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>
diff --git a/mm/slab.c b/mm/slab.c
index 3f16475..e181cfb 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2574,20 +2574,7 @@
}
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 @@
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);