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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 CE19DC54FD0 for ; Thu, 23 Apr 2020 22:57:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5457620736 for ; Thu, 23 Apr 2020 22:57:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5457620736 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A4D6C8E0005; Thu, 23 Apr 2020 18:57:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9FDF48E0003; Thu, 23 Apr 2020 18:57:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8EC1F8E0005; Thu, 23 Apr 2020 18:57:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0189.hostedemail.com [216.40.44.189]) by kanga.kvack.org (Postfix) with ESMTP id 765C88E0003 for ; Thu, 23 Apr 2020 18:57:19 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 36A48181AC9B6 for ; Thu, 23 Apr 2020 22:57:19 +0000 (UTC) X-FDA: 76740632598.20.crown01_5ce57aa999823 X-HE-Tag: crown01_5ce57aa999823 X-Filterd-Recvd-Size: 3670 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by imf04.hostedemail.com (Postfix) with ESMTP for ; Thu, 23 Apr 2020 22:57:18 +0000 (UTC) Received: from fsav109.sakura.ne.jp (fsav109.sakura.ne.jp [27.133.134.236]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 03NMuYT7041111; Fri, 24 Apr 2020 07:56:34 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav109.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav109.sakura.ne.jp); Fri, 24 Apr 2020 07:56:34 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav109.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 03NMuYOm041102 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 24 Apr 2020 07:56:34 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [nacked] mm-oom-avoid-printk-iteration-under-rcu.patch removed from -mm tree To: Sergey Senozhatsky Cc: Michal Hocko , Yafang Shao , Andrew Morton , Roman Gushchin , linux-mm , David Rientjes , Shakeel Butt , Petr Mladek , Steven Rostedt References: <68371d79-dfae-e9b9-38df-dbb916607a82@i-love.sakura.ne.jp> <20200420073305.GD27314@dhcp22.suse.cz> <041d4158-f3dc-a5b5-546e-dd3f71f67b5f@i-love.sakura.ne.jp> <20200422065950.GA30312@dhcp22.suse.cz> <0aa5e490-c5b8-dc5c-334e-9a8d37da215c@i-love.sakura.ne.jp> <20200423073438.GC4206@dhcp22.suse.cz> <20200423110707.GD4206@dhcp22.suse.cz> <20200423155437.GB5385@jagdpanzerIV.localdomain> From: Tetsuo Handa Message-ID: Date: Fri, 24 Apr 2020 07:56:31 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200423155437.GB5385@jagdpanzerIV.localdomain> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 2020/04/24 0:54, Sergey Senozhatsky wrote: > Hmm. Any chance that those NO_CONSOLE messages overflow logbuf so then > we start losing pending YES_CONSOLE messages? Of course there will be such possibility if printk() user is doing something close to while (1) { cond_resched(); printk("hello\n"); } which is not avoidable unless "we allocate huge logbuf" and/or "add a flow control on the caller side". My proposal was to keep printk() synchronous by offloading dump_tasks() to a deferrable context (i.e. a workqueue context) and adding a flow control so that "logbuf will not overflow", and Michal Hocko is still refusing on adding a flow control to dump_tasks() side. The possibility of overflowing logbuf will remain no matter how printk() changes (i.e. even asynchronous printk cannot solve). NO_CONSOLE is not only a way for suppress printing to consoles but also a way for reducing possibility of overflowing logbuf, by hoping that userspace syslog daemon can read logbuf quickly enough to make free space for future NO_CONSOLE/YES_CONSOLE messages.