From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx195.postini.com [74.125.245.195]) by kanga.kvack.org (Postfix) with SMTP id 7BEEB6B014C for ; Wed, 29 May 2013 11:57:59 -0400 (EDT) Date: Wed, 29 May 2013 17:57:56 +0200 From: Michal Hocko Subject: Re: [patch v3 -mm 1/3] memcg: integrate soft reclaim tighter with zone shrinking code Message-ID: <20130529155756.GH10224@dhcp22.suse.cz> References: <20130517160247.GA10023@cmpxchg.org> <1369674791-13861-1-git-send-email-mhocko@suse.cz> <20130529130538.GD10224@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130529130538.GD10224@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , KAMEZAWA Hiroyuki , Ying Han , Hugh Dickins , Glauber Costa , Michel Lespinasse , Greg Thelen , Tejun Heo , Balbir Singh , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Wed 29-05-13 15:05:38, Michal Hocko wrote: > On Mon 27-05-13 19:13:08, Michal Hocko wrote: > [...] > > Nevertheless I have encountered an issue while testing the huge number > > of groups scenario. And the issue is not limitted to only to this > > scenario unfortunately. As memcg iterators use per node-zone-priority > > cache to prevent from over reclaim it might quite easily happen that > > the walk will not visit all groups and will terminate the loop either > > prematurely or skip some groups. An example could be the direct reclaim > > racing with kswapd. This might cause that the loop misses over limit > > groups so no pages are scanned and so we will fall back to all groups > > reclaim. > > And after some more testing and head scratching it turned out that > fallbacks to pass#2 I was seeing are caused by something else. It is > not race between iterators but rather reclaiming from zone DMA which > has troubles to scan anything despite there are pages on LRU and so we > fall back. I have to look into that more but what-ever the issue is it > shouldn't be related to the patch series. Think I know what is going on. get_scan_count sees relatively small amount of pages in the lists (around 2k). This means that get_scan_count will tell us to scan nothing for DEF_PRIORITY (as the DMA32 is usually ~16M) then the DEF_PRIORITY is basically no-op and we have to wait and fall down to a priority which actually let us scan something. Hmm, maybe ignoring soft reclaim for DMA zone would help to reduce one pointless loop over groups. -- Michal Hocko SUSE Labs -- 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