From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753012AbbAVP21 (ORCPT ); Thu, 22 Jan 2015 10:28:27 -0500 Received: from mail-qc0-f171.google.com ([209.85.216.171]:58493 "EHLO mail-qc0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750754AbbAVP2V (ORCPT ); Thu, 22 Jan 2015 10:28:21 -0500 Date: Thu, 22 Jan 2015 10:28:17 -0500 From: Tejun Heo To: Johannes Weiner Cc: Will Deacon , "Suzuki K. Poulose" , Vladimir Davydov , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "mhocko@suse.cz" , "akpm@linux-foundation.org" Subject: Re: [Regression] 3.19-rc3 : memcg: Hang in mount memcg Message-ID: <20150122152817.GD4507@htj.dyndns.org> References: <54B01335.4060901@arm.com> <20150110085525.GD2110@esperanza> <54BCFDCF.9090603@arm.com> <20150121163955.GM4549@arm.com> <20150122134550.GA13876@phnom.home.cmpxchg.org> <20150122143454.GA4507@htj.dyndns.org> <20150122151943.GA27368@phnom.home.cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150122151943.GA27368@phnom.home.cmpxchg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 22, 2015 at 10:19:43AM -0500, Johannes Weiner wrote: > From 3d7ae5aeb16ce6118d8bff17194e791339a1f06c Mon Sep 17 00:00:00 2001 > From: Johannes Weiner > Date: Thu, 22 Jan 2015 08:16:31 -0500 > Subject: [patch] kernel: cgroup: prevent mount hang due to memory controller > lifetime > > Since b2052564e66d ("mm: memcontrol: continue cache reclaim from > offlined groups"), re-mounting the memory controller after using it is > very likely to hang. > > The cgroup core assumes that any remaining references after deleting a > cgroup are temporary in nature, and synchroneously waits for them, but > the above-mentioned commit has left-over page cache pin its css until > it is reclaimed naturally. That being said, swap entries and charged > kernel memory have been doing the same indefinite pinning forever, the > bug is just more likely to trigger with left-over page cache. > > Reparenting kernel memory is highly impractical, which leaves changing > the cgroup assumptions to reflect this: once a controller has been > mounted and used, it has internal state that is independent from mount > and cgroup lifetime. It can be unmounted and remounted, but it can't > be reconfigured during subsequent mounts. > > Don't offline the controller root as long as there are any children, > dead or alive. A remount will no longer wait for these old references > to drain, it will simply mount the persistent controller state again. > > Reported-by: "Suzuki K. Poulose" > Reported-by: Will Deacon > Signed-off-by: Johannes Weiner Applied to cgroup/for-3.19-fixes. Thanks. -- tejun