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[209.132.183.28]) by mx.google.com with ESMTPS id h6si13831512uac.127.2019.07.29.14.06.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Jul 2019 14:06:38 -0700 (PDT) Received-SPF: pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D2FB37FDEC; Mon, 29 Jul 2019 21:06:36 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-160.bos.redhat.com [10.18.17.160]) by smtp.corp.redhat.com (Postfix) with ESMTP id 044505C1A1; Mon, 29 Jul 2019 21:06:35 +0000 (UTC) Subject: Re: [PATCH v2] sched/core: Don't use dying mm as active_mm of kthreads To: Qais Yousef Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Phil Auld References: <20190727171047.31610-1-longman@redhat.com> <20190729081800.qbamrvsf4rjna656@e107158-lin.cambridge.arm.com> From: Waiman Long Organization: Red Hat Message-ID: Date: Mon, 29 Jul 2019 17:06:35 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190729081800.qbamrvsf4rjna656@e107158-lin.cambridge.arm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Mon, 29 Jul 2019 21:06:37 +0000 (UTC) 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 7/29/19 4:18 AM, Qais Yousef wrote: > On 07/27/19 13:10, 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. >> >> 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. > I don't really know a lot about this code, but does the owner field has to > depend on CONFIG_MEMCG? ie: can't the owner be always set? > Yes, the owner field is only used and defined when CONFIG_MEMCG is on. Cheers, Longman