From: Minchan Kim Date: Thu, 1 Feb 2018 00:16:55 +0000 (-0800) Subject: mm: do not stall register_shrinker() X-Git-Tag: v4.16-rc1~122^2~72 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=e496612c5130567fc9d5f1969ca4b86665aa3cbb;p=users%2Fjedix%2Flinux-maple.git mm: do not stall register_shrinker() 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 --- diff --git a/mm/vmscan.c b/mm/vmscan.c index e73274a60b22..153e0795f4f0 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -489,6 +489,15 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, sc.nid = 0; freed += do_shrink_slab(&sc, shrinker, priority); + /* + * 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);