From: Minchan Kim minchan@kernel.org
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.or... Signed-off-by: Minchan Kim minchan@kernel.org Signed-off-by: Shakeel Butt shakeelb@google.com Reported-by: Shakeel Butt shakeelb@google.com Tested-by: Shakeel Butt shakeelb@google.com Acked-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Michal Hocko mhocko@suse.com Cc: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: Anshuman Khandual khandual@linux.vnet.ibm.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [rkolchmeyer: Backported to 4.14: adjusted context] Signed-off-by: Robert Kolchmeyer rkolchmeyer@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/vmscan.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -502,6 +502,15 @@ static unsigned long shrink_slab(gfp_t g 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);