From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757343Ab3DAFh4 (ORCPT ); Mon, 1 Apr 2013 01:37:56 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:38121 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751107Ab3DAFhz (ORCPT ); Mon, 1 Apr 2013 01:37:55 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.8.4 Message-ID: <51591D21.8090401@jp.fujitsu.com> Date: Mon, 01 Apr 2013 14:37:37 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130307 Thunderbird/17.0.4 MIME-Version: 1.0 To: David Rientjes CC: Andrew Morton , Johannes Weiner , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch] mm, memcg: give exiting processes access to memory reserves References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2013/03/28 10:22), David Rientjes wrote: > A memcg may livelock when oom if the process that grabs the hierarchy's > oom lock is never the first process with PF_EXITING set in the memcg's > task iteration. > > The oom killer, both global and memcg, will defer if it finds an eligible > process that is in the process of exiting and it is not being ptraced. > The idea is to allow it to exit without using memory reserves before > needlessly killing another process. > > This normally works fine except in the memcg case with a large number of > threads attached to the oom memcg. In this case, the memcg oom killer > only gets called for the process that grabs the hierarchy's oom lock; all > others end up blocked on the memcg's oom waitqueue. Thus, if the process > that grabs the hierarchy's oom lock is never the first PF_EXITING process > in the memcg's task iteration, the oom killer is constantly deferred > without anything making progress. > > The fix is to give PF_EXITING processes access to memory reserves so that > we've marked them as oom killed without any iteration. This allows > __mem_cgroup_try_charge() to succeed so that the process may exit. This > makes the memcg oom killer exemption for TIF_MEMDIE tasks, now > immediately granted for processes with pending SIGKILLs and those in the > exit path, to be equivalent to what is done for the global oom killer. > > Signed-off-by: David Rientjes Acked-by: KAMEZAWA Hiroyuki > --- > mm/memcontrol.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1686,11 +1686,11 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, > struct task_struct *chosen = NULL; > > /* > - * If current has a pending SIGKILL, then automatically select it. The > - * goal is to allow it to allocate so that it may quickly exit and free > - * its memory. > + * If current has a pending SIGKILL or is exiting, then automatically > + * select it. The goal is to allow it to allocate so that it may > + * quickly exit and free its memory. > */ > - if (fatal_signal_pending(current)) { > + if (fatal_signal_pending(current) || current->flags & PF_EXITING) { > set_thread_flag(TIF_MEMDIE); > return; > } >