From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756422AbdKOG2U (ORCPT ); Wed, 15 Nov 2017 01:28:20 -0500 Received: from mail-wm0-f65.google.com ([74.125.82.65]:42664 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755858AbdKOG2N (ORCPT ); Wed, 15 Nov 2017 01:28:13 -0500 X-Google-Smtp-Source: AGs4zMYN+pZJfssRcBZ3ohEsdCw+BCou5vl+Lc3PnWyGHFAR0KYGSy8GiUK7XrT3uQZCDq4Ryk3xE1tWeqBeqLu+gR4= MIME-Version: 1.0 In-Reply-To: <20171115005602.GB23810@bbox> References: <1510609063-3327-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20171115005602.GB23810@bbox> From: Shakeel Butt Date: Tue, 14 Nov 2017 22:28:10 -0800 Message-ID: Subject: Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock. To: Minchan Kim Cc: Tetsuo Handa , Huang Ying , Mel Gorman , Vladimir Davydov , Michal Hocko , Johannes Weiner , Andrew Morton , Greg Thelen , Linux MM , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 14, 2017 at 4:56 PM, Minchan Kim 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 > > 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. > 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; > + break; > + } > } > > up_read(&shrinker_rwsem); From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id 4DD5A6B0033 for ; Wed, 15 Nov 2017 01:28:14 -0500 (EST) Received: by mail-wr0-f197.google.com with SMTP id o14so12309577wrf.6 for ; Tue, 14 Nov 2017 22:28:14 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id z189sor2437848wmc.47.2017.11.14.22.28.12 for (Google Transport Security); Tue, 14 Nov 2017 22:28:12 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20171115005602.GB23810@bbox> References: <1510609063-3327-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20171115005602.GB23810@bbox> From: Shakeel Butt Date: Tue, 14 Nov 2017 22:28:10 -0800 Message-ID: Subject: Re: [PATCH 1/2] mm,vmscan: Kill global shrinker lock. Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Tetsuo Handa , Huang Ying , Mel Gorman , Vladimir Davydov , Michal Hocko , Johannes Weiner , Andrew Morton , Greg Thelen , Linux MM , LKML On Tue, Nov 14, 2017 at 4:56 PM, Minchan Kim 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 > > 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. > 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; > + 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