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From: Minchan Kim <minchan@kernel.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: 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>,
	Shakeel Butt <shakeelb@google.com>,
	Greg Thelen <gthelen@google.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock.
Date: Wed, 15 Nov 2017 09:56:02 +0900
Message-ID: <20171115005602.GB23810@bbox> (raw)
In-Reply-To: <1510609063-3327-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>

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?

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;
+			break;
+		}
 	}
 
 	up_read(&shrinker_rwsem);

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  parent reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 22:05 ` [PATCH 1/2] mm,vmscan: Kill global shrinker lock Shakeel Butt
2017-11-15  0:56 ` Minchan Kim [this message]
2017-11-15  6:28   ` Shakeel Butt
2017-11-16  0:46     ` Minchan Kim
2017-11-16  1:41       ` Shakeel Butt
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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