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[202.181.97.72]) by mx.google.com with ESMTPS id c82si6150444oia.35.2019.02.12.13.07.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Feb 2019 13:07:40 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of penguin-kernel@i-love.sakura.ne.jp designates 202.181.97.72 as permitted sender) client-ip=202.181.97.72; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of penguin-kernel@i-love.sakura.ne.jp designates 202.181.97.72 as permitted sender) smtp.mailfrom=penguin-kernel@i-love.sakura.ne.jp Received: from fsav301.sakura.ne.jp (fsav301.sakura.ne.jp [153.120.85.132]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x1CL7UsS021116; Wed, 13 Feb 2019 06:07:30 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav301.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav301.sakura.ne.jp); Wed, 13 Feb 2019 06:07:30 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav301.sakura.ne.jp) Received: from [192.168.1.8] (softbank126126163036.bbtec.net [126.126.163.36]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x1CL7OOv021047 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Wed, 13 Feb 2019 06:07:29 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] proc, oom: do not report alien mms when setting oom_score_adj To: Andrew Morton , Michal Hocko Cc: David Rientjes , Johannes Weiner , Linus Torvalds , Yong-Taek Lee , linux-mm@kvack.org, LKML , Michal Hocko References: <20190212102129.26288-1-mhocko@kernel.org> <20190212125635.27742b5741e92a0d47690c53@linux-foundation.org> From: Tetsuo Handa Message-ID: <46b3262e-2a9a-da01-16de-14cd4d7eaa40@i-love.sakura.ne.jp> Date: Wed, 13 Feb 2019 06:07:26 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20190212125635.27742b5741e92a0d47690c53@linux-foundation.org> 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 2019/02/13 5:56, Andrew Morton wrote: > On Tue, 12 Feb 2019 11:21:29 +0100 Michal Hocko wrote: > >> Tetsuo has reported that creating a thousands of processes sharing MM >> without SIGHAND (aka alien threads) and setting >> /proc//oom_score_adj will swamp the kernel log and takes ages [1] >> to finish. This is especially worrisome that all that printing is done >> under RCU lock and this can potentially trigger RCU stall or softlockup >> detector. >> >> The primary reason for the printk was to catch potential users who might >> depend on the behavior prior to 44a70adec910 ("mm, oom_adj: make sure >> processes sharing mm have same view of oom_score_adj") but after more >> than 2 years without a single report I guess it is safe to simply remove >> the printk altogether. >> >> The next step should be moving oom_score_adj over to the mm struct and >> remove all the tasks crawling as suggested by [2] >> >> [1] http://lkml.kernel.org/r/97fce864-6f75-bca5-14bc-12c9f890e740@i-love.sakura.ne.jp >> [2] http://lkml.kernel.org/r/20190117155159.GA4087@dhcp22.suse.cz > > I think I'll put a cc:stable on this. Deleting a might-trigger debug > printk is safe and welcome. > Putting cc:stable is fine. But I doubt the usefulness of this patch. If nobody really depends on the behavior prior to 44a70adec910, we should remove the pointless (otherwise racy) iteration itself.