From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id E15BC8E00FD for ; Sun, 27 Jan 2019 06:40:24 -0500 (EST) Received: by mail-ed1-f69.google.com with SMTP id e29so5542053ede.19 for ; Sun, 27 Jan 2019 03:40:24 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id j21-v6si1735565ejt.227.2019.01.27.03.40.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 27 Jan 2019 03:40:23 -0800 (PST) Date: Sun, 27 Jan 2019 12:40:21 +0100 From: Michal Hocko 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: Sender: owner-linux-mm@kvack.org List-ID: 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 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