, names_size);
                return kr;
        }

        info = (zone_info_t *) info_addr;

        zn = &names[0];
        zi = &info[0];

        for (i = 0; i < max_zones - num_fake_zones; i++) {
                struct zone zcopy;

                assert(z != ZONE_NULL);

                lock_zone(z);
                zcopy = *z;
                unlock_zone(z);

                simple_lock(&all_zones_lock);
                z = z->next_zone;
                simple_unlock(&all_zones_lock);

                /* assuming here the name data is static */
                (void) strncpy(zn->zn_name, zcopy.zone_name,
                               sizeof zn->zn_name);
                zn->zn_name[sizeof zn->zn_name - 1] = '\0';

                zi->zi_count = zcopy.count;
                zi->zi_cur_size = zcopy.cur_size;
                zi->zi_max_size = zcopy.max_size;
                zi->zi_elem_size = zcopy.elem_size;
                zi->zi_alloc_size = zcopy.alloc_size;
                zi->zi_exhaustible = zcopy.exhaustible;
                zi->zi_collectable = zcopy.collectable;

                zn++;
                zi++;
        }

        /*
         * loop through the fake zones and fill them using the specialized
         * functions
         */
        for (i = 0; i < num_fake_zones; i++) {
                int caller_acct;
                uint64_t sum_space;
                strncpy(zn->zn_name, fake_zones[i].name, sizeof zn->zn_name);
                zn->zn_name[sizeof zn->zn_name - 1] = '\0';
                fake_zones[i].query(&zi->zi_count, &zi->zi_cur_size,
                                    &zi->zi_max_size, &zi->zi_elem_size,
                                    &zi->zi_alloc_size, &sum_space,
                                    &zi->zi_collectable, &zi->zi_exhaustible, &caller_acct);
                zn++;
                zi++;
        }

        used = max_zones * sizeof *names;
        if (used != names_size)
                bzero((char *) (names_addr + used), names_size - used);

        kr = vm_map_copyin(ipc_kernel_map, (vm_map_address_t)names_addr,
                           (vm_map_size_t)names_size, TRUE, &copy);
        assert(kr == KERN_SUCCESS);

        *namesp = (zone_name_t *) copy;
        *namesCntp = max_zones;

        used = max_zones * sizeof *info;
        if (used != info_size)
                bzero((char *) (info_addr + used), info_size - used);

        kr = vm_map_copyin(ipc_kernel_map, (vm_map_address_t)info_addr,
                           (vm_map_size_t)info_size, TRUE, &copy);
        assert(kr == KERN_SUCCESS);

        *infop = (zone_info_t *) copy;
        *infoCntp = max_zones;

        return KERN_SUCCESS;
}

kern_return_t
mach_zone_force_gc(
        host_t host)
{

        if (host == HOST_NULL)
                return KERN_INVALID_HOST;

        consider_zone_gc(TRUE);

        return (KERN_SUCCESS);
}

extern unsigned int stack_total;
extern unsigned long long stack_allocs;

#if defined(__i386__) || defined (__x86_64__)
extern unsigned int inuse_ptepages_count;
extern long long alloc_ptepages_count;
#endif

void zone_display_zprint()
{
        unsigned int    i;
        zone_t          the_zone;

        if(first_zone!=NULL) {
                the_zone = first_zone;
                for (i = 0; i < num_zones; i++) {
                        if(the_zone->cur_size > (1024*1024)) {
                                printf("%.20s:\t%lu\n",the_zone->zone_name,(uintptr_t)the_zone->cur_size);
                        }

                        if(the_zone->next_zone == NULL) {
                                break;
                        }

                        the_zone = the_zone->next_zone;
                }
        }

        printf("Kernel Stacks:\t%lu\n",(uintptr_t)(kernel_stack_size * stack_total));

#if defined(__i386__) || defined (__x86_64__)
        printf("PageTables:\t%lu\n",(uintptr_t)(PAGE_SIZE * inuse_ptepages_count));
#endif

        printf("Kalloc.Large:\t%lu\n",(uintptr_t)kalloc_large_total);
}

zone_t
zone_find_largest(void)
{
        unsigned int    i;
        unsigned int    max_zones;
        zone_t          the_zone;
        zone_t          zone_largest;

        simple_lock(&all_zones_lock);
        the_zone = first_zone;
        max_zones = num_zones;
        simple_unlock(&all_zones_lock);
        
        zone_largest = the_zone;
        for (i = 0; i < max_zones; i++) {
                if (the_zone->cur_size > zone_largest->cur_size) {
                        zone_largest = the_zone;
                }

                if (the_zone->next_zone == NULL) {
                        break;
                }

                the_zone = the_zone->next_zone;
        }
        return zone_largest;
}

#if     ZONE_DEBUG

/* should we care about locks here ? */

#define zone_in_use(z)  ( z->count || z->free_elements \
                                                  || !queue_empty(&z->pages.all_free) \
                                                  || !queue_empty(&z->pages.intermediate) \
                                                  || (z->allows_foreign && !queue_empty(&z->pages.any_free_foreign)))

void
zone_debug_enable(
        zone_t          z)
{
        if (zone_debug_enabled(z) || zone_in_use(z) ||
            z->alloc_size < (z->elem_size + ZONE_DEBUG_OFFSET))
                return;
        queue_init(&z->active_zones);
        z->elem_size += ZONE_DEBUG_OFFSET;
}

void
zone_debug_disable(
        zone_t          z)
{
        if (!zone_debug_enabled(z) || zone_in_use(z))
                return;
        z->elem_size -= ZONE_DEBUG_OFFSET;
        z->active_zones.next = z->active_zones.prev = NULL;
}


#endif  /* ZONE_DEBUG */