Pre-2.0 release: Sync with HAMMER 64 - NFS and cross-device link fixes.

[dragonfly.git] / lib / libcaps / slaballoc.c

/*
 * SLABALLOC.C  - Userland SLAB memory allocator
 *
 * Copyright (c) 2003 Matthew Dillon <dillon@backplane.com>
 * 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 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 AUTHOR 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/lib/libcaps/slaballoc.c,v 1.4 2004/07/04 22:44:26 eirikn Exp $
 *
 * This module implements a thread-safe slab allocator for userland.
 *
 * 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.
 * To mitigate this we attempt to select a reasonable zone size based on
 * available system memory.  e.g. 32K instead of 128K.  Also since the
 * slab allocator is operating out of virtual memory in userland the actual
 * physical memory use is not as bad as it might otherwise be.
 *
 * The upside is that overhead is bounded... waste goes down as use goes up.
 *
 * 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.
 *
 *      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 <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stdint.h>
#include <sys/malloc.h>
#include "thread.h"
#include <sys/thread.h>
#include <sys/msgport.h>
#include <sys/errno.h>
#include "globaldata.h"
#include <sys/sysctl.h>
#include <machine/cpufunc.h>
#include <sys/thread2.h>
#include <sys/msgport2.h>

#define arysize(ary)    (sizeof(ary)/sizeof((ary)[0]))
#define slab_min(a,b)   (((a)<(b)) ? (a) : (b))

/*
 * Fixed globals (not per-cpu)
 */
static int ZoneSize;
static int ZoneLimit;
static int ZonePageCount;
static int ZonePageLimit;
static int ZoneMask;
static struct malloc_type *kmemstatistics;
static int32_t weirdary[16];

/*
 * 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)

#define SLOVERSZ_HSIZE          8192
#define SLOVERSZ_HMASK          (SLOVERSZ_HSIZE - 1)

#define SLOVERSZ_HASH(ptr)      ((((uintptr_t)ptr >> PAGE_SHIFT) ^ \
                                ((uintptr_t)ptr >> (PAGE_SHIFT * 2))) & \
                                SLOVERSZ_HMASK)

SLOversized *SLOvHash[SLOVERSZ_HSIZE];

/*
 * 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_OVERSIZED, "overszinfo", "Oversized Info Blocks");

static __inline
SLOversized **
get_oversized(void *ptr)
{
    SLOversized **slovpp;
    SLOversized *slov;

    for (slovpp = &SLOvHash[SLOVERSZ_HASH(ptr)];
        (slov = *slovpp) != NULL;
        slovpp = &slov->ov_Next
    ) {
        if (slov->ov_Ptr == ptr)
            return(slovpp);
    }
    return(NULL);
}
 
/*
 * 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). 
 */
void
slab_init(void)
{
    int i;
    int error;
    int pagecnt;
    int pagecnt_size = sizeof(pagecnt);

    error = sysctlbyname("vm.stats.vm.v_page_count",
                        &pagecnt, &pagecnt_size, NULL, 0);
    if (error == 0) {
        vm_poff_t limsize;
        int usesize;

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

        ZoneSize = ZALLOC_MIN_ZONE_SIZE;
        while (ZoneSize < ZALLOC_MAX_ZONE_SIZE && (ZoneSize << 1) < usesize)
            ZoneSize <<= 1;
    } else {
        ZoneSize = ZALLOC_MIN_ZONE_SIZE;
    }
    ZoneLimit = ZoneSize / 4;
    if (ZoneLimit > ZALLOC_ZONE_LIMIT)
        ZoneLimit = ZALLOC_ZONE_LIMIT;
    ZoneMask = ZoneSize - 1;
    ZonePageLimit = PAGE_SIZE * 4;
    ZonePageCount = ZoneSize / PAGE_SIZE;

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

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

    /*
     * Skip if already initialized
     */
    if (type->ks_limit != 0)
        return;

    type->ks_magic = M_MAGIC;
    limsize = (vm_poff_t)-1;    /* unlimited */
    type->ks_limit = limsize / 10;
    type->ks_next = kmemstatistics;
    kmemstatistics = type;
}

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

#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) {
        printf("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;
}

/*
 * 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);
}

/*
 * slab_malloc()
 *
 *      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_NOWAIT        - return NULL instead of blocking.
 *      M_ZERO          - zero the returned memory.
 */
void *
slab_malloc(unsigned long size, struct malloc_type *type, int flags)
{
    SLZone *z;
    SLChunk *chunk;
    SLGlobalData *slgd;
    struct globaldata *gd;
    int zi;

    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)
            slab_malloc_init(type);
        crit_exit();
    }
    ++type->ks_calls;

    /*
     * Handle the case where the limit is reached.  Panic if can't return
     * NULL.  XXX the original malloc code looped, but this tended to
     * simply deadlock the computer.
     */
    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;
        if (ttl >= type->ks_limit) {
            if (flags & (M_NOWAIT|M_NULLOK))
                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)
        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.
     */
    while (slgd->NFreeZones > ZONE_RELS_THRESH && (flags & M_NOWAIT) == 0) {
        crit_enter();
        if (slgd->NFreeZones > ZONE_RELS_THRESH) {      /* crit sect race */
            z = slgd->FreeZones;
            slgd->FreeZones = z->z_Next;
            --slgd->NFreeZones;
            munmap(z, ZoneSize);
        }
        crit_exit();
    }
    /*
     * XXX handle oversized frees that were queued from free().
     */
    while (slgd->FreeOvZones && (flags & M_NOWAIT) == 0) {
        crit_enter();
        if ((z = slgd->FreeOvZones) != NULL) {
            KKASSERT(z->z_Magic == ZALLOC_OVSZ_MAGIC);
            slgd->FreeOvZones = z->z_Next;
            munmap(z, z->z_ChunkSize);
        }
        crit_exit();
    }

    /*
     * Handle large allocations directly.  There should not be very many of
     * these so performance is not a big issue.
     *
     * Guarentee page alignment for allocations in multiples of PAGE_SIZE
     */
    if (size >= ZoneLimit || (size & PAGE_MASK) == 0) {
        SLOversized **slovpp;
        SLOversized *slov;

        slov = slab_malloc(sizeof(SLOversized), M_OVERSIZED, M_ZERO);
        if (slov == NULL)
            return(NULL);

        size = round_page(size);
        chunk = mmap(NULL, size, PROT_READ|PROT_WRITE,
                        MAP_ANON|MAP_PRIVATE, -1, 0);
        if (chunk == MAP_FAILED) {
            slab_free(slov, M_OVERSIZED);
            return(NULL);
        }
        flags &= ~M_ZERO;       /* result already zero'd if M_ZERO was set */
        flags |= M_PASSIVE_ZERO;

        slov->ov_Ptr = chunk;
        slov->ov_Bytes = size;
        slovpp = &SLOvHash[SLOVERSZ_HASH(chunk)];
        slov->ov_Next = *slovpp;
        *slovpp = slov;
        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) {
        KKASSERT(z->z_NFree > 0);

        /*
         * Remove us from the ZoneAry[] when we become empty
         */
        if (--z->z_NFree == 0) {
            slgd->ZoneAry[zi] = z->z_Next;
            z->z_Next = NULL;
        }

        /*
         * Locate a chunk in a free page.  This attempts to localize
         * reallocations into earlier pages without us having to sort
         * the chunk list.  A chunk may still overlap a page boundary.
         */
        while (z->z_FirstFreePg < ZonePageCount) {
            if ((chunk = z->z_PageAry[z->z_FirstFreePg]) != NULL) {
#ifdef DIAGNOSTIC
                /*
                 * Diagnostic: c_Next is not total garbage.
                 */
                KKASSERT(chunk->c_Next == NULL ||
                        ((intptr_t)chunk->c_Next & IN_SAME_PAGE_MASK) ==
                        ((intptr_t)chunk & IN_SAME_PAGE_MASK));
#endif
#ifdef INVARIANTS
                if ((uintptr_t)chunk < VM_MIN_KERNEL_ADDRESS)
                        panic("chunk %p FFPG %d/%d", chunk, z->z_FirstFreePg, ZonePageCount);
                if (chunk->c_Next && (uintptr_t)chunk->c_Next < VM_MIN_KERNEL_ADDRESS)
                        panic("chunkNEXT %p %p FFPG %d/%d", chunk, chunk->c_Next, z->z_FirstFreePg, ZonePageCount);
#endif
                z->z_PageAry[z->z_FirstFreePg] = chunk->c_Next;
                goto done;
            }
            ++z->z_FirstFreePg;
        }

        /*
         * No chunks are available but NFree said we had some memory, so
         * it must be available in the never-before-used-memory area
         * governed by UIndex.  The consequences are very serious if our zone
         * got corrupted so we use an explicit panic rather then a KASSERT.
         */
        if (z->z_UIndex + 1 != z->z_NMax)
            z->z_UIndex = z->z_UIndex + 1;
        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;
        }
        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;

        if ((z = slgd->FreeZones) != NULL) {
            slgd->FreeZones = z->z_Next;
            --slgd->NFreeZones;
            bzero(z, sizeof(SLZone));
            z->z_Flags |= SLZF_UNOTZEROD;
        } else {
            z = mmap(NULL, ZoneSize, PROT_READ|PROT_WRITE,
                    MAP_ANON|MAP_PRIVATE, -1, 0);
            if (z == MAP_FAILED)
                goto fail;
        }

        /*
         * 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 = (sizeof(SLZone) + size - 1) & ~(size - 1);
        else
            off = (sizeof(SLZone) + 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_FirstFreePg = ZonePageCount;
        z->z_Cpu = gd->gd_cpuid;
        z->z_CpuGd = gd;
        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;
        }

        /*
         * 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;
    crit_exit();
    if (flags & M_ZERO)
        bzero(chunk, size);
#ifdef INVARIANTS
    else if ((flags & (M_ZERO|M_PASSIVE_ZERO)) == 0)
        chunk->c_Next = (void *)-1; /* avoid accidental double-free check */
#endif
    return(chunk);
fail:
    crit_exit();
    return(NULL);
}

void *
slab_realloc(void *ptr, unsigned long size, struct malloc_type *type, int flags)
{
    SLZone *z;
    SLOversized **slovpp;
    SLOversized *slov;
    void *nptr;
    unsigned long osize;

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

    /*
     * Handle oversized allocations. 
     */
    if ((slovpp = get_oversized(ptr)) != NULL) {
        slov = *slovpp;
        osize = slov->ov_Bytes;
        if (osize == round_page(size))
            return(ptr);
        if ((nptr = slab_malloc(size, type, flags)) == NULL)
            return(NULL);
        bcopy(ptr, nptr, slab_min(size, osize));
        slab_free(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 & ~(uintptr_t)ZoneMask);
    KKASSERT(z->z_Magic == ZALLOC_SLAB_MAGIC);

    zoneindex(&size);
    if (z->z_ChunkSize == size)
        return(ptr);

    /*
     * 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.
     */
    if ((nptr = slab_malloc(size, type, flags)) == NULL)
        return(NULL);
    bcopy(ptr, nptr, slab_min(size, z->z_ChunkSize));
    slab_free(ptr, type);
    return(nptr);
}

#ifdef SMP
/*
 * slab_free()  (SLAB ALLOCATOR)
 *
 *      Free the specified chunk of memory.
 */
static
void
slab_free_remote(void *ptr)
{
    slab_free(ptr, *(struct malloc_type **)ptr);
}

#endif

void
slab_free(void *ptr, struct malloc_type *type)
{
    SLZone *z;
    SLOversized **slovpp;
    SLOversized *slov;
    SLChunk *chunk;
    SLGlobalData *slgd;
    struct globaldata *gd;
    int pgno;

    gd = mycpu;
    slgd = &gd->gd_slab;

    /*
     * Handle special 0-byte allocations
     */
    if (ptr == ZERO_LENGTH_PTR)
        return;

    /*
     * Handle oversized allocations.  XXX we really should require that a
     * size be passed to slab_free() instead of this nonsense.
     *
     * This code is never called via an ipi.
     */
    if ((slovpp = get_oversized(ptr)) != NULL) {
        slov = *slovpp;
        *slovpp = slov->ov_Next;

#ifdef INVARIANTS
        KKASSERT(sizeof(weirdary) <= slov->ov_Bytes);
        bcopy(weirdary, ptr, sizeof(weirdary));
#endif
        /*
         * note: we always adjust our cpu's slot, not the originating
         * cpu (kup->ku_cpuid).  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 
         * slab_free().
         */
        crit_enter();
        --type->ks_inuse[gd->gd_cpuid];
        type->ks_memuse[gd->gd_cpuid] -= slov->ov_Bytes;
        if (mycpu->gd_intr_nesting_level || (gd->gd_curthread->td_flags & TDF_INTTHREAD)) {
            z = (SLZone *)ptr;
            z->z_Magic = ZALLOC_OVSZ_MAGIC;
            z->z_Next = slgd->FreeOvZones;
            z->z_ChunkSize = slov->ov_Bytes;
            slgd->FreeOvZones = z;
            crit_exit();
        } else {
            crit_exit();
            munmap(ptr, slov->ov_Bytes);
        }
        slab_free(slov, M_OVERSIZED);
        return;
    }

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

    /*
     * If we do not own the zone then forward the request to the
     * cpu that does.  The freeing code does not need the byte count
     * unless DIAGNOSTIC is set.
     */
    if (z->z_CpuGd != gd) {
        *(struct malloc_type **)ptr = type;
#ifdef SMP
        lwkt_send_ipiq(z->z_CpuGd, slab_free_remote, ptr);
#else
        panic("Corrupt SLZone");
#endif
        return;
    }

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

    crit_enter();
    pgno = ((char *)ptr - (char *)z) >> PAGE_SHIFT;
    chunk = ptr;

#ifdef INVARIANTS
    /*
     * Attempt to detect a double-free.  To reduce overhead we only check
     * if there appears to be link pointer at the base of the data.
     */
    if (((intptr_t)chunk->c_Next - (intptr_t)z) >> PAGE_SHIFT == pgno) {
        SLChunk *scan;
        for (scan = z->z_PageAry[pgno]; scan; scan = scan->c_Next) {
            if (scan == chunk)
                panic("Double free at %p", chunk);
        }
    }
#endif

    /*
     * 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, adjust
     * z_FirstFreePg.
     */
#ifdef INVARIANTS
    if ((uintptr_t)chunk < VM_MIN_KERNEL_ADDRESS)
        panic("BADFREE %p\n", chunk);
#endif
    chunk->c_Next = z->z_PageAry[pgno];
    z->z_PageAry[pgno] = chunk;
#ifdef INVARIANTS
    if (chunk->c_Next && (uintptr_t)chunk->c_Next < VM_MIN_KERNEL_ADDRESS)
        panic("BADFREE2");
#endif
    if (z->z_FirstFreePg > pgno)
        z->z_FirstFreePg = pgno;

    /*
     * 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)
    ) {
        SLZone **pz;

        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;
    }
    crit_exit();
}