From c270cf3041a5cb7c5853d45a794309e66576493a Mon Sep 17 00:00:00 2001 From: Abel Wu Date: Tue, 13 Oct 2020 16:48:40 -0700 Subject: [PATCH] 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 Signed-off-by: Andrew Morton Acked-by: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Hewenliang Cc: Hu Shiyuan Link: http://lkml.kernel.org/r/20200813101812.1617-1-wuyun.wu@huawei.com Signed-off-by: Linus Torvalds --- mm/slub.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 6d3574013b2f..da6438bd8202 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -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; }