Commit 204fd0bd authored by Minchan Kim's avatar Minchan Kim Committed by Greg Kroah-Hartman

mm: do not stall register_shrinker()

commit e496612c 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.orgSigned-off-by: default avatarMinchan Kim <minchan@kernel.org>
Signed-off-by: default avatarShakeel Butt <shakeelb@google.com>
Reported-by: default avatarShakeel Butt <shakeelb@google.com>
Tested-by: default avatarShakeel Butt <shakeelb@google.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarMichal 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
[rkolchmeyer: Backported to 4.14: adjusted context]
Signed-off-by: default avatarRobert Kolchmeyer <rkolchmeyer@google.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 20ea0648
......@@ -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);
......
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