Commit e830c63a authored Apr 05, 2018 by Tetsuo Handa Committed by Linus Torvalds Apr 05, 2018

mm,vmscan: don't pretend forward progress upon shrinker_rwsem contention

Since we no longer use return value of shrink_slab() for normal reclaim,
the comment is no longer true.  If some do_shrink_slab() call takes
unexpectedly long (root cause of stall is currently unknown) when
register_shrinker()/unregister_shrinker() is pending, trying to drop
caches via /proc/sys/vm/drop_caches could become infinite cond_resched()
loop if many mem_cgroup are defined.  For safety, let's not pretend
forward progress.

Link: http://lkml.kernel.org/r/201802202229.GGF26507.LVFtMSOOHFJOQF@I-love.SAKURA.ne.jp


Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 5c9bab59

mm/vmscan.c

+1 −9

Original line number	Diff line number	Diff line
		@@ -442,16 +442,8 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
		if (memcg && (!memcg_kmem_enabled() \|\| !mem_cgroup_online(memcg)))
		return 0;

		if (!down_read_trylock(&shrinker_rwsem)) {
		/*
		* If we would return 0, our callers would understand that we
		* have nothing else to shrink and give up trying. By returning
		* 1 we keep it going and assume we'll be able to shrink next
		* time.
		*/
		freed = 1;
		if (!down_read_trylock(&shrinker_rwsem))
		goto out;
		}

		list_for_each_entry(shrinker, &shrinker_list, list) {
		struct shrink_control sc = {