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=-7.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,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 33C29C433DF for ; Wed, 26 Aug 2020 13:16:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 15EAB2080C for ; Wed, 26 Aug 2020 13:16:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730184AbgHZNQc (ORCPT ); Wed, 26 Aug 2020 09:16:32 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:59488 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729177AbgHZNQc (ORCPT ); Wed, 26 Aug 2020 09:16:32 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04427;MF=xlpang@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0U6w.nFU_1598447788; Received: from xunleideMacBook-Pro.local(mailfrom:xlpang@linux.alibaba.com fp:SMTPD_---0U6w.nFU_1598447788) by smtp.aliyun-inc.com(127.0.0.1); Wed, 26 Aug 2020 21:16:28 +0800 Reply-To: xlpang@linux.alibaba.com Subject: Re: [PATCH] mm: memcg: Fix memcg reclaim soft lockup To: Michal Hocko Cc: Johannes Weiner , Andrew Morton , Vladimir Davydov , linux-kernel@vger.kernel.org, linux-mm@kvack.org 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> <20200826124810.GQ22869@dhcp22.suse.cz> From: xunlei Message-ID: <061e8600-e162-6ac9-2f4f-bf161435a5b2@linux.alibaba.com> Date: Wed, 26 Aug 2020 21:16:28 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200826124810.GQ22869@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/8/26 下午8:48, Michal Hocko wrote: > On Wed 26-08-20 20:21:39, xunlei wrote: >> On 2020/8/26 下午8:07, Michal Hocko wrote: >>> On Wed 26-08-20 20:00:47, xunlei wrote: >>>> On 2020/8/26 下午7:00, Michal Hocko wrote: >>>>> On Wed 26-08-20 18:41:18, xunlei wrote: >>>>>> On 2020/8/26 下午4:11, Michal Hocko wrote: >>>>>>> On Wed 26-08-20 15:27:02, Xunlei Pang wrote: >>>>>>>> We've met softlockup with "CONFIG_PREEMPT_NONE=y", when >>>>>>>> the target memcg doesn't have any reclaimable memory. >>>>>>> >>>>>>> Do you have any scenario when this happens or is this some sort of 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 should >>>>> kill the offender and that in turn bail out from the try_charge lopp >>>>> (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. >>> >>> 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 all >>> tasks are killed. Or is your task living outside of the memcg it tries >>> to charge? >>> >> >> All tasks are in memcgs. Looks like the first oom victim is not finished >> (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? > I reproduced it on "5.9.0-rc2". oom_reaper also can't get scheduled because of 1-cpu, and the mutex uses might_sleep() which is noop in case of "CONFIG_PREEMPT_VOLUNTARY is not set" I mentioned in the commit log. > 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. >