Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758283AbZAOFZg (ORCPT ); Thu, 15 Jan 2009 00:25:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751278AbZAOFZR (ORCPT ); Thu, 15 Jan 2009 00:25:17 -0500 Received: from ausmtp04.au.ibm.com ([202.81.18.152]:38153 "EHLO ausmtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750915AbZAOFZQ (ORCPT ); Thu, 15 Jan 2009 00:25:16 -0500 Date: Thu, 15 Jan 2009 10:47:17 +0530 From: Balbir Singh To: KAMEZAWA Hiroyuki Cc: Daisuke Nishimura , LKML , linux-mm , Andrew Morton , Pavel Emelyanov , Li Zefan , Paul Menage Subject: Re: [RFC][PATCH 5/4] memcg: don't call res_counter_uncharge when obsolete Message-ID: <20090115051717.GH21516@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090113184533.6ffd2af9.nishimura@mxp.nes.nec.co.jp> <20090114175121.275ecd59.nishimura@mxp.nes.nec.co.jp> <20090114135539.GA21516@balbir.in.ibm.com> <20090115122416.e15d88a7.kamezawa.hiroyu@jp.fujitsu.com> <20090115041750.GE21516@balbir.in.ibm.com> <20090115135223.1789e639.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20090115135223.1789e639.kamezawa.hiroyu@jp.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3125 Lines: 88 * KAMEZAWA Hiroyuki [2009-01-15 13:52:23]: > On Thu, 15 Jan 2009 09:47:50 +0530 > Balbir Singh wrote: > > > * KAMEZAWA Hiroyuki [2009-01-15 12:24:16]: > > > > > On Wed, 14 Jan 2009 19:25:39 +0530 > > > Balbir Singh wrote: > > > > > > > * Daisuke Nishimura [2009-01-14 17:51:21]: > > > > > > > > > This is a new one. Please review. > > > > > > > > > > === > > > > > From: Daisuke Nishimura > > > > > > > > > > mem_cgroup_get ensures that the memcg that has been got can be accessed > > > > > even after the directory has been removed, but it doesn't ensure that parents > > > > > of it can be accessed: parents might have been freed already by rmdir. > > > > > > > > > > This causes a bug in case of use_hierarchy==1, because res_counter_uncharge > > > > > climb up the tree. > > > > > > > > > > Check if the memcg is obsolete, and don't call res_counter_uncharge when obsole. > > > > > > > > > > Signed-off-by: Daisuke Nishimura > > > > > > > > I liked the earlier, EBUSY approach that ensured that parents could > > > > not go away if children exist. IMHO, the code has gotten too complex > > > > and has too many corner cases. Time to revisit it. > > > > > > > > > > But I don't like -EBUSY ;) > > > > > > When rmdir() returns -EBUSY even if there are no (visible) children and tasks, > > > our customer will take kdump and send it to me "please explain this kernel bug" > > > > > > I'm sure it will happen ;) > > > > > > > OK, but memory.stat can show why the group is busy and with > > move_to_parent() such issues should not occur right? I'll relook at > > the code. Thanks for your input. > > > Write a shell script as following ? > == > TASKS=`cat /xxx/xxx/xxx/tasks` > if [ -n $TASKS ]; then > echo "there is alive tasks in group /xxx/xxx/xxx/" > fi > > rmdir /xxx/xxx/xxx/ > CODE=$? > if [ $CODE = EBUSY ]; then > investigate why.... > fi > == > I don't want. > I agree with that. > I think rmdir() should succeed everywhen "there are no tasks and children". > And that can be done. > All I am saying is that let rmdir() fail if there are tasks or children, which I suspect cgroup takes care of. The second thing to do would be to add a mem_cgroup_get_hierarchical() and _put_hierarchical() API's so that we can get references all the way up to the parents. My concern is that not calling res_counter_uncharge() can lead to dangling references and bad behaviour. > With Paul's suggestion, I'll add wait_queue for rmdir of cgroup. > That might be a good idea and also a good idea to maintain the hierarchy (since we will walk up when we do uncharge) until we know that css reference count is down to 0. -- Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/