From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id AE11C5F0001 for ; Tue, 3 Feb 2009 00:34:10 -0500 (EST) Received: from d28relay02.in.ibm.com (d28relay02.in.ibm.com [9.184.220.59]) by e28smtp05.in.ibm.com (8.13.1/8.13.1) with ESMTP id n135Y1JQ016487 for ; Tue, 3 Feb 2009 11:04:01 +0530 Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67]) by d28relay02.in.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id n135VhUo3588308 for ; Tue, 3 Feb 2009 11:01:43 +0530 Received: from d28av05.in.ibm.com (loopback [127.0.0.1]) by d28av05.in.ibm.com (8.13.1/8.13.3) with ESMTP id n135Y0eS012090 for ; Tue, 3 Feb 2009 16:34:01 +1100 Date: Tue, 3 Feb 2009 11:03:58 +0530 From: Balbir Singh Subject: Re: [-mm patch] Show memcg information during OOM Message-ID: <20090203053358.GO918@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090202125240.GA918@balbir.in.ibm.com> <20090202140849.GB918@balbir.in.ibm.com> <49879DE5.8030505@cn.fujitsu.com> <20090203044143.GM918@balbir.in.ibm.com> <20090203045556.GN918@balbir.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: David Rientjes Cc: Li Zefan , KAMEZAWA Hiroyuki , Andrew Morton , "linux-kernel@vger.kernel.org" , "nishimura@mxp.nes.nec.co.jp" , "linux-mm@kvack.org" List-ID: * David Rientjes [2009-02-02 21:25:52]: > On Tue, 3 Feb 2009, Balbir Singh wrote: > > > > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > > > > > index d3b9bac..b8e53ae 100644 > > > > > > --- a/mm/oom_kill.c > > > > > > +++ b/mm/oom_kill.c > > > > > > @@ -392,6 +392,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, > > > > > > current->comm, gfp_mask, order, current->oomkilladj); > > > > > > task_lock(current); > > > > > > cpuset_print_task_mems_allowed(current); > > > > > > + mem_cgroup_print_mem_info(mem); > > > > > > > > > > I think this can be put outside the task lock. The lock is used to call task_cs() safely in > > > > > cpuset_print_task_mems_allowed(). > > > > > > > > > > > > > Thanks, I'll work on that in the next version. > > > > > > > > > > I was also wondering about this and assumed that it was necessary to > > > prevent the cgroup from disappearing during the oom. If task_lock() isn't > > > held, is the memcg->css.cgroup->dentry->d_name.name dereference always > > > safe without rcu? > > > > > > > oom_kill_process is called with tasklist_lock held (read-mode). That > > should suffice, no? The memcg cannot go away since it has other groups > > or tasks associated with it. > > > > I don't see how this prevents a task from being reattached to a different > cgroup and then a rmdir on memcg->css.cgroup would destroy the dentry > without cgroup_mutex or dereferencing via rcu. That scenario is not possible today from the memory controller perspective. We hold memcg_tasklist during task movement and during OOM, task migration is held till OOM completes. -- Balbir -- 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