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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 7BDB7C28CF6 for ; Tue, 24 Jul 2018 22:31:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0268320874 for ; Tue, 24 Jul 2018 22:31:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0268320874 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 S2388699AbeGXXkV (ORCPT ); Tue, 24 Jul 2018 19:40:21 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:39860 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727353AbeGXXkV (ORCPT ); Tue, 24 Jul 2018 19:40:21 -0400 Received: from fsav302.sakura.ne.jp (fsav302.sakura.ne.jp [153.120.85.133]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w6OMVXdK098348; Wed, 25 Jul 2018 07:31:33 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav302.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav302.sakura.ne.jp); Wed, 25 Jul 2018 07:31:33 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav302.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 w6OMVT8F098339 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 25 Jul 2018 07:31:33 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [patch v4] mm, oom: fix unnecessary killing of additional processes To: David Rientjes Cc: Andrew Morton , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: From: Tetsuo Handa Message-ID: <05dbc69a-1c26-adec-15c6-f7192f8d2ae0@i-love.sakura.ne.jp> Date: Wed, 25 Jul 2018 07:31:24 +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: 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 2018/07/25 6:45, David Rientjes wrote: > On Sat, 21 Jul 2018, Tetsuo Handa wrote: > >> You can't apply "[patch v4] mm, oom: fix unnecessary killing of additional processes" >> because Michal's patch which removes oom_lock serialization was added to -mm tree. >> > > I've rebased the patch to linux-next and posted a v5. > >> You might worry about situations where __oom_reap_task_mm() is a no-op. >> But that is not always true. There is no point with emitting >> >> pr_info("oom_reaper: unable to reap pid:%d (%s)\n", ...); >> debug_show_all_locks(); >> >> noise and doing >> >> set_bit(MMF_OOM_SKIP, &mm->flags); >> >> because exit_mmap() will not release oom_lock until __oom_reap_task_mm() >> completes. That is, except extra noise, there is no difference with >> current behavior which sets set_bit(MMF_OOM_SKIP, &mm->flags) after >> returning from __oom_reap_task_mm(). >> > > v5 has restructured how exit_mmap() serializes its unmapping with the oom > reaper. It sets MMF_OOM_SKIP while holding mm->mmap_sem. > I think that v5 is still wrong. exit_mmap() keeps mmap_sem held for write does not prevent oom_reap_task() from emitting the noise and setting MMF_OOM_SKIP after timeout. Since your purpose is to wait for release of memory which could not be reclaimed by __oom_reap_task_mm(), what if __oom_reap_task_mm() was no-op and exit_mmap() was preempted immediately after returning from __oom_reap_task_mm() ? Also, I believe that userspace visible knob is not needed.