From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 31CEB6B0003 for ; Tue, 23 Oct 2018 08:48:51 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id 31-v6so923738edr.19 for ; Tue, 23 Oct 2018 05:48:51 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id p14-v6si1069630edi.343.2018.10.23.05.48.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Oct 2018 05:48:49 -0700 (PDT) Date: Tue, 23 Oct 2018 14:48:47 +0200 From: Michal Hocko Subject: Re: [RFC PATCH 2/2] memcg: do not report racy no-eligible OOM tasks Message-ID: <20181023124847.GT18839@dhcp22.suse.cz> References: <20181022120308.GB18839@dhcp22.suse.cz> <201810230101.w9N118i3042448@www262.sakura.ne.jp> <20181023114246.GR18839@dhcp22.suse.cz> <20181023121055.GS18839@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: Johannes Weiner , linux-mm@kvack.org, David Rientjes , Andrew Morton , LKML On Tue 23-10-18 21:33:43, Tetsuo Handa wrote: > On 2018/10/23 21:10, Michal Hocko wrote: > > On Tue 23-10-18 13:42:46, Michal Hocko wrote: > >> On Tue 23-10-18 10:01:08, Tetsuo Handa wrote: > >>> Michal Hocko wrote: > >>>> On Mon 22-10-18 20:45:17, Tetsuo Handa wrote: > >>>>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c > >>>>>> index e79cb59552d9..a9dfed29967b 100644 > >>>>>> --- a/mm/memcontrol.c > >>>>>> +++ b/mm/memcontrol.c > >>>>>> @@ -1380,10 +1380,22 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, > >>>>>> .gfp_mask = gfp_mask, > >>>>>> .order = order, > >>>>>> }; > >>>>>> - bool ret; > >>>>>> + bool ret = true; > >>>>>> > >>>>>> mutex_lock(&oom_lock); > >>>>>> + > >>>>>> + /* > >>>>>> + * multi-threaded tasks might race with oom_reaper and gain > >>>>>> + * MMF_OOM_SKIP before reaching out_of_memory which can lead > >>>>>> + * to out_of_memory failure if the task is the last one in > >>>>>> + * memcg which would be a false possitive failure reported > >>>>>> + */ > >>>>>> + if (tsk_is_oom_victim(current)) > >>>>>> + goto unlock; > >>>>>> + > >>>>> > >>>>> This is not wrong but is strange. We can use mutex_lock_killable(&oom_lock) > >>>>> so that any killed threads no longer wait for oom_lock. > >>>> > >>>> tsk_is_oom_victim is stronger because it doesn't depend on > >>>> fatal_signal_pending which might be cleared throughout the exit process. > >>>> > >>> > >>> I still want to propose this. No need to be memcg OOM specific. > >> > >> Well, I maintain what I've said [1] about simplicity and specific fix > >> for a specific issue. Especially in the tricky code like this where all > >> the consequences are far more subtle than they seem to be. > >> > >> This is obviously a matter of taste but I don't see much point discussing > >> this back and forth for ever. Unless there is a general agreement that > >> the above is less appropriate then I am willing to consider a different > >> change but I simply do not have energy to nit pick for ever. > >> > >> [1] http://lkml.kernel.org/r/20181022134315.GF18839@dhcp22.suse.cz > > > > In other words. Having a memcg specific fix means, well, a memcg > > maintenance burden. Like any other memcg specific oom decisions we > > already have. So are you OK with that Johannes or you would like to see > > a more generic fix which might turn out to be more complex? > > > > I don't know what "that Johannes" refers to. let me rephrase Johannes, are you OK with that (memcg specific fix) or you would like to see a more generic fix which might turn out to be more complex. -- Michal Hocko SUSE Labs