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[195.135.220.15]) by mx.google.com with ESMTPS id e52si8253327ede.345.2019.07.24.01.07.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Jul 2019 01:07:27 -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 14DCEAD3E; Wed, 24 Jul 2019 08:07:27 +0000 (UTC) Date: Wed, 24 Jul 2019 10:07:26 +0200 From: Michal Hocko To: Tetsuo Handa Cc: Roman Gushchin , David Rientjes , Shakeel Butt , linux-mm@kvack.org, Andrew Morton Subject: Re: [PATCH] mm, oom: simplify task's refcount handling Message-ID: <20190724080726.GA5584@dhcp22.suse.cz> References: <1563940476-6162-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20190724064110.GC10882@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Wed 24-07-19 16:37:35, Tetsuo Handa wrote: > On 2019/07/24 15:41, Michal Hocko wrote: [...] > > That being said, I do not think this patch gives any improvement. > > > > This patch avoids RCU during select_bad_process(). It just shifts where the RCU is taken. Do you have any numbers to show that this is an improvement? Basically the only potentially expensive thing down the oom_evaluate_task that I can see is the task_lock but I am not aware of a single report that this would be a contributor for RCU stalls. I can be proven wrong but > This patch allows > possibility of doing reschedulable things there; e.g. directly reaping > only a portion of OOM victim's memory rather than wasting CPU resource > by spinning until MMF_OOM_SKIP is set by the OOM reaper. We have been through direct oom reaping before and I haven't changed my possition there. It is just too tricky to be worth it. -- Michal Hocko SUSE Labs