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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 E4D36C46471 for ; Tue, 7 Aug 2018 20:38:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68B21215F1 for ; Tue, 7 Aug 2018 20:38:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 68B21215F1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726704AbeHGWyy (ORCPT ); Tue, 7 Aug 2018 18:54:54 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:57062 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726359AbeHGWyy (ORCPT ); Tue, 7 Aug 2018 18:54:54 -0400 Received: from fsav401.sakura.ne.jp (fsav401.sakura.ne.jp [133.242.250.100]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w77Kcfea069550; Wed, 8 Aug 2018 05:38:42 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav401.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav401.sakura.ne.jp); Wed, 08 Aug 2018 05:38:41 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav401.sakura.ne.jp) Received: from [192.168.1.8] (softbank126074194044.bbtec.net [126.74.194.44]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w77KcfIq069547 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 8 Aug 2018 05:38:41 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] memcg, oom: be careful about races when warning about no reclaimable task To: Johannes Weiner Cc: Michal Hocko , Andrew Morton , Vladimir Davydov , linux-mm@kvack.org, Greg Thelen , Dmitry Vyukov , LKML , Michal Hocko , David Rientjes References: <20180807072553.14941-1-mhocko@kernel.org> <863d73ce-fae9-c117-e361-12c415c787de@i-love.sakura.ne.jp> <20180807201935.GB4251@cmpxchg.org> From: Tetsuo Handa Message-ID: <1308e0bd-e194-7b35-484c-fc18f493f8da@i-love.sakura.ne.jp> Date: Wed, 8 Aug 2018 05:38:39 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180807201935.GB4251@cmpxchg.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/08/08 5:19, Johannes Weiner wrote: > On Tue, Aug 07, 2018 at 07:15:11PM +0900, Tetsuo Handa wrote: >> On 2018/08/07 16:25, Michal Hocko wrote: >>> @@ -1703,7 +1703,8 @@ static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int >>> return OOM_ASYNC; >>> } >>> >>> - if (mem_cgroup_out_of_memory(memcg, mask, order)) >>> + if (mem_cgroup_out_of_memory(memcg, mask, order) || >>> + tsk_is_oom_victim(current)) >>> return OOM_SUCCESS; >>> >>> WARN(1,"Memory cgroup charge failed because of no reclaimable memory! " >>> >> >> I don't think this patch is appropriate. This patch only avoids hitting WARN(1). >> This patch does not address the root cause: >> >> The task_will_free_mem(current) test in out_of_memory() is returning false >> because test_bit(MMF_OOM_SKIP, &mm->flags) test in task_will_free_mem() is >> returning false because MMF_OOM_SKIP was already set by the OOM reaper. The OOM >> killer does not need to start selecting next OOM victim until "current thread >> completes __mmput()" or "it fails to complete __mmput() within reasonable >> period". > > I don't see why it matters whether the OOM victim exits or not, unless > you count the memory consumed by struct task_struct. We are not counting memory consumed by struct task_struct. But David is counting memory released between set_bit(MMF_OOM_SKIP, &mm->flags) and completion of exit_mmap(). > >> According to https://syzkaller.appspot.com/text?tag=CrashLog&x=15a1c770400000 , >> PID=23767 selected PID=23766 as an OOM victim and the OOM reaper set MMF_OOM_SKIP >> before PID=23766 unnecessarily selects PID=23767 as next OOM victim. >> At uptime = 366.550949, out_of_memory() should have returned true without selecting >> next OOM victim because tsk_is_oom_victim(current) == true. > > The code works just fine. We have to kill tasks until we a) free > enough memory or b) run out of tasks or c) kill current. When one of > these outcomes is reached, we allow the charge and return. > > The only problem here is a warning in the wrong place. > If forced charge contained a bug, removing this WARN(1) deprives users of chance to know that something is going wrong.