/*
 * KERN_KMALLOC.C       - Kernel memory allocator
 *
 * Copyright (c) 2021 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.
 */

/*
 * This module implements the kmalloc_obj allocator.  This is a type-stable
 * allocator that uses the same base structures (e.g. malloc_type) plus
 * some extensions to efficiently implement single-type zones.
 *
 * All memory management is zone based.  When a zone is destroyed, all of
 * its memory is returned to the system with no fragmentation.
 *
 * A mini-slab allocator hangs directly off the zone structure (malloc_type).
 * Since the object zones are single-size-only, the slab allocator is very
 * simple and currently utilizes just two per-zone/per-cpu slabs (active and
 * alternate) before kicking up to the per-zone cache.  Beyond that we just
 * have the per-cpu globaldata-based 'free slab' cache to avoid unnecessary
 * kernel_map mappings and unmappings.
 *
 * The advantage of this that zones don't stomp over each other and cause
 * excessive fragmentation in the slabs.  For example, when you umount a
 * large tmpfs filesystem, most of its memory (all of its kmalloc_obj memory)
 * is returned to the system.
 */

#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/spinlock.h>
#include <sys/lock.h>
#include <sys/thread.h>
#include <sys/globaldata.h>
#include <sys/sysctl.h>
#include <sys/ktr.h>
#include <sys/malloc.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/spinlock2.h>
#include <sys/thread2.h>
#include <sys/exislock2.h>
#include <vm/vm_page2.h>

#define MEMORY_STRING   "ptr=%p type=%p size=%lu flags=%04x"
#define MEMORY_ARGS     void *ptr, void *type, unsigned long size, int flags

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

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

__read_frequently static int KMGDMaxFreeSlabs = KMGD_MAXFREESLABS;
SYSCTL_INT(_kern, OID_AUTO, kzone_cache, CTLFLAG_RW, &KMGDMaxFreeSlabs, 0, "");
__read_frequently static int kzone_bretire = 4;
SYSCTL_INT(_kern, OID_AUTO, kzone_bretire, CTLFLAG_RW, &kzone_bretire, 0, "");
__read_frequently static int kzone_debug;
SYSCTL_INT(_kern, OID_AUTO, kzone_debug, CTLFLAG_RW, &kzone_debug, 0, "");

__read_frequently struct kmalloc_slab kslab_dummy;

static void malloc_slab_destroy(struct malloc_type *type,
                        struct kmalloc_slab **slabp);

/*
 * Cache a chain of slabs onto their respective cpu slab caches.  Any slabs
 * which we cannot cache will be returned.
 *
 * free_slabs        - Current structure may only be accessed by current cpu
 * remote_free_slabs - Only atomic swap operations are allowed.
 * free_count        - Only atomic operations are allowed.
 *
 * If the count is sufficient to cache the entire list, NULL is returned.
 * Otherwise the portion that was not cached is returned.
 */
static __noinline
struct kmalloc_slab *
gslab_cache(struct kmalloc_slab *slab)
{
        struct kmalloc_slab *save;
        struct kmalloc_slab *next;
        struct kmalloc_slab *res;
        struct kmalloc_slab **resp;
        struct kmalloc_slab **slabp;
        globaldata_t rgd;
        size_t count;
        int cpuid;

        res = NULL;
        resp = &res;
        KKASSERT(((uintptr_t)slab & KMALLOC_SLAB_MASK) == 0);

        /*
         * Given the slab list, get the cpuid and clip off as many matching
         * elements as fits in the cache.
         */
        while (slab) {
                cpuid = slab->orig_cpuid;
                rgd = globaldata_find(cpuid);

                KKASSERT(((uintptr_t)slab & KMALLOC_SLAB_MASK) == 0);
                /*
                 * Doesn't fit in cache, put on return list.
                 */
                if (rgd->gd_kmslab.free_count >= KMGDMaxFreeSlabs) {
                        *resp = slab;
                        resp = &slab->next;
                        slab = slab->next;
                        continue;
                }

                /*
                 * Collect.  We aren't required to match-up the original cpu
                 * with the disposal cpu, but its a good idea to retain
                 * memory locality.
                 *
                 * The slabs we collect are going into the global cache,
                 * remove the type association.
                 */
                KKASSERT(((uintptr_t)slab & KMALLOC_SLAB_MASK) == 0);
                slabp = &slab->next;
                count = 1;
                slab->type = NULL;

                while ((next = *slabp) != NULL &&
                       next->orig_cpuid == cpuid &&
                       rgd->gd_kmslab.free_count + count < KMGDMaxFreeSlabs)
                {
                        KKASSERT(((uintptr_t)next & KMALLOC_SLAB_MASK) == 0);
                        next->type = NULL;
                        ++count;
                        slabp = &next->next;
                }

                /*
                 * Safety, unhook before next, next is not included in the
                 * list starting with slab that is being pre-pended
                 * to remote_free_slabs.
                 */
                *slabp = NULL;

                /*
                 * Now atomically pre-pend slab...*slabp to remote_free_slabs.
                 * Pump the count first (its ok if the actual chain length
                 * races the count update).
                 *
                 * NOTE: In the loop, (save) is updated by fcmpset.
                 */
                atomic_add_long(&rgd->gd_kmslab.free_count, count);
                save = rgd->gd_kmslab.remote_free_slabs;
                for (;;) {
                        KKASSERT(((uintptr_t)save & KMALLOC_SLAB_MASK) == 0);
                        *slabp = save;  /* end of slab list chain to... */
                        cpu_ccfence();
                        if (atomic_fcmpset_ptr(
                                &rgd->gd_kmslab.remote_free_slabs,
                                &save, slab))
                        {
                                break;
                        }
                }

                /*
                 * Setup for next loop
                 */
                slab = next;
        }

        /*
         * Terminate the result list and return it
         */
        *resp = NULL;

        return res;
}

/*
 * May only be called on current cpu.  Pull a free slab from the
 * pcpu cache.  If we run out, move any slabs that have built-up
 * from remote cpus.
 *
 * We are only allowed to swap the remote_free_slabs head, we cannot
 * manipulate any next pointers while structures are sitting on that list.
 */
static __inline
struct kmalloc_slab *
gslab_alloc(globaldata_t gd)
{
        struct kmalloc_slab *slab;

        slab = gd->gd_kmslab.free_slabs;
        if (slab == NULL) {
                slab = atomic_swap_ptr(
                        (volatile void **)&gd->gd_kmslab.remote_free_slabs,
                        NULL);
                KKASSERT(((uintptr_t)slab & KMALLOC_SLAB_MASK) == 0);
        }
        if (slab) {
                gd->gd_kmslab.free_slabs = slab->next;
                slab->next = NULL;
                atomic_add_long(&gd->gd_kmslab.free_count, -1);
                KKASSERT(((uintptr_t)slab & KMALLOC_SLAB_MASK) == 0);
        }
        return slab;
}

void
malloc_mgt_init(struct malloc_type *type __unused,
                struct kmalloc_mgt *mgt, size_t size)
{
        size_t offset;
        size_t count;

        bzero(mgt, sizeof(*mgt));
        spin_init(&mgt->spin, "kmmgt");

        /*
         * Allows us to avoid a conditional.  The dummy slabs are empty
         * and have no objects.
         */
        mgt->active = &kslab_dummy;
        mgt->alternate = &kslab_dummy;
        mgt->empty_tailp = &mgt->empty;

        /*
         * Figure out the count by taking into account the size of the fobjs[]
         * array by adding it to the object size.  This initial calculation
         * ignores alignment edge-cases that might require the count to be
         * reduced.
         */
        offset = offsetof(struct kmalloc_slab, fobjs[0]);
        count = (KMALLOC_SLAB_SIZE - offset) / (size + sizeof(void *));

        /*
         * Recalculate the offset of the first object, this time including
         * the required alignment.  (size) should already be aligned.  This
         * may push the last object beyond the slab so check and loop with
         * a reduced count as necessary.
         *
         * Ok, theoretically the count should not actually change since the
         * division above rounds-down (that is, any mis-alignment is already
         * not included in the count calculation).  But I'm not going to take
         * any chances and check anyway as a safety in case some programmer
         * changes the code above later.  This is not a time-critical code
         * path.
         */
        offset = offsetof(struct kmalloc_slab, fobjs[count]);
        offset = __VM_CACHELINE_ALIGN(offset);

        while (offset + size * count > KMALLOC_SLAB_SIZE) {
                --count;
                offset = offsetof(struct kmalloc_slab, fobjs[count]);
                offset = __VM_CACHELINE_ALIGN(offset);
                KKASSERT (offset + size * count <= KMALLOC_SLAB_SIZE);
        }

        mgt->slab_offset = offset;
        mgt->slab_count  = count;
}

void
malloc_mgt_relocate(struct kmalloc_mgt *src, struct kmalloc_mgt *dst)
{
        struct kmalloc_slab **slabp;

        spin_init(&dst->spin, "kmmgt");
        slabp = &dst->empty;

        while (*slabp) {
                slabp = &(*slabp)->next;
        }
        dst->empty_tailp = slabp;
}

void
malloc_mgt_uninit(struct malloc_type *type, struct kmalloc_mgt *mgt)
{
        if (mgt->active != &kslab_dummy)
                malloc_slab_destroy(type, &mgt->active);
        mgt->active = NULL;

        if (mgt->alternate != &kslab_dummy)
                malloc_slab_destroy(type, &mgt->alternate);
        mgt->alternate = NULL;

        malloc_slab_destroy(type, &mgt->partial);
        malloc_slab_destroy(type, &mgt->full);
        malloc_slab_destroy(type, &mgt->empty);
        mgt->npartial = 0;
        mgt->nfull = 0;
        mgt->nempty = 0;
        mgt->empty_tailp = &mgt->empty;

        spin_uninit(&mgt->spin);
}

/*
 * Destroy a list of slabs.  Attempt to cache the slabs on the specified
 * (possibly remote) cpu.  This allows slabs that were operating on a
 * particular cpu to be disposed of back to that same cpu.
 */
static void
malloc_slab_destroy(struct malloc_type *type, struct kmalloc_slab **slabp)
{
        struct kmalloc_slab *slab;
        struct kmalloc_slab *base;
        struct kmalloc_slab **basep;
        size_t delta;

        if (*slabp == NULL)
                return;

        /*
         * Collect all slabs that can actually be destroyed, complain
         * about the rest.
         */
        base = NULL;
        basep = &base;
        while ((slab = *slabp) != NULL) {
                KKASSERT(((uintptr_t)slab & KMALLOC_SLAB_MASK) == 0);

                delta = slab->findex - slab->aindex;
                if (delta == slab->ncount) {
                        *slabp = slab->next;    /* unlink */
                        *basep = slab;          /* link into base list */
                        basep = &slab->next;
                } else {
                        kprintf("%s: slab %p %zd objects "
                                "were still allocated\n",
                                type->ks_shortdesc, slab,
                                slab->ncount - delta);
                        /* leave link intact and iterate */
                        slabp = &slab->next;
                }
        }

        /*
         * Terminate the base list of slabs that can be destroyed,
         * then cache as many of them as possible.
         */
        *basep = NULL;
        if (base == NULL)
                return;
        base = gslab_cache(base);

        /*
         * Destroy the remainder
         */
        while ((slab = base) != NULL) {
                base = slab->next;
                slab->next = (void *)(uintptr_t)-1;
                kmem_slab_free(slab, KMALLOC_SLAB_SIZE);
        }
}

/*
 * Objects can be freed to an empty slab at any time, causing it to no
 * longer be empty.  To improve performance, we do not try to pro-actively
 * move such slabs to the appropriate partial or full list upon kfree_obj().
 * Instead, a poller comes along and tests the slabs on the empty list
 * periodically, and moves slabs that are no longer empty to the appropriate
 * list.
 *
 * --
 *
 * Poll a limited number of slabs on the empty list and move them
 * to the appropriate full or partial list.  Slabs left on the empty
 * list are rotated to the tail.
 *
 * If gcache is non-zero this function will try to place full slabs into
 * the globaldata cache, if it isn't already too full.
 *
 * The mgt is spin-locked
 *
 * Returns non-zero if the ggm updates possibly made slabs available for
 * allocation.
 */
static int
malloc_mgt_poll_empty_locked(struct kmalloc_mgt *ggm, int count)
{
        struct kmalloc_slab *marker;
        struct kmalloc_slab *slab;
        size_t delta;
        int got_something;

        if (ggm->empty == NULL)
                return 0;

        got_something = 0;
        marker = ggm->empty;

        while (count-- && (slab = ggm->empty) != NULL) {
                /*
                 * Unlink from empty
                 */
                ggm->empty = slab->next;
                slab->next = NULL;
                --ggm->nempty;
                if (ggm->empty_tailp == &slab->next)
                        ggm->empty_tailp = &ggm->empty;

                /*
                 * Check partial, full, and empty.  We rotate
                 * empty entries to the end of the empty list.
                 *
                 * NOTE: For a fully-freeable slab we also have
                 *       to check xindex.
                 */
                delta = slab->findex - slab->aindex;
                if (delta == slab->ncount) {
                        /*
                         * Stuff into the full list.  This requires setting
                         * the exis sequence number via exis_terminate().
                         */
                        KKASSERT(slab->next == NULL);
                        exis_terminate(&slab->exis);
                        slab->next = ggm->full;
                        ggm->full = slab;
                        got_something = 1;
                        ++ggm->nfull;
                } else if (delta) {
                        /*
                         * Partially full
                         */
                        KKASSERT(slab->next == NULL);
                        slab->next = ggm->partial;
                        ggm->partial = slab;
                        got_something = 1;
                        ++ggm->npartial;
                } else {
                        /*
                         * Empty
                         */
                        KKASSERT(slab->next == NULL);
                        *ggm->empty_tailp = slab;
                        ggm->empty_tailp = &slab->next;
                        ++ggm->nempty;
                        if (ggm->empty == marker)
                                break;
                }
        }
        return got_something;
}

/*
 * Called once a second with the zone interlocked against destruction.
 *
 * Returns non-zero to tell the caller to iterate to the next type,
 * else the caller should stay on the current type.
 */
int
malloc_mgt_poll(struct malloc_type *type)
{
        struct kmalloc_mgt *ggm;
        struct kmalloc_slab *slab;
        struct kmalloc_slab **slabp;
        struct kmalloc_slab *base;
        struct kmalloc_slab **basep;
        size_t delta;
        int donext;
        int count;
        int retired;

        if ((type->ks_flags & KSF_OBJSIZE) == 0)
                return 1;

        /*
         * Check the partial, full, and empty lists for full freeable slabs
         * in excess of desired caching count.
         */
        ggm = &type->ks_mgt;
        spin_lock(&ggm->spin);

        /*
         * Move empty slabs to partial or full as appropriate.  We
         * don't bother checking partial slabs to see if they are full
         * for now.
         */
        malloc_mgt_poll_empty_locked(ggm, 16);

        /*
         * Ok, cleanout some of the full mags from the full list
         */
        base = NULL;
        basep = &base;
        count = ggm->nfull;
        retired = 0;
        cpu_ccfence();

        if (count > KMALLOC_MAXFREEMAGS) {
                slabp = &ggm->full;
                count -= KMALLOC_MAXFREEMAGS;
                if (count > 16)
                        count = 16;

                while (count && (slab = *slabp) != NULL) {
                        delta = slab->findex - slab->aindex;
                        if (delta == slab->ncount &&
                            slab->xindex == slab->findex &&
                            exis_freeable(&slab->exis))
                        {
                                /*
                                 * (1) No allocated entries in the structure,
                                 *     this should always be the case from the
                                 *     full list.
                                 *
                                 * (2) kfree_obj() has fully completed.  Just
                                 *     checking findex is not sufficient since
                                 *     it is incremented to reserve the slot
                                 *     before the element is loaded into it.
                                 *
                                 * (3) The slab has been on the full list for
                                 *     a sufficient number of EXIS
                                 *     pseudo_ticks, for type-safety.
                                 */
                                *slabp = slab->next;
                                *basep = slab;
                                basep = &slab->next;
                                --ggm->nfull;
                                ++ggm->gcache_count;
                                if (++retired == kzone_bretire)
                                        break;
                        } else {
                                slabp = &slab->next;
                        }
                        --count;
                }
                *basep = NULL;  /* terminate the retirement list */
                donext = (*slabp == NULL);
        } else {
                donext = 1;
        }
        spin_unlock(&ggm->spin);

        /*
         * Clean out any slabs that we couldn't stow in the globaldata cache.
         */
        if (retired) {
                if (kzone_debug) {
                        kprintf("kmalloc_poll: %s retire %d\n",
                                type->ks_shortdesc, retired);
                }
                base = gslab_cache(base);
                while ((slab = base) != NULL) {
                        base = base->next;
                        slab->next = NULL;
                        kmem_slab_free(slab, KMALLOC_SLAB_SIZE);
                }
        }

        return donext;
}

/*
 * Optional bitmap double-free check.  This is typically turned on by
 * default for safety (sys/_malloc.h)
 */
#ifdef KMALLOC_CHECK_DOUBLE_FREE

static __inline void
bmap_set(struct kmalloc_slab *slab, void *obj)
{
        uint64_t *ptr;
        uint64_t mask;
        size_t i = (((uintptr_t)obj & KMALLOC_SLAB_MASK) - slab->offset) /
                   slab->objsize;

        ptr = &slab->bmap[i >> 6];
        mask = (uint64_t)1U << (i & 63);
        KKASSERT(i < slab->ncount && (*ptr & mask) == 0);
        atomic_set_64(ptr, mask);
}

static __inline void
bmap_clr(struct kmalloc_slab *slab, void *obj)
{
        uint64_t *ptr;
        uint64_t mask;
        size_t i = (((uintptr_t)obj & KMALLOC_SLAB_MASK) - slab->offset) /
                   slab->objsize;

        ptr = &slab->bmap[i >> 6];
        mask = (uint64_t)1U << (i & 63);
        KKASSERT(i < slab->ncount && (*ptr & mask) != 0);
        atomic_clear_64(ptr, mask);
}

#endif

/*
 * Cleanup a mgt structure.
 *
 * Always called from the current cpu, so we can manipulate the various
 * lists freely.
 *
 * WARNING: findex can race, fobjs[n] is updated after findex is incremented,
 *          and 'full'
 */
#if 0
static void
mgt_cleanup(struct kmalloc_mgt *mgt)
{
#if 0
        struct kmalloc_slab **slabp;
        struct kmalloc_slab *slab;
        size_t delta;
        size_t total;
#endif
}
#endif

#ifdef SLAB_DEBUG
void *
_kmalloc_obj_debug(unsigned long size, struct malloc_type *type, int flags,
              const char *file, int line)
#else
void *
_kmalloc_obj(unsigned long size, struct malloc_type *type, int flags)
#endif
{
        struct kmalloc_slab *slab;
        struct kmalloc_use *use;
        struct kmalloc_mgt *mgt;
        struct kmalloc_mgt *ggm;
        globaldata_t gd;
        void *obj;
        size_t delta;

        /*
         * Check limits
         */
        while (__predict_false(type->ks_loosememuse >= type->ks_limit)) {
                long ttl;
                int n;

                for (n = ttl = 0; n < ncpus; ++n)
                        ttl += type->ks_use[n].memuse;
                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)
                                return(NULL);
                        panic("%s: malloc limit exceeded", type->ks_shortdesc);
                }
        }

        /*
         * Setup
         */
        crit_enter();
        logmemory_quick(malloc_beg);
        KKASSERT(size == type->ks_objsize);
        gd = mycpu;
        use = &type->ks_use[gd->gd_cpuid];

retry:
        /*
         * Check active
         *
         * NOTE: obj can be NULL if racing a _kfree_obj().
         */
        mgt = &use->mgt;
        slab = mgt->active;                     /* Might be dummy */
        delta = slab->findex - slab->aindex;
        if (__predict_true(delta != 0)) {       /* Cannot be dummy */
                size_t i;

                i = slab->aindex % slab->ncount;
                obj = slab->fobjs[i];
                if (__predict_true(obj != NULL)) {
                        slab->fobjs[i] = NULL;
                        ++slab->aindex;
#ifdef KMALLOC_CHECK_DOUBLE_FREE
                        bmap_set(slab, obj);
#endif
                        goto found;
                }
        }

        /*
         * Check alternate.  If we find something, swap it with
         * the active.
         *
         * NOTE: It is possible for exhausted slabs to recover entries
         *       via _kfree_obj(), so we just keep swapping until both
         *       are empty.
         *
         * NOTE: obj can be NULL if racing a _kfree_obj().
         */
        slab = mgt->alternate;                  /* Might be dummy */
        delta = slab->findex - slab->aindex;
        if (__predict_true(delta != 0)) {       /* Cannot be dummy */
                size_t i;

                mgt->alternate = mgt->active;
                mgt->active = slab;
                i = slab->aindex % slab->ncount;
                obj = slab->fobjs[i];
                if (__predict_true(obj != NULL)) {
                        slab->fobjs[i] = NULL;
                        ++slab->aindex;
#ifdef KMALLOC_CHECK_DOUBLE_FREE
                        bmap_set(slab, obj);
#endif
                        goto found;
                }
        }

        /*
         * Rotate a slab from the global mgt into the pcpu mgt.
         *
         *      G(partial, full) -> active -> alternate -> G(empty)
         *
         * We try to exhaust partials first to reduce fragmentation, then
         * dig into the fulls.
         */
        ggm = &type->ks_mgt;
        spin_lock(&ggm->spin);

rerotate:
        if (ggm->partial) {
                slab = mgt->alternate;          /* Might be dummy */
                mgt->alternate = mgt->active;   /* Might be dummy */
                mgt->active = ggm->partial;
                ggm->partial = ggm->partial->next;
                mgt->active->next = NULL;
                --ggm->npartial;
                if (slab != &kslab_dummy) {
                        KKASSERT(slab->next == NULL);
                        *ggm->empty_tailp = slab;
                        ggm->empty_tailp = &slab->next;
                        ++ggm->nempty;
                }
                spin_unlock(&ggm->spin);
                goto retry;
        }

        if (ggm->full) {
                slab = mgt->alternate;          /* Might be dummy */
                mgt->alternate = mgt->active;   /* Might be dummy */
                mgt->active = ggm->full;
                ggm->full = ggm->full->next;
                mgt->active->next = NULL;
                --ggm->nfull;
                exis_setlive(&mgt->active->exis);
                if (slab != &kslab_dummy) {
                        KKASSERT(slab->next == NULL);
                        *ggm->empty_tailp = slab;
                        ggm->empty_tailp = &slab->next;
                        ++ggm->nempty;
                }
                spin_unlock(&ggm->spin);
                goto retry;
        }

        /*
         * We couldn't find anything, scan a limited number of empty entries
         * looking for something with objects.  This will also free excess
         * full lists that meet requirements.
         */
        if (malloc_mgt_poll_empty_locked(ggm, 16))
                goto rerotate;

        /*
         * Absolutely nothing is available, allocate a new slab and
         * rotate it in.
         *
         * Try to get a slab from the global pcpu slab cache (very cheap).
         * If that fails, allocate a new slab (very expensive).
         */
        spin_unlock(&ggm->spin);

        if (gd->gd_kmslab.free_count == 0 || (slab = gslab_alloc(gd)) == NULL) {
                slab = kmem_slab_alloc(KMALLOC_SLAB_SIZE, KMALLOC_SLAB_SIZE,
                                       M_WAITOK);
        }

        bzero(slab, sizeof(*slab));
        KKASSERT(offsetof(struct kmalloc_slab, fobjs[use->mgt.slab_count]) <=
                 use->mgt.slab_offset);

        obj = (char *)slab + use->mgt.slab_offset;
        slab->type = type;
        slab->orig_cpuid = gd->gd_cpuid;
        slab->ncount = use->mgt.slab_count;
        slab->offset = use->mgt.slab_offset;
        slab->objsize = type->ks_objsize;
        slab->aindex = 0;
        slab->findex = slab->ncount;
        slab->xindex = slab->ncount;
        for (delta = 0; delta < slab->ncount; ++delta) {
                slab->fobjs[delta] = obj;
                obj = (char *)obj + type->ks_objsize;
        }

        /*
         * Sanity check, assert that the last byte of last object is still
         * in the slab.
         */
#if 0
        KKASSERT(((((uintptr_t)obj - 1) ^ (uintptr_t)slab) &
                  ~KMALLOC_SLAB_MASK) == 0);
#endif
        KASSERT(((((uintptr_t)obj - 1) ^ (uintptr_t)slab) &
                  ~KMALLOC_SLAB_MASK) == 0, ("SLAB %p ncount %zd objsize %zd obj=%p\n", slab, slab->ncount, slab->objsize, obj));
        slab->magic = KMALLOC_SLAB_MAGIC;
        spin_init(&slab->spin, "kmslb");

        /*
         * Rotate it in, then retry.
         *
         *      (NEW)slab -> active -> alternate -> G(empty)
         */
        spin_lock(&ggm->spin);
        if (mgt->alternate != &kslab_dummy) {
                struct kmalloc_slab *slab_tmp;

                slab_tmp = mgt->alternate;
                slab_tmp->next = NULL;
                *ggm->empty_tailp = slab_tmp;
                ggm->empty_tailp = &slab_tmp->next;
                ++ggm->nempty;
        }
        mgt->alternate = mgt->active;           /* Might be dummy */
        mgt->active = slab;
        spin_unlock(&ggm->spin);

        goto retry;

        /*
         * Found object, adjust statistics and return
         */
found:
        ++use->inuse;
        ++use->calls;
        use->memuse += size;
        use->loosememuse += size;
        if (__predict_false(use->loosememuse >= KMALLOC_LOOSE_SIZE)) {
            /* not MP synchronized */
            type->ks_loosememuse += use->loosememuse;
            use->loosememuse = 0;
        }

        /*
         * Handle remaining flags.  M_ZERO is typically not set because
         * the inline macro deals with zeroing for constant sizes.
         */
        if (__predict_false(flags & M_ZERO))
            bzero(obj, size);

        crit_exit();
        logmemory(malloc_end, NULL, type, size, flags);

        return(obj);
}

/*
 * Free a type-stable object.  We have the base structure and can
 * calculate the slab, but from this direction we don't know which
 * mgt structure or list the slab might be on.
 */
void
_kfree_obj(void *obj, struct malloc_type *type)
{
        struct kmalloc_slab *slab;
        struct kmalloc_use *use;
        globaldata_t gd;
        size_t  delta;
        size_t  i;

        logmemory_quick(free_beg);
        gd = mycpu;

        /*
         * Calculate the slab from the pointer
         */
        slab = (void *)((uintptr_t)obj & ~KMALLOC_SLAB_MASK);
        delta = slab->findex - slab->aindex;
        KKASSERT(slab->magic == KMALLOC_SLAB_MAGIC && delta != slab->ncount);

        /*
         * We can only safely adjust the statistics for the current cpu.
         * Don't try to track down the original cpu.  The statistics will
         * be collected and fixed up by vmstat -m  (etc).
         */
        use = &slab->type->ks_use[gd->gd_cpuid];
        --use->inuse;
        use->memuse -= slab->objsize;

        /*
         * There MUST be free space in the slab since we are returning
         * the obj to the same slab it was allocated from.
         */
        i = atomic_fetchadd_long(&slab->findex, 1);
        i = i % slab->ncount;
        if (slab->fobjs[i] != NULL) {
                kprintf("_kfree_obj failure %zd/%zd/%zd\n",
                        slab->aindex, slab->findex, slab->ncount);
        }
#ifdef KMALLOC_CHECK_DOUBLE_FREE
        bmap_clr(slab, obj);
#endif
        KKASSERT(slab->fobjs[i] == NULL);
        slab->fobjs[i] = obj;
        atomic_add_long(&slab->xindex, 1);      /* synchronizer */

        logmemory_quick(free_end);
}