From 204fd0bdccca09d21a5d4608e370b31071a84de5 Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Wed, 31 Jan 2018 16:16:55 -0800 Subject: mm: do not stall register_shrinker() commit e496612c5130567fc9d5f1969ca4b86665aa3cbb upstream. Shakeel Butt reported he has observed in production systems that the job loader gets stuck for 10s of seconds while doing a mount operation. It turns out that it was stuck in register_shrinker() because some unrelated job was under memory pressure and was spending time in shrink_slab(). Machines have a lot of shrinkers registered and jobs under memory pressure have to traverse all of those memcg-aware shrinkers and affect unrelated jobs which want to register their own shrinkers. To solve the issue, this patch simply bails out slab shrinking if it is found that someone wants to register a shrinker in parallel. A downside is it could cause unfair shrinking between shrinkers. However, it should be rare and we can add compilcated logic if we find it's not enough. [akpm@linux-foundation.org: tweak code comment] Link: http://lkml.kernel.org/r/20171115005602.GB23810@bbox Link: http://lkml.kernel.org/r/1511481899-20335-1-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim Signed-off-by: Shakeel Butt Reported-by: Shakeel Butt Tested-by: Shakeel Butt Acked-by: Johannes Weiner Acked-by: Michal Hocko Cc: Tetsuo Handa Cc: Anshuman Khandual Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [rkolchmeyer: Backported to 4.14: adjusted context] Signed-off-by: Robert Kolchmeyer Signed-off-by: Greg Kroah-Hartman --- mm/vmscan.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'mm/vmscan.c') diff --git a/mm/vmscan.c b/mm/vmscan.c index 9734e62654fa..99837e931f53 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -502,6 +502,15 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, sc.nid = 0; freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible); + /* + * Bail out if someone want to register a new shrinker to + * prevent the regsitration from being stalled for long periods + * by parallel ongoing shrinking. + */ + if (rwsem_is_contended(&shrinker_rwsem)) { + freed = freed ? : 1; + break; + } } up_read(&shrinker_rwsem); -- cgit v1.2.3