The patch titled
Subject: mm/slab: racy access/modify the slab color
has been added to the -mm tree. Its filename is
mm-slab-racy-access-modify-the-slab-color.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-slab-racy-access-modify-the-slab-color.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-slab-racy-access-modify-the-slab-color.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Subject: 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@xxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slab.c | 26 +++++++++++++-------------
1 file changed, 13 insertions(+), 13 deletions(-)
diff -puN mm/slab.c~mm-slab-racy-access-modify-the-slab-color mm/slab.c
--- a/mm/slab.c~mm-slab-racy-access-modify-the-slab-color
+++ a/mm/slab.c
@@ -2543,20 +2543,7 @@ static int cache_grow(struct kmem_cache
}
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();
@@ -2577,6 +2564,19 @@ static int cache_grow(struct kmem_cache
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);
_
Patches currently in -mm which might be from iamjoonsoo.kim@xxxxxxx are
mm-page_ref-use-page_ref-helper-instead-of-direct-modification-of-_count.patch
mm-rename-_count-field-of-the-struct-page-to-_refcount.patch
mm-slab-hold-a-slab_mutex-when-calling-__kmem_cache_shrink.patch
mm-slab-remove-bad_alien_magic-again.patch
mm-slab-drain-the-free-slab-as-much-as-possible.patch
mm-slab-factor-out-kmem_cache_node-initialization-code.patch
mm-slab-clean-up-kmem_cache_node-setup.patch
mm-slab-dont-keep-free-slabs-if-free_objects-exceeds-free_limit.patch
mm-slab-racy-access-modify-the-slab-color.patch
mm-slab-make-cache_grow-handle-the-page-allocated-on-arbitrary-node.patch
mm-slab-separate-cache_grow-to-two-parts.patch
mm-slab-refill-cpu-cache-through-a-new-slab-without-holding-a-node-lock.patch
mm-slab-lockless-decision-to-grow-cache.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
