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mm/slab: racy access/modify the slab color 

Slab color isn't needed to be changed strictly.  Because locking for
changing slab color could cause more lock contention so this patch
implements racy access/modify the slab color.  This is a preparation
step to implement lockless allocation path when there is no free objects
in the kmem_cache.

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=365/806
  Kmalloc N*alloc N*free(64): Average=452/690
  Kmalloc N*alloc N*free(128): Average=736/886
  Kmalloc N*alloc N*free(256): Average=1167/985
  Kmalloc N*alloc N*free(512): Average=2088/1125
  Kmalloc N*alloc N*free(1024): Average=4115/1184
  Kmalloc N*alloc N*free(2048): Average=8451/1748
  Kmalloc N*alloc N*free(4096): Average=16024/2048

  * After
  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

It shows that contention is reduced for object size >= 1024 and
performance increases by roughly 15%.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.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 17:10:20 -07:00 committed by Linus Torvalds
parent 6052b7880a
commit 03d1d43a12
1 changed files with 13 additions and 13 deletions
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26
mm/slab.c
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@ -2574,20 +2574,7 @@ static int cache_grow(struct kmem_cache *cachep,
}
local_flags = flags & (GFP_CONSTRAINT_MASK|GFP_RECLAIM_MASK);
/* Take the node list lock to change the colour_next on this node */
check_irq_off();
n = get_node(cachep, nodeid);
spin_lock(&n->list_lock);
/* Get colour for the slab, and cal the next value. */
offset = n->colour_next;
n->colour_next++;
if (n->colour_next >= cachep->colour)
n->colour_next = 0;
spin_unlock(&n->list_lock);
offset *= cachep->colour_off;
if (gfpflags_allow_blocking(local_flags))
local_irq_enable();
@ -2608,6 +2595,19 @@ static int cache_grow(struct kmem_cache *cachep,
if (!page)
goto failed;
n = get_node(cachep, nodeid);
/* Get colour for the slab, and cal the next value. */
n->colour_next++;
if (n->colour_next >= cachep->colour)
n->colour_next = 0;
offset = n->colour_next;
if (offset >= cachep->colour)
offset = 0;
offset *= cachep->colour_off;
/* Get slab management. */
freelist = alloc_slabmgmt(cachep, page, offset,
local_flags & ~GFP_CONSTRAINT_MASK, nodeid);