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

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This 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 OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_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 <norma_vm.h>
#include <mach_kdb.h>
#include <kern/ast.h>
#include <kern/assert.h>
#include <kern/macro_help.h>
#include <kern/sched.h>
#include <kern/lock.h>
#include <kern/sched_prim.h>
#include <kern/misc_protos.h>
#include <kern/thread_call.h>
#include <kern/zalloc.h>
#include <mach/vm_param.h>
#include <vm/vm_kern.h>
#include <machine/machparam.h>


#if     MACH_ASSERT
/* Detect use of zone elt after freeing it by two methods:
 * (1) Range-check the free-list "next" ptr for sanity.
 * (2) Store the ptr in two different words, and compare them against
 *     each other when re-using the zone elt, to detect modifications;
 */

#if defined(__alpha)

#define is_kernel_data_addr(a)                                          \
                (!(a) || IS_SYS_VA(a) && !((a) & (sizeof(long)-1)))

#else /* !defined(__alpha) */

#define is_kernel_data_addr(a)                                          \
                (!(a) || (a) >= VM_MIN_KERNEL_ADDRESS && !((a) & 0x3))

#endif /* defined(__alpha) */

/* Should we set all words of the zone element to an illegal address
 * when it is freed, to help catch usage after freeing?  The down-side
 * is that this obscures the identity of the freed element.
 */
boolean_t zfree_clear = FALSE;

#define ADD_TO_ZONE(zone, element)                                      \
MACRO_BEGIN                                                             \
                if (zfree_clear)                                        \
                {   int i;                                              \
                    for (i=1;                                           \
                         i < zone->elem_size/sizeof(vm_offset_t) - 1;   \
                         i++)                                           \
                    ((vm_offset_t *)(element))[i] = 0xdeadbeef;         \
                }                                                       \
                ((vm_offset_t *)(element))[0] = (zone)->free_elements;  \
                (zone)->free_elements = (vm_offset_t) (element);        \
                (zone)->count--;                                        \
MACRO_END

#define REMOVE_FROM_ZONE(zone, ret, type)                               \
MACRO_BEGIN                                                             \
        (ret) = (type) (zone)->free_elements;                           \
        if ((ret) != (type) 0) {                                        \
            if (!is_kernel_data_addr(((vm_offset_t *)(ret))[0])) {      \
                panic("A freed zone element has been modified.\n");     \
            }                                                           \
            (zone)->count++;                                            \
            (zone)->free_elements = *((vm_offset_t *)(ret));            \
        }                                                               \
MACRO_END
#else   /* MACH_ASSERT */

#define ADD_TO_ZONE(zone, element)                                      \
MACRO_BEGIN                                                             \
                *((vm_offset_t *)(element)) = (zone)->free_elements;    \
                (zone)->free_elements = (vm_offset_t) (element);        \
                (zone)->count--;                                        \
MACRO_END

#define REMOVE_FROM_ZONE(zone, ret, type)                               \
MACRO_BEGIN                                                             \
        (ret) = (type) (zone)->free_elements;                           \
        if ((ret) != (type) 0) {                                        \
                (zone)->count++;                                        \
                (zone)->free_elements = *((vm_offset_t *)(ret));        \
        }                                                               \
MACRO_END

#endif  /* MACH_ASSERT */

#if     ZONE_DEBUG
#define zone_debug_enabled(z) z->active_zones.next
#endif  /* ZONE_DEBUG */

/*
 * Support for garbage collection of unused zone pages:
 */

struct zone_page_table_entry {
        struct  zone_page_table_entry   *next;
        short   in_free_list;
        short   alloc_count;
};

extern struct zone_page_table_entry * zone_page_table;

#define lock_zone_page_table() simple_lock(&zone_page_table_lock)
#define unlock_zone_page_table() simple_unlock(&zone_page_table_lock)

#define zone_page(addr) \
    (&(zone_page_table[(atop(((vm_offset_t)addr) - zone_map_min_address))]))

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

void            zone_page_alloc(
                                vm_offset_t     addr,
                                vm_size_t       size);

void            zone_add_free_page_list(
                                struct zone_page_table_entry    **free_list,
                                vm_offset_t     addr,
                                vm_size_t       size);
void            zone_page_dealloc(
                                vm_offset_t     addr,
                                vm_size_t       size);

void            zone_page_in_use(
                                vm_offset_t     addr,
                                vm_size_t       size);

void            zone_page_free(
                                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            zalloc_async(
                                thread_call_param_t     p0,  
                                thread_call_param_t     p1);


#if     ZONE_DEBUG && MACH_KDB
int             zone_count(
                                zone_t          z,
                                int             tail);
#endif  /* ZONE_DEBUG && MACH_KDB */

vm_map_t        zone_map = VM_MAP_NULL;

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

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

vm_offset_t     zdata;
vm_size_t       zdata_size;

#define lock_zone(zone)                                 \
MACRO_BEGIN                                             \
        simple_lock(&zone->lock);                       \
MACRO_END

#define unlock_zone(zone)                               \
MACRO_BEGIN                                             \
        simple_unlock(&zone->lock);                     \
MACRO_END

#define lock_zone_init(zone)                            \
MACRO_BEGIN                                             \
        simple_lock_init(&zone->lock, ETAP_MISC_ZONE);  \
MACRO_END

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

kern_return_t           zget_space(
                                vm_offset_t size,
                                vm_offset_t *result);

decl_simple_lock_data(,zget_space_lock)
vm_offset_t     zalloc_next_space;
vm_offset_t     zalloc_end_of_space;
vm_size_t       zalloc_wasted_space;

/*
 *      Garbage collection map information
 */
decl_simple_lock_data(,         zone_page_table_lock)
struct zone_page_table_entry *  zone_page_table;
vm_offset_t                     zone_map_min_address;
vm_offset_t                     zone_map_max_address;
integer_t                       zone_pages;

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

#define from_zone_map(addr) \
        ((vm_offset_t)(addr) >= zone_map_min_address && \
         (vm_offset_t)(addr) <  zone_map_max_address)

#define ZONE_PAGE_USED  0
#define ZONE_PAGE_UNUSED -1


/*
 *      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;
int                     num_zones;

boolean_t zone_gc_allowed = TRUE;
boolean_t zone_gc_forced = FALSE;
unsigned zone_gc_last_tick = 0;
unsigned zone_gc_max_rate = 0;          /* in ticks */


/*
 *      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 */
        char            *name)          /* a name for the zone */
{
        zone_t          z;

        if (zone_zone == ZONE_NULL) {
                if (zget_space(sizeof(struct zone), (vm_offset_t *)&z)
                    != KERN_SUCCESS)
                        return(ZONE_NULL);
        } else
                z = (zone_t) zalloc(zone_zone);
        if (z == ZONE_NULL)
                return(ZONE_NULL);

        /*
         *      Round off all the parameters appropriately.
         */
        if (size < sizeof(z->free_elements))
                size = sizeof(z->free_elements);
        size = ((size-1)  + sizeof(z->free_elements)) -
                ((size-1) % sizeof(z->free_elements));
        if (alloc == 0)
                alloc = PAGE_SIZE;
        alloc = round_page(alloc);
        max   = round_page(max);
        /*
         * 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
         */
        {       vm_size_t best, waste; unsigned int i;
                best  = PAGE_SIZE;
                waste = best % size;
                for (i = 2; i <= 5; i++){       vm_size_t tsize, twaste;
                        tsize  = i * PAGE_SIZE;
                        twaste = tsize % size;
                        if (twaste < waste)
                                best = tsize, waste = twaste;
                }
                if (alloc <= best || (alloc % size >= waste))
                        alloc = best;
        }
        if (max && (max < alloc))
                max = alloc;

        z->free_elements = 0;
        z->cur_size = 0;
        z->max_size = max;
        z->elem_size = size;
        z->alloc_size = alloc;
        z->zone_name = name;
        z->count = 0;
        z->doing_alloc = FALSE;
        z->exhaustible = FALSE;
        z->collectable = TRUE;
        z->allows_foreign = FALSE;
        z->expandable  = TRUE;
        z->waiting = FALSE;
        z->async_pending = FALSE;

#if     ZONE_DEBUG
        z->active_zones.next = z->active_zones.prev = 0;        
        zone_debug_enable(z);
#endif  /* ZONE_DEBUG */
        lock_zone_init(z);

        /*
         *      Add the zone to the all-zones list.
         */

        z->next_zone = ZONE_NULL;
        thread_call_setup(&z->call_async_alloc, zalloc_async, z);
        simple_lock(&all_zones_lock);
        *last_zone = z;
        last_zone = &z->next_zone;
        num_zones++;
        simple_unlock(&all_zones_lock);

        return(z);
}

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

        /* Basic sanity checks */
        assert(zone != ZONE_NULL && newmem != (vm_offset_t)0);
        assert(!zone->collectable || zone->allows_foreign
                || (from_zone_map(newmem) && from_zone_map(newmem+size-1)));

        elem_size = zone->elem_size;

        lock_zone(zone);
        while (size >= elem_size) {
                ADD_TO_ZONE(zone, newmem);
                if (from_zone_map(newmem))
                        zone_page_alloc(newmem, elem_size);
                zone->count++;  /* compensate for ADD_TO_ZONE */
                size -= elem_size;
                newmem += elem_size;
                zone->cur_size += elem_size;
        }
        unlock_zone(zone);
}

/*
 * Contiguous space allocator for non-paged zones. Allocates "size" amount
 * of memory from zone_map.
 */

kern_return_t
zget_space(
        vm_offset_t size,
        vm_offset_t *result)
{
        vm_offset_t     new_space = 0;
        vm_size_t       space_to_add;

        simple_lock(&zget_space_lock);
        while ((zalloc_next_space + size) > zalloc_end_of_space) {
                /*
                 *      Add at least one page to allocation area.
                 */

                space_to_add = round_page(size);

                if (new_space == 0) {
                        kern_return_t retval;
                        /*
                         *      Memory cannot be wired down while holding
                         *      any locks that the pageout daemon might
                         *      need to free up pages.  [Making the zget_space
                         *      lock a complex lock does not help in this
                         *      regard.]
                         *
                         *      Unlock and allocate memory.  Because several
                         *      threads might try to do this at once, don't
                         *      use the memory before checking for available
                         *      space again.
                         */

                        simple_unlock(&zget_space_lock);

                        retval = kernel_memory_allocate(zone_map, &new_space,
                                space_to_add, 0, KMA_KOBJECT|KMA_NOPAGEWAIT);
                        if (retval != KERN_SUCCESS)
                                return(retval);
                        zone_page_init(new_space, space_to_add,
                                                        ZONE_PAGE_USED);
                        simple_lock(&zget_space_lock);
                        continue;
                }

                
                /*
                 *      Memory was allocated in a previous iteration.
                 *
                 *      Check whether the new region is contiguous
                 *      with the old one.
                 */

                if (new_space != zalloc_end_of_space) {
                        /*
                         *      Throw away the remainder of the
                         *      old space, and start a new one.
                         */
                        zalloc_wasted_space +=
                                zalloc_end_of_space - zalloc_next_space;
                        zalloc_next_space = new_space;
                }

                zalloc_end_of_space = new_space + space_to_add;

                new_space = 0;
        }
        *result = zalloc_next_space;
        zalloc_next_space += size;              
        simple_unlock(&zget_space_lock);

        if (new_space != 0)
                kmem_free(zone_map, new_space, space_to_add);

        return(KERN_SUCCESS);
}


/*
 *      Steal memory for the zone package.  Called from
 *      vm_page_bootstrap().
 */
void
zone_steal_memory(void)
{
        zdata_size = round_page(128*sizeof(struct zone));
        zdata = pmap_steal_memory(zdata_size);
}


/*
 * Fill a zone with enough memory to contain at least nelem elements.
 * Memory is obtained with kmem_alloc_wired 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_wired(kernel_map, &memory, size);
        if (kr != KERN_SUCCESS)
                return 0;

        zone_change(zone, Z_FOREIGN, TRUE);
        zcram(zone, memory, size);
        nalloc = 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)
{
        vm_size_t zone_zone_size;
        vm_offset_t zone_zone_space;

        simple_lock_init(&all_zones_lock, ETAP_MISC_ZONE_ALL);

        first_zone = ZONE_NULL;
        last_zone = &first_zone;
        num_zones = 0;

        simple_lock_init(&zget_space_lock, ETAP_MISC_ZONE_GET);
        zalloc_next_space = zdata;
        zalloc_end_of_space = zdata + zdata_size;
        zalloc_wasted_space = 0;

        /* assertion: nobody else called zinit before us */
        assert(zone_zone == ZONE_NULL);
        zone_zone = zinit(sizeof(struct zone), 128 * sizeof(struct zone),
                          sizeof(struct zone), "zones");
        zone_change(zone_zone, Z_COLLECT, FALSE);
        zone_zone_size = zalloc_end_of_space - zalloc_next_space;
        zget_space(zone_zone_size, &zone_zone_space);
        zcram(zone_zone, zone_zone_space, zone_zone_size);
}

void
zone_init(
        vm_size_t max_zonemap_size)
{
        kern_return_t   retval;
        vm_offset_t     zone_min;
        vm_offset_t     zone_max;
        vm_size_t       zone_table_size;

        retval = kmem_suballoc(kernel_map, &zone_min, max_zonemap_size,
                                                FALSE, TRUE, &zone_map);
        if (retval != KERN_SUCCESS)
                panic("zone_init: kmem_suballoc failed");
        zone_max = zone_min + round_page(max_zonemap_size);
        /*
         * Setup garbage collection information:
         */
        zone_table_size = atop(zone_max - zone_min) * 
                                sizeof(struct zone_page_table_entry);
        if (kmem_alloc_wired(zone_map, (vm_offset_t *) &zone_page_table,
                             zone_table_size) != KERN_SUCCESS)
                panic("zone_init");
        zone_min = (vm_offset_t)zone_page_table + round_page(zone_table_size);
        zone_pages = atop(zone_max - zone_min);
        zone_map_min_address = zone_min;
        zone_map_max_address = zone_max;
        simple_lock_init(&zone_page_table_lock, ETAP_MISC_ZONE_PTABLE);
        mutex_init(&zone_gc_lock, ETAP_NO_TRACE);
        zone_page_init(zone_min, zone_max - zone_min, ZONE_PAGE_UNUSED);
}


/*
 *      zalloc returns an element from the specified zone.
 */
vm_offset_t
zalloc_canblock(
        register zone_t zone,
        boolean_t canblock)
{
        vm_offset_t     addr;
        kern_return_t retval;

        assert(zone != ZONE_NULL);
        check_simple_locks();

        lock_zone(zone);

        REMOVE_FROM_ZONE(zone, addr, vm_offset_t);

        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.
                         */
                        assert_wait((event_t)zone, THREAD_UNINT);
                        zone->waiting = TRUE;
                        unlock_zone(zone);
                        thread_block((void (*)(void)) 0);
                        lock_zone(zone);
                }
                else {
                        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("zalloc: zone \"%s\" empty.", zone->zone_name);
                                }
                        }
                        zone->doing_alloc = TRUE;
                        unlock_zone(zone);

                        if (zone->collectable) {
                                vm_offset_t space;
                                vm_size_t alloc_size;

                                if (vm_pool_low())
                                        alloc_size = 
                                          round_page(zone->elem_size);
                                else
                                        alloc_size = zone->alloc_size;

                                retval = kernel_memory_allocate(zone_map,
                                        &space, alloc_size, 0,
                                        KMA_KOBJECT|KMA_NOPAGEWAIT);
                                if (retval == KERN_SUCCESS) {
                                        zone_page_init(space, alloc_size,
                                                ZONE_PAGE_USED);
                                        zcram(zone, space, alloc_size);
                                } else if (retval != KERN_RESOURCE_SHORTAGE) {
                                        /* would like to cause a zone_gc() */

                                        panic("zalloc");
                                }
                                lock_zone(zone);
                                zone->doing_alloc = FALSE; 
                                if (zone->waiting) {
                                        zone->waiting = FALSE;
                                        thread_wakeup((event_t)zone);
                                }
                                REMOVE_FROM_ZONE(zone, addr, vm_offset_t);
                                if (addr == 0 &&
                                        retval == KERN_RESOURCE_SHORTAGE) {
                                        unlock_zone(zone);
                                        
                                        VM_PAGE_WAIT();
                                        lock_zone(zone);
                                }
                        } else {
                                vm_offset_t space;
                                retval = zget_space(zone->elem_size, &space);

                                lock_zone(zone);
                                zone->doing_alloc = FALSE; 
                                if (zone->waiting) {
                                        zone->waiting = FALSE;
                                        thread_wakeup((event_t)zone);
                                }
                                if (retval == KERN_SUCCESS) {
                                        zone->count++;
                                        zone->cur_size += zone->elem_size;
#if     ZONE_DEBUG
                                        if (zone_debug_enabled(zone)) {
                                            enqueue_tail(&zone->active_zones, (queue_entry_t)space);
                                        }
#endif
                                        unlock_zone(zone);
                                        zone_page_alloc(space, zone->elem_size);
#if     ZONE_DEBUG
                                        if (zone_debug_enabled(zone))
                                                space += sizeof(queue_chain_t);
#endif
                                        return(space);
                                }
                                if (retval == KERN_RESOURCE_SHORTAGE) {
                                        unlock_zone(zone);
                                        
                                        VM_PAGE_WAIT();
                                        lock_zone(zone);
                                } else {
                                        panic("zalloc");
                                }
                        }
                }
                if (addr == 0)
                        REMOVE_FROM_ZONE(zone, addr, vm_offset_t);
        }

        if ((addr == 0) && !canblock && (zone->async_pending == FALSE) && (!vm_pool_low())) {
                zone->async_pending = TRUE;
                unlock_zone(zone);
                thread_call_enter(&zone->call_async_alloc);
                lock_zone(zone);
                REMOVE_FROM_ZONE(zone, addr, vm_offset_t);
        }

#if     ZONE_DEBUG
        if (addr && zone_debug_enabled(zone)) {
                enqueue_tail(&zone->active_zones, (queue_entry_t)addr);
                addr += sizeof(queue_chain_t);
        }
#endif

        unlock_zone(zone);

        return(addr);
}


vm_offset_t
zalloc(
       register zone_t zone)
{
  return( zalloc_canblock(zone, TRUE) );
}

vm_offset_t
zalloc_noblock(
               register zone_t zone)
{
  return( zalloc_canblock(zone, FALSE) );
}

void
zalloc_async(
        thread_call_param_t     p0,
        thread_call_param_t     p1)
{
        vm_offset_t     elt;

        elt = zalloc_canblock((zone_t)p0, TRUE);
        zfree((zone_t)p0, elt);
        lock_zone(((zone_t)p0));
        ((zone_t)p0)->async_pending = FALSE;
        unlock_zone(((zone_t)p0));
}


/*
 *      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).
 */
vm_offset_t
zget(
        register zone_t zone)
{
        register vm_offset_t    addr;

        assert( zone != ZONE_NULL );

        if (!lock_try_zone(zone))
            return ((vm_offset_t)0);

        REMOVE_FROM_ZONE(zone, addr, vm_offset_t);
#if     ZONE_DEBUG
        if (addr && zone_debug_enabled(zone)) {
                enqueue_tail(&zone->active_zones, (queue_entry_t)addr);
                addr += sizeof(queue_chain_t);
        }
#endif  /* ZONE_DEBUG */
        unlock_zone(zone);

        return(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 */
boolean_t zone_check = FALSE;

void
zfree(
        register zone_t zone,
        vm_offset_t     elem)
{

#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!");
        if (zone->collectable && !zone->allows_foreign &&
            (!from_zone_map(elem) || !from_zone_map(elem+zone->elem_size-1)))
                panic("zfree: non-allocated memory in collectable zone!");
#endif

        lock_zone(zone);
#if     ZONE_DEBUG
        if (zone_debug_enabled(zone)) {
                queue_t tmp_elem;

                elem -= sizeof(queue_chain_t);
                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(&zone->active_zones, (queue_t) elem);
        }
#endif  /* ZONE_DEBUG */
        if (zone_check) {
                vm_offset_t this;

                /* check the zone's consistency */

                for (this = zone->free_elements;
                     this != 0;
                     this = * (vm_offset_t *) this)
                        if (!pmap_kernel_va(this) || this == elem)
                                panic("zfree");
        }
        ADD_TO_ZONE(zone, elem);

        /*
         * 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);
}


/*      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_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;
#if MACH_ASSERT
                default:
                        panic("Zone_change: Wrong Item Type!");
                        /* break; */
#endif
        }
        lock_zone_init(zone);
}

/*
 * 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->cur_size/zone->elem_size - zone->count;
        unlock_zone(zone);

        assert(free_count >= 0);

        return(free_count);
}

/*
 *      zprealloc preallocates wired memory, exanding the specified
 *      zone to the specified size
 */
void
zprealloc(
        zone_t  zone,
        vm_size_t size)
{
        vm_offset_t addr;

        if (size != 0) {
                if (kmem_alloc_wired(zone_map, &addr, size) != KERN_SUCCESS)
                  panic("zprealloc");
                zone_page_init(addr, size, ZONE_PAGE_USED);
                zcram(zone, addr, size);
        }
}

/*
 *  Zone garbage collection subroutines
 *
 *  These routines have in common the modification of entries in the
 *  zone_page_table.  The latter contains one entry for every page
 *  in the zone_map.  
 *
 *  For each page table entry in the given range:
 *
 *      zone_page_collectable   - test if one (in_free_list == alloc_count)
 *      zone_page_keep          - reset in_free_list
 *      zone_page_in_use        - decrements in_free_list
 *      zone_page_free          - increments in_free_list
 *      zone_page_init          - initializes in_free_list and alloc_count
 *      zone_page_alloc         - increments alloc_count
 *      zone_page_dealloc       - decrements alloc_count
 *      zone_add_free_page_list - adds the page to the free list
 *   
 *  Two counts are maintained for each page, the in_free_list count and
 *  alloc_count.  The alloc_count is how many zone elements have been
 *  allocated from a page.  (Note that the page could contain elements
 *  that span page boundaries.  The count includes these elements so
 *  one element may be counted in two pages.) In_free_list is a count
 *  of how many zone elements are currently free.  If in_free_list is
 *  equal to alloc_count then the page is eligible for garbage
 *  collection.
 *
 *  Alloc_count and in_free_list are initialized to the correct values
 *  for a particular zone when a page is zcram'ed into a zone.  Subsequent
 *  gets and frees of zone elements will call zone_page_in_use and 
 *  zone_page_free which modify the in_free_list count.  When the zones
 *  garbage collector runs it will walk through a zones free element list,
 *  remove the elements that reside on collectable pages, and use 
 *  zone_add_free_page_list to create a list of pages to be collected.
 */
boolean_t
zone_page_collectable(
        vm_offset_t     addr,
        vm_size_t       size)
{
        natural_t i, j;

#if MACH_ASSERT
        if (!from_zone_map(addr) || !from_zone_map(addr+size-1))
                panic("zone_page_collectable");
#endif

        i = atop(addr-zone_map_min_address);
        j = atop((addr+size-1) - zone_map_min_address);
        lock_zone_page_table();
        for (; i <= j; i++) {
                if (zone_page_table[i].in_free_list ==
                    zone_page_table[i].alloc_count) {
                        unlock_zone_page_table();
                        return (TRUE);
                }
        }
        unlock_zone_page_table();
        return (FALSE);
}

void
zone_page_keep(
        vm_offset_t     addr,
        vm_size_t       size)
{
        natural_t i, j;

#if MACH_ASSERT
        if (!from_zone_map(addr) || !from_zone_map(addr+size-1))
                panic("zone_page_keep");
#endif

        i = atop(addr-zone_map_min_address);
        j = atop((addr+size-1) - zone_map_min_address);
        lock_zone_page_table();
        for (; i <= j; i++) {
                zone_page_table[i].in_free_list = 0;
        }
        unlock_zone_page_table();
}

void
zone_page_in_use(
        vm_offset_t     addr,
        vm_size_t       size)
{
        natural_t i, j;

#if MACH_ASSERT
        if (!from_zone_map(addr) || !from_zone_map(addr+size-1))
                panic("zone_page_in_use");
#endif

        i = atop(addr-zone_map_min_address);
        j = atop((addr+size-1) - zone_map_min_address);
        lock_zone_page_table();
        for (; i <= j; i++) {
                if (zone_page_table[i].in_free_list > 0)
                        zone_page_table[i].in_free_list--;
        }
        unlock_zone_page_table();
}

void
zone_page_free(
        vm_offset_t     addr,
        vm_size_t       size)
{
        natural_t i, j;

#if MACH_ASSERT
        if (!from_zone_map(addr) || !from_zone_map(addr+size-1))
                panic("zone_page_free");
#endif

        i = atop(addr-zone_map_min_address);
        j = atop((addr+size-1) - zone_map_min_address);
        lock_zone_page_table();
        for (; i <= j; i++) {
                assert(zone_page_table[i].in_free_list >= 0);
                zone_page_table[i].in_free_list++;
        }
        unlock_zone_page_table();
}

void
zone_page_init(
        vm_offset_t     addr,
        vm_size_t       size,
        int             value)
{
        natural_t i, j;

#if MACH_ASSERT
        if (!from_zone_map(addr) || !from_zone_map(addr+size-1))
                panic("zone_page_init");
#endif

        i = atop(addr-zone_map_min_address);
        j = atop((addr+size-1) - zone_map_min_address);
        lock_zone_page_table();
        for (; i <= j; i++) {
                zone_page_table[i].alloc_count = value;
                zone_page_table[i].in_free_list = 0;
        }
        unlock_zone_page_table();
}

void
zone_page_alloc(
        vm_offset_t     addr,
        vm_size_t       size)
{
        natural_t i, j;

#if MACH_ASSERT
        if (!from_zone_map(addr) || !from_zone_map(addr+size-1))
                panic("zone_page_alloc");
#endif

        i = atop(addr-zone_map_min_address);
        j = atop((addr+size-1) - zone_map_min_address);
        lock_zone_page_table();
        for (; i <= j; i++) {
                /* Set alloc_count to (ZONE_PAGE_USED + 1) if
                 * it was previously set to ZONE_PAGE_UNUSED.
                 */
                if (zone_page_table[i].alloc_count == ZONE_PAGE_UNUSED) {
                        zone_page_table[i].alloc_count = 1;
                } else {
                        zone_page_table[i].alloc_count++;
                }
        }
        unlock_zone_page_table();
}

void
zone_page_dealloc(
        vm_offset_t     addr,
        vm_size_t       size)
{
        natural_t i, j;

#if MACH_ASSERT
        if (!from_zone_map(addr) || !from_zone_map(addr+size-1))
                panic("zone_page_dealloc");
#endif

        i = atop(addr-zone_map_min_address);
        j = atop((addr+size-1) - zone_map_min_address);
        lock_zone_page_table();
        for (; i <= j; i++) {
                zone_page_table[i].alloc_count--;
        }
        unlock_zone_page_table();
}

void
zone_add_free_page_list(
        struct zone_page_table_entry    **free_list,
        vm_offset_t     addr,
        vm_size_t       size)
{
        natural_t i, j;

#if MACH_ASSERT
        if (!from_zone_map(addr) || !from_zone_map(addr+size-1))
                panic("zone_add_free_page_list");
#endif

        i = atop(addr-zone_map_min_address);
        j = atop((addr+size-1) - zone_map_min_address);
        lock_zone_page_table();
        for (; i <= j; i++) {
                if (zone_page_table[i].alloc_count == 0) {
                        zone_page_table[i].next = *free_list;
                        *free_list = &zone_page_table[i];
                        zone_page_table[i].alloc_count  = ZONE_PAGE_UNUSED;
                        zone_page_table[i].in_free_list = 0;
                }
        }
        unlock_zone_page_table();
}


/* This is used for walking through a zone's free element list.
 */
struct zone_free_entry {
        struct zone_free_entry * next;
};

int reclaim_page_count = 0;

/*      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(void)
{
        unsigned int    max_zones;
        zone_t          z;
        unsigned int    i;
        struct zone_page_table_entry    *freep;
        struct zone_page_table_entry    *zone_free_page_list;

        mutex_lock(&zone_gc_lock);

        /*
         * Note that this scheme of locking only to walk the zone list
         * assumes that zones are never freed (checked by zfree)
         */ 
        simple_lock(&all_zones_lock);
        max_zones = num_zones;
        z = first_zone;
        simple_unlock(&all_zones_lock);

#if MACH_ASSERT
        lock_zone_page_table();
        for (i = 0; i < zone_pages; i++)
                assert(zone_page_table[i].in_free_list == 0);
        unlock_zone_page_table();
#endif /* MACH_ASSERT */

        zone_free_page_list = (struct zone_page_table_entry *) 0;

        for (i = 0; i < max_zones; i++, z = z->next_zone) {
                struct zone_free_entry * prev;
                struct zone_free_entry * elt;
                struct zone_free_entry * end;

                assert(z != ZONE_NULL);

                if (!z->collectable)
                        continue;

                lock_zone(z);

                /*
                 * Do a quick feasability check before we scan the zone: 
                 * skip unless there is likelihood of getting 1+ pages back.
                 */
                if ((z->cur_size - z->count * z->elem_size) <= (2*PAGE_SIZE)){
                        unlock_zone(z);         
                        continue;
                }

                /* Count the free elements in each page.  This loop
                 * requires that all in_free_list entries are zero.
                 *
                 * Exit the loop early if we need to hurry up and drop
                 * the lock to allow preemption - but we must fully process
                 * all elements we looked at so far.
                 */
                elt = (struct zone_free_entry *)(z->free_elements);
                while (!ast_urgency() && (elt != (struct zone_free_entry *)0)) {
                        if (from_zone_map(elt))
                                zone_page_free((vm_offset_t)elt, z->elem_size);
                        elt = elt->next;
                }
                end = elt;

                /* Now determine which elements should be removed
                 * from the free list and, after all the elements
                 * on a page have been removed, add the element's
                 * page to a list of pages to be freed.
                 */
                prev = elt = (struct zone_free_entry *)(z->free_elements);
                while (elt != end) {
                        if (!from_zone_map(elt)) {
                                prev = elt;
                                elt = elt->next;
                                continue;
                        }
                        if (zone_page_collectable((vm_offset_t)elt,
                                                  z->elem_size)) {
                                z->cur_size -= z->elem_size;
                                zone_page_in_use((vm_offset_t)elt,
                                                 z->elem_size);
                                zone_page_dealloc((vm_offset_t)elt,
                                                  z->elem_size);
                                zone_add_free_page_list(&zone_free_page_list, 
                                                        (vm_offset_t)elt,
                                                        z->elem_size);
                                if (elt == prev) {
                                        elt = elt->next;
                                        z->free_elements =(vm_offset_t)elt;
                                        prev = elt;
                                } else {
                                        prev->next = elt->next;
                                        elt = elt->next;
                                }
                        } else {
                                /* This element is not eligible for collection
                                 * so clear in_free_list in preparation for a
                                 * subsequent garbage collection pass.
                                 */
                                zone_page_keep((vm_offset_t)elt, z->elem_size);
                                prev = elt;
                                elt = elt->next;
                        }
                } /* end while(elt != end) */

                unlock_zone(z);
        }

        for (freep = zone_free_page_list; freep != 0; freep = freep->next) {
                vm_offset_t     free_addr;

                free_addr = zone_map_min_address + 
                            PAGE_SIZE * (freep - zone_page_table);
                kmem_free(zone_map, free_addr, PAGE_SIZE);
                reclaim_page_count++;
        }
        mutex_unlock(&zone_gc_lock);
}

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

void
consider_zone_gc(void)
{
        /*
         *      By default, don't attempt zone GC more frequently
         *      than once a second.
         */

        if (zone_gc_max_rate == 0)
                zone_gc_max_rate = (1 << SCHED_TICK_SHIFT) + 1;

        if (zone_gc_allowed &&
            ((sched_tick > (zone_gc_last_tick + zone_gc_max_rate)) ||
             zone_gc_forced)) {
                zone_gc_forced = FALSE;
                zone_gc_last_tick = sched_tick;
                zone_gc();
        }
}

#include <mach/kern_return.h>
#include <mach/machine/vm_types.h>
#include <mach_debug/zone_info.h>
#include <kern/host.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>

#include <mach/mach_host_server.h>

kern_return_t
host_zone_info(
        host_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;

        if (host == HOST_NULL)
                return KERN_INVALID_HOST;

        /*
         *      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);
#ifdef ppc
        max_zones = num_zones + 4;
#else
        max_zones = num_zones + 2;
#endif
        z = first_zone;
        simple_unlock(&all_zones_lock);

        if (max_zones <= *namesCntp) {
                /* use in-line memory */

                names = *namesp;
        } else {
                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;
        }

        if (max_zones <= *infoCntp) {
                /* use in-line memory */

                info = *infop;
        } else {
                info_size = round_page(max_zones * sizeof *info);
                kr = kmem_alloc_pageable(ipc_kernel_map,
                                         &info_addr, info_size);
                if (kr != KERN_SUCCESS) {
                        if (names != *namesp)
                                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 < num_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);

                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++;
        }
        strcpy(zn->zn_name, "kernel_stacks");
        stack_fake_zone_info(&zi->zi_count, &zi->zi_cur_size, &zi->zi_max_size, &zi->zi_elem_size,
                             &zi->zi_alloc_size, &zi->zi_collectable, &zi->zi_exhaustible);
        zn++;
        zi++;
#ifdef ppc
        strcpy(zn->zn_name, "save_areas");
        save_fake_zone_info(&zi->zi_count, &zi->zi_cur_size, &zi->zi_max_size, &zi->zi_elem_size,
                            &zi->zi_alloc_size, &zi->zi_collectable, &zi->zi_exhaustible);
        zn++;
        zi++;

        strcpy(zn->zn_name, "pmap_mappings");
        mapping_fake_zone_info(&zi->zi_count, &zi->zi_cur_size, &zi->zi_max_size, &zi->zi_elem_size,
                               &zi->zi_alloc_size, &zi->zi_collectable, &zi->zi_exhaustible);
        zn++;
        zi++;
#endif
        strcpy(zn->zn_name, "kalloc.large");
        kalloc_fake_zone_info(&zi->zi_count, &zi->zi_cur_size, &zi->zi_max_size, &zi->zi_elem_size,
                               &zi->zi_alloc_size, &zi->zi_collectable, &zi->zi_exhaustible);

        if (names != *namesp) {
                vm_size_t used;
                vm_map_copy_t copy;

                used = max_zones * sizeof *names;

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

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

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

        if (info != *infop) {
                vm_size_t used;
                vm_map_copy_t copy;

                used = max_zones * sizeof *info;

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

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

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

        return KERN_SUCCESS;
}

#if     MACH_KDB
#include <ddb/db_command.h>
#include <ddb/db_output.h>
#include <kern/kern_print.h>

const char *zone_labels =
"ENTRY       COUNT   TOT_SZ   MAX_SZ ELT_SZ ALLOC_SZ NAME";

/* Forwards */
void    db_print_zone(
                zone_t          addr);

#if     ZONE_DEBUG
void    db_zone_check_active(
                zone_t          zone);
void    db_zone_print_active(
                zone_t          zone);
#endif  /* ZONE_DEBUG */
void    db_zone_print_free(
                zone_t          zone);
void
db_print_zone(
        zone_t          addr)
{
        struct zone zcopy;

        zcopy = *addr;

        db_printf("%8x %8x %8x %8x %6x %8x %s ",
                  addr, zcopy.count, zcopy.cur_size,
                  zcopy.max_size, zcopy.elem_size,
                  zcopy.alloc_size, zcopy.zone_name);
        if (zcopy.exhaustible)
                db_printf("H");
        if (zcopy.collectable)
                db_printf("C");
        if (zcopy.expandable)
                db_printf("X");
        db_printf("\n");
}

/*ARGSUSED*/
void
db_show_one_zone(
        db_expr_t       addr,
        int             have_addr,
        db_expr_t       count,
        char *          modif)
{
        struct zone *z = (zone_t)addr;

        if (z == ZONE_NULL || !have_addr){
                db_error("No Zone\n");
                /*NOTREACHED*/
        }

        db_printf("%s\n", zone_labels);
        db_print_zone(z);
}

/*ARGSUSED*/
void
db_show_all_zones(
        db_expr_t       addr,
        int             have_addr,
        db_expr_t       count,
        char *          modif)
{
        zone_t          z;
        unsigned total = 0;

        /*
         * Don't risk hanging by unconditionally locking,
         * risk of incoherent data is small (zones aren't freed).
         */
        have_addr = simple_lock_try(&all_zones_lock);
        count = num_zones;
        z = first_zone;
        if (have_addr) {
                simple_unlock(&all_zones_lock);
        }

        db_printf("%s\n", zone_labels);
        for (  ; count > 0; count--) {
                if (!z) {
                        db_error("Mangled Zone List\n");
                        /*NOTREACHED*/
                }
                db_print_zone(z);
                total += z->cur_size,

                have_addr = simple_lock_try(&all_zones_lock);
                z = z->next_zone;
                if (have_addr) {
                        simple_unlock(&all_zones_lock);
                }
        }
        db_printf("\nTotal              %8x", total);
        db_printf("\n\nzone_gc() has reclaimed %d pages\n",
                  reclaim_page_count);
}

#if     ZONE_DEBUG
void
db_zone_check_active(
        zone_t  zone)
{
        int count = 0;
        queue_t tmp_elem;

        if (!zone_debug_enabled(zone) || !zone_check)
                return;
        tmp_elem = queue_first(&zone->active_zones);
        while (count < zone->count) {
                count++;
                if (tmp_elem == 0) {
                        printf("unexpected zero element, zone=0x%x, count=%d\n",
                                zone, count);
                        assert(FALSE);
                        break;
                }
                if (queue_end(tmp_elem, &zone->active_zones)) {
                        printf("unexpected queue_end, zone=0x%x, count=%d\n",
                                zone, count);
                        assert(FALSE);
                        break;
                }
                tmp_elem = queue_next(tmp_elem);
        }
        if (!queue_end(tmp_elem, &zone->active_zones)) {
                printf("not at queue_end, zone=0x%x, tmp_elem=0x%x\n",
                        zone, tmp_elem);
                assert(FALSE);
        }
}

void
db_zone_print_active(
        zone_t  zone)
{
        int count = 0;
        queue_t tmp_elem;

        if (!zone_debug_enabled(zone)) {
                printf("zone 0x%x debug not enabled\n", zone);
                return;
        }
        if (!zone_check) {
                printf("zone_check FALSE\n");
                return;
        }

        printf("zone 0x%x, active elements %d\n", zone, zone->count);
        printf("active list:\n");
        tmp_elem = queue_first(&zone->active_zones);
        while (count < zone->count) {
                printf("  0x%x", tmp_elem);
                count++;
                if ((count % 6) == 0)
                        printf("\n");
                if (tmp_elem == 0) {
                        printf("\nunexpected zero element, count=%d\n", count);
                        break;
                }
                if (queue_end(tmp_elem, &zone->active_zones)) {
                        printf("\nunexpected queue_end, count=%d\n", count);
                        break;
                }
                tmp_elem = queue_next(tmp_elem);
        }
        if (!queue_end(tmp_elem, &zone->active_zones))
                printf("\nnot at queue_end, tmp_elem=0x%x\n", tmp_elem);
        else
                printf("\n");
}
#endif  /* ZONE_DEBUG */

void
db_zone_print_free(
        zone_t  zone)
{
        int count = 0;
        int freecount;
        vm_offset_t elem;

        freecount = zone_free_count(zone);
        printf("zone 0x%x, free elements %d\n", zone, freecount);
        printf("free list:\n");
        elem = zone->free_elements;
        while (count < freecount) {
                printf("  0x%x", elem);
                count++;
                if ((count % 6) == 0)
                        printf("\n");
                if (elem == 0) {
                        printf("\nunexpected zero element, count=%d\n", count);
                        break;
                }
                elem = *((vm_offset_t *)elem);
        }
        if (elem != 0)
                printf("\nnot at end of free list, elem=0x%x\n", elem);
        else
                printf("\n");
}

#endif /* MACH_KDB */


#if     ZONE_DEBUG

/* should we care about locks here ? */

#if     MACH_KDB
vm_offset_t
next_element(
        zone_t          z,
        vm_offset_t     elt)
{
        if (!zone_debug_enabled(z))
                return(0);
        elt -= sizeof(queue_chain_t);
        elt = (vm_offset_t) queue_next((queue_t) elt);
        if ((queue_t) elt == &z->active_zones)
                return(0);
        elt += sizeof(queue_chain_t);
        return(elt);
}

vm_offset_t
first_element(
        zone_t          z)
{
        vm_offset_t     elt;

        if (!zone_debug_enabled(z))
                return(0);
        if (queue_empty(&z->active_zones))
                return(0);
        elt = (vm_offset_t) queue_first(&z->active_zones);
        elt += sizeof(queue_chain_t);
        return(elt);
}

/*
 * Second arg controls how many zone elements are printed:
 *   0 => none
 *   n, n < 0 => all
 *   n, n > 0 => last n on active list
 */
int
zone_count(
        zone_t          z,
        int             tail)
{
        vm_offset_t     elt;
        int             count = 0;
        boolean_t       print = (tail != 0);

        if (tail < 0)
                tail = z->count;
        if (z->count < tail)
                tail = 0;
        tail = z->count - tail;
        for (elt = first_element(z); elt; elt = next_element(z, elt)) {
                if (print && tail <= count)
                        db_printf("%8x\n", elt);
                count++;
        }
        assert(count == z->count);
        return(count);
}
#endif /* MACH_KDB */

#define zone_in_use(z)  ( z->count || z->free_elements )

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

void
zone_debug_disable(
        zone_t          z)
{
        if (!zone_debug_enabled(z) || zone_in_use(z))
                return;
        z->elem_size -= sizeof(queue_chain_t);
        z->active_zones.next = z->active_zones.prev = 0;        
}
#endif  /* ZONE_DEBUG */