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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 C8EBAC433DF for ; Wed, 26 Aug 2020 12:48:17 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6E4BA2080C for ; Wed, 26 Aug 2020 12:48:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6E4BA2080C 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 C6F3E6B0005; Wed, 26 Aug 2020 08:48:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C1F366B0006; Wed, 26 Aug 2020 08:48:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B63B86B0007; Wed, 26 Aug 2020 08:48:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0249.hostedemail.com [216.40.44.249]) by kanga.kvack.org (Postfix) with ESMTP id A15316B0005 for ; Wed, 26 Aug 2020 08:48:16 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 5ADB2381E for ; Wed, 26 Aug 2020 12:48:16 +0000 (UTC) X-FDA: 77192697792.16.pet52_3e04d8e27064 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin16.hostedemail.com (Postfix) with ESMTP id 20E0E100E6903 for ; Wed, 26 Aug 2020 12:48:16 +0000 (UTC) X-HE-Tag: pet52_3e04d8e27064 X-Filterd-Recvd-Size: 3559 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Wed, 26 Aug 2020 12:48:15 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id BCDECB17A; Wed, 26 Aug 2020 12:48:45 +0000 (UTC) Date: Wed, 26 Aug 2020 14:48:10 +0200 From: Michal Hocko To: xunlei Cc: Johannes Weiner , Andrew Morton , Vladimir Davydov , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: memcg: Fix memcg reclaim soft lockup Message-ID: <20200826124810.GQ22869@dhcp22.suse.cz> References: <1598426822-93737-1-git-send-email-xlpang@linux.alibaba.com> <20200826081102.GM22869@dhcp22.suse.cz> <99efed0e-050a-e313-46ab-8fe6228839d5@linux.alibaba.com> <20200826110015.GO22869@dhcp22.suse.cz> <20200826120740.GP22869@dhcp22.suse.cz> <19eb48db-7d5e-0f55-5dfc-6a71274fd896@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <19eb48db-7d5e-0f55-5dfc-6a71274fd896@linux.alibaba.com> X-Rspamd-Queue-Id: 20E0E100E6903 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 Content-Transfer-Encoding: quoted-printable 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 Wed 26-08-20 20:21:39, xunlei wrote: > On 2020/8/26 =E4=B8=8B=E5=8D=888:07, Michal Hocko wrote: > > On Wed 26-08-20 20:00:47, xunlei wrote: > >> On 2020/8/26 =E4=B8=8B=E5=8D=887:00, Michal Hocko wrote: > >>> On Wed 26-08-20 18:41:18, xunlei wrote: > >>>> On 2020/8/26 =E4=B8=8B=E5=8D=884:11, Michal Hocko wrote: > >>>>> On Wed 26-08-20 15:27:02, Xunlei Pang wrote: > >>>>>> We've met softlockup with "CONFIG_PREEMPT_NONE=3Dy", when > >>>>>> the target memcg doesn't have any reclaimable memory. > >>>>> > >>>>> Do you have any scenario when this happens or is this some sort o= f a > >>>>> test case? > >>>> > >>>> It can happen on tiny guest scenarios. > >>> > >>> OK, you made me more curious. If this is a tiny guest and this is a= hard > >>> limit reclaim path then we should trigger an oom killer which shoul= d > >>> kill the offender and that in turn bail out from the try_charge lop= p > >>> (see should_force_charge). So how come this repeats enough in your = setup > >>> that it causes soft lockups? > >>> > >> > >> should_force_charge() is false, the current trapped in endless loop = is > >> not the oom victim. > >=20 > > How is that possible? If the oom killer kills a task and that doesn't > > resolve the oom situation then it would go after another one until al= l > > tasks are killed. Or is your task living outside of the memcg it trie= s > > to charge? > >=20 >=20 > All tasks are in memcgs. Looks like the first oom victim is not finishe= d > (unable to schedule), later mem_cgroup_oom()->...->oom_evaluate_task() > will set oc->chosen to -1 and abort. This shouldn't be possible for too long because oom_reaper would make it invisible to the oom killer so it should proceed. Also mem_cgroup_out_of_memory takes a mutex and that is an implicit scheduling point already. Which kernel version is this? And just for the clarification. I am not against the additional cond_resched. That sounds like a good thing in general because we do want to have a predictable scheduling during reclaim which is independent on reclaimability as much as possible. But I would like to drill down to why you are seeing the lockup because those shouldn't really happen. --=20 Michal Hocko SUSE Labs