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author | Joonsoo Kim <iamjoonsoo.kim@lge.com> | 2016-05-20 02:10:29 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-05-20 04:12:14 +0200 |
commit | 213b46958c65c7adaaf3201102da16ce0264e9cf (patch) | |
tree | 0f1a9a7bf4a6501b7a4e3016758c5b227651c03e | |
parent | mm/slab: separate cache_grow() to two parts (diff) | |
download | linux-213b46958c65c7adaaf3201102da16ce0264e9cf.tar.xz linux-213b46958c65c7adaaf3201102da16ce0264e9cf.zip |
mm/slab: refill cpu cache through a new slab without holding a node lock
Until now, cache growing makes a free slab on node's slab list and then
we can allocate free objects from it. This necessarily requires to hold
a node lock which is very contended. If we refill cpu cache before
attaching it to node's slab list, we can avoid holding a node lock as
much as possible because this newly allocated slab is only visible to
the current task. This will reduce lock contention.
Below is the result of concurrent allocation/free in slab allocation
benchmark made by Christoph a long time ago. I make the output simpler.
The number shows cycle count during alloc/free respectively so less is
better.
* Before
Kmalloc N*alloc N*free(32): Average=355/750
Kmalloc N*alloc N*free(64): Average=452/812
Kmalloc N*alloc N*free(128): Average=559/1070
Kmalloc N*alloc N*free(256): Average=1176/980
Kmalloc N*alloc N*free(512): Average=1939/1189
Kmalloc N*alloc N*free(1024): Average=3521/1278
Kmalloc N*alloc N*free(2048): Average=7152/1838
Kmalloc N*alloc N*free(4096): Average=13438/2013
* After
Kmalloc N*alloc N*free(32): Average=248/966
Kmalloc N*alloc N*free(64): Average=261/949
Kmalloc N*alloc N*free(128): Average=314/1016
Kmalloc N*alloc N*free(256): Average=741/1061
Kmalloc N*alloc N*free(512): Average=1246/1152
Kmalloc N*alloc N*free(1024): Average=2437/1259
Kmalloc N*alloc N*free(2048): Average=4980/1800
Kmalloc N*alloc N*free(4096): Average=9000/2078
It shows that contention is reduced for all the object sizes and
performance increases by 30 ~ 40%.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | mm/slab.c | 68 |
1 files changed, 36 insertions, 32 deletions
diff --git a/mm/slab.c b/mm/slab.c index 8c4db214b05b..37600e91742f 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -2865,6 +2865,30 @@ static noinline void *cache_alloc_pfmemalloc(struct kmem_cache *cachep, return obj; } +/* + * Slab list should be fixed up by fixup_slab_list() for existing slab + * or cache_grow_end() for new slab + */ +static __always_inline int alloc_block(struct kmem_cache *cachep, + struct array_cache *ac, struct page *page, int batchcount) +{ + /* + * There must be at least one object available for + * allocation. + */ + BUG_ON(page->active >= cachep->num); + + while (page->active < cachep->num && batchcount--) { + STATS_INC_ALLOCED(cachep); + STATS_INC_ACTIVE(cachep); + STATS_SET_HIGH(cachep); + + ac->entry[ac->avail++] = slab_get_obj(cachep, page); + } + + return batchcount; +} + static void *cache_alloc_refill(struct kmem_cache *cachep, gfp_t flags) { int batchcount; @@ -2877,7 +2901,6 @@ static void *cache_alloc_refill(struct kmem_cache *cachep, gfp_t flags) check_irq_off(); node = numa_mem_id(); -retry: ac = cpu_cache_get(cachep); batchcount = ac->batchcount; if (!ac->touched && batchcount > BATCHREFILL_LIMIT) { @@ -2907,21 +2930,7 @@ retry: check_spinlock_acquired(cachep); - /* - * The slab was either on partial or free list so - * there must be at least one object available for - * allocation. - */ - BUG_ON(page->active >= cachep->num); - - while (page->active < cachep->num && batchcount--) { - STATS_INC_ALLOCED(cachep); - STATS_INC_ACTIVE(cachep); - STATS_SET_HIGH(cachep); - - ac->entry[ac->avail++] = slab_get_obj(cachep, page); - } - + batchcount = alloc_block(cachep, ac, page, batchcount); fixup_slab_list(cachep, n, page, &list); } @@ -2941,21 +2950,18 @@ alloc_done: } page = cache_grow_begin(cachep, gfp_exact_node(flags), node); - cache_grow_end(cachep, page); /* * cache_grow_begin() can reenable interrupts, * then ac could change. */ ac = cpu_cache_get(cachep); - node = numa_mem_id(); + if (!ac->avail && page) + alloc_block(cachep, ac, page, batchcount); + cache_grow_end(cachep, page); - /* no objects in sight? abort */ - if (!page && ac->avail == 0) + if (!ac->avail) return NULL; - - if (!ac->avail) /* objects refilled by interrupt? */ - goto retry; } ac->touched = 1; @@ -3149,14 +3155,13 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, { struct page *page; struct kmem_cache_node *n; - void *obj; + void *obj = NULL; void *list = NULL; VM_BUG_ON(nodeid < 0 || nodeid >= MAX_NUMNODES); n = get_node(cachep, nodeid); BUG_ON(!n); -retry: check_irq_off(); spin_lock(&n->list_lock); page = get_first_slab(n, false); @@ -3178,19 +3183,18 @@ retry: spin_unlock(&n->list_lock); fixup_objfreelist_debug(cachep, &list); - goto done; + return obj; must_grow: spin_unlock(&n->list_lock); page = cache_grow_begin(cachep, gfp_exact_node(flags), nodeid); + if (page) { + /* This slab isn't counted yet so don't update free_objects */ + obj = slab_get_obj(cachep, page); + } cache_grow_end(cachep, page); - if (page) - goto retry; - return fallback_alloc(cachep, flags); - -done: - return obj; + return obj ? obj : fallback_alloc(cachep, flags); } static __always_inline void * |