From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 287436B0033 for ; Tue, 14 Nov 2017 19:56:05 -0500 (EST) Received: by mail-pf0-f197.google.com with SMTP id p2so19340975pfk.13 for ; Tue, 14 Nov 2017 16:56:05 -0800 (PST) Received: from lgeamrelo13.lge.com (LGEAMRELO13.lge.com. [156.147.23.53]) by mx.google.com with ESMTP id 17si5599390pfh.401.2017.11.14.16.56.03 for ; Tue, 14 Nov 2017 16:56:04 -0800 (PST) Date: Wed, 15 Nov 2017 09:56:02 +0900 From: Minchan Kim 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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); -- 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: email@kvack.org