From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753195AbaBERX3 (ORCPT ); Wed, 5 Feb 2014 12:23:29 -0500 Received: from mail-ee0-f45.google.com ([74.125.83.45]:35780 "EHLO mail-ee0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752681AbaBERX2 (ORCPT ); Wed, 5 Feb 2014 12:23:28 -0500 Date: Wed, 5 Feb 2014 18:23:23 +0100 From: Michal Hocko To: Johannes Weiner Cc: Andrew Morton , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Tejun Heo , LKML , linux-mm@kvack.org Subject: Re: [PATCH -v2 4/6] memcg: make sure that memcg is not offline when charging Message-ID: <20140205172323.GA13743@dhcp22.suse.cz> References: <1391520540-17436-1-git-send-email-mhocko@suse.cz> <1391520540-17436-5-git-send-email-mhocko@suse.cz> <20140204162939.GP6963@cmpxchg.org> <20140205133834.GB2425@dhcp22.suse.cz> <20140205152821.GY6963@cmpxchg.org> <20140205161940.GE2425@dhcp22.suse.cz> <20140205164543.GZ6963@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140205164543.GZ6963@cmpxchg.org> 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 On Wed 05-02-14 11:45:43, Johannes Weiner wrote: > On Wed, Feb 05, 2014 at 05:19:40PM +0100, Michal Hocko wrote: > > On Wed 05-02-14 10:28:21, Johannes Weiner wrote: > > > Here is the only exception to the above: swapout records maintain > > > permanent css references, so they prevent css_free() from running. > > > For that reason alone we should run one optimistic reparenting in > > > css_offline() to make sure one swap record does not pin gigabytes of > > > pages in an offlined cgroup, which is unreachable for reclaim. But > > > > How can reparenting help for swapped out pages? Or did you mean to at > > least get rid of swapcache pages? > > I was thinking primarily of page cache. There could be a lot of it > left in the group and once css_tryget() is disabled we can't reclaim > it anymore. Good point. > So we'd clean that out at offline time optimistically and > at css_free() we catch any charges raced that showed up afterwards. OK, care to send a patch which would clarify the reparenting usage in both css_offline and css_free? -- Michal Hocko SUSE Labs