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[195.135.220.15]) by mx.google.com with ESMTPS id i13si15309590eja.216.2019.07.29.11.58.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Jul 2019 11:58:54 -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 E2B4CAD85; Mon, 29 Jul 2019 18:58:53 +0000 (UTC) Date: Mon, 29 Jul 2019 20:58:53 +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: <20190729185853.GJ9330@dhcp22.suse.cz> References: <20190727171047.31610-1-longman@redhat.com> <20190729091249.GE9330@dhcp22.suse.cz> <556445a2-8912-c017-413c-7a4f36c4b89e@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <556445a2-8912-c017-413c-7a4f36c4b89e@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 Mon 29-07-19 11:27:35, Waiman Long wrote: > On 7/29/19 5:12 AM, Michal Hocko wrote: > > 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? > > As explained in my response to Peter, I found that resource like swap > space were depleted even after the exit of the offending program in a > mostly idle system. This patch is to make sure that those resources get > freed after program exit ASAP. Could you elaborate more? How can a mm counter (do not confuse with mm_users) prevent address space to be torn down on exit? -- Michal Hocko SUSE Labs