From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753434AbdJaNXC (ORCPT ); Tue, 31 Oct 2017 09:23:02 -0400 Received: from mx2.suse.de ([195.135.220.15]:42335 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751172AbdJaNXB (ORCPT ); Tue, 31 Oct 2017 09:23:01 -0400 Date: Tue, 31 Oct 2017 14:22:59 +0100 From: Michal Hocko To: Tetsuo Handa Cc: aarcange@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rientjes@google.com, hannes@cmpxchg.org, mjaggi@caviumnetworks.com, mgorman@suse.de, oleg@redhat.com, vdavydov.dev@gmail.com, vbabka@suse.cz Subject: Re: [PATCH] mm,oom: Try last second allocation before and after selecting an OOM victim. Message-ID: <20171031132259.irkladqbucz2qa3g@dhcp22.suse.cz> References: <20171030141815.lk76bfetmspf7f4x@dhcp22.suse.cz> <201710311940.FDJ52199.OHMtSFVFOJLOQF@I-love.SAKURA.ne.jp> <20171031121032.lm3wxx3l5tkpo2ni@dhcp22.suse.cz> <201710312142.DBB81723.FOOFJMQLStFVOH@I-love.SAKURA.ne.jp> <20171031124855.rszis5gefbxwriiz@dhcp22.suse.cz> <201710312213.BDB35457.MtFJOQVLOFSOHF@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201710312213.BDB35457.MtFJOQVLOFSOHF@I-love.SAKURA.ne.jp> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 31-10-17 22:13:05, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Tue 31-10-17 21:42:23, Tetsuo Handa wrote: > > > > While both have some merit, the first reason is mostly historical > > > > because we have the explicit locking now and it is really unlikely that > > > > the memory would be available right after we have given up trying. > > > > Last attempt allocation makes some sense of course but considering that > > > > the oom victim selection is quite an expensive operation which can take > > > > a considerable amount of time it makes much more sense to retry the > > > > allocation after the most expensive part rather than before. Therefore > > > > move the last attempt right before we are trying to kill an oom victim > > > > to rule potential races when somebody could have freed a lot of memory > > > > in the meantime. This will reduce the time window for potentially > > > > pre-mature OOM killing considerably. > > > > > > But this is about "doing last second allocation attempt after selecting > > > an OOM victim". This is not about "allowing OOM victims to try ALLOC_OOM > > > before selecting next OOM victim" which is the actual problem I'm trying > > > to deal with. > > > > then split it into two. First make the general case and then add a more > > sophisticated on top. Dealing with multiple issues at once is what makes > > all those brain cells suffer. > > I'm failing to understand. I was dealing with single issue at once. > The single issue is "MMF_OOM_SKIP prematurely prevents OOM victims from trying > ALLOC_OOM before selecting next OOM victims". Then, what are the general case and > a more sophisticated? I wonder what other than "MMF_OOM_SKIP should allow OOM > victims to try ALLOC_OOM for once before selecting next OOM victims" can exist... Try to think little bit out of your very specific and borderline usecase and it will become obvious. ALLOC_OOM is a trivial update on top of moving get_page_from_freelist to oom_kill_process which is a more generic race window reducer. -- Michal Hocko SUSE Labs