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[195.135.220.15]) by mx.google.com with ESMTPS id w7si18303005edw.223.2019.07.29.02.12.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Jul 2019 02:12:50 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org 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 0304BB60C; Mon, 29 Jul 2019 09:12:50 +0000 (UTC) Date: Mon, 29 Jul 2019 11:12:49 +0200 From: Michal Hocko To: Waiman Long Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Phil Auld Subject: Re: [PATCH v2] sched/core: Don't use dying mm as active_mm of kthreads Message-ID: <20190729091249.GE9330@dhcp22.suse.cz> References: <20190727171047.31610-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190727171047.31610-1-longman@redhat.com> 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 Sat 27-07-19 13:10:47, Waiman Long wrote: > It was found that a dying mm_struct where the owning task has exited > can stay on as active_mm of kernel threads as long as no other user > tasks run on those CPUs that use it as active_mm. This prolongs the > life time of dying mm holding up memory and other resources like swap > space that cannot be freed. IIRC use_mm doesn't pin the address space. It only pins the mm_struct itself. So what exactly is the problem here? > > Fix that by forcing the kernel threads to use init_mm as the active_mm > if the previous active_mm is dying. > > The determination of a dying mm is based on the absence of an owning > task. The selection of the owning task only happens with the CONFIG_MEMCG > option. Without that, there is no simple way to determine the life span > of a given mm. So it falls back to the old behavior. Please don't. We really wont to remove mm->owner long term. -- Michal Hocko SUSE Labs