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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 1D7FFC282C0 for ; Sun, 27 Jan 2019 11:40:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D9EB0214C6 for ; Sun, 27 Jan 2019 11:40:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548589225; bh=vyTfpJCa0yS8juXi+m5bmyXv1CY6zBBNmlO1H/X9Df0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=thQ7ybxlFCuEM2an/n751D177FAe/GKR72tsUwfvJZ+oHwv3mlTjJw9Gnt4ocKDwv agQdOxTedLidqAYbAqqlFO8mtT4tb4JwlAGq+w7IDWxleGr2/Fn6SAgGDJFGX8uWAg cRThXq0tAOi2A+sS/+Y9vNP5yyehwS03FGYGTIUo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726995AbfA0LkY (ORCPT ); Sun, 27 Jan 2019 06:40:24 -0500 Received: from mx2.suse.de ([195.135.220.15]:60504 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726774AbfA0LkX (ORCPT ); Sun, 27 Jan 2019 06:40:23 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 63A56AD18; Sun, 27 Jan 2019 11:40:22 +0000 (UTC) Date: Sun, 27 Jan 2019 12:40:21 +0100 From: Michal Hocko To: Tetsuo Handa Cc: Arkadiusz =?utf-8?Q?Mi=C5=9Bkiewicz?= , Andrew Morton , Tejun Heo , cgroups@vger.kernel.org, Aleksa Sarai , Jay Kamat , Roman Gushchin , Johannes Weiner , linux-kernel@vger.kernel.org, Linus Torvalds , linux-mm Subject: Re: [PATCH v2] oom, oom_reaper: do not enqueue same task twice Message-ID: <20190127114021.GB18811@dhcp22.suse.cz> References: <480296c4-ed7a-3265-e84a-298e42a0f1d5@I-love.SAKURA.ne.jp> <6da6ca69-5a6e-a9f6-d091-f89a8488982a@gmail.com> <72aa8863-a534-b8df-6b9e-f69cf4dd5c4d@i-love.sakura.ne.jp> <33a07810-6dbc-36be-5bb6-a279773ccf69@i-love.sakura.ne.jp> <34e97b46-0792-cc66-e0f2-d72576cdec59@i-love.sakura.ne.jp> <2b0c7d6c-c58a-da7d-6f0a-4900694ec2d3@gmail.com> <1d161137-55a5-126f-b47e-b2625bd798ca@i-love.sakura.ne.jp> <20190127083724.GA18811@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Sun 27-01-19 19:56:06, Tetsuo Handa wrote: > On 2019/01/27 17:37, Michal Hocko wrote: > > Thanks for the analysis and the patch. This should work, I believe but > > I am not really thrilled to overload the meaning of the MMF_UNSTABLE. > > The flag is meant to signal accessing address space is not stable and it > > is not aimed to synchronize oom reaper with the oom path. > > > > Can we make use mark_oom_victim directly? I didn't get to think that > > through right now so I might be missing something but this should > > prevent repeating queueing as well. > > Yes, TIF_MEMDIE would work. But you are planning to remove TIF_MEMDIE. Also, > TIF_MEMDIE can't avoid enqueuing many threads sharing mm_struct to the OOM > reaper. There is no need to enqueue many threads sharing mm_struct because > the OOM reaper acts on mm_struct rather than task_struct. Thus, enqueuing > based on per mm_struct flag sounds better, but MMF_OOM_VICTIM cannot be > set from wake_oom_reaper(victim) because victim's mm might be already inside > exit_mmap() when wake_oom_reaper(victim) is called after task_unlock(victim). > > We could reintroduce MMF_OOM_KILLED in commit 855b018325737f76 > ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task") > if you don't like overloading the meaning of the MMF_UNSTABLE. But since > MMF_UNSTABLE is available in Linux 4.9+ kernels (which covers all LTS stable > versions with the OOM reaper support), we can temporarily use MMF_UNSTABLE > for ease of backporting. I agree that a per-mm state is more optimal but I would rather fix the issue in a clear way first and only then think about an optimization on top. Queueing based on mark_oom_victim (whatever that uses to guarantee the victim is marked atomically and only once) makes sense from the conceptual point of view and it makes a lot of sense to start from there. MMF_UNSTABLE has a completely different purpose. So unless you see a correctness issue with that then I would rather go that way. -- Michal Hocko SUSE Labs