From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx199.postini.com [74.125.245.199]) by kanga.kvack.org (Postfix) with SMTP id 2F29D6B0068 for ; Mon, 1 Oct 2012 05:48:49 -0400 (EDT) Date: Mon, 1 Oct 2012 11:48:46 +0200 From: Michal Hocko Subject: Re: [PATCH v3 06/13] memcg: kmem controller infrastructure Message-ID: <20121001094846.GC8622@dhcp22.suse.cz> References: <1347977050-29476-1-git-send-email-glommer@parallels.com> <1347977050-29476-7-git-send-email-glommer@parallels.com> <20120926155108.GE15801@dhcp22.suse.cz> <5064392D.5040707@parallels.com> <20120927134432.GE29104@dhcp22.suse.cz> <50658B3B.9020303@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50658B3B.9020303@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com, devel@openvz.org, Tejun Heo , linux-mm@kvack.org, Suleiman Souhlal , Frederic Weisbecker , Mel Gorman , David Rientjes , Christoph Lameter , Pekka Enberg , Johannes Weiner On Fri 28-09-12 15:34:19, Glauber Costa wrote: > On 09/27/2012 05:44 PM, Michal Hocko wrote: > >> > the reference count aquired by mem_cgroup_get will still prevent the > >> > memcg from going away, no? > > Yes but you are outside of the rcu now and we usually do css_get before > > we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get > > deallocated but it could be gone before you call it. Or I am just > > confused - these 2 levels of ref counting is really not nice. > > > > Anyway, I have just noticed that __mem_cgroup_try_charge does > > VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should > > keep css ref count up as well. > > > > IIRC, css_get will prevent the cgroup directory from being removed. > Because some allocations are expected to outlive the cgroup, we > specifically don't want that. Yes, but how do you guarantee that the above VM_BUG_ON doesn't trigger? Task could have been moved to another group between mem_cgroup_from_task and mem_cgroup_get, no? -- 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