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mm/slab: refill cpu cache through a new slab without holding a node lock

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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>
This commit is contained in:
Joonsoo Kim 2016-05-19 17:10:29 -07:00 committed by Linus Torvalds
parent 76b342bdc7
commit 213b46958c
1 changed files with 36 additions and 32 deletions
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68
mm/slab.c
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@ -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 *