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[195.135.220.15]) by mx.google.com with ESMTPS id o15si346639ejj.248.2019.07.18.07.02.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 18 Jul 2019 07:02:26 -0700 (PDT) Received-SPF: pass (google.com: domain of mhocko@suse.com designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of mhocko@suse.com designates 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 8EA56AF77; Thu, 18 Jul 2019 14:02:25 +0000 (UTC) Date: Thu, 18 Jul 2019 16:02:24 +0200 From: Michal Hocko To: Tetsuo Handa Cc: Roman Gushchin , Shakeel Butt , linux-mm@kvack.org, Andrew Morton , Linus Torvalds Subject: Re: [PATCH] mm, oom: avoid printk() iteration under RCU Message-ID: <20190718140224.GC30461@dhcp22.suse.cz> References: <1563360901-8277-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20190718083014.GB30461@dhcp22.suse.cz> <7478e014-e5ce-504c-34b6-f2f9da952600@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7478e014-e5ce-504c-34b6-f2f9da952600@i-love.sakura.ne.jp> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Thu 18-07-19 22:50:14, Tetsuo Handa wrote: > 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. -ENOARGUMENT > 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()") removes fatal_signal_pending rather than focusing on printk > commit b2b469939e934587 ("proc, oom: do not report alien mms when setting oom_score_adj")) removes a printk of a dubious value. > ) under RCU and this patch is one of them (except that we can't remove > printk() for dump_tasks() case). No, this one adds a complexity for something that is not clearly a huge win or the win is not explained properly. -- Michal Hocko SUSE Labs