From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751962AbaBMPfH (ORCPT ); Thu, 13 Feb 2014 10:35:07 -0500 Received: from mail-qc0-f179.google.com ([209.85.216.179]:37613 "EHLO mail-qc0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751533AbaBMPfE (ORCPT ); Thu, 13 Feb 2014 10:35:04 -0500 Date: Thu, 13 Feb 2014 10:35:01 -0500 From: Tejun Heo To: Michal Hocko Cc: Hugh Dickins , Johannes Weiner , Filipe Brandenburger , Li Zefan , Andrew Morton , Greg Thelen , Michel Lespinasse , Markus Blank-Burian , Shawn Bohrer , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/2] memcg: reparent charges of children before processing parent Message-ID: <20140213153501.GA17608@htj.dyndns.org> References: <20140213152745.GE11986@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140213152745.GE11986@dhcp22.suse.cz> 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 Hello, On Thu, Feb 13, 2014 at 04:27:45PM +0100, Michal Hocko wrote: > > Further testing showed that an ordered workqueue for cgroup_destroy_wq > > is not always good enough: percpu_ref_kill_and_confirm's call_rcu_sched > > stage on the way can mess up the order before reaching the workqueue. > > This whole code path is so complicated by different types of delayed > work that I am not wondering that we have missed that :/ Yeah, I know. Good part of the complexity comes from RCU -> wq bouncing. I wonder whether we just should bite the bullet and add something along the line of call_rcu_work(). The other part is percpu ref shutdown. For me that part is easier to swallow, as the benefits are quite clear. > > Instead, when offlining a memcg, call mem_cgroup_reparent_charges() on > > all its children (and grandchildren, in the correct order) to have their > > charges reparented first. > > That is basically what I was suggesting > http://marc.info/?l=linux-mm&m=139178386407184&w=2 as #1 option. I > cannot say I would like it and I think that reparenting LRUs in > css_offline and then reparent the remaining charges from css_free is a > better solution but let's keep this for later. I'm kinda wishing the reparenting things works out. Even if that involves a bit of overhead at offline, I think it'd be worthwhile to be able to follow the same object lifetime rules as other controllers, as long as the overhead is reasonable. Thanks. -- tejun