From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f50.google.com (mail-wm0-f50.google.com [74.125.82.50]) by kanga.kvack.org (Postfix) with ESMTP id A36E16B0038 for ; Wed, 25 Nov 2015 17:12:37 -0500 (EST) Received: by wmvv187 with SMTP id v187so6122846wmv.1 for ; Wed, 25 Nov 2015 14:12:37 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id q5si37409959wjq.6.2015.11.25.14.12.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 25 Nov 2015 14:12:36 -0800 (PST) Date: Wed, 25 Nov 2015 14:12:33 -0800 From: Andrew Morton Subject: Re: [PATCH] mm, vmstat: Allow WQ concurrency to discover memory reclaim doesn't make any progress Message-Id: <20151125141233.aa6dcb1a35527a363cb0776a@linux-foundation.org> In-Reply-To: <20151125110705.GC27283@dhcp22.suse.cz> References: <1447936253-18134-1-git-send-email-mhocko@kernel.org> <20151124154448.ac124e62528db313279224ef@linux-foundation.org> <20151125110705.GC27283@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Tetsuo Handa , Tejun Heo , Cristopher Lameter , Arkadiusz =?UTF-8?Q?Mi=C5=9Bkiewicz?= , linux-mm@kvack.org, LKML , Joonsoo Kim , Christoph Lameter On Wed, 25 Nov 2015 12:07:05 +0100 Michal Hocko wrote: > 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 outdated and the issue went away when this patch was used.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 hmpf, OK, I stuck a cc:stable in there. It looks like the current changelog is sufficient to explain to Greg (and others) why we think backporting is needed. -- 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