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mm/slub.c: branch optimization in free slowpath 

The two conditions are mutually exclusive and gcc compiler will optimise
this into if-else-like pattern.  Given that the majority of free_slowpath
is free_frozen, let's provide some hint to the compilers.

Tests (perf bench sched messaging -g 20 -l 400000, executed 10x
after reboot) are done and the summarized result:

	un-patched	patched
max.	192.316		189.851
min.	187.267		186.252
avg.	189.154		188.086
stdev.	1.37		0.99

Signed-off-by: Abel Wu <wuyun.wu@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Hewenliang <hewenliang4@huawei.com>
Cc: Hu Shiyuan <hushiyuan@huawei.com>
Link: http://lkml.kernel.org/r/20200813101812.1617-1-wuyun.wu@huawei.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Abel Wu 2020-10-13 16:48:40 -07:00 committed by Linus Torvalds
parent d7cff4ded8
commit c270cf3041
1 changed files with 12 additions and 11 deletions
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23
mm/slub.c
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@ -3019,20 +3019,21 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
if (likely(!n)) {
/*
* If we just froze the page then put it onto the
* per cpu partial list.
*/
if (new.frozen && !was_frozen) {
if (likely(was_frozen)) {
/*
* The list lock was not taken therefore no list
* activity can be necessary.
*/
stat(s, FREE_FROZEN);
} else if (new.frozen) {
/*
* If we just froze the page then put it onto the
* per cpu partial list.
*/
put_cpu_partial(s, page, 1);
stat(s, CPU_PARTIAL_FREE);
}
/*
* The list lock was not taken therefore no list
* activity can be necessary.
*/
if (was_frozen)
stat(s, FREE_FROZEN);
return;
}