From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755706AbdKOA4L (ORCPT ); Tue, 14 Nov 2017 19:56:11 -0500 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:49359 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754278AbdKOA4E (ORCPT ); Tue, 14 Nov 2017 19:56:04 -0500 X-Original-SENDERIP: 156.147.1.151 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.220.163 X-Original-MAILFROM: minchan@kernel.org Date: Wed, 15 Nov 2017 09:56:02 +0900 From: Minchan Kim To: Tetsuo Handa Cc: Huang Ying , Mel Gorman , Vladimir Davydov , Michal Hocko , Johannes Weiner , Andrew Morton , Shakeel Butt , Greg Thelen , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock. Message-ID: <20171115005602.GB23810@bbox> References: <1510609063-3327-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1510609063-3327-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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);