The patch titled
Subject: mm/slub.c: branch optimization in free slowpath
has been added to the -mm tree. Its filename is
mm-slub-branch-optimization-in-free-slowpath.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-slub-branch-optimization-in-free-slowpath.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-slub-branch-optimization-in-free-slowpath.patch
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------------------------------------------------------
From: Abel Wu <wuyun.wu@xxxxxxxxxx>
Subject: 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
Link: http://lkml.kernel.org/r/20200813101812.1617-1-wuyun.wu@xxxxxxxxxx
Signed-off-by: Abel Wu <wuyun.wu@xxxxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Hewenliang <hewenliang4@xxxxxxxxxx>
Cc: Hu Shiyuan <hushiyuan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slub.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)
--- a/mm/slub.c~mm-slub-branch-optimization-in-free-slowpath
+++ a/mm/slub.c
@@ -3024,20 +3024,21 @@ static void __slab_free(struct kmem_cach
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;
}
_
Patches currently in -mm which might be from wuyun.wu@xxxxxxxxxx are
mm-slub-branch-optimization-in-free-slowpath.patch
