From: Minchan Kim <minchan@kernel.org> To: Shakeel Butt <shakeelb@google.com> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>, Huang Ying <ying.huang@intel.com>, Mel Gorman <mgorman@techsingularity.net>, Vladimir Davydov <vdavydov.dev@gmail.com>, Michal Hocko <mhocko@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, Andrew Morton <akpm@linux-foundation.org>, Greg Thelen <gthelen@google.com>, Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock. Date: Thu, 16 Nov 2017 09:46:14 +0900 [thread overview] Message-ID: <20171116004614.GB12222@bbox> (raw) In-Reply-To: <CALvZod44uBUJdaRSqAB4Kym9u9KX0pgitYmWVbM-Ww30HdFpzQ@mail.gmail.com> On Tue, Nov 14, 2017 at 10:28:10PM -0800, Shakeel Butt wrote: > On Tue, Nov 14, 2017 at 4:56 PM, Minchan Kim <minchan@kernel.org> wrote: > > On Tue, Nov 14, 2017 at 06:37:42AM +0900, Tetsuo Handa wrote: > >> When shrinker_rwsem was introduced, it was assumed that > >> register_shrinker()/unregister_shrinker() are really unlikely paths > >> which are called during initialization and tear down. But nowadays, > >> register_shrinker()/unregister_shrinker() might be called regularly. > >> This patch prepares for allowing parallel registration/unregistration > >> of shrinkers. > >> > >> Since do_shrink_slab() can reschedule, we cannot protect shrinker_list > >> using one RCU section. But using atomic_inc()/atomic_dec() for each > >> do_shrink_slab() call will not impact so much. > >> > >> This patch uses polling loop with short sleep for unregister_shrinker() > >> rather than wait_on_atomic_t(), for we can save reader's cost (plain > >> atomic_dec() compared to atomic_dec_and_test()), we can expect that > >> do_shrink_slab() of unregistering shrinker likely returns shortly, and > >> we can avoid khungtaskd warnings when do_shrink_slab() of unregistering > >> shrinker unexpectedly took so long. > >> > >> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > > > > Before reviewing this patch, can't we solve the problem with more > > simple way? Like this. > > > > Shakeel, What do you think? > > > > Seems simple enough. I will run my test (running fork bomb in one > memcg and separately time a mount operation) and update if numbers > differ significantly. Thanks. > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 13d711dd8776..cbb624cb9baa 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -498,6 +498,14 @@ 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 > > + * long time stall by parallel ongoing shrinking. > > + */ > > + if (rwsem_is_contended(&shrinker_rwsem)) { > > + freed = 1; > > freed = freed ?: 1; Yub.
WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan@kernel.org> To: Shakeel Butt <shakeelb@google.com> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>, Huang Ying <ying.huang@intel.com>, Mel Gorman <mgorman@techsingularity.net>, Vladimir Davydov <vdavydov.dev@gmail.com>, Michal Hocko <mhocko@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, Andrew Morton <akpm@linux-foundation.org>, Greg Thelen <gthelen@google.com>, Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock. Date: Thu, 16 Nov 2017 09:46:14 +0900 [thread overview] Message-ID: <20171116004614.GB12222@bbox> (raw) In-Reply-To: <CALvZod44uBUJdaRSqAB4Kym9u9KX0pgitYmWVbM-Ww30HdFpzQ@mail.gmail.com> On Tue, Nov 14, 2017 at 10:28:10PM -0800, Shakeel Butt wrote: > On Tue, Nov 14, 2017 at 4:56 PM, Minchan Kim <minchan@kernel.org> wrote: > > On Tue, Nov 14, 2017 at 06:37:42AM +0900, Tetsuo Handa wrote: > >> When shrinker_rwsem was introduced, it was assumed that > >> register_shrinker()/unregister_shrinker() are really unlikely paths > >> which are called during initialization and tear down. But nowadays, > >> register_shrinker()/unregister_shrinker() might be called regularly. > >> This patch prepares for allowing parallel registration/unregistration > >> of shrinkers. > >> > >> Since do_shrink_slab() can reschedule, we cannot protect shrinker_list > >> using one RCU section. But using atomic_inc()/atomic_dec() for each > >> do_shrink_slab() call will not impact so much. > >> > >> This patch uses polling loop with short sleep for unregister_shrinker() > >> rather than wait_on_atomic_t(), for we can save reader's cost (plain > >> atomic_dec() compared to atomic_dec_and_test()), we can expect that > >> do_shrink_slab() of unregistering shrinker likely returns shortly, and > >> we can avoid khungtaskd warnings when do_shrink_slab() of unregistering > >> shrinker unexpectedly took so long. > >> > >> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > > > > Before reviewing this patch, can't we solve the problem with more > > simple way? Like this. > > > > Shakeel, What do you think? > > > > Seems simple enough. I will run my test (running fork bomb in one > memcg and separately time a mount operation) and update if numbers > differ significantly. Thanks. > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 13d711dd8776..cbb624cb9baa 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -498,6 +498,14 @@ 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 > > + * long time stall by parallel ongoing shrinking. > > + */ > > + if (rwsem_is_contended(&shrinker_rwsem)) { > > + freed = 1; > > freed = freed ?: 1; Yub. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-11-16 0:46 UTC|newest] Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-13 21:37 [PATCH 1/2] mm,vmscan: Kill global shrinker lock Tetsuo Handa 2017-11-13 21:37 ` Tetsuo Handa 2017-11-13 21:37 ` [PATCH 2/2] mm,vmscan: Allow parallel registration/unregistration of shrinkers Tetsuo Handa 2017-11-13 21:37 ` Tetsuo Handa 2017-11-13 22:05 ` [PATCH 1/2] mm,vmscan: Kill global shrinker lock Shakeel Butt 2017-11-13 22:05 ` Shakeel Butt 2017-11-15 0:56 ` Minchan Kim 2017-11-15 0:56 ` Minchan Kim 2017-11-15 6:28 ` Shakeel Butt 2017-11-15 6:28 ` Shakeel Butt 2017-11-16 0:46 ` Minchan Kim [this message] 2017-11-16 0:46 ` Minchan Kim 2017-11-16 1:41 ` Shakeel Butt 2017-11-16 1:41 ` Shakeel Butt 2017-11-16 4:50 ` Minchan Kim 2017-11-16 4:50 ` Minchan Kim 2017-11-15 8:56 ` Michal Hocko 2017-11-15 8:56 ` Michal Hocko 2017-11-15 9:18 ` Michal Hocko 2017-11-15 9:18 ` Michal Hocko 2017-11-16 17:44 ` Johannes Weiner 2017-11-16 17:44 ` Johannes Weiner 2017-11-23 23:46 ` Minchan Kim 2017-11-23 23:46 ` Minchan Kim 2017-11-15 9:02 ` Michal Hocko 2017-11-15 9:02 ` Michal Hocko 2017-11-15 10:58 ` Tetsuo Handa 2017-11-15 10:58 ` Tetsuo Handa 2017-11-15 11:51 ` Michal Hocko 2017-11-15 11:51 ` Michal Hocko 2017-11-16 0:56 ` Minchan Kim 2017-11-16 0:56 ` Minchan Kim 2017-11-15 13:28 ` Johannes Weiner 2017-11-15 13:28 ` Johannes Weiner 2017-11-16 10:56 ` Tetsuo Handa 2017-11-16 10:56 ` Tetsuo Handa 2017-11-15 14:00 ` Johannes Weiner 2017-11-15 14:00 ` Johannes Weiner 2017-11-15 14:11 ` Michal Hocko 2017-11-15 14:11 ` Michal Hocko 2018-01-25 2:04 ` Tetsuo Handa 2018-01-25 2:04 ` Tetsuo Handa 2018-01-25 8:36 ` Michal Hocko 2018-01-25 8:36 ` Michal Hocko 2018-01-25 10:56 ` Tetsuo Handa 2018-01-25 10:56 ` Tetsuo Handa 2018-01-25 11:41 ` Michal Hocko 2018-01-25 11:41 ` Michal Hocko 2018-01-25 22:19 ` Eric Wheeler 2018-01-25 22:19 ` Eric Wheeler 2018-01-26 3:12 ` Tetsuo Handa 2018-01-26 3:12 ` Tetsuo Handa 2018-01-26 10:08 ` Michal Hocko 2018-01-26 10:08 ` Michal Hocko 2017-11-17 17:35 ` Christoph Hellwig 2017-11-17 17:35 ` Christoph Hellwig 2017-11-17 17:41 ` Shakeel Butt 2017-11-17 17:41 ` Shakeel Butt 2017-11-17 17:53 ` Shakeel Butt 2017-11-17 17:53 ` Shakeel Butt 2017-11-17 18:36 ` Christoph Hellwig 2017-11-17 18:36 ` Christoph Hellwig 2017-11-20 9:25 ` Michal Hocko 2017-11-20 9:25 ` Michal Hocko 2017-11-20 9:33 ` Christoph Hellwig 2017-11-20 9:33 ` Christoph Hellwig 2017-11-20 9:42 ` Michal Hocko 2017-11-20 9:42 ` Michal Hocko 2017-11-20 10:41 ` Christoph Hellwig 2017-11-20 10:41 ` Christoph Hellwig 2017-11-20 10:56 ` Tetsuo Handa 2017-11-20 10:56 ` Tetsuo Handa 2017-11-20 18:28 ` Paul E. McKenney 2017-11-20 18:28 ` Paul E. McKenney
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