Merge branch 'master' of git://git.dragonflybsd.org/dragonfly

[dragonfly.git] / sys / kern / kern_slaballoc.c

/*
 * (MPSAFE)
 *
 * KERN_SLABALLOC.C     - Kernel SLAB memory allocator
 * 
 * Copyright (c) 2003,2004,2010 The DragonFly Project.  All rights reserved.
 * 
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 * 
 * 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.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``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
 * COPYRIGHT HOLDERS OR CONTRIBUTORS 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.
 * 
 * $DragonFly: src/sys/kern/kern_slaballoc.c,v 1.55 2008/10/22 01:42:17 dillon Exp $
 *
 * This module implements a slab allocator drop-in replacement for the
 * kernel malloc().
 *
 * A slab allocator reserves a ZONE for each chunk size, then lays the
 * chunks out in an array within the zone.  Allocation and deallocation
 * is nearly instantanious, and fragmentation/overhead losses are limited
 * to a fixed worst-case amount.
 *
 * The downside of this slab implementation is in the chunk size
 * multiplied by the number of zones.  ~80 zones * 128K = 10MB of VM per cpu.
 * In a kernel implementation all this memory will be physical so
 * the zone size is adjusted downward on machines with less physical
 * memory.  The upside is that overhead is bounded... this is the *worst*
 * case overhead.
 *
 * Slab management is done on a per-cpu basis and no locking or mutexes
 * are required, only a critical section.  When one cpu frees memory
 * belonging to another cpu's slab manager an asynchronous IPI message
 * will be queued to execute the operation.   In addition, both the
 * high level slab allocator and the low level zone allocator optimize
 * M_ZERO requests, and the slab allocator does not have to pre initialize
 * the linked list of chunks.
 *
 * XXX Balancing is needed between cpus.  Balance will be handled through
 * asynchronous IPIs primarily by reassigning the z_Cpu ownership of chunks.
 *
 * XXX If we have to allocate a new zone and M_USE_RESERVE is set, use of
 * the new zone should be restricted to M_USE_RESERVE requests only.
 *
 *      Alloc Size      Chunking        Number of zones
 *      0-127           8               16
 *      128-255         16              8
 *      256-511         32              8
 *      512-1023        64              8
 *      1024-2047       128             8
 *      2048-4095       256             8
 *      4096-8191       512             8
 *      8192-16383      1024            8
 *      16384-32767     2048            8
 *      (if PAGE_SIZE is 4K the maximum zone allocation is 16383)
 *
 *      Allocations >= ZoneLimit go directly to kmem.
 *
 *                      API REQUIREMENTS AND SIDE EFFECTS
 *
 *    To operate as a drop-in replacement to the FreeBSD-4.x malloc() we
 *    have remained compatible with the following API requirements:
 *
 *    + small power-of-2 sized allocations are power-of-2 aligned (kern_tty)
 *    + all power-of-2 sized allocations are power-of-2 aligned (twe)
 *    + malloc(0) is allowed and returns non-NULL (ahc driver)
 *    + ability to allocate arbitrarily large chunks of memory
 */

#include "opt_vm.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/slaballoc.h>
#include <sys/mbuf.h>
#include <sys/vmmeter.h>
#include <sys/lock.h>
#include <sys/thread.h>
#include <sys/globaldata.h>
#include <sys/sysctl.h>
#include <sys/ktr.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/vm_object.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>

#include <machine/cpu.h>

#include <sys/thread2.h>

#define arysize(ary)    (sizeof(ary)/sizeof((ary)[0]))

#define btokup(z)       (&pmap_kvtom((vm_offset_t)(z))->ku_pagecnt)

#define MEMORY_STRING   "ptr=%p type=%p size=%d flags=%04x"
#define MEMORY_ARG_SIZE (sizeof(void *) * 2 + sizeof(unsigned long) +   \
                        sizeof(int))

#if !defined(KTR_MEMORY)
#define KTR_MEMORY      KTR_ALL
#endif
KTR_INFO_MASTER(memory);
KTR_INFO(KTR_MEMORY, memory, malloc_beg, 0, "malloc begin", 0);
KTR_INFO(KTR_MEMORY, memory, malloc_end, 1, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_zero, 2, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_ovsz, 3, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_ovsz_delayed, 4, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_chunk, 5, MEMORY_STRING, MEMORY_ARG_SIZE);
#ifdef SMP
KTR_INFO(KTR_MEMORY, memory, free_request, 6, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_rem_beg, 7, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_rem_end, 8, MEMORY_STRING, MEMORY_ARG_SIZE);
#endif
KTR_INFO(KTR_MEMORY, memory, free_beg, 9, "free begin", 0);
KTR_INFO(KTR_MEMORY, memory, free_end, 10, "free end", 0);

#define logmemory(name, ptr, type, size, flags)                         \
        KTR_LOG(memory_ ## name, ptr, type, size, flags)
#define logmemory_quick(name)                                           \
        KTR_LOG(memory_ ## name)

/*
 * Fixed globals (not per-cpu)
 */
static int ZoneSize;
static int ZoneLimit;
static int ZonePageCount;
static uintptr_t ZoneMask;
static int ZoneBigAlloc;                /* in KB */
static int ZoneGenAlloc;                /* in KB */
struct malloc_type *kmemstatistics;     /* exported to vmstat */
static int32_t weirdary[16];

static void *kmem_slab_alloc(vm_size_t bytes, vm_offset_t align, int flags);
static void kmem_slab_free(void *ptr, vm_size_t bytes);

#if defined(INVARIANTS)
static void chunk_mark_allocated(SLZone *z, void *chunk);
static void chunk_mark_free(SLZone *z, void *chunk);
#else
#define chunk_mark_allocated(z, chunk)
#define chunk_mark_free(z, chunk)
#endif

/*
 * Misc constants.  Note that allocations that are exact multiples of 
 * PAGE_SIZE, or exceed the zone limit, fall through to the kmem module.
 * IN_SAME_PAGE_MASK is used to sanity-check the per-page free lists.
 */
#define MIN_CHUNK_SIZE          8               /* in bytes */
#define MIN_CHUNK_MASK          (MIN_CHUNK_SIZE - 1)
#define ZONE_RELS_THRESH        2               /* threshold number of zones */
#define IN_SAME_PAGE_MASK       (~(intptr_t)PAGE_MASK | MIN_CHUNK_MASK)

/*
 * The WEIRD_ADDR is used as known text to copy into free objects to
 * try to create deterministic failure cases if the data is accessed after
 * free.
 */    
#define WEIRD_ADDR      0xdeadc0de
#define MAX_COPY        sizeof(weirdary)
#define ZERO_LENGTH_PTR ((void *)-8)

/*
 * Misc global malloc buckets
 */

MALLOC_DEFINE(M_CACHE, "cache", "Various Dynamically allocated caches");
MALLOC_DEFINE(M_DEVBUF, "devbuf", "device driver memory");
MALLOC_DEFINE(M_TEMP, "temp", "misc temporary data buffers");
 
MALLOC_DEFINE(M_IP6OPT, "ip6opt", "IPv6 options");
MALLOC_DEFINE(M_IP6NDP, "ip6ndp", "IPv6 Neighbor Discovery");

/*
 * Initialize the slab memory allocator.  We have to choose a zone size based
 * on available physical memory.  We choose a zone side which is approximately
 * 1/1024th of our memory, so if we have 128MB of ram we have a zone size of
 * 128K.  The zone size is limited to the bounds set in slaballoc.h
 * (typically 32K min, 128K max). 
 */
static void kmeminit(void *dummy);

char *ZeroPage;

SYSINIT(kmem, SI_BOOT1_ALLOCATOR, SI_ORDER_FIRST, kmeminit, NULL)

#ifdef INVARIANTS
/*
 * If enabled any memory allocated without M_ZERO is initialized to -1.
 */
static int  use_malloc_pattern;
SYSCTL_INT(_debug, OID_AUTO, use_malloc_pattern, CTLFLAG_RW,
                &use_malloc_pattern, 0, "");
#endif

SYSCTL_INT(_kern, OID_AUTO, zone_big_alloc, CTLFLAG_RD, &ZoneBigAlloc, 0, "");
SYSCTL_INT(_kern, OID_AUTO, zone_gen_alloc, CTLFLAG_RD, &ZoneGenAlloc, 0, "");

static void
kmeminit(void *dummy)
{
    size_t limsize;
    int usesize;
    int i;

    limsize = (size_t)vmstats.v_page_count * PAGE_SIZE;
    if (limsize > KvaSize)
        limsize = KvaSize;

    usesize = (int)(limsize / 1024);    /* convert to KB */

    ZoneSize = ZALLOC_MIN_ZONE_SIZE;
    while (ZoneSize < ZALLOC_MAX_ZONE_SIZE && (ZoneSize << 1) < usesize)
        ZoneSize <<= 1;
    ZoneLimit = ZoneSize / 4;
    if (ZoneLimit > ZALLOC_ZONE_LIMIT)
        ZoneLimit = ZALLOC_ZONE_LIMIT;
    ZoneMask = ~(uintptr_t)(ZoneSize - 1);
    ZonePageCount = ZoneSize / PAGE_SIZE;

    for (i = 0; i < arysize(weirdary); ++i)
        weirdary[i] = WEIRD_ADDR;

    ZeroPage = kmem_slab_alloc(PAGE_SIZE, PAGE_SIZE, M_WAITOK|M_ZERO);

    if (bootverbose)
        kprintf("Slab ZoneSize set to %dKB\n", ZoneSize / 1024);
}

/*
 * Initialize a malloc type tracking structure.
 */
void
malloc_init(void *data)
{
    struct malloc_type *type = data;
    size_t limsize;

    if (type->ks_magic != M_MAGIC)
        panic("malloc type lacks magic");
                                           
    if (type->ks_limit != 0)
        return;

    if (vmstats.v_page_count == 0)
        panic("malloc_init not allowed before vm init");

    limsize = (size_t)vmstats.v_page_count * PAGE_SIZE;
    if (limsize > KvaSize)
        limsize = KvaSize;
    type->ks_limit = limsize / 10;

    type->ks_next = kmemstatistics;
    kmemstatistics = type;
}

void
malloc_uninit(void *data)
{
    struct malloc_type *type = data;
    struct malloc_type *t;
#ifdef INVARIANTS
    int i;
    long ttl;
#endif

    if (type->ks_magic != M_MAGIC)
        panic("malloc type lacks magic");

    if (vmstats.v_page_count == 0)
        panic("malloc_uninit not allowed before vm init");

    if (type->ks_limit == 0)
        panic("malloc_uninit on uninitialized type");

#ifdef SMP
    /* Make sure that all pending kfree()s are finished. */
    lwkt_synchronize_ipiqs("muninit");
#endif

#ifdef INVARIANTS
    /*
     * memuse is only correct in aggregation.  Due to memory being allocated
     * on one cpu and freed on another individual array entries may be 
     * negative or positive (canceling each other out).
     */
    for (i = ttl = 0; i < ncpus; ++i)
        ttl += type->ks_memuse[i];
    if (ttl) {
        kprintf("malloc_uninit: %ld bytes of '%s' still allocated on cpu %d\n",
            ttl, type->ks_shortdesc, i);
    }
#endif
    if (type == kmemstatistics) {
        kmemstatistics = type->ks_next;
    } else {
        for (t = kmemstatistics; t->ks_next != NULL; t = t->ks_next) {
            if (t->ks_next == type) {
                t->ks_next = type->ks_next;
                break;
            }
        }
    }
    type->ks_next = NULL;
    type->ks_limit = 0;
}

/*
 * Increase the kmalloc pool limit for the specified pool.  No changes
 * are the made if the pool would shrink.
 */
void
kmalloc_raise_limit(struct malloc_type *type, size_t bytes)
{
    if (type->ks_limit == 0)
        malloc_init(type);
    if (bytes == 0)
        bytes = KvaSize;
    if (type->ks_limit < bytes)
        type->ks_limit = bytes;
}

/*
 * Dynamically create a malloc pool.  This function is a NOP if *typep is
 * already non-NULL.
 */
void
kmalloc_create(struct malloc_type **typep, const char *descr)
{
        struct malloc_type *type;

        if (*typep == NULL) {
                type = kmalloc(sizeof(*type), M_TEMP, M_WAITOK | M_ZERO);
                type->ks_magic = M_MAGIC;
                type->ks_shortdesc = descr;
                malloc_init(type);
                *typep = type;
        }
}

/*
 * Destroy a dynamically created malloc pool.  This function is a NOP if
 * the pool has already been destroyed.
 */
void
kmalloc_destroy(struct malloc_type **typep)
{
        if (*typep != NULL) {
                malloc_uninit(*typep);
                kfree(*typep, M_TEMP);
                *typep = NULL;
        }
}

/*
 * Calculate the zone index for the allocation request size and set the
 * allocation request size to that particular zone's chunk size.
 */
static __inline int
zoneindex(unsigned long *bytes)
{
    unsigned int n = (unsigned int)*bytes;      /* unsigned for shift opt */
    if (n < 128) {
        *bytes = n = (n + 7) & ~7;
        return(n / 8 - 1);              /* 8 byte chunks, 16 zones */
    }
    if (n < 256) {
        *bytes = n = (n + 15) & ~15;
        return(n / 16 + 7);
    }
    if (n < 8192) {
        if (n < 512) {
            *bytes = n = (n + 31) & ~31;
            return(n / 32 + 15);
        }
        if (n < 1024) {
            *bytes = n = (n + 63) & ~63;
            return(n / 64 + 23);
        } 
        if (n < 2048) {
            *bytes = n = (n + 127) & ~127;
            return(n / 128 + 31);
        }
        if (n < 4096) {
            *bytes = n = (n + 255) & ~255;
            return(n / 256 + 39);
        }
        *bytes = n = (n + 511) & ~511;
        return(n / 512 + 47);
    }
#if ZALLOC_ZONE_LIMIT > 8192
    if (n < 16384) {
        *bytes = n = (n + 1023) & ~1023;
        return(n / 1024 + 55);
    }
#endif
#if ZALLOC_ZONE_LIMIT > 16384
    if (n < 32768) {
        *bytes = n = (n + 2047) & ~2047;
        return(n / 2048 + 63);
    }
#endif
    panic("Unexpected byte count %d", n);
    return(0);
}

/*
 * kmalloc()    (SLAB ALLOCATOR)
 *
 *      Allocate memory via the slab allocator.  If the request is too large,
 *      or if it page-aligned beyond a certain size, we fall back to the
 *      KMEM subsystem.  A SLAB tracking descriptor must be specified, use
 *      &SlabMisc if you don't care.
 *
 *      M_RNOWAIT       - don't block.
 *      M_NULLOK        - return NULL instead of blocking.
 *      M_ZERO          - zero the returned memory.
 *      M_USE_RESERVE   - allow greater drawdown of the free list
 *      M_USE_INTERRUPT_RESERVE - allow the freelist to be exhausted
 *
 * MPSAFE
 */
void *
kmalloc(unsigned long size, struct malloc_type *type, int flags)
{
    SLZone *z;
    SLChunk *chunk;
#ifdef SMP
    SLChunk *bchunk;
#endif
    SLGlobalData *slgd;
    struct globaldata *gd;
    int zi;
#ifdef INVARIANTS
    int i;
#endif

    logmemory_quick(malloc_beg);
    gd = mycpu;
    slgd = &gd->gd_slab;

    /*
     * XXX silly to have this in the critical path.
     */
    if (type->ks_limit == 0) {
        crit_enter();
        if (type->ks_limit == 0)
            malloc_init(type);
        crit_exit();
    }
    ++type->ks_calls;

    /*
     * Handle the case where the limit is reached.  Panic if we can't return
     * NULL.  The original malloc code looped, but this tended to
     * simply deadlock the computer.
     *
     * ks_loosememuse is an up-only limit that is NOT MP-synchronized, used
     * to determine if a more complete limit check should be done.  The
     * actual memory use is tracked via ks_memuse[cpu].
     */
    while (type->ks_loosememuse >= type->ks_limit) {
        int i;
        long ttl;

        for (i = ttl = 0; i < ncpus; ++i)
            ttl += type->ks_memuse[i];
        type->ks_loosememuse = ttl;     /* not MP synchronized */
        if ((ssize_t)ttl < 0)           /* deal with occassional race */
                ttl = 0;
        if (ttl >= type->ks_limit) {
            if (flags & M_NULLOK) {
                logmemory(malloc_end, NULL, type, size, flags);
                return(NULL);
            }
            panic("%s: malloc limit exceeded", type->ks_shortdesc);
        }
    }

    /*
     * Handle the degenerate size == 0 case.  Yes, this does happen.
     * Return a special pointer.  This is to maintain compatibility with
     * the original malloc implementation.  Certain devices, such as the
     * adaptec driver, not only allocate 0 bytes, they check for NULL and
     * also realloc() later on.  Joy.
     */
    if (size == 0) {
        logmemory(malloc_end, ZERO_LENGTH_PTR, type, size, flags);
        return(ZERO_LENGTH_PTR);
    }

    /*
     * Handle hysteresis from prior frees here in malloc().  We cannot
     * safely manipulate the kernel_map in free() due to free() possibly
     * being called via an IPI message or from sensitive interrupt code.
     *
     * NOTE: ku_pagecnt must be cleared before we free the slab or we
     *       might race another cpu allocating the kva and setting
     *       ku_pagecnt.
     */
    while (slgd->NFreeZones > ZONE_RELS_THRESH && (flags & M_RNOWAIT) == 0) {
        crit_enter();
        if (slgd->NFreeZones > ZONE_RELS_THRESH) {      /* crit sect race */
            int *kup;

            z = slgd->FreeZones;
            slgd->FreeZones = z->z_Next;
            --slgd->NFreeZones;
            kup = btokup(z);
            *kup = 0;
            kmem_slab_free(z, ZoneSize);        /* may block */
            atomic_add_int(&ZoneGenAlloc, -(int)ZoneSize / 1024);
        }
        crit_exit();
    }

    /*
     * XXX handle oversized frees that were queued from kfree().
     */
    while (slgd->FreeOvZones && (flags & M_RNOWAIT) == 0) {
        crit_enter();
        if ((z = slgd->FreeOvZones) != NULL) {
            vm_size_t tsize;

            KKASSERT(z->z_Magic == ZALLOC_OVSZ_MAGIC);
            slgd->FreeOvZones = z->z_Next;
            tsize = z->z_ChunkSize;
            kmem_slab_free(z, tsize);   /* may block */
            atomic_add_int(&ZoneBigAlloc, -(int)tsize / 1024);
        }
        crit_exit();
    }

    /*
     * Handle large allocations directly.  There should not be very many of
     * these so performance is not a big issue.
     *
     * The backend allocator is pretty nasty on a SMP system.   Use the
     * slab allocator for one and two page-sized chunks even though we lose
     * some efficiency.  XXX maybe fix mmio and the elf loader instead.
     */
    if (size >= ZoneLimit || ((size & PAGE_MASK) == 0 && size > PAGE_SIZE*2)) {
        int *kup;

        size = round_page(size);
        chunk = kmem_slab_alloc(size, PAGE_SIZE, flags);
        if (chunk == NULL) {
            logmemory(malloc_end, NULL, type, size, flags);
            return(NULL);
        }
        atomic_add_int(&ZoneBigAlloc, (int)size / 1024);
        flags &= ~M_ZERO;       /* result already zero'd if M_ZERO was set */
        flags |= M_PASSIVE_ZERO;
        kup = btokup(chunk);
        *kup = size / PAGE_SIZE;
        crit_enter();
        goto done;
    }

    /*
     * Attempt to allocate out of an existing zone.  First try the free list,
     * then allocate out of unallocated space.  If we find a good zone move
     * it to the head of the list so later allocations find it quickly
     * (we might have thousands of zones in the list).
     *
     * Note: zoneindex() will panic of size is too large.
     */
    zi = zoneindex(&size);
    KKASSERT(zi < NZONES);
    crit_enter();

    if ((z = slgd->ZoneAry[zi]) != NULL) {
        /*
         * Locate a chunk - we have to have at least one.  If this is the
         * last chunk go ahead and do the work to retrieve chunks freed
         * from remote cpus, and if the zone is still empty move it off
         * the ZoneAry.
         */
        if (--z->z_NFree <= 0) {
            KKASSERT(z->z_NFree == 0);

#ifdef SMP
            /*
             * WARNING! This code competes with other cpus.  It is ok
             * for us to not drain RChunks here but we might as well, and
             * it is ok if more accumulate after we're done.
             *
             * Set RSignal before pulling rchunks off, indicating that we
             * will be moving ourselves off of the ZoneAry.  Remote ends will
             * read RSignal before putting rchunks on thus interlocking
             * their IPI signaling.
             */
            if (z->z_RChunks == NULL)
                atomic_swap_int(&z->z_RSignal, 1);

            while ((bchunk = z->z_RChunks) != NULL) {
                cpu_ccfence();
                if (atomic_cmpset_ptr(&z->z_RChunks, bchunk, NULL)) {
                    *z->z_LChunksp = bchunk;
                    while (bchunk) {
                        chunk_mark_free(z, bchunk);
                        z->z_LChunksp = &bchunk->c_Next;
                        bchunk = bchunk->c_Next;
                        ++z->z_NFree;
                    }
                    break;
                }
            }
#endif
            /*
             * Remove from the zone list if no free chunks remain.
             * Clear RSignal
             */
            if (z->z_NFree == 0) {
                slgd->ZoneAry[zi] = z->z_Next;
                z->z_Next = NULL;
            } else {
                z->z_RSignal = 0;
            }
        }

        /*
         * Fast path, we have chunks available in z_LChunks.
         */
        chunk = z->z_LChunks;
        if (chunk) {
                chunk_mark_allocated(z, chunk);
                z->z_LChunks = chunk->c_Next;
                if (z->z_LChunks == NULL)
                        z->z_LChunksp = &z->z_LChunks;
                goto done;
        }

        /*
         * No chunks are available in LChunks, the free chunk MUST be
         * in the never-before-used memory area, controlled by UIndex.
         *
         * The consequences are very serious if our zone got corrupted so
         * we use an explicit panic rather than a KASSERT.
         */
        if (z->z_UIndex + 1 != z->z_NMax)
            ++z->z_UIndex;
        else
            z->z_UIndex = 0;

        if (z->z_UIndex == z->z_UEndIndex)
            panic("slaballoc: corrupted zone");

        chunk = (SLChunk *)(z->z_BasePtr + z->z_UIndex * size);
        if ((z->z_Flags & SLZF_UNOTZEROD) == 0) {
            flags &= ~M_ZERO;
            flags |= M_PASSIVE_ZERO;
        }
        chunk_mark_allocated(z, chunk);
        goto done;
    }

    /*
     * If all zones are exhausted we need to allocate a new zone for this
     * index.  Use M_ZERO to take advantage of pre-zerod pages.  Also see
     * UAlloc use above in regards to M_ZERO.  Note that when we are reusing
     * a zone from the FreeZones list UAlloc'd data will not be zero'd, and
     * we do not pre-zero it because we do not want to mess up the L1 cache.
     *
     * At least one subsystem, the tty code (see CROUND) expects power-of-2
     * allocations to be power-of-2 aligned.  We maintain compatibility by
     * adjusting the base offset below.
     */
    {
        int off;
        int *kup;

        if ((z = slgd->FreeZones) != NULL) {
            slgd->FreeZones = z->z_Next;
            --slgd->NFreeZones;
            bzero(z, sizeof(SLZone));
            z->z_Flags |= SLZF_UNOTZEROD;
        } else {
            z = kmem_slab_alloc(ZoneSize, ZoneSize, flags|M_ZERO);
            if (z == NULL)
                goto fail;
            atomic_add_int(&ZoneGenAlloc, (int)ZoneSize / 1024);
        }

        /*
         * How big is the base structure?
         */
#if defined(INVARIANTS)
        /*
         * Make room for z_Bitmap.  An exact calculation is somewhat more
         * complicated so don't make an exact calculation.
         */
        off = offsetof(SLZone, z_Bitmap[(ZoneSize / size + 31) / 32]);
        bzero(z->z_Bitmap, (ZoneSize / size + 31) / 8);
#else
        off = sizeof(SLZone);
#endif

        /*
         * Guarentee power-of-2 alignment for power-of-2-sized chunks.
         * Otherwise just 8-byte align the data.
         */
        if ((size | (size - 1)) + 1 == (size << 1))
            off = (off + size - 1) & ~(size - 1);
        else
            off = (off + MIN_CHUNK_MASK) & ~MIN_CHUNK_MASK;
        z->z_Magic = ZALLOC_SLAB_MAGIC;
        z->z_ZoneIndex = zi;
        z->z_NMax = (ZoneSize - off) / size;
        z->z_NFree = z->z_NMax - 1;
        z->z_BasePtr = (char *)z + off;
        z->z_UIndex = z->z_UEndIndex = slgd->JunkIndex % z->z_NMax;
        z->z_ChunkSize = size;
        z->z_CpuGd = gd;
        z->z_Cpu = gd->gd_cpuid;
        z->z_LChunksp = &z->z_LChunks;
        chunk = (SLChunk *)(z->z_BasePtr + z->z_UIndex * size);
        z->z_Next = slgd->ZoneAry[zi];
        slgd->ZoneAry[zi] = z;
        if ((z->z_Flags & SLZF_UNOTZEROD) == 0) {
            flags &= ~M_ZERO;   /* already zero'd */
            flags |= M_PASSIVE_ZERO;
        }
        kup = btokup(z);
        *kup = -(z->z_Cpu + 1); /* -1 to -(N+1) */
        chunk_mark_allocated(z, chunk);

        /*
         * Slide the base index for initial allocations out of the next
         * zone we create so we do not over-weight the lower part of the
         * cpu memory caches.
         */
        slgd->JunkIndex = (slgd->JunkIndex + ZALLOC_SLAB_SLIDE)
                                & (ZALLOC_MAX_ZONE_SIZE - 1);
    }

done:
    ++type->ks_inuse[gd->gd_cpuid];
    type->ks_memuse[gd->gd_cpuid] += size;
    type->ks_loosememuse += size;       /* not MP synchronized */
    crit_exit();

    if (flags & M_ZERO)
        bzero(chunk, size);
#ifdef INVARIANTS
    else if ((flags & (M_ZERO|M_PASSIVE_ZERO)) == 0) {
        if (use_malloc_pattern) {
            for (i = 0; i < size; i += sizeof(int)) {
                *(int *)((char *)chunk + i) = -1;
            }
        }
        chunk->c_Next = (void *)-1; /* avoid accidental double-free check */
    }
#endif
    logmemory(malloc_end, chunk, type, size, flags);
    return(chunk);
fail:
    crit_exit();
    logmemory(malloc_end, NULL, type, size, flags);
    return(NULL);
}

/*
 * kernel realloc.  (SLAB ALLOCATOR) (MP SAFE)
 *
 * Generally speaking this routine is not called very often and we do
 * not attempt to optimize it beyond reusing the same pointer if the
 * new size fits within the chunking of the old pointer's zone.
 */
void *
krealloc(void *ptr, unsigned long size, struct malloc_type *type, int flags)
{
    unsigned long osize;
    SLZone *z;
    void *nptr;
    int *kup;

    KKASSERT((flags & M_ZERO) == 0);    /* not supported */

    if (ptr == NULL || ptr == ZERO_LENGTH_PTR)
        return(kmalloc(size, type, flags));
    if (size == 0) {
        kfree(ptr, type);
        return(NULL);
    }

    /*
     * Handle oversized allocations.  XXX we really should require that a
     * size be passed to free() instead of this nonsense.
     */
    kup = btokup(ptr);
    if (*kup > 0) {
        osize = *kup << PAGE_SHIFT;
        if (osize == round_page(size))
            return(ptr);
        if ((nptr = kmalloc(size, type, flags)) == NULL)
            return(NULL);
        bcopy(ptr, nptr, min(size, osize));
        kfree(ptr, type);
        return(nptr);
    }

    /*
     * Get the original allocation's zone.  If the new request winds up
     * using the same chunk size we do not have to do anything.
     */
    z = (SLZone *)((uintptr_t)ptr & ZoneMask);
    kup = btokup(z);
    KKASSERT(*kup < 0);
    KKASSERT(z->z_Magic == ZALLOC_SLAB_MAGIC);

    /*
     * Allocate memory for the new request size.  Note that zoneindex has
     * already adjusted the request size to the appropriate chunk size, which
     * should optimize our bcopy().  Then copy and return the new pointer.
     *
     * Resizing a non-power-of-2 allocation to a power-of-2 size does not
     * necessary align the result.
     *
     * We can only zoneindex (to align size to the chunk size) if the new
     * size is not too large.
     */
    if (size < ZoneLimit) {
        zoneindex(&size);
        if (z->z_ChunkSize == size)
            return(ptr);
    }
    if ((nptr = kmalloc(size, type, flags)) == NULL)
        return(NULL);
    bcopy(ptr, nptr, min(size, z->z_ChunkSize));
    kfree(ptr, type);
    return(nptr);
}

/*
 * Return the kmalloc limit for this type, in bytes.
 */
long
kmalloc_limit(struct malloc_type *type)
{
    if (type->ks_limit == 0) {
        crit_enter();
        if (type->ks_limit == 0)
            malloc_init(type);
        crit_exit();
    }
    return(type->ks_limit);
}

/*
 * Allocate a copy of the specified string.
 *
 * (MP SAFE) (MAY BLOCK)
 */
char *
kstrdup(const char *str, struct malloc_type *type)
{
    int zlen;   /* length inclusive of terminating NUL */
    char *nstr;

    if (str == NULL)
        return(NULL);
    zlen = strlen(str) + 1;
    nstr = kmalloc(zlen, type, M_WAITOK);
    bcopy(str, nstr, zlen);
    return(nstr);
}

#ifdef SMP
/*
 * Notify our cpu that a remote cpu has freed some chunks in a zone that
 * we own.  RCount will be bumped so the memory should be good, but validate
 * that it really is.
 */
static
void
kfree_remote(void *ptr)
{
    SLGlobalData *slgd;
    SLChunk *bchunk;
    SLZone *z;
    int nfree;
    int *kup;

    slgd = &mycpu->gd_slab;
    z = ptr;
    kup = btokup(z);
    KKASSERT(*kup == -((int)mycpuid + 1));
    KKASSERT(z->z_RCount > 0);
    atomic_subtract_int(&z->z_RCount, 1);

    logmemory(free_rem_beg, z, NULL, 0, 0);
    KKASSERT(z->z_Magic == ZALLOC_SLAB_MAGIC);
    KKASSERT(z->z_Cpu  == mycpu->gd_cpuid);
    nfree = z->z_NFree;

    /*
     * Indicate that we will no longer be off of the ZoneAry by
     * clearing RSignal.
     */
    if (z->z_RChunks)
        z->z_RSignal = 0;

    /*
     * Atomically extract the bchunks list and then process it back
     * into the lchunks list.  We want to append our bchunks to the
     * lchunks list and not prepend since we likely do not have
     * cache mastership of the related data (not that it helps since
     * we are using c_Next).
     */
    while ((bchunk = z->z_RChunks) != NULL) {
        cpu_ccfence();
        if (atomic_cmpset_ptr(&z->z_RChunks, bchunk, NULL)) {
            *z->z_LChunksp = bchunk;
            while (bchunk) {
                    chunk_mark_free(z, bchunk);
                    z->z_LChunksp = &bchunk->c_Next;
                    bchunk = bchunk->c_Next;
                    ++z->z_NFree;
            }
            break;
        }
    }
    if (z->z_NFree && nfree == 0) {
        z->z_Next = slgd->ZoneAry[z->z_ZoneIndex];
        slgd->ZoneAry[z->z_ZoneIndex] = z;
    }

    /*
     * If the zone becomes totally free, and there are other zones we
     * can allocate from, move this zone to the FreeZones list.  Since
     * this code can be called from an IPI callback, do *NOT* try to mess
     * with kernel_map here.  Hysteresis will be performed at malloc() time.
     *
     * Do not move the zone if there is an IPI inflight, otherwise MP
     * races can result in our free_remote code accessing a destroyed
     * zone.
     */
    if (z->z_NFree == z->z_NMax &&
        (z->z_Next || slgd->ZoneAry[z->z_ZoneIndex] != z) &&
        z->z_RCount == 0
    ) {
        SLZone **pz;
        int *kup;

        for (pz = &slgd->ZoneAry[z->z_ZoneIndex];
             z != *pz;
             pz = &(*pz)->z_Next) {
            ;
        }
        *pz = z->z_Next;
        z->z_Magic = -1;
        z->z_Next = slgd->FreeZones;
        slgd->FreeZones = z;
        ++slgd->NFreeZones;
        kup = btokup(z);
        *kup = 0;
    }
    logmemory(free_rem_end, z, bchunk, 0, 0);
}

#endif

/*
 * free (SLAB ALLOCATOR)
 *
 * Free a memory block previously allocated by malloc.  Note that we do not
 * attempt to update ks_loosememuse as MP races could prevent us from
 * checking memory limits in malloc.
 *
 * MPSAFE
 */
void
kfree(void *ptr, struct malloc_type *type)
{
    SLZone *z;
    SLChunk *chunk;
    SLGlobalData *slgd;
    struct globaldata *gd;
    int *kup;
    unsigned long size;
#ifdef SMP
    SLChunk *bchunk;
    int rsignal;
#endif

    logmemory_quick(free_beg);
    gd = mycpu;
    slgd = &gd->gd_slab;

    if (ptr == NULL)
        panic("trying to free NULL pointer");

    /*
     * Handle special 0-byte allocations
     */
    if (ptr == ZERO_LENGTH_PTR) {
        logmemory(free_zero, ptr, type, -1, 0);
        logmemory_quick(free_end);
        return;
    }

    /*
     * Panic on bad malloc type
     */
    if (type->ks_magic != M_MAGIC)
        panic("free: malloc type lacks magic");

    /*
     * Handle oversized allocations.  XXX we really should require that a
     * size be passed to free() instead of this nonsense.
     *
     * This code is never called via an ipi.
     */
    kup = btokup(ptr);
    if (*kup > 0) {
        size = *kup << PAGE_SHIFT;
        *kup = 0;
#ifdef INVARIANTS
        KKASSERT(sizeof(weirdary) <= size);
        bcopy(weirdary, ptr, sizeof(weirdary));
#endif
        /*
         * NOTE: For oversized allocations we do not record the
         *           originating cpu.  It gets freed on the cpu calling
         *           kfree().  The statistics are in aggregate.
         *
         * note: XXX we have still inherited the interrupts-can't-block
         * assumption.  An interrupt thread does not bump
         * gd_intr_nesting_level so check TDF_INTTHREAD.  This is
         * primarily until we can fix softupdate's assumptions about free().
         */
        crit_enter();
        --type->ks_inuse[gd->gd_cpuid];
        type->ks_memuse[gd->gd_cpuid] -= size;
        if (mycpu->gd_intr_nesting_level ||
            (gd->gd_curthread->td_flags & TDF_INTTHREAD))
        {
            logmemory(free_ovsz_delayed, ptr, type, size, 0);
            z = (SLZone *)ptr;
            z->z_Magic = ZALLOC_OVSZ_MAGIC;
            z->z_Next = slgd->FreeOvZones;
            z->z_ChunkSize = size;
            slgd->FreeOvZones = z;
            crit_exit();
        } else {
            crit_exit();
            logmemory(free_ovsz, ptr, type, size, 0);
            kmem_slab_free(ptr, size);  /* may block */
            atomic_add_int(&ZoneBigAlloc, -(int)size / 1024);
        }
        logmemory_quick(free_end);
        return;
    }

    /*
     * Zone case.  Figure out the zone based on the fact that it is
     * ZoneSize aligned. 
     */
    z = (SLZone *)((uintptr_t)ptr & ZoneMask);
    kup = btokup(z);
    KKASSERT(*kup < 0);
    KKASSERT(z->z_Magic == ZALLOC_SLAB_MAGIC);

    /*
     * If we do not own the zone then use atomic ops to free to the
     * remote cpu linked list and notify the target zone using a
     * passive message.
     *
     * The target zone cannot be deallocated while we own a chunk of it,
     * so the zone header's storage is stable until the very moment
     * we adjust z_RChunks.  After that we cannot safely dereference (z).
     *
     * (no critical section needed)
     */
    if (z->z_CpuGd != gd) {
#ifdef SMP
        /*
         * Making these adjustments now allow us to avoid passing (type)
         * to the remote cpu.  Note that ks_inuse/ks_memuse is being
         * adjusted on OUR cpu, not the zone cpu, but it should all still
         * sum up properly and cancel out.
         */
        crit_enter();
        --type->ks_inuse[gd->gd_cpuid];
        type->ks_memuse[gd->gd_cpuid] -= z->z_ChunkSize;
        crit_exit();

        /*
         * WARNING! This code competes with other cpus.  Once we
         *          successfully link the chunk to RChunks the remote
         *          cpu can rip z's storage out from under us.
         *
         *          Bumping RCount prevents z's storage from getting
         *          ripped out.
         */
        rsignal = z->z_RSignal;
        cpu_lfence();
        if (rsignal)
                atomic_add_int(&z->z_RCount, 1);

        chunk = ptr;
        for (;;) {
            bchunk = z->z_RChunks;
            cpu_ccfence();
            chunk->c_Next = bchunk;
            cpu_sfence();

            if (atomic_cmpset_ptr(&z->z_RChunks, bchunk, chunk))
                break;
        }

        /*
         * We have to signal the remote cpu if our actions will cause
         * the remote zone to be placed back on ZoneAry so it can
         * move the zone back on.
         *
         * We only need to deal with NULL->non-NULL RChunk transitions
         * and only if z_RSignal is set.  We interlock by reading rsignal
         * before adding our chunk to RChunks.  This should result in
         * virtually no IPI traffic.
         *
         * We can use a passive IPI to reduce overhead even further.
         */
        if (bchunk == NULL && rsignal) {
            logmemory(free_request, ptr, type, z->z_ChunkSize, 0);
            lwkt_send_ipiq_passive(z->z_CpuGd, kfree_remote, z);
            /* z can get ripped out from under us from this point on */
        } else if (rsignal) {
            atomic_subtract_int(&z->z_RCount, 1);
            /* z can get ripped out from under us from this point on */
        }
#else
        panic("Corrupt SLZone");
#endif
        logmemory_quick(free_end);
        return;
    }

    /*
     * kfree locally
     */
    logmemory(free_chunk, ptr, type, z->z_ChunkSize, 0);

    crit_enter();
    chunk = ptr;
    chunk_mark_free(z, chunk);

    /*
     * Put weird data into the memory to detect modifications after freeing,
     * illegal pointer use after freeing (we should fault on the odd address),
     * and so forth.  XXX needs more work, see the old malloc code.
     */
#ifdef INVARIANTS
    if (z->z_ChunkSize < sizeof(weirdary))
        bcopy(weirdary, chunk, z->z_ChunkSize);
    else
        bcopy(weirdary, chunk, sizeof(weirdary));
#endif

    /*
     * Add this free non-zero'd chunk to a linked list for reuse.  Add
     * to the front of the linked list so it is more likely to be
     * reallocated, since it is already in our L1 cache.
     */
#ifdef INVARIANTS
    if ((vm_offset_t)chunk < KvaStart || (vm_offset_t)chunk >= KvaEnd)
        panic("BADFREE %p", chunk);
#endif
    chunk->c_Next = z->z_LChunks;
    z->z_LChunks = chunk;
    if (chunk->c_Next == NULL)
            z->z_LChunksp = &chunk->c_Next;

#ifdef INVARIANTS
    if (chunk->c_Next && (vm_offset_t)chunk->c_Next < KvaStart)
        panic("BADFREE2");
#endif

    /*
     * Bump the number of free chunks.  If it becomes non-zero the zone
     * must be added back onto the appropriate list.
     */
    if (z->z_NFree++ == 0) {
        z->z_Next = slgd->ZoneAry[z->z_ZoneIndex];
        slgd->ZoneAry[z->z_ZoneIndex] = z;
    }

    --type->ks_inuse[z->z_Cpu];
    type->ks_memuse[z->z_Cpu] -= z->z_ChunkSize;

    /*
     * If the zone becomes totally free, and there are other zones we
     * can allocate from, move this zone to the FreeZones list.  Since
     * this code can be called from an IPI callback, do *NOT* try to mess
     * with kernel_map here.  Hysteresis will be performed at malloc() time.
     */
    if (z->z_NFree == z->z_NMax && 
        (z->z_Next || slgd->ZoneAry[z->z_ZoneIndex] != z) &&
        z->z_RCount == 0
    ) {
        SLZone **pz;
        int *kup;

        for (pz = &slgd->ZoneAry[z->z_ZoneIndex]; z != *pz; pz = &(*pz)->z_Next)
            ;
        *pz = z->z_Next;
        z->z_Magic = -1;
        z->z_Next = slgd->FreeZones;
        slgd->FreeZones = z;
        ++slgd->NFreeZones;
        kup = btokup(z);
        *kup = 0;
    }
    logmemory_quick(free_end);
    crit_exit();
}

#if defined(INVARIANTS)

/*
 * Helper routines for sanity checks
 */
static
void
chunk_mark_allocated(SLZone *z, void *chunk)
{
    int bitdex = ((char *)chunk - (char *)z->z_BasePtr) / z->z_ChunkSize;
    __uint32_t *bitptr;

    KKASSERT((((intptr_t)chunk ^ (intptr_t)z) & ZoneMask) == 0);
    KASSERT(bitdex >= 0 && bitdex < z->z_NMax,
            ("memory chunk %p bit index %d is illegal", chunk, bitdex));
    bitptr = &z->z_Bitmap[bitdex >> 5];
    bitdex &= 31;
    KASSERT((*bitptr & (1 << bitdex)) == 0,
            ("memory chunk %p is already allocated!", chunk));
    *bitptr |= 1 << bitdex;
}

static
void
chunk_mark_free(SLZone *z, void *chunk)
{
    int bitdex = ((char *)chunk - (char *)z->z_BasePtr) / z->z_ChunkSize;
    __uint32_t *bitptr;

    KKASSERT((((intptr_t)chunk ^ (intptr_t)z) & ZoneMask) == 0);
    KASSERT(bitdex >= 0 && bitdex < z->z_NMax,
            ("memory chunk %p bit index %d is illegal!", chunk, bitdex));
    bitptr = &z->z_Bitmap[bitdex >> 5];
    bitdex &= 31;
    KASSERT((*bitptr & (1 << bitdex)) != 0,
            ("memory chunk %p is already free!", chunk));
    *bitptr &= ~(1 << bitdex);
}

#endif

/*
 * kmem_slab_alloc()
 *
 *      Directly allocate and wire kernel memory in PAGE_SIZE chunks with the
 *      specified alignment.  M_* flags are expected in the flags field.
 *
 *      Alignment must be a multiple of PAGE_SIZE.
 *
 *      NOTE! XXX For the moment we use vm_map_entry_reserve/release(),
 *      but when we move zalloc() over to use this function as its backend
 *      we will have to switch to kreserve/krelease and call reserve(0)
 *      after the new space is made available.
 *
 *      Interrupt code which has preempted other code is not allowed to
 *      use PQ_CACHE pages.  However, if an interrupt thread is run
 *      non-preemptively or blocks and then runs non-preemptively, then
 *      it is free to use PQ_CACHE pages.
 */
static void *
kmem_slab_alloc(vm_size_t size, vm_offset_t align, int flags)
{
    vm_size_t i;
    vm_offset_t addr;
    int count, vmflags, base_vmflags;
    thread_t td;

    size = round_page(size);
    addr = vm_map_min(&kernel_map);

    /*
     * Reserve properly aligned space from kernel_map.  RNOWAIT allocations
     * cannot block.
     */
    if (flags & M_RNOWAIT) {
        if (lwkt_trytoken(&vm_token) == 0)
            return(NULL);
    } else {
        lwkt_gettoken(&vm_token);
    }
    count = vm_map_entry_reserve(MAP_RESERVE_COUNT);
    crit_enter();
    vm_map_lock(&kernel_map);
    if (vm_map_findspace(&kernel_map, addr, size, align, 0, &addr)) {
        vm_map_unlock(&kernel_map);
        if ((flags & M_NULLOK) == 0)
            panic("kmem_slab_alloc(): kernel_map ran out of space!");
        vm_map_entry_release(count);
        crit_exit();
        lwkt_reltoken(&vm_token);
        return(NULL);
    }

    /*
     * kernel_object maps 1:1 to kernel_map.
     */
    vm_object_reference(&kernel_object);
    vm_map_insert(&kernel_map, &count, 
                    &kernel_object, addr, addr, addr + size,
                    VM_MAPTYPE_NORMAL,
                    VM_PROT_ALL, VM_PROT_ALL,
                    0);

    td = curthread;

    base_vmflags = 0;
    if (flags & M_ZERO)
        base_vmflags |= VM_ALLOC_ZERO;
    if (flags & M_USE_RESERVE)
        base_vmflags |= VM_ALLOC_SYSTEM;
    if (flags & M_USE_INTERRUPT_RESERVE)
        base_vmflags |= VM_ALLOC_INTERRUPT;
    if ((flags & (M_RNOWAIT|M_WAITOK)) == 0) {
        panic("kmem_slab_alloc: bad flags %08x (%p)",
              flags, ((int **)&size)[-1]);
    }


    /*
     * Allocate the pages.  Do not mess with the PG_ZERO flag yet.
     */
    for (i = 0; i < size; i += PAGE_SIZE) {
        vm_page_t m;

        /*
         * VM_ALLOC_NORMAL can only be set if we are not preempting.
         *
         * VM_ALLOC_SYSTEM is automatically set if we are preempting and
         * M_WAITOK was specified as an alternative (i.e. M_USE_RESERVE is
         * implied in this case), though I'm not sure if we really need to
         * do that.
         */
        vmflags = base_vmflags;
        if (flags & M_WAITOK) {
            if (td->td_preempted)
                vmflags |= VM_ALLOC_SYSTEM;
            else
                vmflags |= VM_ALLOC_NORMAL;
        }

        m = vm_page_alloc(&kernel_object, OFF_TO_IDX(addr + i), vmflags);

        /*
         * If the allocation failed we either return NULL or we retry.
         *
         * If M_WAITOK is specified we wait for more memory and retry.
         * If M_WAITOK is specified from a preemption we yield instead of
         * wait.  Livelock will not occur because the interrupt thread
         * will not be preempting anyone the second time around after the
         * yield.
         */
        if (m == NULL) {
            if (flags & M_WAITOK) {
                if (td->td_preempted) {
                    vm_map_unlock(&kernel_map);
                    lwkt_switch();
                    vm_map_lock(&kernel_map);
                } else {
                    vm_map_unlock(&kernel_map);
                    vm_wait(0);
                    vm_map_lock(&kernel_map);
                }
                i -= PAGE_SIZE; /* retry */
                continue;
            }

            /*
             * We were unable to recover, cleanup and return NULL
             *
             * (vm_token already held)
             */
            while (i != 0) {
                i -= PAGE_SIZE;
                m = vm_page_lookup(&kernel_object, OFF_TO_IDX(addr + i));
                /* page should already be busy */
                vm_page_free(m);
            }
            vm_map_delete(&kernel_map, addr, addr + size, &count);
            vm_map_unlock(&kernel_map);
            vm_map_entry_release(count);
            crit_exit();
            lwkt_reltoken(&vm_token);
            return(NULL);
        }
    }

    /*
     * Success!
     *
     * Mark the map entry as non-pageable using a routine that allows us to
     * populate the underlying pages.
     *
     * The pages were busied by the allocations above.
     */
    vm_map_set_wired_quick(&kernel_map, addr, size, &count);
    crit_exit();

    /*
     * Enter the pages into the pmap and deal with PG_ZERO and M_ZERO.
     */
    lwkt_gettoken(&vm_token);
    for (i = 0; i < size; i += PAGE_SIZE) {
        vm_page_t m;

        m = vm_page_lookup(&kernel_object, OFF_TO_IDX(addr + i));
        m->valid = VM_PAGE_BITS_ALL;
        /* page should already be busy */
        vm_page_wire(m);
        vm_page_wakeup(m);
        pmap_enter(&kernel_pmap, addr + i, m, VM_PROT_ALL, 1);
        if ((m->flags & PG_ZERO) == 0 && (flags & M_ZERO))
            bzero((char *)addr + i, PAGE_SIZE);
        vm_page_flag_clear(m, PG_ZERO);
        KKASSERT(m->flags & (PG_WRITEABLE | PG_MAPPED));
        vm_page_flag_set(m, PG_REFERENCED);
    }
    lwkt_reltoken(&vm_token);
    vm_map_unlock(&kernel_map);
    vm_map_entry_release(count);
    lwkt_reltoken(&vm_token);
    return((void *)addr);
}

/*
 * kmem_slab_free()
 */
static void
kmem_slab_free(void *ptr, vm_size_t size)
{
    crit_enter();
    lwkt_gettoken(&vm_token);
    vm_map_remove(&kernel_map, (vm_offset_t)ptr, (vm_offset_t)ptr + size);
    lwkt_reltoken(&vm_token);
    crit_exit();
}