From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f50.google.com (mail-ee0-f50.google.com [74.125.83.50]) by kanga.kvack.org (Postfix) with ESMTP id 8BC416B0038 for ; Fri, 2 May 2014 05:43:54 -0400 (EDT) Received: by mail-ee0-f50.google.com with SMTP id c13so2944945eek.23 for ; Fri, 02 May 2014 02:43:53 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 45si1129392eeh.63.2014.05.02.02.43.52 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 02 May 2014 02:43:52 -0700 (PDT) Date: Fri, 2 May 2014 11:43:51 +0200 From: Michal Hocko Subject: Re: [PATCH 3/4] memcg, doc: clarify global vs. limit reclaims Message-ID: <20140502094351.GD3446@dhcp22.suse.cz> References: <1398688005-26207-1-git-send-email-mhocko@suse.cz> <1398688005-26207-4-git-send-email-mhocko@suse.cz> <20140430230350.GF26041@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140430230350.GF26041@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Greg Thelen , Michel Lespinasse , Tejun Heo , Hugh Dickins , Roman Gushchin , LKML , linux-mm@kvack.org On Wed 30-04-14 19:03:50, Johannes Weiner wrote: > On Mon, Apr 28, 2014 at 02:26:44PM +0200, Michal Hocko wrote: > > Be explicit about global and hard limit reclaims in our documentation. > > > > Signed-off-by: Michal Hocko > > --- > > Documentation/cgroups/memory.txt | 31 +++++++++++++++++-------------- > > 1 file changed, 17 insertions(+), 14 deletions(-) > > > > diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt > > index 4937e6fff9b4..add1be001416 100644 > > --- a/Documentation/cgroups/memory.txt > > +++ b/Documentation/cgroups/memory.txt > > @@ -236,23 +236,26 @@ it by cgroup. > > 2.5 Reclaim > > > > Each cgroup maintains a per cgroup LRU which has the same structure as > > -global VM. When a cgroup goes over its limit, we first try > > -to reclaim memory from the cgroup so as to make space for the new > > -pages that the cgroup has touched. If the reclaim is unsuccessful, > > -an OOM routine is invoked to select and kill the bulkiest task in the > > -cgroup. (See 10. OOM Control below.) > > - > > -The reclaim algorithm has not been modified for cgroups, except that > > -pages that are selected for reclaiming come from the per-cgroup LRU > > -list. > > - > > -NOTE: Reclaim does not work for the root cgroup, since we cannot set any > > -limits on the root cgroup. > > +global VM. Cgroups can get reclaimed basically under two conditions > > + - under global memory pressure when all cgroups are reclaimed > > + proportionally wrt. their LRU size in a round robin fashion > > + - when a cgroup or its hierarchical parent (see 6. Hierarchical support) > > + hits hard limit. If the reclaim is unsuccessful, an OOM routine is invoked > > + to select and kill the bulkiest task in the cgroup. (See 10. OOM Control > > + below.) > > In the whole hierarchy, not just that cgroup. Right. Fixed > > +Global and hard-limit reclaims share the same code the only difference > > +is the objective of the reclaim. The global reclaim aims at balancing > > +zones' watermarks while the limit reclaim frees some memory to allow new > > +charges. > > This is a kswapd vs. direct reclaim issue, not global vs. memcg. > Memcg reclaim just happens to be direct reclaim. Either way, I'd > rather not have such implementation details in the user documentation. OK, removed > > +NOTE: Hard limit reclaim does not work for the root cgroup, since we cannot set > > +any limits on the root cgroup. > > Not sure it's necessary to include this... removed as well. Incremental patch on top: ---