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[202.181.97.72]) by mx.google.com with ESMTPS id z5si2077321plo.434.2019.07.18.07.47.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 18 Jul 2019 07:47:45 -0700 (PDT) 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 fsav303.sakura.ne.jp (fsav303.sakura.ne.jp [153.120.85.134]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x6IDoKAJ016195; Thu, 18 Jul 2019 22:50:20 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav303.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav303.sakura.ne.jp); Thu, 18 Jul 2019 22:50:19 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav303.sakura.ne.jp) Received: from [192.168.1.8] (softbank126012062002.bbtec.net [126.12.62.2]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x6IDoJ60016190 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Thu, 18 Jul 2019 22:50:19 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] mm, oom: avoid printk() iteration under RCU To: Michal Hocko Cc: linux-mm@kvack.org, Roman Gushchin , Shakeel Butt , Andrew Morton , Linus Torvalds References: <1563360901-8277-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20190718083014.GB30461@dhcp22.suse.cz> From: Tetsuo Handa Message-ID: <7478e014-e5ce-504c-34b6-f2f9da952600@i-love.sakura.ne.jp> Date: Thu, 18 Jul 2019 22:50:14 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190718083014.GB30461@dhcp22.suse.cz> 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 2019/07/18 17:30, Michal Hocko wrote: > On Wed 17-07-19 19:55:01, Tetsuo Handa wrote: >> Currently dump_tasks() might call printk() for many thousands times under >> RCU, which might take many minutes for slow consoles. > > Is is even wise to enable dumping tasks on systems with thousands of > tasks and slow consoles? I mean you still have to call printk that is > slow that many times. So why do we actually care? Because of RCU stall > warnings? > That's a stupid question. WE DO CARE. We are making efforts for avoid calling printk() on each thread group (e.g. commit 0c1b2d783cf34324 ("mm/oom_kill: remove the wrong fatal_signal_pending() check in oom_kill_process()") commit b2b469939e934587 ("proc, oom: do not report alien mms when setting oom_score_adj")) ) under RCU and this patch is one of them (except that we can't remove printk() for dump_tasks() case).