Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752999AbbKYLHM (ORCPT ); Wed, 25 Nov 2015 06:07:12 -0500 Received: from mail-wm0-f41.google.com ([74.125.82.41]:35927 "EHLO mail-wm0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752447AbbKYLHI (ORCPT ); Wed, 25 Nov 2015 06:07:08 -0500 Date: Wed, 25 Nov 2015 12:07:05 +0100 From: Michal Hocko To: Andrew Morton Cc: Tetsuo Handa , Tejun Heo , Cristopher Lameter , Arkadiusz =?utf-8?Q?Mi=C5=9Bkiewicz?= , linux-mm@kvack.org, LKML , Joonsoo Kim , Christoph Lameter Subject: Re: [PATCH] mm, vmstat: Allow WQ concurrency to discover memory reclaim doesn't make any progress Message-ID: <20151125110705.GC27283@dhcp22.suse.cz> References: <1447936253-18134-1-git-send-email-mhocko@kernel.org> <20151124154448.ac124e62528db313279224ef@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151124154448.ac124e62528db313279224ef@linux-foundation.org> 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 Content-Length: 1820 Lines: 38 On Tue 24-11-15 15:44:48, Andrew Morton wrote: [...] > > Even though we haven't seen bug reports in the past I would suggest > > backporting this to the stable trees. The issue is present since we have > > stopped useing congestion_wait in the retry loop because WQ concurrency > > is older as well as vmstat worqueue based refresh AFAICS. > > hm, I'm reluctant. If the patch fixes something that real people are > really hurting from then yes. But I suspect this is just one fly-swat > amongst many. Arkadiusz was seeing reclaim issues [1] on 4.1 kernel. I didn't have time to look deeper in that report but vmstat counters seemed terribly outdated and the issue went away when this patch was used. The thing is that there were others in the bundle so it is not 100% clear whether the patch alone helped or it was just a part of the puzzle. Anyway I think that the issue is not solely theoretical. WQ_MEM_RECLAIM is simply not working if the allocation path doesn't sleep currently and my understanding of what Tejun claims [2] is that that reimplementing WQ concurrency would be too intrusive and lacks sufficient justification because other kernel paths do sleep. This patch tries to reduce the sleep only to worker threads which should not cause any problems to regular tasks. I am open to any other suggestions. I do not like artificial sleep as well but this sounds like the most practical way to go now. [1] http://lkml.kernel.org/r/201511102313.36685.arekm@maven.pl [2] http://lkml.kernel.org/r/20151106001648.GA18183@mtj.duckdns.org -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/