Commit c270cf30 authored Oct 13, 2020 by Abel Wu Committed by Linus Torvalds Oct 13, 2020

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>

parent d7cff4de

mm/slub.c

+12 −11

Original line number	Diff line number	Diff line
		@@ -3019,20 +3019,21 @@ static void __slab_free(struct kmem_cache s, struct page page,

		if (likely(!n)) {

		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.
		*/
		if (new.frozen && !was_frozen) {
		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;
		}

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