From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CBAA9C67863 for ; Tue, 23 Oct 2018 12:10:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7ACB12080A for ; Tue, 23 Oct 2018 12:10:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7ACB12080A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728069AbeJWUeK (ORCPT ); Tue, 23 Oct 2018 16:34:10 -0400 Received: from mx2.suse.de ([195.135.220.15]:59598 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727264AbeJWUeK (ORCPT ); Tue, 23 Oct 2018 16:34:10 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 789C9AF4D; Tue, 23 Oct 2018 12:10:56 +0000 (UTC) Date: Tue, 23 Oct 2018 14:10:55 +0200 From: Michal Hocko To: Johannes Weiner Cc: linux-mm@kvack.org, Tetsuo Handa , David Rientjes , Andrew Morton , LKML Subject: Re: [RFC PATCH 2/2] memcg: do not report racy no-eligible OOM tasks Message-ID: <20181023121055.GS18839@dhcp22.suse.cz> References: <20181022120308.GB18839@dhcp22.suse.cz> <201810230101.w9N118i3042448@www262.sakura.ne.jp> <20181023114246.GR18839@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181023114246.GR18839@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? -- Michal Hocko SUSE Labs