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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 2CF2EC3A589 for ; Tue, 20 Aug 2019 08:34:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C6BC9239BA for ; Tue, 20 Aug 2019 08:34:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C6BC9239BA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 670A96B0007; Tue, 20 Aug 2019 04:34:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 621B86B0008; Tue, 20 Aug 2019 04:34:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 537F56B000A; Tue, 20 Aug 2019 04:34:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0215.hostedemail.com [216.40.44.215]) by kanga.kvack.org (Postfix) with ESMTP id 2E8366B0007 for ; Tue, 20 Aug 2019 04:34:16 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id D786D8248AB3 for ; Tue, 20 Aug 2019 08:34:15 +0000 (UTC) X-FDA: 75842144070.05.horn64_7ef5f8ee3213 X-HE-Tag: horn64_7ef5f8ee3213 X-Filterd-Recvd-Size: 5657 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Tue, 20 Aug 2019 08:34:14 +0000 (UTC) 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 1CFA1ABBE; Tue, 20 Aug 2019 08:34:13 +0000 (UTC) Date: Tue, 20 Aug 2019 10:34:12 +0200 From: Michal Hocko To: Yafang Shao Cc: Johannes Weiner , Yafang Shao , Roman Gushchin , Souptick Joarder , Vladimir Davydov , Tetsuo Handa , Randy Dunlap , "linux-mm@kvack.org" , "akpm@linux-foundation.org" Subject: Re: [PATCH v2] mm, memcg: skip killing processes under memcg protection at first scan Message-ID: <20190820083412.GK3111@dhcp22.suse.cz> References: <1566177486-2649-1-git-send-email-laoar.shao@gmail.com> <20190819211200.GA24956@tower.dhcp.thefacebook.com> <20190820064018.GE3111@dhcp22.suse.cz> <20190820072703.GF3111@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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 20-08-19 15:49:20, Yafang Shao wrote: > On Tue, Aug 20, 2019 at 3:27 PM Michal Hocko wrote: > > > > On Tue 20-08-19 15:15:54, Yafang Shao wrote: > > > On Tue, Aug 20, 2019 at 2:40 PM Michal Hocko wrote: > > > > > > > > On Tue 20-08-19 09:16:01, Yafang Shao wrote: > > > > > On Tue, Aug 20, 2019 at 5:12 AM Roman Gushchin wrote: > > > > > > > > > > > > On Sun, Aug 18, 2019 at 09:18:06PM -0400, Yafang Shao wrote: > > > > > > > In the current memory.min design, the system is going to do OOM instead > > > > > > > of reclaiming the reclaimable pages protected by memory.min if the > > > > > > > system is lack of free memory. While under this condition, the OOM > > > > > > > killer may kill the processes in the memcg protected by memory.min. > > > > > > > This behavior is very weird. > > > > > > > In order to make it more reasonable, I make some changes in the OOM > > > > > > > killer. In this patch, the OOM killer will do two-round scan. It will > > > > > > > skip the processes under memcg protection at the first scan, and if it > > > > > > > can't kill any processes it will rescan all the processes. > > > > > > > > > > > > > > Regarding the overhead this change may takes, I don't think it will be a > > > > > > > problem because this only happens under system memory pressure and > > > > > > > the OOM killer can't find any proper victims which are not under memcg > > > > > > > protection. > > > > > > > > > > > > Hi Yafang! > > > > > > > > > > > > The idea makes sense at the first glance, but actually I'm worried > > > > > > about mixing per-memcg and per-process characteristics. > > > > > > Actually, it raises many questions: > > > > > > 1) if we do respect memory.min, why not memory.low too? > > > > > > > > > > memroy.low is different with memory.min, as the OOM killer will not be > > > > > invoked when it is reached. > > > > > > > > Responded in other email thread (please do not post two versions of the > > > > patch on the same day because it makes conversation too scattered and > > > > confusing). > > > > > > > (This is an issue about time zone :-) ) > > > > Normally we wait few days until feedback on the particular patch is > > settled before a new version is posted. > > > > > > Think of min limit protection as some sort of a more inteligent mlock. > > > > > > Per my perspective, it is a less inteligent mlock, because what it > > > protected may be a garbage memory. > > > As I said before, what it protected is the memroy usage, rather than a > > > specified file memory or anon memory or somethin else. > > > > > > The advantage of it is easy to use. > > > > > > > It protects from the regular memory reclaim and it can lead to the OOM > > > > situation (be it global or memcg) but by no means it doesn't prevent > > > > from the system to kill the workload if there is a need. Those two > > > > decisions are simply orthogonal IMHO. The later is a an emergency action > > > > while the former is to help guanratee a runtime behavior of the workload. > > > > > > > > > > If it can handle OOM memory reclaim, it will be more inteligent. > > > > Can we get back to an actual usecase please? > > > > No real usecase. > What we concerned is if it can lead to more OOMs but can't protect > itself in OOM then this behavior seems a little wierd. This is a natural side effect of protecting memory from the reclaim. Read mlock kind of protection. Weird? I dunno. Unexpected, no! > Setting oom_score_adj is another choice, but there's no memcg-level > oom_score_adj. > memory.min is memcg-level, while oom_score_adj is process-level, that > is wierd as well. OOM, is per process operation. Sure we have that group kill option but then still the selection is per-process. Without any clear usecase in sight I do not think it makes sense to pursue this further. Thanks! -- Michal Hocko SUSE Labs