HAMMER 18B/many: Stabilization pass

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

/*
 * KERN_SLABALLOC.C     - Kernel SLAB memory allocator
 * 
 * Copyright (c) 2003,2004 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 1.51 2007/11/18 09:53:19 sephe 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 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, 0, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_zero, 1, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_ovsz, 2, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_ovsz_delayed, 3, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_chunk, 4, MEMORY_STRING, MEMORY_ARG_SIZE);
#ifdef SMP
KTR_INFO(KTR_MEMORY, memory, free_request, 5, MEMORY_STRING, MEMORY_ARG_SIZE);
KTR_INFO(KTR_MEMORY, memory, free_remote, 6, MEMORY_STRING, MEMORY_ARG_SIZE);
#endif
KTR_INFO(KTR_MEMORY, memory, malloc_beg, 0, "malloc begin", 0);
KTR_INFO(KTR_MEMORY, memory, free_beg, 0, "free begin", 0);
KTR_INFO(KTR_MEMORY, memory, free_end, 0, "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 int ZoneMask;
struct malloc_type *kmemstatistics;     /* exported to vmstat */
static struct kmemusage *kmemusage;
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);
#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);

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

static void
kmeminit(void *dummy)
{
    vm_poff_t limsize;
    int usesize;
    int i;
    vm_pindex_t npg;

    limsize = (vm_poff_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 = ZoneSize - 1;
    ZonePageCount = ZoneSize / PAGE_SIZE;

    npg = KvaSize / PAGE_SIZE;
    kmemusage = kmem_slab_alloc(npg * sizeof(struct kmemusage), 
                                PAGE_SIZE, M_WAITOK|M_ZERO);

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

    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;
    vm_poff_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 = (vm_poff_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;
}

/*
 * 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);
}

/*
 * malloc()     (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;
    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 (ttl >= type->ks_limit) {
            if (flags & M_NULLOK) {
                logmemory(malloc, 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, 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.
     */
    while (slgd->NFreeZones > ZONE_RELS_THRESH && (flags & M_RNOWAIT) == 0) {
        crit_enter();
        if (slgd->NFreeZones > ZONE_RELS_THRESH) {      /* crit sect race */
            z = slgd->FreeZones;
            slgd->FreeZones = z->z_Next;
            --slgd->NFreeZones;
            kmem_slab_free(z, ZoneSize);        /* may block */
        }
        crit_exit();
    }
    /*
     * XXX handle oversized frees that were queued from free().
     */
    while (slgd->FreeOvZones && (flags & M_RNOWAIT) == 0) {
        crit_enter();
        if ((z = slgd->FreeOvZones) != NULL) {
            KKASSERT(z->z_Magic == ZALLOC_OVSZ_MAGIC);
            slgd->FreeOvZones = z->z_Next;
            kmem_slab_free(z, z->z_ChunkSize);  /* may block */
        }
        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)) {
        struct kmemusage *kup;

        size = round_page(size);
        chunk = kmem_slab_alloc(size, PAGE_SIZE, flags);
        if (chunk == NULL) {
            logmemory(malloc, NULL, type, size, flags);
            return(NULL);
        }
        flags &= ~M_ZERO;       /* result already zero'd if M_ZERO was set */
        flags |= M_PASSIVE_ZERO;
        kup = btokup(chunk);
        kup->ku_pagecnt = size / PAGE_SIZE;
        kup->ku_cpu = gd->gd_cpuid;
        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 ((vm_offset_t)chunk < KvaStart || (vm_offset_t)chunk >= KvaEnd)
                        panic("chunk %p FFPG %d/%d", chunk, z->z_FirstFreePg, ZonePageCount);
                if (chunk->c_Next && (vm_offset_t)chunk->c_Next < KvaStart)
                        panic("chunkNEXT %p %p FFPG %d/%d", chunk, chunk->c_Next, z->z_FirstFreePg, ZonePageCount);
                chunk_mark_allocated(z, chunk);
#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;
        }
#if defined(INVARIANTS)
        chunk_mark_allocated(z, chunk);
#endif
        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 = kmem_slab_alloc(ZoneSize, ZoneSize, flags|M_ZERO);
            if (z == NULL)
                goto fail;
        }

        /*
         * 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_FirstFreePg = ZonePageCount;
        z->z_CpuGd = gd;
        z->z_Cpu = gd->gd_cpuid;
        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;
        }
#if defined(INVARIANTS)
        chunk_mark_allocated(z, chunk);
#endif

        /*
         * 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, chunk, type, size, flags);
    return(chunk);
fail:
    crit_exit();
    logmemory(malloc, 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)
{
    SLZone *z;
    void *nptr;
    unsigned long osize;

    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.
     */
    {
        struct kmemusage *kup;

        kup = btokup(ptr);
        if (kup->ku_pagecnt) {
            osize = kup->ku_pagecnt << 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 & ~(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 = kmalloc(size, type, flags)) == NULL)
        return(NULL);
    bcopy(ptr, nptr, min(size, z->z_ChunkSize));
    kfree(ptr, type);
    return(nptr);
}

/*
 * 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
/*
 * free()       (SLAB ALLOCATOR)
 *
 *      Free the specified chunk of memory.
 */
static
void
free_remote(void *ptr)
{
    logmemory(free_remote, ptr, *(struct malloc_type **)ptr, -1, 0);
    kfree(ptr, *(struct malloc_type **)ptr);
}

#endif

/*
 * free (SLAB ALLOCATOR)
 *
 * Free a memory block previously allocated by malloc.  Note that we do not
 * attempt to uplodate 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 pgno;

    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;
    }

    /*
     * 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.
     */
    {
        struct kmemusage *kup;
        unsigned long size;

        kup = btokup(ptr);
        if (kup->ku_pagecnt) {
            size = kup->ku_pagecnt << PAGE_SHIFT;
            kup->ku_pagecnt = 0;
#ifdef INVARIANTS
            KKASSERT(sizeof(weirdary) <= size);
            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 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 */
            }
            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 & ~(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.  Since the timing is non-critical, a passive
     * message is sent.
     */
    if (z->z_CpuGd != gd) {
        *(struct malloc_type **)ptr = type;
#ifdef SMP
        logmemory(free_request, ptr, type, z->z_ChunkSize, 0);
        lwkt_send_ipiq_passive(z->z_CpuGd, free_remote, ptr);
#else
        panic("Corrupt SLZone");
#endif
        logmemory_quick(free_end);
        return;
    }

    logmemory(free_chunk, ptr, type, z->z_ChunkSize, 0);

    if (type->ks_magic != M_MAGIC)
        panic("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);
        }
    }
    chunk_mark_free(z, 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 ((vm_offset_t)chunk < KvaStart || (vm_offset_t)chunk >= KvaEnd)
        panic("BADFREE %p", chunk);
#endif
    chunk->c_Next = z->z_PageAry[pgno];
    z->z_PageAry[pgno] = chunk;
#ifdef INVARIANTS
    if (chunk->c_Next && (vm_offset_t)chunk->c_Next < KvaStart)
        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;
    }
    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;

    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;

    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.
 *
 *      This routine will currently obtain the BGL.
 *
 * MPALMOSTSAFE - acquires mplock
 */
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 (try_mplock() == 0)
            return(NULL);
    } else {
        get_mplock();
    }
    count = vm_map_entry_reserve(MAP_RESERVE_COUNT);
    crit_enter();
    vm_map_lock(&kernel_map);
    if (vm_map_findspace(&kernel_map, addr, size, align, &addr)) {
        vm_map_unlock(&kernel_map);
        if ((flags & M_NULLOK) == 0)
            panic("kmem_slab_alloc(): kernel_map ran out of space!");
        crit_exit();
        vm_map_entry_release(count);
        rel_mplock();
        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 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_yield();
                    vm_map_lock(&kernel_map);
                } else {
                    vm_map_unlock(&kernel_map);
                    vm_wait();
                    vm_map_lock(&kernel_map);
                }
                i -= PAGE_SIZE; /* retry */
                continue;
            }

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

    /*
     * Success!
     *
     * Mark the map entry as non-pageable using a routine that allows us to
     * populate the underlying pages.
     */
    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.
     */
    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;
        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);
        vm_page_flag_set(m, PG_MAPPED | PG_WRITEABLE | PG_REFERENCED);
    }
    vm_map_unlock(&kernel_map);
    vm_map_entry_release(count);
    rel_mplock();
    return((void *)addr);
}

/*
 * kmem_slab_free()
 *
 * MPALMOSTSAFE - acquires mplock
 */
static void
kmem_slab_free(void *ptr, vm_size_t size)
{
    get_mplock();
    crit_enter();
    vm_map_remove(&kernel_map, (vm_offset_t)ptr, (vm_offset_t)ptr + size);
    crit_exit();
    rel_mplock();
}