path: root/kern/slab.c

/*
 * Copyright (c) 2011 Free Software Foundation.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

/*
 * Copyright (c) 2010, 2011 Richard Braun.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 *
 * Object caching and general purpose memory allocator.
 *
 * This allocator is based on the paper "The Slab Allocator: An Object-Caching
 * Kernel Memory Allocator" by Jeff Bonwick.
 *
 * It allows the allocation of objects (i.e. fixed-size typed buffers) from
 * caches and is efficient in both space and time. This implementation follows
 * many of the indications from the paper mentioned. The most notable
 * differences are outlined below.
 *
 * The per-cache self-scaling hash table for buffer-to-bufctl conversion,
 * described in 3.2.3 "Slab Layout for Large Objects", has been replaced by
 * a red-black tree storing slabs, sorted by address. The use of a
 * self-balancing tree for buffer-to-slab conversions provides a few advantages
 * over a hash table. Unlike a hash table, a BST provides a "lookup nearest"
 * operation, so obtaining the slab data (whether it is embedded in the slab or
 * off slab) from a buffer address simply consists of a "lookup nearest towards
 * 0" tree search. Storing slabs instead of buffers also considerably reduces
 * the number of elements to retain. Finally, a self-balancing tree is a true
 * self-scaling data structure, whereas a hash table requires periodic
 * maintenance and complete resizing, which is expensive. The only drawback is
 * that releasing a buffer to the slab layer takes logarithmic time instead of
 * constant time. But as the data set size is kept reasonable (because slabs
 * are stored instead of buffers) and because the CPU pool layer services most
 * requests, avoiding many accesses to the slab layer, it is considered an
 * acceptable tradeoff.
 *
 * This implementation uses per-cpu pools of objects, which service most
 * allocation requests. These pools act as caches (but are named differently
 * to avoid confusion with CPU caches) that reduce contention on multiprocessor
 * systems. When a pool is empty and cannot provide an object, it is filled by
 * transferring multiple objects from the slab layer. The symmetric case is
 * handled likewise.
 */

#include <string.h>
#include <kern/assert.h>
#include <kern/mach_clock.h>
#include <kern/macros.h>
#include <kern/printf.h>
#include <kern/slab.h>
#include <kern/kalloc.h>
#include <kern/cpu_number.h>
#include <mach/vm_param.h>
#include <mach/machine/vm_types.h>
#include <vm/vm_kern.h>
#include <vm/vm_types.h>
#include <sys/types.h>

#ifdef MACH_DEBUG
#include <mach_debug/slab_info.h>
#endif

/*
 * Utility macros.
 */
#define P2ALIGNED(x, a) (((x) & ((a) - 1)) == 0)
#define ISP2(x)         P2ALIGNED(x, x)
#define P2ALIGN(x, a)   ((x) & -(a))
#define P2ROUND(x, a)   (-(-(x) & -(a)))
#define P2END(x, a)     (-(~(x) & -(a)))
#define likely(expr)    __builtin_expect(!!(expr), 1)
#define unlikely(expr)  __builtin_expect(!!(expr), 0)

/*
 * Minimum required alignment.
 */
#define KMEM_ALIGN_MIN 8

/*
 * Minimum number of buffers per slab.
 *
 * This value is ignored when the slab size exceeds a threshold.
 */
#define KMEM_MIN_BUFS_PER_SLAB 8

/*
 * Special slab size beyond which the minimum number of buffers per slab is
 * ignored when computing the slab size of a cache.
 */
#define KMEM_SLAB_SIZE_THRESHOLD (8 * PAGE_SIZE)

/*
 * Special buffer size under which slab data is unconditionnally allocated
 * from its associated slab.
 */
#define KMEM_BUF_SIZE_THRESHOLD (PAGE_SIZE / 8)

/*
 * Time (in ticks) between two garbage collection operations.
 */
#define KMEM_GC_INTERVAL (5 * hz)

/*
 * The transfer size of a CPU pool is computed by dividing the pool size by
 * this value.
 */
#define KMEM_CPU_POOL_TRANSFER_RATIO 2

/*
 * Redzone guard word.
 */
#ifdef __LP64__
#if _HOST_BIG_ENDIAN
#define KMEM_REDZONE_WORD 0xfeedfacefeedfaceUL
#else /* _HOST_BIG_ENDIAN */
#define KMEM_REDZONE_WORD 0xcefaedfecefaedfeUL
#endif /* _HOST_BIG_ENDIAN */
#else /* __LP64__ */
#if _HOST_BIG_ENDIAN
#define KMEM_REDZONE_WORD 0xfeedfaceUL
#else /* _HOST_BIG_ENDIAN */
#define KMEM_REDZONE_WORD 0xcefaedfeUL
#endif /* _HOST_BIG_ENDIAN */
#endif /* __LP64__ */

/*
 * Redzone byte for padding.
 */
#define KMEM_REDZONE_BYTE 0xbb

/*
 * Size of the VM submap from which default backend functions allocate.
 */
#define KMEM_MAP_SIZE (96 * 1024 * 1024)

/*
 * Shift for the first kalloc cache size.
 */
#define KALLOC_FIRST_SHIFT 5

/*
 * Number of caches backing general purpose allocations.
 */
#define KALLOC_NR_CACHES 13

/*
 * Values the buftag state member can take.
 */
#ifdef __LP64__
#if _HOST_BIG_ENDIAN
#define KMEM_BUFTAG_ALLOC   0xa110c8eda110c8edUL
#define KMEM_BUFTAG_FREE    0xf4eeb10cf4eeb10cUL
#else /* _HOST_BIG_ENDIAN */
#define KMEM_BUFTAG_ALLOC   0xedc810a1edc810a1UL
#define KMEM_BUFTAG_FREE    0x0cb1eef40cb1eef4UL
#endif /* _HOST_BIG_ENDIAN */
#else /* __LP64__ */
#if _HOST_BIG_ENDIAN
#define KMEM_BUFTAG_ALLOC   0xa110c8edUL
#define KMEM_BUFTAG_FREE    0xf4eeb10cUL
#else /* _HOST_BIG_ENDIAN */
#define KMEM_BUFTAG_ALLOC   0xedc810a1UL
#define KMEM_BUFTAG_FREE    0x0cb1eef4UL
#endif /* _HOST_BIG_ENDIAN */
#endif /* __LP64__ */

/*
 * Free and uninitialized patterns.
 *
 * These values are unconditionnally 64-bit wide since buffers are at least
 * 8-byte aligned.
 */
#if _HOST_BIG_ENDIAN
#define KMEM_FREE_PATTERN   0xdeadbeefdeadbeefULL
#define KMEM_UNINIT_PATTERN 0xbaddcafebaddcafeULL
#else /* _HOST_BIG_ENDIAN */
#define KMEM_FREE_PATTERN   0xefbeaddeefbeaddeULL
#define KMEM_UNINIT_PATTERN 0xfecaddbafecaddbaULL
#endif /* _HOST_BIG_ENDIAN */

/*
 * Cache flags.
 *
 * The flags don't change once set and can be tested without locking.
 */
#define KMEM_CF_NO_CPU_POOL     0x01    /* CPU pool layer disabled */
#define KMEM_CF_SLAB_EXTERNAL   0x02    /* Slab data is off slab */
#define KMEM_CF_NO_RECLAIM      0x04    /* Slabs are not reclaimable */
#define KMEM_CF_VERIFY          0x08    /* Debugging facilities enabled */
#define KMEM_CF_DIRECT          0x10    /* No buf-to-slab tree lookup */

/*
 * Options for kmem_cache_alloc_verify().
 */
#define KMEM_AV_NOCONSTRUCT 0
#define KMEM_AV_CONSTRUCT   1

/*
 * Error codes for kmem_cache_error().
 */
#define KMEM_ERR_INVALID    0   /* Invalid address being freed */
#define KMEM_ERR_DOUBLEFREE 1   /* Freeing already free address */
#define KMEM_ERR_BUFTAG     2   /* Invalid buftag content */
#define KMEM_ERR_MODIFIED   3   /* Buffer modified while free */
#define KMEM_ERR_REDZONE    4   /* Redzone violation */

#if SLAB_USE_CPU_POOLS
/*
 * Available CPU pool types.
 *
 * For each entry, the CPU pool size applies from the entry buf_size
 * (excluded) up to (and including) the buf_size of the preceding entry.
 *
 * See struct kmem_cpu_pool_type for a description of the values.
 */
static struct kmem_cpu_pool_type kmem_cpu_pool_types[] = {
    {  32768,   1, 0,           NULL },
    {   4096,   8, CPU_L1_SIZE, NULL },
    {    256,  64, CPU_L1_SIZE, NULL },
    {      0, 128, CPU_L1_SIZE, NULL }
};

/*
 * Caches where CPU pool arrays are allocated from.
 */
static struct kmem_cache kmem_cpu_array_caches[ARRAY_SIZE(kmem_cpu_pool_types)];
#endif /* SLAB_USE_CPU_POOLS */

/*
 * Cache for off slab data.
 */
static struct kmem_cache kmem_slab_cache;

/*
 * General purpose caches array.
 */
static struct kmem_cache kalloc_caches[KALLOC_NR_CACHES];

/*
 * List of all caches managed by the allocator.
 */
static struct list kmem_cache_list;
static unsigned int kmem_nr_caches;
static simple_lock_data_t __attribute__((used)) kmem_cache_list_lock;

/*
 * VM submap for slab caches.
 */
static struct vm_map kmem_map_store;
vm_map_t kmem_map = &kmem_map_store;

/*
 * Time of the last memory reclaim, in clock ticks.
 */
static unsigned long kmem_gc_last_tick;

#define kmem_error(format, ...)                         \
    panic("mem: error: %s(): " format "\n", __func__,   \
          ## __VA_ARGS__)

#define kmem_warn(format, ...)                              \
    printf("mem: warning: %s(): " format "\n", __func__,    \
           ## __VA_ARGS__)

#define kmem_print(format, ...) \
    printf(format "\n", ## __VA_ARGS__)

static void kmem_cache_error(struct kmem_cache *cache, void *buf, int error,
                             void *arg);
static void * kmem_cache_alloc_from_slab(struct kmem_cache *cache);
static void kmem_cache_free_to_slab(struct kmem_cache *cache, void *buf);

static void * kmem_buf_verify_bytes(void *buf, void *pattern, size_t size)
{
    char *ptr, *pattern_ptr, *end;

    end = buf + size;

    for (ptr = buf, pattern_ptr = pattern; ptr < end; ptr++, pattern_ptr++)
        if (*ptr != *pattern_ptr)
            return ptr;

    return NULL;
}

static void * kmem_buf_verify(void *buf, uint64_t pattern, vm_size_t size)
{
    uint64_t *ptr, *end;

    assert(P2ALIGNED((unsigned long)buf, sizeof(uint64_t)));
    assert(P2ALIGNED(size, sizeof(uint64_t)));

    end = buf + size;

    for (ptr = buf; ptr < end; ptr++)
        if (*ptr != pattern)
            return kmem_buf_verify_bytes(ptr, &pattern, sizeof(pattern));

    return NULL;
}

static void kmem_buf_fill(void *buf, uint64_t pattern, size_t size)
{
    uint64_t *ptr, *end;

    assert(P2ALIGNED((unsigned long)buf, sizeof(uint64_t)));
    assert(P2ALIGNED(size, sizeof(uint64_t)));

    end = buf + size;

    for (ptr = buf; ptr < end; ptr++)
        *ptr = pattern;
}

static void * kmem_buf_verify_fill(void *buf, uint64_t old, uint64_t new,
                                   size_t size)
{
    uint64_t *ptr, *end;

    assert(P2ALIGNED((unsigned long)buf, sizeof(uint64_t)));
    assert(P2ALIGNED(size, sizeof(uint64_t)));

    end = buf + size;

    for (ptr = buf; ptr < end; ptr++) {
        if (*ptr != old)
            return kmem_buf_verify_bytes(ptr, &old, sizeof(old));

        *ptr = new;
    }

    return NULL;
}

static inline union kmem_bufctl *
kmem_buf_to_bufctl(void *buf, struct kmem_cache *cache)
{
    return (union kmem_bufctl *)(buf + cache->bufctl_dist);
}

static inline struct kmem_buftag *
kmem_buf_to_buftag(void *buf, struct kmem_cache *cache)
{
    return (struct kmem_buftag *)(buf + cache->buftag_dist);
}

static inline void * kmem_bufctl_to_buf(union kmem_bufctl *bufctl,
                                        struct kmem_cache *cache)
{
    return (void *)bufctl - cache->bufctl_dist;
}

static vm_offset_t kmem_pagealloc(vm_size_t size)
{
    vm_offset_t addr;
    kern_return_t kr;

    kr = kmem_alloc_wired(kmem_map, &addr, size);

    if (kr != KERN_SUCCESS)
        return 0;

    return addr;
}

static void kmem_pagefree(vm_offset_t ptr, vm_size_t size)
{
    kmem_free(kmem_map, ptr, size);
}

static void kmem_slab_create_verify(struct kmem_slab *slab,
                                    struct kmem_cache *cache)
{
    struct kmem_buftag *buftag;
    size_t buf_size;
    unsigned long buffers;
    void *buf;

    buf_size = cache->buf_size;
    buf = slab->addr;
    buftag = kmem_buf_to_buftag(buf, cache);

    for (buffers = cache->bufs_per_slab; buffers != 0; buffers--) {
        kmem_buf_fill(buf, KMEM_FREE_PATTERN, cache->bufctl_dist);
        buftag->state = KMEM_BUFTAG_FREE;
        buf += buf_size;
        buftag = kmem_buf_to_buftag(buf, cache);
    }
}

/*
 * Create an empty slab for a cache.
 *
 * The caller must drop all locks before calling this function.
 */
static struct kmem_slab * kmem_slab_create(struct kmem_cache *cache,
                                           size_t color)
{
    struct kmem_slab *slab;
    union kmem_bufctl *bufctl;
    size_t buf_size;
    unsigned long buffers;
    void *slab_buf;

    if (cache->slab_alloc_fn == NULL)
        slab_buf = (void *)kmem_pagealloc(cache->slab_size);
    else
        slab_buf = (void *)cache->slab_alloc_fn(cache->slab_size);

    if (slab_buf == NULL)
        return NULL;

    if (cache->flags & KMEM_CF_SLAB_EXTERNAL) {
        assert(!(cache->flags & KMEM_CF_NO_RECLAIM));
        slab = (struct kmem_slab *)kmem_cache_alloc(&kmem_slab_cache);

        if (slab == NULL) {
            if (cache->slab_free_fn == NULL)
                kmem_pagefree((vm_offset_t)slab_buf, cache->slab_size);
            else
                cache->slab_free_fn((vm_offset_t)slab_buf, cache->slab_size);

            return NULL;
        }
    } else {
        slab = (struct kmem_slab *)(slab_buf + cache->slab_size) - 1;
    }

    list_node_init(&slab->list_node);
    rbtree_node_init(&slab->tree_node);
    slab->nr_refs = 0;
    slab->first_free = NULL;
    slab->addr = slab_buf + color;

    buf_size = cache->buf_size;
    bufctl = kmem_buf_to_bufctl(slab->addr, cache);

    for (buffers = cache->bufs_per_slab; buffers != 0; buffers--) {
        bufctl->next = slab->first_free;
        slab->first_free = bufctl;
        bufctl = (union kmem_bufctl *)((void *)bufctl + buf_size);
    }

    if (cache->flags & KMEM_CF_VERIFY)
        kmem_slab_create_verify(slab, cache);

    return slab;
}

static void kmem_slab_destroy_verify(struct kmem_slab *slab,
                                     struct kmem_cache *cache)
{
    struct kmem_buftag *buftag;
    size_t buf_size;
    unsigned long buffers;
    void *buf, *addr;

    buf_size = cache->buf_size;
    buf = slab->addr;
    buftag = kmem_buf_to_buftag(buf, cache);

    for (buffers = cache->bufs_per_slab; buffers != 0; buffers--) {
        if (buftag->state != KMEM_BUFTAG_FREE)
            kmem_cache_error(cache, buf, KMEM_ERR_BUFTAG, buftag);

        addr = kmem_buf_verify(buf, KMEM_FREE_PATTERN, cache->bufctl_dist);

        if (addr != NULL)
            kmem_cache_error(cache, buf, KMEM_ERR_MODIFIED, addr);

        buf += buf_size;
        buftag = kmem_buf_to_buftag(buf, cache);
    }
}

/*
 * Destroy a slab.
 *
 * The caller must drop all locks before calling this function.
 */
static void kmem_slab_destroy(struct kmem_slab *slab, struct kmem_cache *cache)
{
    vm_offset_t slab_buf;

    assert(slab->nr_refs == 0);
    assert(slab->first_free != NULL);
    assert(!(cache->flags & KMEM_CF_NO_RECLAIM));

    if (cache->flags & KMEM_CF_VERIFY)
        kmem_slab_destroy_verify(slab, cache);

    slab_buf = (vm_offset_t)P2ALIGN((unsigned long)slab->addr, PAGE_SIZE);

    if (cache->slab_free_fn == NULL)
        kmem_pagefree(slab_buf, cache->slab_size);
    else
        cache->slab_free_fn(slab_buf, cache->slab_size);

    if (cache->flags & KMEM_CF_SLAB_EXTERNAL)
        kmem_cache_free(&kmem_slab_cache, (vm_offset_t)slab);
}

static inline int kmem_slab_use_tree(int flags)
{
    return !(flags & KMEM_CF_DIRECT) || (flags & KMEM_CF_VERIFY);
}

static inline int kmem_slab_cmp_lookup(const void *addr,
                                       const struct rbtree_node *node)
{
    struct kmem_slab *slab;

    slab = rbtree_entry(node, struct kmem_slab, tree_node);

    if (addr == slab->addr)
        return 0;
    else if (addr < slab->addr)
        return -1;
    else
        return 1;
}

static inline int kmem_slab_cmp_insert(const struct rbtree_node *a,
                                       const struct rbtree_node *b)
{
    struct kmem_slab *slab;

    slab = rbtree_entry(a, struct kmem_slab, tree_node);
    return kmem_slab_cmp_lookup(slab->addr, b);
}

#if SLAB_USE_CPU_POOLS
static void kmem_cpu_pool_init(struct kmem_cpu_pool *cpu_pool,
                               struct kmem_cache *cache)
{
    simple_lock_init(&cpu_pool->lock);
    cpu_pool->flags = cache->flags;
    cpu_pool->size = 0;
    cpu_pool->transfer_size = 0;
    cpu_pool->nr_objs = 0;
    cpu_pool->array = NULL;
}

/*
 * Return a CPU pool.
 *
 * This function will generally return the pool matching the CPU running the
 * calling thread. Because of context switches and thread migration, the
 * caller might be running on another processor after this function returns.
 * Although not optimal, this should rarely happen, and it doesn't affect the
 * allocator operations in any other way, as CPU pools are always valid, and
 * their access is serialized by a lock.
 */
static inline struct kmem_cpu_pool * kmem_cpu_pool_get(struct kmem_cache *cache)
{
    return &cache->cpu_pools[cpu_number()];
}

static inline void kmem_cpu_pool_build(struct kmem_cpu_pool *cpu_pool,
                                       struct kmem_cache *cache, void **array)
{
    cpu_pool->size = cache->cpu_pool_type->array_size;
    cpu_pool->transfer_size = (cpu_pool->size
                               + KMEM_CPU_POOL_TRANSFER_RATIO - 1)
                              / KMEM_CPU_POOL_TRANSFER_RATIO;
    cpu_pool->array = array;
}

static inline void * kmem_cpu_pool_pop(struct kmem_cpu_pool *cpu_pool)
{
    cpu_pool->nr_objs--;
    return cpu_pool->array[cpu_pool->nr_objs];
}

static inline void kmem_cpu_pool_push(struct kmem_cpu_pool *cpu_pool, void *obj)
{
    cpu_pool->array[cpu_pool->nr_objs] = obj;
    cpu_pool->nr_objs++;
}

static int kmem_cpu_pool_fill(struct kmem_cpu_pool *cpu_pool,
                              struct kmem_cache *cache)
{
    kmem_cache_ctor_t ctor;
    void *buf;
    int i;

    ctor = (cpu_pool->flags & KMEM_CF_VERIFY) ? NULL : cache->ctor;

    simple_lock(&cache->lock);

    for (i = 0; i < cpu_pool->transfer_size; i++) {
        buf = kmem_cache_alloc_from_slab(cache);

        if (buf == NULL)
            break;

        if (ctor != NULL)
            ctor(buf);

        kmem_cpu_pool_push(cpu_pool, buf);
    }

    simple_unlock(&cache->lock);

    return i;
}

static void kmem_cpu_pool_drain(struct kmem_cpu_pool *cpu_pool,
                                struct kmem_cache *cache)
{
    void *obj;
    int i;

    simple_lock(&cache->lock);

    for (i = cpu_pool->transfer_size; i > 0; i--) {
        obj = kmem_cpu_pool_pop(cpu_pool);
        kmem_cache_free_to_slab(cache, obj);
    }

    simple_unlock(&cache->lock);
}
#endif /* SLAB_USE_CPU_POOLS */

static void kmem_cache_error(struct kmem_cache *cache, void *buf, int error,
                             void *arg)
{
    struct kmem_buftag *buftag;

    kmem_warn("cache: %s, buffer: %p", cache->name, (void *)buf);

    switch(error) {
    case KMEM_ERR_INVALID:
        kmem_error("freeing invalid address");
        break;
    case KMEM_ERR_DOUBLEFREE:
        kmem_error("attempting to free the same address twice");
        break;
    case KMEM_ERR_BUFTAG:
        buftag = arg;
        kmem_error("invalid buftag content, buftag state: %p",
                   (void *)buftag->state);
        break;
    case KMEM_ERR_MODIFIED:
        kmem_error("free buffer modified, fault address: %p, "
                   "offset in buffer: %td", arg, arg - buf);
        break;
    case KMEM_ERR_REDZONE:
        kmem_error("write beyond end of buffer, fault address: %p, "
                   "offset in buffer: %td", arg, arg - buf);
        break;
    default:
        kmem_error("unknown error");
    }

    /*
     * Never reached.
     */
}

/*
 * Compute an appropriate slab size for the given cache.
 *
 * Once the slab size is known, this function sets the related properties
 * (buffers per slab and maximum color). It can also set the KMEM_CF_DIRECT
 * and/or KMEM_CF_SLAB_EXTERNAL flags depending on the resulting layout.
 */
static void kmem_cache_compute_sizes(struct kmem_cache *cache, int flags)
{
    size_t i, buffers, buf_size, slab_size, free_slab_size, optimal_size = 0;
    size_t waste, waste_min;
    int embed, optimal_embed = 0;

    buf_size = cache->buf_size;

    if (buf_size < KMEM_BUF_SIZE_THRESHOLD)
        flags |= KMEM_CACHE_NOOFFSLAB;

    i = 0;
    waste_min = (size_t)-1;

    do {
        i++;
        slab_size = P2ROUND(i * buf_size, PAGE_SIZE);
        free_slab_size = slab_size;

        if (flags & KMEM_CACHE_NOOFFSLAB)
            free_slab_size -= sizeof(struct kmem_slab);

        buffers = free_slab_size / buf_size;
        waste = free_slab_size % buf_size;

        if (buffers > i)
            i = buffers;

        if (flags & KMEM_CACHE_NOOFFSLAB)
            embed = 1;
        else if (sizeof(struct kmem_slab) <= waste) {
            embed = 1;
            waste -= sizeof(struct kmem_slab);
        } else {
            embed = 0;
        }

        if (waste <= waste_min) {
            waste_min = waste;
            optimal_size = slab_size;
            optimal_embed = embed;
        }
    } while ((buffers < KMEM_MIN_BUFS_PER_SLAB)
             && (slab_size < KMEM_SLAB_SIZE_THRESHOLD));

    assert(optimal_size > 0);
    assert(!(flags & KMEM_CACHE_NOOFFSLAB) || optimal_embed);

    cache->slab_size = optimal_size;
    slab_size = cache->slab_size - (optimal_embed
                ? sizeof(struct kmem_slab)
                : 0);
    cache->bufs_per_slab = slab_size / buf_size;
    cache->color_max = slab_size % buf_size;

    if (cache->color_max >= PAGE_SIZE)
        cache->color_max = PAGE_SIZE - 1;

    if (optimal_embed) {
        if (cache->slab_size == PAGE_SIZE)
            cache->flags |= KMEM_CF_DIRECT;
    } else {
        cache->flags |= KMEM_CF_SLAB_EXTERNAL;
    }
}

void kmem_cache_init(struct kmem_cache *cache, const char *name,
                     size_t obj_size, size_t align, kmem_cache_ctor_t ctor,
                     kmem_slab_alloc_fn_t slab_alloc_fn,
                     kmem_slab_free_fn_t slab_free_fn, int flags)
{
#if SLAB_USE_CPU_POOLS
    struct kmem_cpu_pool_type *cpu_pool_type;
    size_t i;
#endif /* SLAB_USE_CPU_POOLS */
    size_t buf_size;

#if SLAB_VERIFY
    cache->flags = KMEM_CF_VERIFY;
#else /* SLAB_VERIFY */
    cache->flags = 0;
#endif /* SLAB_VERIFY */

    if (flags & KMEM_CACHE_NOCPUPOOL)
        cache->flags |= KMEM_CF_NO_CPU_POOL;

    if (flags & KMEM_CACHE_NORECLAIM) {
        assert(slab_free_fn == NULL);
        flags |= KMEM_CACHE_NOOFFSLAB;
        cache->flags |= KMEM_CF_NO_RECLAIM;
    }

    if (flags & KMEM_CACHE_VERIFY)
        cache->flags |= KMEM_CF_VERIFY;

    if (align < KMEM_ALIGN_MIN)
        align = KMEM_ALIGN_MIN;

    assert(obj_size > 0);
    assert(ISP2(align));

    buf_size = P2ROUND(obj_size, align);

    simple_lock_init(&cache->lock);
    list_node_init(&cache->node);
    list_init(&cache->partial_slabs);
    list_init(&cache->free_slabs);
    rbtree_init(&cache->active_slabs);
    cache->obj_size = obj_size;
    cache->align = align;
    cache->buf_size = buf_size;
    cache->bufctl_dist = buf_size - sizeof(union kmem_bufctl);
    cache->color = 0;
    cache->nr_objs = 0;
    cache->nr_bufs = 0;
    cache->nr_slabs = 0;
    cache->nr_free_slabs = 0;
    cache->ctor = ctor;
    cache->slab_alloc_fn = slab_alloc_fn;
    cache->slab_free_fn = slab_free_fn;
    strncpy(cache->name, name, sizeof(cache->name));
    cache->name[sizeof(cache->name) - 1] = '\0';
    cache->buftag_dist = 0;
    cache->redzone_pad = 0;

    if (cache->flags & KMEM_CF_VERIFY) {
        cache->bufctl_dist = buf_size;
        cache->buftag_dist = cache->bufctl_dist + sizeof(union kmem_bufctl);
        cache->redzone_pad = cache->bufctl_dist - cache->obj_size;
        buf_size += sizeof(union kmem_bufctl) + sizeof(struct kmem_buftag);
        buf_size = P2ROUND(buf_size, align);
        cache->buf_size = buf_size;
    }

    kmem_cache_compute_sizes(cache, flags);

#if SLAB_USE_CPU_POOLS
    for (cpu_pool_type = kmem_cpu_pool_types;
         buf_size <= cpu_pool_type->buf_size;
         cpu_pool_type++);

    cache->cpu_pool_type = cpu_pool_type;

    for (i = 0; i < ARRAY_SIZE(cache->cpu_pools); i++)
        kmem_cpu_pool_init(&cache->cpu_pools[i], cache);
#endif /* SLAB_USE_CPU_POOLS */

    simple_lock(&kmem_cache_list_lock);
    list_insert_tail(&kmem_cache_list, &cache->node);
    kmem_nr_caches++;
    simple_unlock(&kmem_cache_list_lock);
}

static inline int kmem_cache_empty(struct kmem_cache *cache)
{
    return cache->nr_objs == cache->nr_bufs;
}

static int kmem_cache_grow(struct kmem_cache *cache)
{
    struct kmem_slab *slab;
    size_t color;
    int empty;

    simple_lock(&cache->lock);

    if (!kmem_cache_empty(cache)) {
        simple_unlock(&cache->lock);
        return 1;
    }

    color = cache->color;
    cache->color += cache->align;

    if (cache->color > cache->color_max)
        cache->color = 0;

    simple_unlock(&cache->lock);

    slab = kmem_slab_create(cache, color);

    simple_lock(&cache->lock);

    if (slab != NULL) {
        list_insert_head(&cache->free_slabs, &slab->list_node);
        cache->nr_bufs += cache->bufs_per_slab;
        cache->nr_slabs++;
        cache->nr_free_slabs++;
    }

    /*
     * Even if our slab creation failed, another thread might have succeeded
     * in growing the cache.
     */
    empty = kmem_cache_empty(cache);

    simple_unlock(&cache->lock);

    return !empty;
}

static void kmem_cache_reap(struct kmem_cache *cache)
{
    struct kmem_slab *slab;
    struct list dead_slabs;
    unsigned long nr_free_slabs;

    if (cache->flags & KMEM_CF_NO_RECLAIM)
        return;

    simple_lock(&cache->lock);
    list_set_head(&dead_slabs, &cache->free_slabs);
    list_init(&cache->free_slabs);
    nr_free_slabs = cache->nr_free_slabs;
    cache->nr_bufs -= cache->bufs_per_slab * nr_free_slabs;
    cache->nr_slabs -= nr_free_slabs;
    cache->nr_free_slabs = 0;
    simple_unlock(&cache->lock);

    while (!list_empty(&dead_slabs)) {
        slab = list_first_entry(&dead_slabs, struct kmem_slab, list_node);
        list_remove(&slab->list_node);
        kmem_slab_destroy(slab, cache);
        nr_free_slabs--;
    }

    assert(nr_free_slabs == 0);
}

/*
 * Allocate a raw (unconstructed) buffer from the slab layer of a cache.
 *
 * The cache must be locked before calling this function.
 */
static void * kmem_cache_alloc_from_slab(struct kmem_cache *cache)
{
    struct kmem_slab *slab;
    union kmem_bufctl *bufctl;

    if (!list_empty(&cache->partial_slabs))
        slab = list_first_entry(&cache->partial_slabs, struct kmem_slab,
                                list_node);
    else if (!list_empty(&cache->free_slabs))
        slab = list_first_entry(&cache->free_slabs, struct kmem_slab,
                                list_node);
    else
        return NULL;

    bufctl = slab->first_free;
    assert(bufctl != NULL);
    slab->first_free = bufctl->next;
    slab->nr_refs++;
    cache->nr_objs++;

    if (slab->nr_refs == cache->bufs_per_slab) {
        /* The slab has become complete */
        list_remove(&slab->list_node);

        if (slab->nr_refs == 1)
            cache->nr_free_slabs--;
    } else if (slab->nr_refs == 1) {
        /*
         * The slab has become partial. Insert the new slab at the end of
         * the list to reduce fragmentation.
         */
        list_remove(&slab->list_node);
        list_insert_tail(&cache->partial_slabs, &slab->list_node);
        cache->nr_free_slabs--;
    }

    if ((slab->nr_refs == 1) && kmem_slab_use_tree(cache->flags))
        rbtree_insert(&cache->active_slabs, &slab->tree_node,
                      kmem_slab_cmp_insert);

    return kmem_bufctl_to_buf(bufctl, cache);
}

/*
 * Release a buffer to the slab layer of a cache.
 *
 * The cache must be locked before calling this function.
 */
static void kmem_cache_free_to_slab(struct kmem_cache *cache, void *buf)
{
    struct kmem_slab *slab;
    union kmem_bufctl *bufctl;

    if (cache->flags & KMEM_CF_DIRECT) {
        assert(cache->slab_size == PAGE_SIZE);
        slab = (struct kmem_slab *)P2END((unsigned long)buf, cache->slab_size)
               - 1;
    } else {
        struct rbtree_node *node;

        node = rbtree_lookup_nearest(&cache->active_slabs, buf,
                                     kmem_slab_cmp_lookup, RBTREE_LEFT);
        assert(node != NULL);
        slab = rbtree_entry(node, struct kmem_slab, tree_node);
        assert((unsigned long)buf < (P2ALIGN((unsigned long)slab->addr
                                             + cache->slab_size, PAGE_SIZE)));
    }

    assert(slab->nr_refs >= 1);
    assert(slab->nr_refs <= cache->bufs_per_slab);
    bufctl = kmem_buf_to_bufctl(buf, cache);
    bufctl->next = slab->first_free;
    slab->first_free = bufctl;
    slab->nr_refs--;
    cache->nr_objs--;

    if (slab->nr_refs == 0) {
        /* The slab has become free */

        if (kmem_slab_use_tree(cache->flags))
            rbtree_remove(&cache->active_slabs, &slab->tree_node);

        if (cache->bufs_per_slab > 1)
            list_remove(&slab->list_node);

        list_insert_head(&cache->free_slabs, &slab->list_node);
        cache->nr_free_slabs++;
    } else if (slab->nr_refs == (cache->bufs_per_slab - 1)) {
        /* The slab has become partial */
        list_insert_head(&cache->partial_slabs, &slab->list_node);
    }
}

static void kmem_cache_alloc_verify(struct kmem_cache *cache, void *buf,
                                    int construct)
{
    struct kmem_buftag *buftag;
    union kmem_bufctl *bufctl;
    void *addr;

    buftag = kmem_buf_to_buftag(buf, cache);

    if (buftag->state != KMEM_BUFTAG_FREE)
        kmem_cache_error(cache, buf, KMEM_ERR_BUFTAG, buftag);

    addr = kmem_buf_verify_fill(buf, KMEM_FREE_PATTERN, KMEM_UNINIT_PATTERN,
                                cache->bufctl_dist);

    if (addr != NULL)
        kmem_cache_error(cache, buf, KMEM_ERR_MODIFIED, addr);

    addr = buf + cache->obj_size;
    memset(addr, KMEM_REDZONE_BYTE, cache->redzone_pad);

    bufctl = kmem_buf_to_bufctl(buf, cache);
    bufctl->redzone = KMEM_REDZONE_WORD;
    buftag->state = KMEM_BUFTAG_ALLOC;

    if (construct && (cache->ctor != NULL))
        cache->ctor(buf);
}

vm_offset_t kmem_cache_alloc(struct kmem_cache *cache)
{
    int filled;
    void *buf;

#if SLAB_USE_CPU_POOLS
    struct kmem_cpu_pool *cpu_pool;

    cpu_pool = kmem_cpu_pool_get(cache);

    if (cpu_pool->flags & KMEM_CF_NO_CPU_POOL)
        goto slab_alloc;

    simple_lock(&cpu_pool->lock);

fast_alloc:
    if (likely(cpu_pool->nr_objs > 0)) {
        buf = kmem_cpu_pool_pop(cpu_pool);
        simple_unlock(&cpu_pool->lock);

        if (cpu_pool->flags & KMEM_CF_VERIFY)
            kmem_cache_alloc_verify(cache, buf, KMEM_AV_CONSTRUCT);

        return (vm_offset_t)buf;
    }

    if (cpu_pool->array != NULL) {
        filled = kmem_cpu_pool_fill(cpu_pool, cache);

        if (!filled) {
            simple_unlock(&cpu_pool->lock);

            filled = kmem_cache_grow(cache);

            if (!filled)
                return 0;

            simple_lock(&cpu_pool->lock);
        }

        goto fast_alloc;
    }

    simple_unlock(&cpu_pool->lock);
#endif /* SLAB_USE_CPU_POOLS */

slab_alloc:
    simple_lock(&cache->lock);
    buf = kmem_cache_alloc_from_slab(cache);
    simple_unlock(&cache->lock);

    if (buf == NULL) {
        filled = kmem_cache_grow(cache);

        if (!filled)
            return 0;

        goto slab_alloc;
    }

    if (cache->flags & KMEM_CF_VERIFY)
        kmem_cache_alloc_verify(cache, buf, KMEM_AV_NOCONSTRUCT);

    if (cache->ctor != NULL)
        cache->ctor(buf);

    return (vm_offset_t)buf;
}

static void kmem_cache_free_verify(struct kmem_cache *cache, void *buf)
{
    struct rbtree_node *node;
    struct kmem_buftag *buftag;
    struct kmem_slab *slab;
    union kmem_bufctl *bufctl;
    unsigned char *redzone_byte;
    unsigned long slabend;

    simple_lock(&cache->lock);
    node = rbtree_lookup_nearest(&cache->active_slabs, buf,
                                 kmem_slab_cmp_lookup, RBTREE_LEFT);
    simple_unlock(&cache->lock);

    if (node == NULL)
        kmem_cache_error(cache, buf, KMEM_ERR_INVALID, NULL);

    slab = rbtree_entry(node, struct kmem_slab, tree_node);
    slabend = P2ALIGN((unsigned long)slab->addr + cache->slab_size, PAGE_SIZE);

    if ((unsigned long)buf >= slabend)
        kmem_cache_error(cache, buf, KMEM_ERR_INVALID, NULL);

    if ((((unsigned long)buf - (unsigned long)slab->addr) % cache->buf_size)
        != 0)
        kmem_cache_error(cache, buf, KMEM_ERR_INVALID, NULL);

    /*
     * As the buffer address is valid, accessing its buftag is safe.
     */
    buftag = kmem_buf_to_buftag(buf, cache);

    if (buftag->state != KMEM_BUFTAG_ALLOC) {
        if (buftag->state == KMEM_BUFTAG_FREE)
            kmem_cache_error(cache, buf, KMEM_ERR_DOUBLEFREE, NULL);
        else
            kmem_cache_error(cache, buf, KMEM_ERR_BUFTAG, buftag);
    }

    redzone_byte = buf + cache->obj_size;
    bufctl = kmem_buf_to_bufctl(buf, cache);

    while (redzone_byte < (unsigned char *)bufctl) {
        if (*redzone_byte != KMEM_REDZONE_BYTE)
            kmem_cache_error(cache, buf, KMEM_ERR_REDZONE, redzone_byte);

        redzone_byte++;
    }

    if (bufctl->redzone != KMEM_REDZONE_WORD) {
        unsigned long word;

        word = KMEM_REDZONE_WORD;
        redzone_byte = kmem_buf_verify_bytes(&bufctl->redzone, &word,
                                             sizeof(bufctl->redzone));
        kmem_cache_error(cache, buf, KMEM_ERR_REDZONE, redzone_byte);
    }

    kmem_buf_fill(buf, KMEM_FREE_PATTERN, cache->bufctl_dist);
    buftag->state = KMEM_BUFTAG_FREE;
}

void kmem_cache_free(struct kmem_cache *cache, vm_offset_t obj)
{
#if SLAB_USE_CPU_POOLS
    struct kmem_cpu_pool *cpu_pool;
    void **array;

    cpu_pool = kmem_cpu_pool_get(cache);

    if (cpu_pool->flags & KMEM_CF_VERIFY) {
#else /* SLAB_USE_CPU_POOLS */
    if (cache->flags & KMEM_CF_VERIFY) {
#endif /* SLAB_USE_CPU_POOLS */
        kmem_cache_free_verify(cache, (void *)obj);
    }

#if SLAB_USE_CPU_POOLS
    if (cpu_pool->flags & KMEM_CF_NO_CPU_POOL)
        goto slab_free;

    simple_lock(&cpu_pool->lock);

fast_free:
    if (likely(cpu_pool->nr_objs < cpu_pool->size)) {
        kmem_cpu_pool_push(cpu_pool, (void *)obj);
        simple_unlock(&cpu_pool->lock);
        return;
    }

    if (cpu_pool->array != NULL) {
        kmem_cpu_pool_drain(cpu_pool, cache);
        goto fast_free;
    }

    simple_unlock(&cpu_pool->lock);

    array = (void *)kmem_cache_alloc(cache->cpu_pool_type->array_cache);

    if (array != NULL) {
        simple_lock(&cpu_pool->lock);

        /*
         * Another thread may have built the CPU pool while the lock was
         * dropped.
         */
        if (cpu_pool->array != NULL) {
            simple_unlock(&cpu_pool->lock);
            kmem_cache_free(cache->cpu_pool_type->array_cache,
                            (vm_offset_t)array);
            simple_lock(&cpu_pool->lock);
            goto fast_free;
        }

        kmem_cpu_pool_build(cpu_pool, cache, array);
        goto fast_free;
    }

slab_free:
#endif /* SLAB_USE_CPU_POOLS */

    simple_lock(&cache->lock);
    kmem_cache_free_to_slab(cache, (void *)obj);
    simple_unlock(&cache->lock);
}

void slab_collect(void)
{
    struct kmem_cache *cache;

    if (elapsed_ticks <= (kmem_gc_last_tick + KMEM_GC_INTERVAL))
        return;

    kmem_gc_last_tick = elapsed_ticks;

    simple_lock(&kmem_cache_list_lock);

    list_for_each_entry(&kmem_cache_list, cache, node)
        kmem_cache_reap(cache);

    simple_unlock(&kmem_cache_list_lock);
}

void slab_bootstrap(void)
{
    /* Make sure a bufctl can always be stored in a buffer */
    assert(sizeof(union kmem_bufctl) <= KMEM_ALIGN_MIN);

    list_init(&kmem_cache_list);
    simple_lock_init(&kmem_cache_list_lock);
}

void slab_init(void)
{
    vm_offset_t min, max;

#if SLAB_USE_CPU_POOLS
    struct kmem_cpu_pool_type *cpu_pool_type;
    char name[KMEM_CACHE_NAME_SIZE];
    size_t i, size;
#endif /* SLAB_USE_CPU_POOLS */

    kmem_submap(kmem_map, kernel_map, &min, &max, KMEM_MAP_SIZE, FALSE);

#if SLAB_USE_CPU_POOLS
    for (i = 0; i < ARRAY_SIZE(kmem_cpu_pool_types); i++) {
        cpu_pool_type = &kmem_cpu_pool_types[i];
        cpu_pool_type->array_cache = &kmem_cpu_array_caches[i];
        sprintf(name, "kmem_cpu_array_%d", cpu_pool_type->array_size);
        size = sizeof(void *) * cpu_pool_type->array_size;
        kmem_cache_init(cpu_pool_type->array_cache, name, size,
                        cpu_pool_type->array_align, NULL, NULL, NULL, 0);
    }
#endif /* SLAB_USE_CPU_POOLS */

    /*
     * Prevent off slab data for the slab cache to avoid infinite recursion.
     */
    kmem_cache_init(&kmem_slab_cache, "kmem_slab", sizeof(struct kmem_slab),
                    0, NULL, NULL, NULL, KMEM_CACHE_NOOFFSLAB);
}

static vm_offset_t kalloc_pagealloc(vm_size_t size)
{
    vm_offset_t addr;
    kern_return_t kr;

    kr = kmem_alloc_wired(kmem_map, &addr, size);

    if (kr != KERN_SUCCESS)
        return 0;

    return addr;
}

static void kalloc_pagefree(vm_offset_t ptr, vm_size_t size)
{
    kmem_free(kmem_map, ptr, size);
}

void kalloc_init(void)
{
    char name[KMEM_CACHE_NAME_SIZE];
    size_t i, size;

    size = 1 << KALLOC_FIRST_SHIFT;

    for (i = 0; i < ARRAY_SIZE(kalloc_caches); i++) {
        sprintf(name, "kalloc_%lu", size);
        kmem_cache_init(&kalloc_caches[i], name, size, 0, NULL,
                        kalloc_pagealloc, kalloc_pagefree, 0);
        size <<= 1;
    }
}

/*
 * Return the kalloc cache index matching the given allocation size, which
 * must be strictly greater than 0.
 */
static inline size_t kalloc_get_index(unsigned long size)
{
    assert(size != 0);

    size = (size - 1) >> KALLOC_FIRST_SHIFT;

    if (size == 0)
        return 0;
    else
        return (sizeof(long) * 8) - __builtin_clzl(size);
}

static void kalloc_verify(struct kmem_cache *cache, void *buf, size_t size)
{
    size_t redzone_size;
    void *redzone;

    assert(size <= cache->obj_size);

    redzone = buf + size;
    redzone_size = cache->obj_size - size;
    memset(redzone, KMEM_REDZONE_BYTE, redzone_size);
}

vm_offset_t kalloc(vm_size_t size)
{
    size_t index;
    void *buf;

    if (size == 0)
        return 0;

    index = kalloc_get_index(size);

    if (index < ARRAY_SIZE(kalloc_caches)) {
        struct kmem_cache *cache;

        cache = &kalloc_caches[index];
        buf = (void *)kmem_cache_alloc(cache);

        if ((buf != 0) && (cache->flags & KMEM_CF_VERIFY))
            kalloc_verify(cache, buf, size);
    } else
        buf = (void *)kalloc_pagealloc(size);

    return (vm_offset_t)buf;
}

static void kfree_verify(struct kmem_cache *cache, void *buf, size_t size)
{
    unsigned char *redzone_byte, *redzone_end;

    assert(size <= cache->obj_size);

    redzone_byte = buf + size;
    redzone_end = buf + cache->obj_size;

    while (redzone_byte < redzone_end) {
        if (*redzone_byte != KMEM_REDZONE_BYTE)
            kmem_cache_error(cache, buf, KMEM_ERR_REDZONE, redzone_byte);

        redzone_byte++;
    }
}

void kfree(vm_offset_t data, vm_size_t size)
{
    size_t index;

    if ((data == 0) || (size == 0))
        return;

    index = kalloc_get_index(size);

    if (index < ARRAY_SIZE(kalloc_caches)) {
        struct kmem_cache *cache;

        cache = &kalloc_caches[index];

        if (cache->flags & KMEM_CF_VERIFY)
            kfree_verify(cache, (void *)data, size);

        kmem_cache_free(cache, data);
    } else {
        kalloc_pagefree(data, size);
    }
}

void slab_info(void)
{
    struct kmem_cache *cache;
    vm_size_t mem_usage, mem_reclaimable;

    printf("cache                  obj slab  bufs   objs   bufs "
           "   total reclaimable\n"
           "name                  size size /slab  usage  count "
           "  memory      memory\n");

    simple_lock(&kmem_cache_list_lock);

    list_for_each_entry(&kmem_cache_list, cache, node) {
        simple_lock(&cache->lock);

        mem_usage = (cache->nr_slabs * cache->slab_size) >> 10;
        mem_reclaimable = (cache->nr_free_slabs * cache->slab_size) >> 10;

        printf("%-19s %6lu %3luk  %4lu %6lu %6lu %7uk %10uk\n",
               cache->name, cache->obj_size, cache->slab_size >> 10,
               cache->bufs_per_slab, cache->nr_objs, cache->nr_bufs,
               mem_usage, mem_reclaimable);

        simple_unlock(&cache->lock);
    }

    simple_unlock(&kmem_cache_list_lock);
}

#if MACH_DEBUG
kern_return_t host_slab_info(host_t host, cache_info_array_t *infop,
                             unsigned int *infoCntp)
{
    struct kmem_cache *cache;
    cache_info_t *info;
    unsigned int i, nr_caches;
    vm_size_t info_size = 0;
    kern_return_t kr;

    if (host == HOST_NULL)
        return KERN_INVALID_HOST;

    /*
     * Assume the cache list is unaltered once the kernel is ready.
     */

    simple_lock(&kmem_cache_list_lock);
    nr_caches = kmem_nr_caches;
    simple_unlock(&kmem_cache_list_lock);

    if (nr_caches <= *infoCntp)
        info = *infop;
    else {
        vm_offset_t info_addr;

        info_size = round_page(nr_caches * sizeof(*info));
        kr = kmem_alloc_pageable(ipc_kernel_map, &info_addr, info_size);

        if (kr != KERN_SUCCESS)
            return kr;

        info = (cache_info_t *)info_addr;
    }

    if (info == NULL)
        return KERN_RESOURCE_SHORTAGE;

    i = 0;

    list_for_each_entry(&kmem_cache_list, cache, node) {
        simple_lock(&cache->lock);
        info[i].flags = ((cache->flags & KMEM_CF_NO_CPU_POOL)
                         ? CACHE_FLAGS_NO_CPU_POOL : 0)
                        | ((cache->flags & KMEM_CF_SLAB_EXTERNAL)
                           ? CACHE_FLAGS_SLAB_EXTERNAL : 0)
                        | ((cache->flags & KMEM_CF_NO_RECLAIM)
                           ? CACHE_FLAGS_NO_RECLAIM : 0)
                        | ((cache->flags & KMEM_CF_VERIFY)
                           ? CACHE_FLAGS_VERIFY : 0)
                        | ((cache->flags & KMEM_CF_DIRECT)
                           ? CACHE_FLAGS_DIRECT : 0);
#if SLAB_USE_CPU_POOLS
        info[i].cpu_pool_size = cache->cpu_pool_type->array_size;
#else /* SLAB_USE_CPU_POOLS */
        info[i].cpu_pool_size = 0;
#endif /* SLAB_USE_CPU_POOLS */
        info[i].obj_size = cache->obj_size;
        info[i].align = cache->align;
        info[i].buf_size = cache->buf_size;
        info[i].slab_size = cache->slab_size;
        info[i].bufs_per_slab = cache->bufs_per_slab;
        info[i].nr_objs = cache->nr_objs;
        info[i].nr_bufs = cache->nr_bufs;
        info[i].nr_slabs = cache->nr_slabs;
        info[i].nr_free_slabs = cache->nr_free_slabs;
        strncpy(info[i].name, cache->name, sizeof(info[i].name));
        info[i].name[sizeof(info[i].name) - 1] = '\0';
        simple_unlock(&cache->lock);

        i++;
    }

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

        used = nr_caches * sizeof(*info);

        if (used != info_size)
            memset((char *)info + used, 0, info_size - used);

        kr = vm_map_copyin(ipc_kernel_map, (vm_offset_t)info, used, TRUE,
                           &copy);

        assert(kr == KERN_SUCCESS);
        *infop = (cache_info_t *)copy;
    }

    *infoCntp = nr_caches;

    return KERN_SUCCESS;
}
#endif /* MACH_DEBUG */