From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx121.postini.com [74.125.245.121]) by kanga.kvack.org (Postfix) with SMTP id 3C4506B0071 for ; Wed, 30 May 2012 11:33:07 -0400 (EDT) Received: by vcbfl10 with SMTP id fl10so3794262vcb.14 for ; Wed, 30 May 2012 08:33:06 -0700 (PDT) Date: Wed, 30 May 2012 17:33:00 +0200 From: Frederic Weisbecker Subject: Re: [PATCH v3 16/28] memcg: kmem controller charge/uncharge infrastructure Message-ID: <20120530153256.GA27008@somewhere.redhat.com> References: <1337951028-3427-1-git-send-email-glommer@parallels.com> <1337951028-3427-17-git-send-email-glommer@parallels.com> <20120530130416.GD25094@somewhere.redhat.com> <4FC61B4E.2060206@parallels.com> <20120530133736.GF25094@somewhere.redhat.com> <4FC622B5.9080600@parallels.com> <20120530135319.GG25094@somewhere.redhat.com> <4FC626DA.3030408@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FC626DA.3030408@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, Tejun Heo , Li Zefan , Greg Thelen , Suleiman Souhlal , Michal Hocko , Johannes Weiner , devel@openvz.org, David Rientjes , Christoph Lameter , Pekka Enberg On Wed, May 30, 2012 at 05:55:38PM +0400, Glauber Costa wrote: > On 05/30/2012 05:53 PM, Frederic Weisbecker wrote: > >On Wed, May 30, 2012 at 05:37:57PM +0400, Glauber Costa wrote: > >>On 05/30/2012 05:37 PM, Frederic Weisbecker wrote: > >>>Right. __mem_cgroup_get_kmem_cache() fetches the memcg of the owner > >>>and calls memcg_create_cache_enqueue() which does css_tryget(&memcg->css). > >>>After this tryget I think you're fine. And in-between you're safe against > >>>css_set removal due to rcu_read_lock(). > >>> > >>>I'm less clear with __mem_cgroup_new_kmem_page() though... > >> > >>That one does not get memcg->css but it does call mem_cgroup_get(), > >>that does prevent against the memcg structure being freed, which I > >>believe to be good enough. > > > >What if the owner calls cgroup_exit() between mem_cgroup_from_task() > >and mem_cgroup_get()? The css_set which contains the memcg gets freed. > >Also the reference on the memcg doesn't even prevent the css_set to > >be removed, does it? > It doesn't, but we don't really care. The css can go away, if the > memcg structure stays. Ah right, the memcg itself is only freed at destroy time. > The caches will outlive the memcg anyway, > since it is possible that you delete it, with some caches still > holding objects that > are not freed (they will be marked as dead). I guess I need to look at how the destroy path is handled in your patchset then. Or how you ensure that __mem_cgroup_new_kmem_page() can't race against destroy. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org