From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751675AbaBKSsu (ORCPT ); Tue, 11 Feb 2014 13:48:50 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:60263 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751071AbaBKSst (ORCPT ); Tue, 11 Feb 2014 13:48:49 -0500 Date: Tue, 11 Feb 2014 13:48:43 -0500 From: Johannes Weiner To: Hugh Dickins Cc: Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch 3/8] memcg: update comment about charge reparenting on cgroup exit Message-ID: <20140211184843.GL6963@cmpxchg.org> References: <1391792665-21678-1-git-send-email-hannes@cmpxchg.org> <1391792665-21678-4-git-send-email-hannes@cmpxchg.org> <20140210142344.GI7117@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 10, 2014 at 12:12:42PM -0800, Hugh Dickins wrote: > On Mon, 10 Feb 2014, Michal Hocko wrote: > > On Fri 07-02-14 12:04:20, Johannes Weiner wrote: > > > Reparenting memory charges in the css_free() callback was meant as a > > > temporary fix for charges that race with offlining, but after some > > > follow-up discussion, it turns out that this is really the right place > > > to reparent charges because it guarantees none are in-flight. > > Perhaps: I'm not as gung-ho for this new orthodoxy as you are. > > > > Make clear that the reparenting in css_offline() is an optimistic > > > sweep of established charges because swapout records might hold up > > > css_free() indefinitely, but that in fact the css_free() reparenting > > > is the properly synchronized one. > > It worries me that you keep referring to the memsw usage, but > forget the kmem usage, which also delays css_free() indefinitely. > > Or am I out-of-date? Seems not, mem_cgroup_reparent_chages() still > waits for memcg->res - memcg->kmem to reach 0, knowing there's not > much certainty that kmem will reach 0 any time soon. > > I think you need a plan for what to do with the kmem pinning, > before going much further in reworking the memsw pinning. > > Or at the least, please mention it in this patch's comment. It think the discussion from the other thread bled over into this one a little bit, this patch was merely about clarifying that .css_free() reparenting is not the crude hack it was described as. Yes, I forgot about kmem and it should be mentioned in this patch.