From 24fa9d19e113ab8dd219aaa270451921d513a0d8 Mon Sep 17 00:00:00 2001

From: Jeff Darcy <jdarcy@redhat.com>

Date: Fri, 14 Oct 2016 10:04:07 -0400

Subject: [PATCH 322/361] libglusterfs: make memory pools more thread-friendly

Early multiplexing tests revealed *massive* contention on certain

pools' global locks - especially for dictionaries and secondarily for

call stubs.  For the thread counts that multiplexing can create, a

more lock-free solution is clearly needed.  Also, the current mem-pool

implementation does a poor job releasing memory back to the system,

artificially inflating memory usage to match whatever the worst case

was since the process started.  This is bad in general, but especially

so for multiplexing where there are more pools and a major point of

the whole exercise is to reduce memory consumption.

The basic ideas for the new design are these

  There is one pool, globally, for each power-of-two size range.

  Every attempt to create a new pool within this range will instead

  add a reference to the existing pool.

  Instead of adding pools for each translator within each multiplexed

  brick (potentially infinite and quite possibly thousands), we

  allocate one set of size-based pools per *thread* (hundreds at

  worst).

  Each per-thread pool is divided into hot and cold lists.  Every

  allocation first attempts to use the hot list, then the cold list.

  When objects are freed, they always go on the hot list.

  There is one global "pool sweeper" thread, which periodically

  reclaims everything in each pool's cold list and then "demotes" the

  current hot list to be the new cold list.

  For normal allocation activity, only a per-thread lock need be

  taken, and even that only to guard against very rare contention from

  the pool sweeper.  When threads start and stop, a global lock must

  be taken to add them to the pool sweeper's list.  Lock contention is

  therefore extremely low, and the hot/cold lists also provide good

  locality.

A more complete explanation (of a similar earlier design) can be found

here:

 http://www.gluster.org/pipermail/gluster-devel/2016-October/051160.html

mainline:

> BUG: 1385758

> Reviewed-on: https://review.gluster.org/15645

> Smoke: Gluster Build System <jenkins@build.gluster.org>

> NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>

> CentOS-regression: Gluster Build System <jenkins@build.gluster.org>

> Reviewed-by: Xavier Hernandez <xhernandez@datalab.es>

> Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>

(cherry picked from commit 2d539668aa608ba885e5a4e1aed5e188f83f4a2f)

BUG: 1417815

Change-Id: I5bc8a1ba57cfb553998f979a498886e0d006e665

Signed-off-by: Jeff Darcy <jdarcy@redhat.com>

Reviewed-on: https://code.engineering.redhat.com/gerrit/101303

Tested-by: Milind Changire <mchangir@redhat.com>

Reviewed-by: Atin Mukherjee <amukherj@redhat.com>

---

 glusterfsd/src/glusterfsd.c     |   7 +

 libglusterfs/src/mem-pool.c     | 515 ++++++++++++++++++++++++----------------

 libglusterfs/src/mem-pool.h     |  67 ++++--

 libglusterfs/src/statedump.c    |   6 +-

 tests/basic/quota-anon-fd-nfs.t |   9 +

 5 files changed, 377 insertions(+), 227 deletions(-)

diff --git a/glusterfsd/src/glusterfsd.c b/glusterfsd/src/glusterfsd.c

index e16c943..485da4e 100644

--- a/glusterfsd/src/glusterfsd.c

+++ b/glusterfsd/src/glusterfsd.c

@@ -2429,6 +2429,13 @@ main (int argc, char *argv[])

         if (ret)

                 goto out;

+        /*

+         * If we do this before daemonize, the pool-sweeper thread dies with

+         * the parent, but we want to do it as soon as possible after that in

+         * case something else depends on pool allocations.

+         */

+        mem_pools_init ();

+

 #ifdef GF_LINUX_HOST_OS

 #ifdef HAVE_LINUX_OOM_H

         ret = set_oom_score_adj (ctx);

diff --git a/libglusterfs/src/mem-pool.c b/libglusterfs/src/mem-pool.c

index 88fbdf5..2b3208c 100644

--- a/libglusterfs/src/mem-pool.c

+++ b/libglusterfs/src/mem-pool.c

@@ -338,8 +338,20 @@ free:

 }

-/* Based on the mem-type that is used for the allocation, GF_FREE can be

+/*

+ * Based on the mem-type that is used for the allocation, GF_FREE can be

  * called, or something more intelligent for the structure can be done.

+ *

+ * NOTE: this will not work for allocations from a memory pool.  It never did,

+ * because those allocations never set the type in the first place.  Any caller

+ * that relies on knowing whether a particular type was allocated via a pool or

+ * not is *BROKEN*, or will be any time either this module or the module

+ * "owning" the type changes.  The proper way to handle this, assuming the

+ * caller is not smart enough to call a type-specific free function themselves,

+ * would be to create a callback interface where destructors for specific types

+ * can be registered so that code *here* (GF_FREE, mem_put, etc.) can do the

+ * right thing.  That allows type-specific behavior without creating the kind

+ * of fragile coupling that we have now.

  */

 int

 gf_get_mem_type (void *ptr)

@@ -358,78 +370,201 @@ gf_get_mem_type (void *ptr)

 }

+#define POOL_SMALLEST   7       /* i.e. 128 */

+#define POOL_LARGEST    20      /* i.e. 1048576 */

+#define NPOOLS          (POOL_LARGEST - POOL_SMALLEST + 1)

+#define N_COLD_LISTS    1024

+#define POOL_SWEEP_SECS 30

-struct mem_pool *

-mem_pool_new_fn (unsigned long sizeof_type,

-                 unsigned long count, char *name)

+static pthread_key_t            pool_key;

+static pthread_mutex_t          pool_lock       = PTHREAD_MUTEX_INITIALIZER;

+static struct list_head         pool_threads;

+static pthread_mutex_t          pool_free_lock  = PTHREAD_MUTEX_INITIALIZER;

+static struct list_head         pool_free_threads;

+static struct mem_pool          pools[NPOOLS];

+static size_t                   pool_list_size;

+static unsigned long            sweep_times;

+static unsigned long            sweep_usecs;

+static unsigned long            frees_to_system;

+

+typedef struct {

+        struct list_head        death_row;

+        pooled_obj_hdr_t        *cold_lists[N_COLD_LISTS];

+        unsigned int            n_cold_lists;

+} sweep_state_t;

+

+

+void

+collect_garbage (sweep_state_t *state, per_thread_pool_list_t *pool_list)

 {

-        struct mem_pool  *mem_pool = NULL;

-        unsigned long     padded_sizeof_type = 0;

-        GF_UNUSED void             *pool = NULL;

-        GF_UNUSED int               i = 0;

-        int               ret = 0;

-        GF_UNUSED struct list_head *list = NULL;

-        glusterfs_ctx_t  *ctx = NULL;

-

-        if (!sizeof_type || !count) {

-                gf_msg_callingfn ("mem-pool", GF_LOG_ERROR, EINVAL,

-                                  LG_MSG_INVALID_ARG, "invalid argument");

-                return NULL;

+        unsigned int            i;

+        per_thread_pool_t       *pt_pool;

+

+        if (pool_list->poison) {

+                list_del (&pool_list->thr_list);

+                list_add (&pool_list->thr_list, &state->death_row);

+                return;

         }

-        padded_sizeof_type = sizeof_type + GF_MEM_POOL_PAD_BOUNDARY;

-        mem_pool = GF_CALLOC (sizeof (*mem_pool), 1, gf_common_mt_mem_pool);

-        if (!mem_pool)

-                return NULL;

+        if (state->n_cold_lists >= N_COLD_LISTS) {

+                return;

+        }

-        ret = gf_asprintf (&mem_pool->name, "%s:%s", THIS->name, name);

-        if (ret < 0)

-                return NULL;

+        (void) pthread_spin_lock (&pool_list->lock);

+        for (i = 0; i < NPOOLS; ++i) {

+                pt_pool = &pool_list->pools[i];

+                if (pt_pool->cold_list) {

+                        state->cold_lists[state->n_cold_lists++]

+                                = pt_pool->cold_list;

+                }

+                pt_pool->cold_list = pt_pool->hot_list;

+                pt_pool->hot_list = NULL;

+                if (state->n_cold_lists >= N_COLD_LISTS) {

+                        /* We'll just catch up on a future pass. */

+                        break;

+                }

+        }

+        (void) pthread_spin_unlock (&pool_list->lock);

+}

-        if (!mem_pool->name) {

-                GF_FREE (mem_pool);

-                return NULL;

+

+void

+free_obj_list (pooled_obj_hdr_t *victim)

+{

+        pooled_obj_hdr_t        *next;

+

+        while (victim) {

+                next = victim->next;

+                free (victim);

+                victim = next;

+                ++frees_to_system;

         }

+}

-        LOCK_INIT (&mem_pool->lock);

-        INIT_LIST_HEAD (&mem_pool->list);

-        INIT_LIST_HEAD (&mem_pool->global_list);

+void *

+pool_sweeper (void *arg)

+{

+        sweep_state_t           state;

+        per_thread_pool_list_t  *pool_list;

+        per_thread_pool_list_t  *next_pl;

+        per_thread_pool_t       *pt_pool;

+        unsigned int            i;

+        struct timeval          begin_time;

+        struct timeval          end_time;

+        struct timeval          elapsed;

-        mem_pool->padded_sizeof_type = padded_sizeof_type;

-        mem_pool->real_sizeof_type = sizeof_type;

+        /*

+         * This is all a bit inelegant, but the point is to avoid doing

+         * expensive things (like freeing thousands of objects) while holding a

+         * global lock.  Thus, we split each iteration into three passes, with

+         * only the first and fastest holding the lock.

+         */

-#ifndef DEBUG

-        mem_pool->cold_count = count;

-        pool = GF_CALLOC (count, padded_sizeof_type, gf_common_mt_long);

-        if (!pool) {

-                GF_FREE (mem_pool->name);

-                GF_FREE (mem_pool);

-                return NULL;

+        for (;;) {

+                sleep (POOL_SWEEP_SECS);

+                INIT_LIST_HEAD (&state.death_row);

+                state.n_cold_lists = 0;

+

+                /* First pass: collect stuff that needs our attention. */

+                (void) gettimeofday (&begin_time, NULL);

+                (void) pthread_mutex_lock (&pool_lock);

+                list_for_each_entry_safe (pool_list, next_pl,

+                                          &pool_threads, thr_list) {

+                        collect_garbage (&state, pool_list);

+                }

+                (void) pthread_mutex_unlock (&pool_lock);

+                (void) gettimeofday (&end_time, NULL);

+                timersub (&end_time, &begin_time, &elapsed);

+                sweep_usecs += elapsed.tv_sec * 1000000 + elapsed.tv_usec;

+                sweep_times += 1;

+

+                /* Second pass: free dead pools. */

+                (void) pthread_mutex_lock (&pool_free_lock);

+                list_for_each_entry_safe (pool_list, next_pl,

+                                          &state.death_row, thr_list) {

+                        for (i = 0; i < NPOOLS; ++i) {

+                                pt_pool = &pool_list->pools[i];

+                                free_obj_list (pt_pool->cold_list);

+                                free_obj_list (pt_pool->hot_list);

+                                pt_pool->hot_list = pt_pool->cold_list = NULL;

+                        }

+                        list_del (&pool_list->thr_list);

+                        list_add (&pool_list->thr_list, &pool_free_threads);

+                }

+                (void) pthread_mutex_unlock (&pool_free_lock);

+

+                /* Third pass: free cold objects from live pools. */

+                for (i = 0; i < state.n_cold_lists; ++i) {

+                        free_obj_list (state.cold_lists[i]);

+                }

+        }

+}

+

+

+void

+pool_destructor (void *arg)

+{

+        per_thread_pool_list_t  *pool_list      = arg;

+

+        /* The pool-sweeper thread will take it from here. */

+        pool_list->poison = 1;

+}

+

+

+static __attribute__((constructor)) void

+mem_pools_preinit (void)

+{

+#if !defined(GF_DISABLE_MEMPOOL)

+        unsigned int    i;

+

+        /* Use a pthread_key destructor to clean up when a thread exits. */

+        if (pthread_key_create (&pool_key, pool_destructor) != 0) {

+                gf_log ("mem-pool", GF_LOG_CRITICAL,

+                        "failed to initialize mem-pool key");

         }

-        for (i = 0; i < count; i++) {

-                list = pool + (i * (padded_sizeof_type));

-                INIT_LIST_HEAD (list);

-                list_add_tail (list, &mem_pool->list);

+        INIT_LIST_HEAD (&pool_threads);

+        INIT_LIST_HEAD (&pool_free_threads);

+

+        for (i = 0; i < NPOOLS; ++i) {

+                pools[i].power_of_two = POOL_SMALLEST + i;

         }

-        mem_pool->pool = pool;

-        mem_pool->pool_end = pool + (count * (padded_sizeof_type));

+        pool_list_size = sizeof (per_thread_pool_list_t)

+                       + sizeof (per_thread_pool_t) * (NPOOLS - 1);

 #endif

+}

-        /* add this pool to the global list */

-        ctx = THIS->ctx;

-        if (!ctx)

-                goto out;

+void

+mem_pools_init (void)

+{

+        pthread_t       kid;

-        LOCK (&ctx->lock);

-        {

-                list_add (&mem_pool->global_list, &ctx->mempool_list);

+        (void) pthread_create (&kid, NULL, pool_sweeper, NULL);

+        (void) pthread_detach (kid);

+}

+ 

+struct mem_pool *

+mem_pool_new_fn (unsigned long sizeof_type,

+                 unsigned long count, char *name)

+{

+        unsigned int            i;

+

+        if (!sizeof_type) {

+                gf_msg_callingfn ("mem-pool", GF_LOG_ERROR, EINVAL,

+                                  LG_MSG_INVALID_ARG, "invalid argument");

+                return NULL;

+        }

+

+        for (i = 0; i < NPOOLS; ++i) {

+                if (sizeof_type <= AVAILABLE_SIZE(pools[i].power_of_two)) {

+                        return &pools[i];

+                }

         }

-        UNLOCK (&ctx->lock);

-out:

-        return mem_pool;

+        gf_msg_callingfn ("mem-pool", GF_LOG_ERROR, EINVAL,

+                          LG_MSG_INVALID_ARG, "invalid argument");

+        return NULL;

 }

 void*

@@ -445,117 +580,132 @@ mem_get0 (struct mem_pool *mem_pool)

         ptr = mem_get(mem_pool);

-        if (ptr)

-                memset(ptr, 0, mem_pool->real_sizeof_type);

+        if (ptr) {

+                memset (ptr, 0, AVAILABLE_SIZE(mem_pool->power_of_two));

+        }

         return ptr;

 }

-void *

-mem_get (struct mem_pool *mem_pool)

+

+per_thread_pool_list_t *

+mem_get_pool_list (void)

 {

-        struct list_head *list = NULL;

-        void             *ptr = NULL;

-        int             *in_use = NULL;

-        struct mem_pool **pool_ptr = NULL;

+        per_thread_pool_list_t  *pool_list;

+        unsigned int            i;

-        if (!mem_pool) {

-                gf_msg_callingfn ("mem-pool", GF_LOG_ERROR, EINVAL,

-                                  LG_MSG_INVALID_ARG, "invalid argument");

-                return NULL;

+        pool_list = pthread_getspecific (pool_key);

+        if (pool_list) {

+                return pool_list;

         }

-        LOCK (&mem_pool->lock);

-        {

-                mem_pool->alloc_count++;

-                if (mem_pool->cold_count) {

-                        list = mem_pool->list.next;

-                        list_del (list);

+        (void) pthread_mutex_lock (&pool_free_lock);

+        if (!list_empty (&pool_free_threads)) {

+                pool_list = list_entry (pool_free_threads.next,

+                                        per_thread_pool_list_t, thr_list);

+                list_del (&pool_list->thr_list);

+        }

+        (void) pthread_mutex_unlock (&pool_free_lock);

-                        mem_pool->hot_count++;

-                        mem_pool->cold_count--;

+        if (!pool_list) {

+                pool_list = GF_CALLOC (pool_list_size, 1,

+                                       gf_common_mt_mem_pool);

+                if (!pool_list) {

+                        return NULL;

+                }

-                        if (mem_pool->max_alloc < mem_pool->hot_count)

-                                mem_pool->max_alloc = mem_pool->hot_count;

+                INIT_LIST_HEAD (&pool_list->thr_list);

+                (void) pthread_spin_init (&pool_list->lock,

+                                          PTHREAD_PROCESS_PRIVATE);

+                for (i = 0; i < NPOOLS; ++i) {

+                        pool_list->pools[i].parent = &pools[i];

+                        pool_list->pools[i].hot_list = NULL;

+                        pool_list->pools[i].cold_list = NULL;

+                }

+        }

-                        ptr = list;

-                        in_use = (ptr + GF_MEM_POOL_LIST_BOUNDARY +

-                                  GF_MEM_POOL_PTR);

-                        *in_use = 1;

+        (void) pthread_mutex_lock (&pool_lock);

+        pool_list->poison = 0;

+        list_add (&pool_list->thr_list, &pool_threads);

+        (void) pthread_mutex_unlock (&pool_lock);

-                        goto fwd_addr_out;

-                }

+        (void) pthread_setspecific (pool_key, pool_list);

+        return pool_list;

+}

-                /* This is a problem area. If we've run out of

-                 * chunks in our slab above, we need to allocate

-                 * enough memory to service this request.

-                 * The problem is, these individual chunks will fail

-                 * the first address range check in __is_member. Now, since

-                 * we're not allocating a full second slab, we wont have

-                 * enough info perform the range check in __is_member.

-                 *

-                 * I am working around this by performing a regular allocation

-                 * , just the way the caller would've done when not using the

-                 * mem-pool. That also means, we're not padding the size with

-                 * the list_head structure because, this will not be added to

-                 * the list of chunks that belong to the mem-pool allocated

-                 * initially.

-                 *

-                 * This is the best we can do without adding functionality for

-                 * managing multiple slabs. That does not interest us at present

-                 * because it is too much work knowing that a better slab

-                 * allocator is coming RSN.

-                 */

-                mem_pool->pool_misses++;

-                mem_pool->curr_stdalloc++;

-                if (mem_pool->max_stdalloc < mem_pool->curr_stdalloc)

-                        mem_pool->max_stdalloc = mem_pool->curr_stdalloc;

-                ptr = GF_CALLOC (1, mem_pool->padded_sizeof_type,

-                                 gf_common_mt_mem_pool);

-

-                /* Memory coming from the heap need not be transformed from a

-                 * chunkhead to a usable pointer since it is not coming from

-                 * the pool.

-                 */

+pooled_obj_hdr_t *

+mem_get_from_pool (per_thread_pool_t *pt_pool)

+{

+        pooled_obj_hdr_t        *retval;

+

+        retval = pt_pool->hot_list;

+        if (retval) {

+                (void) __sync_fetch_and_add (&pt_pool->parent->allocs_hot, 1);

+                pt_pool->hot_list = retval->next;

+                return retval;

         }

-fwd_addr_out:

-        pool_ptr = mem_pool_from_ptr (ptr);

-        *pool_ptr = (struct mem_pool *)mem_pool;

-        ptr = mem_pool_chunkhead2ptr (ptr);

-        UNLOCK (&mem_pool->lock);

-        return ptr;

+        retval = pt_pool->cold_list;

+        if (retval) {

+                (void) __sync_fetch_and_add (&pt_pool->parent->allocs_cold, 1);

+                pt_pool->cold_list = retval->next;

+                return retval;

+        }

+

+        (void) __sync_fetch_and_add (&pt_pool->parent->allocs_stdc, 1);

+        return malloc (1 << pt_pool->parent->power_of_two);

 }

-static int

-__is_member (struct mem_pool *pool, void *ptr)

+void *

+mem_get (struct mem_pool *mem_pool)

 {

-        if (!pool || !ptr) {

+#if defined(GF_DISABLE_MEMPOOL)

+        return GF_CALLOC (1, mem_pool->real_sizeof_type,

+                          gf_common_mt_mem_pool);

+#else

+        per_thread_pool_list_t  *pool_list;

+        per_thread_pool_t       *pt_pool;

+        pooled_obj_hdr_t        *retval;

+

+        if (!mem_pool) {

                 gf_msg_callingfn ("mem-pool", GF_LOG_ERROR, EINVAL,

                                   LG_MSG_INVALID_ARG, "invalid argument");

-                return -1;

+                return NULL;

         }

-        if (ptr < pool->pool || ptr >= pool->pool_end)

-                return 0;

+        pool_list = mem_get_pool_list ();

+        if (!pool_list || pool_list->poison) {

+                return NULL;

+        }

-        if ((mem_pool_ptr2chunkhead (ptr) - pool->pool)

-            % pool->padded_sizeof_type)

-                return -1;

+        (void) pthread_spin_lock (&pool_list->lock);

+        pt_pool = &pool_list->pools[mem_pool->power_of_two-POOL_SMALLEST];

+        retval = mem_get_from_pool (pt_pool);

+        (void) pthread_spin_unlock (&pool_list->lock);

-        return 1;

-}

+        if (!retval) {

+                return NULL;

+        }

+        retval->magic = GF_MEM_HEADER_MAGIC;

+        retval->next = NULL;

+        retval->pool_list = pool_list;;

+        retval->power_of_two = mem_pool->power_of_two;

+

+        return retval + 1;

+}

+#endif /* GF_DISABLE_MEMPOOL */

 void

 mem_put (void *ptr)

 {

-        struct list_head *list = NULL;

-        int    *in_use = NULL;

-        void   *head = NULL;

-        struct mem_pool **tmp = NULL;

-        struct mem_pool *pool = NULL;

+#if defined(GF_DISABLE_MEMPOOL)

+        GF_FREE (ptr);

+#else

+        pooled_obj_hdr_t        *hdr;

+        per_thread_pool_list_t  *pool_list;

+        per_thread_pool_t       *pt_pool;

         if (!ptr) {

                 gf_msg_callingfn ("mem-pool", GF_LOG_ERROR, EINVAL,

@@ -563,71 +713,21 @@ mem_put (void *ptr)

                 return;

         }

-        list = head = mem_pool_ptr2chunkhead (ptr);

-        tmp = mem_pool_from_ptr (head);

-        if (!tmp) {

-                gf_msg_callingfn ("mem-pool", GF_LOG_ERROR, 0,

-                                  LG_MSG_PTR_HEADER_CORRUPTED,

-                                  "ptr header is corrupted");

-                return;

-        }

-

-        pool = *tmp;

-        if (!pool) {

-                gf_msg_callingfn ("mem-pool", GF_LOG_ERROR, 0,

-                                  LG_MSG_MEMPOOL_PTR_NULL,

-                                  "mem-pool ptr is NULL");

+        hdr = ((pooled_obj_hdr_t *)ptr) - 1;

+        if (hdr->magic != GF_MEM_HEADER_MAGIC) {

+                /* Not one of ours; don't touch it. */

                 return;

         }

-        LOCK (&pool->lock);

-        {

-

-                switch (__is_member (pool, ptr))

-                {

-                case 1:

-                        in_use = (head + GF_MEM_POOL_LIST_BOUNDARY +

-                                  GF_MEM_POOL_PTR);

-                        if (!is_mem_chunk_in_use(in_use)) {

-                                gf_msg_callingfn ("mem-pool", GF_LOG_CRITICAL,

-                                                  0,

-                                                  LG_MSG_MEMPOOL_INVALID_FREE,

-                                                  "mem_put called on freed ptr"

-                                                  " %p of mem pool %p", ptr,

-                                                  pool);

-                                break;

-                        }

-                        pool->hot_count--;

-                        pool->cold_count++;

-                        *in_use = 0;

-                        list_add (list, &pool->list);

-                        break;

-                case -1:

-                        /* For some reason, the address given is within

-                         * the address range of the mem-pool but does not align

-                         * with the expected start of a chunk that includes

-                         * the list headers also. Sounds like a problem in

-                         * layers of clouds up above us. ;)

-                         */

-                        abort ();

-                        break;

-                case 0:

-                        /* The address is outside the range of the mem-pool. We

-                         * assume here that this address was allocated at a

-                         * point when the mem-pool was out of chunks in mem_get

-                         * or the programmer has made a mistake by calling the

-                         * wrong de-allocation interface. We do

-                         * not have enough info to distinguish between the two

-                         * situations.

-                         */

-                        pool->curr_stdalloc--;

-                        GF_FREE (list);

-                        break;

-                default:

-                        /* log error */

-                        break;

-                }

-        }

-        UNLOCK (&pool->lock);

+        pool_list = hdr->pool_list;

+        pt_pool = &pool_list->pools[hdr->power_of_two-POOL_SMALLEST];

+

+        (void) pthread_spin_lock (&pool_list->lock);

+        hdr->magic = GF_MEM_INVALID_MAGIC;

+        hdr->next = pt_pool->hot_list;

+        pt_pool->hot_list = hdr;

+        (void) __sync_fetch_and_add (&pt_pool->parent->frees_to_list, 1);

+        (void) pthread_spin_unlock (&pool_list->lock);

+#endif /* GF_DISABLE_MEMPOOL */

 }

 void

@@ -636,16 +736,11 @@ mem_pool_destroy (struct mem_pool *pool)

         if (!pool)

                 return;

-        gf_msg (THIS->name, GF_LOG_INFO, 0, LG_MSG_MEM_POOL_DESTROY, "size=%lu "

-                "max=%d total=%"PRIu64, pool->padded_sizeof_type,

-                pool->max_alloc, pool->alloc_count);

-

-        list_del (&pool->global_list);

-

-        LOCK_DESTROY (&pool->lock);

-        GF_FREE (pool->name);

-        GF_FREE (pool->pool);

-        GF_FREE (pool);

-

-        return;

+        /*

+         * Pools are now permanent, so this does nothing.  Yes, this means we

+         * can keep allocating from a pool after calling mem_destroy on it, but

+         * that's kind of OK.  All of the objects *in* the pool will eventually

+         * be freed via the pool-sweeper thread, and this way we don't have to

+         * add a lot of reference-counting complexity.

+         */

 }

diff --git a/libglusterfs/src/mem-pool.h b/libglusterfs/src/mem-pool.h

index 6cff7be..0dc1863 100644

--- a/libglusterfs/src/mem-pool.h

+++ b/libglusterfs/src/mem-pool.h

@@ -209,24 +209,61 @@ out:

         return dup_mem;

 }

+typedef struct pooled_obj_hdr {

+        unsigned long                   magic;

+        struct pooled_obj_hdr           *next;

+        struct per_thread_pool_list     *pool_list;

+        unsigned int                    power_of_two;

+} pooled_obj_hdr_t;

+

+#define AVAILABLE_SIZE(p2)      ((1 << (p2)) - sizeof(pooled_obj_hdr_t))

+

+typedef struct per_thread_pool {

+        /* This never changes, so doesn't need a lock. */

+        struct mem_pool         *parent;

+        /* Everything else is protected by our own lock. */

+        pooled_obj_hdr_t        *hot_list;

+        pooled_obj_hdr_t        *cold_list;

+} per_thread_pool_t;

+