From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934001Ab3BMM4Y (ORCPT ); Wed, 13 Feb 2013 07:56:24 -0500 Received: from cantor2.suse.de ([195.135.220.15]:41539 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933921Ab3BMM4W (ORCPT ); Wed, 13 Feb 2013 07:56:22 -0500 Date: Wed, 13 Feb 2013 13:56:17 +0100 From: Michal Hocko To: Johannes Weiner Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, KAMEZAWA Hiroyuki , Ying Han , Tejun Heo , Glauber Costa , Li Zefan Subject: Re: [PATCH v3 4/7] memcg: remove memcg from the reclaim iterators Message-ID: <20130213125617.GD23562@dhcp22.suse.cz> References: <20130211223943.GC15951@cmpxchg.org> <20130212095419.GB4863@dhcp22.suse.cz> <20130212151002.GD15951@cmpxchg.org> <20130212154330.GG4863@dhcp22.suse.cz> <20130212161332.GI4863@dhcp22.suse.cz> <20130212162442.GJ4863@dhcp22.suse.cz> <63d3b5fa-dbc6-4bc9-8867-f9961e644305@email.android.com> <20130212171216.GA17663@dhcp22.suse.cz> <20130212173741.GD25235@cmpxchg.org> <20130213103459.GB23562@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130213103459.GB23562@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 13-02-13 11:34:59, Michal Hocko wrote: > On Tue 12-02-13 12:37:41, Johannes Weiner wrote: > > On Tue, Feb 12, 2013 at 06:12:16PM +0100, Michal Hocko wrote: > [...] > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > > index 727ec39..31bb9b0 100644 > > > --- a/mm/memcontrol.c > > > +++ b/mm/memcontrol.c > > > @@ -144,8 +144,13 @@ struct mem_cgroup_stat_cpu { > > > }; > > > > > > struct mem_cgroup_reclaim_iter { > > > - /* last scanned hierarchy member with elevated css ref count */ > > > + /* > > > + * last scanned hierarchy member. Valid only if last_dead_count > > > + * matches memcg->dead_count of the hierarchy root group. > > > + */ > > > struct mem_cgroup *last_visited; > > > + unsigned int last_dead_count; > > > > Since we read and write this without a lock, I would feel more > > comfortable if this were a full word, i.e. unsigned long. That > > guarantees we don't see any partial states. > > OK. Changed. Although I though that int is read/modified atomically as > well if it is aligned to its size. Ohh, I guess what was your concern. If last_dead_count was int then it would fit into the same full word slot with generation and so the parallel read-modify-update cycle could be an issue. -- Michal Hocko SUSE Labs