From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f169.google.com (mail-wi0-f169.google.com [209.85.212.169]) by kanga.kvack.org (Postfix) with ESMTP id 755AC6B0035 for ; Tue, 17 Dec 2013 08:14:13 -0500 (EST) Received: by mail-wi0-f169.google.com with SMTP id hn6so3542894wib.2 for ; Tue, 17 Dec 2013 05:14:13 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id h45si4839646eeo.235.2013.12.17.05.14.12 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 17 Dec 2013 05:14:12 -0800 (PST) Date: Tue, 17 Dec 2013 14:14:11 +0100 From: Michal Hocko Subject: Re: 3.13-rc breaks MEMCG_SWAP Message-ID: <20131217131411.GF28991@dhcp22.suse.cz> References: <52AEC989.4080509@huawei.com> <20131216095345.GB23582@dhcp22.suse.cz> <20131216104042.GC23582@dhcp22.suse.cz> <20131216163530.GH32509@htj.dyndns.org> <20131216171937.GG26797@dhcp22.suse.cz> <20131216172143.GJ32509@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Tejun Heo , Li Zefan , Johannes Weiner , Andrew Morton , KAMEZAWA Hiroyuki , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org On Mon 16-12-13 17:41:38, Hugh Dickins wrote: > On Mon, 16 Dec 2013, Tejun Heo wrote: > > On Mon, Dec 16, 2013 at 06:19:37PM +0100, Michal Hocko wrote: > > > I have to think about it some more (the brain is not working anymore > > > today). But what we really need is that nobody gets the same id while > > > the css is alive. So css_from_id returning NULL doesn't seem to be > > > enough. > > > > Oh, I meant whether it's necessary to keep css_from_id() working > > (ie. doing successful lookups) between offline and release, because > > that's where lifetimes are coupled. IOW, if it's enough for cgroup to > > not recycle the ID until all css's are released && fail css_from_id() > > lookup after the css is offlined, I can make a five liner quick fix. > > Don't take my word on it, I'm too fuzzy on this: but although it would > be good to refrain from recycling the ID until all css's are released, > I believe that it would not be good enough to fail css_from_id() once > the css is offlined - mem_cgroup_uncharge_swap() needs to uncharge the > hierarchy of the dead memcg (for example, when tmpfs file is removed). > > Uncharging the dead memcg itself is presumably irrelevant, but it does > need to locate the right parent to uncharge, and NULL css_from_id() > would make that impossible. Exactly! -- 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