From: Shakeel Butt <shakeelb@google.com>
To: Minchan Kim <minchan@kernel.org>
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: Wed, 15 Nov 2017 17:41:41 -0800 [thread overview]
Message-ID: <CALvZod4r7AWGiRpcxSsOf2ZdUyNUvzFnqTkcxa5F8wb2ssV7gQ@mail.gmail.com> (raw)
In-Reply-To: <20171116004614.GB12222@bbox>
On Wed, Nov 15, 2017 at 4:46 PM, Minchan Kim <minchan@kernel.org> wrote:
> 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.
Thanks Minchan, you can add
Reviewed-and-tested-by: Shakeel Butt <shakeelb@google.com>
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next prev parent reply other threads:[~2017-11-16 1:41 UTC|newest]
Thread overview: 37+ 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 ` [PATCH 2/2] mm,vmscan: Allow parallel registration/unregistration of shrinkers Tetsuo Handa
2017-11-13 22:05 ` [PATCH 1/2] mm,vmscan: Kill global shrinker lock Shakeel Butt
2017-11-15 0:56 ` Minchan Kim
2017-11-15 6:28 ` Shakeel Butt
2017-11-16 0:46 ` Minchan Kim
2017-11-16 1:41 ` Shakeel Butt [this message]
2017-11-16 4:50 ` Minchan Kim
2017-11-15 8:56 ` Michal Hocko
2017-11-15 9:18 ` Michal Hocko
2017-11-16 17:44 ` Johannes Weiner
2017-11-23 23:46 ` Minchan Kim
2017-11-15 9:02 ` Michal Hocko
2017-11-15 10:58 ` Tetsuo Handa
2017-11-15 11:51 ` Michal Hocko
2017-11-16 0:56 ` Minchan Kim
2017-11-15 13:28 ` Johannes Weiner
2017-11-16 10:56 ` Tetsuo Handa
2017-11-15 14:00 ` Johannes Weiner
2017-11-15 14:11 ` Michal Hocko
2018-01-25 2:04 ` Tetsuo Handa
2018-01-25 8:36 ` Michal Hocko
2018-01-25 10:56 ` Tetsuo Handa
2018-01-25 11:41 ` Michal Hocko
2018-01-25 22:19 ` Eric Wheeler
2018-01-26 3:12 ` Tetsuo Handa
2018-01-26 10:08 ` Michal Hocko
2017-11-17 17:35 ` Christoph Hellwig
2017-11-17 17:41 ` Shakeel Butt
2017-11-17 17:53 ` Shakeel Butt
2017-11-17 18:36 ` Christoph Hellwig
2017-11-20 9:25 ` Michal Hocko
2017-11-20 9:33 ` Christoph Hellwig
2017-11-20 9:42 ` Michal Hocko
2017-11-20 10:41 ` Christoph Hellwig
2017-11-20 10:56 ` Tetsuo Handa
2017-11-20 18:28 ` Paul E. McKenney
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