From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932912AbaDBSAa (ORCPT ); Wed, 2 Apr 2014 14:00:30 -0400 Received: from mail-qa0-f53.google.com ([209.85.216.53]:50827 "EHLO mail-qa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932653AbaDBSAX (ORCPT ); Wed, 2 Apr 2014 14:00:23 -0400 Date: Wed, 2 Apr 2014 14:00:19 -0400 From: Tejun Heo To: Glyn Normington Cc: linux-kernel@vger.kernel.org, Johannes Weiner , Michal Hocko , cgroups@vger.kernel.org Subject: Re: Kernel scanning/freeing to relieve cgroup memory pressure Message-ID: <20140402180019.GL16631@htj.dyndns.org> References: <533C0BB4.4070009@gopivotal.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <533C0BB4.4070009@gopivotal.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (cc'ing memcg maintainers and cgroup ML) On Wed, Apr 02, 2014 at 02:08:04PM +0100, Glyn Normington wrote: > Currently, a memory cgroup can hit its oom limit when pages could, in > principle, be reclaimed by the kernel except that the kernel does not > respond directly to cgroup-local memory pressure. So, ummm, it does. > A use case where this is important is running a moderately large Java > application in a memory cgroup in a PaaS environment where cost to the > user depends on the memory limit ([1]). Users need to tune the memory > limit to reduce their costs. During application initialisation large > numbers of JAR files are opened (read-only) and read while loading the > application code and its dependencies. This is reflected in a peak of > file cache usage which can push the memory cgroup memory usage > significantly higher than the value actually needed to run the application. > > Possible approaches include (1) automatic response to cgroup-local > memory pressure in the kernel, and (2) a kernel API for reclaiming > memory from a cgroup which could be driven under oom notification (with > the oom killer disabled for the cgroup - it would be enabled if the > cgroup was still oom after calling the kernel to reclaim memory). > > Clearly (1) is the preferred approach. The closest facility in the > kernel to (2) is to ask the kernel to free pagecache using `echo 1 > > /proc/sys/vms/drop_caches`, but that is too wide-ranging, especially in > a PaaS environment hosting multiple applications. A similar facility > could be provided for a cgroup via a cgroup pseudo-file > `memory.drop_caches`. > > Other approaches include a mempressure cgroup ([2]) which would not be > suitable for PaaS applications. See [3] for Andrew Morton's response. A > related workaround ([4]) was included in the 3.6 kernel. > > Related discussions: > [1] https://groups.google.com/a/cloudfoundry.org/d/topic/vcap-dev/6M8BDV_tq7w/discussion > [2]https://lwn.net/Articles/531077/ > [3]https://lwn.net/Articles/531138/ > [4]https://lkml.org/lkml/2013/6/6/462 & > https://github.com/torvalds/linux/commit/e62e384e > . -- tejun