Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751924AbdG0OgX (ORCPT ); Thu, 27 Jul 2017 10:36:23 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:52140 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751804AbdG0OgV (ORCPT ); Thu, 27 Jul 2017 10:36:21 -0400 Date: Thu, 27 Jul 2017 10:36:17 -0400 From: Johannes Weiner To: Roman Gushchin Cc: linux-kernel@vger.kernel.org, Vladimir Davydov , Tejun Heo , Michal Hocko , kernel-team@fb.com, cgroups@vger.kernel.org, linux-mm@kvack.org, Andrew Morton Subject: Re: [PATCH 2/2] cgroup: revert fa06235b8eb0 ("cgroup: reset css on destruction") Message-ID: <20170727143617.GC19738@cmpxchg.org> References: <20170726083017.3yzeucmi7lcj46qd@esperanza> <20170727130428.28856-1-guro@fb.com> <20170727130428.28856-2-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170727130428.28856-2-guro@fb.com> User-Agent: Mutt/1.8.3 (2017-05-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1403 Lines: 32 On Thu, Jul 27, 2017 at 02:04:28PM +0100, Roman Gushchin wrote: > Commit fa06235b8eb0 ("cgroup: reset css on destruction") caused > css_reset callback to be called from the offlining path. Although > it solves the problem mentioned in the commit description > ("For instance, memory cgroup needs to reset memory.low, otherwise > pages charged to a dead cgroup might never get reclaimed."), > generally speaking, it's not correct. > > An offline cgroup can still be a resource domain, and we shouldn't > grant it more resources than it had before deletion. > > For instance, if an offline memory cgroup has dirty pages, we should > still imply i/o limits during writeback. > > The css_reset callback is designed to return the cgroup state > into the original state, that means reset all limits and counters. > It's spomething different from the offlining, and we shouldn't use > it from the offlining path. Instead, we should adjust necessary > settings from the per-controller css_offline callbacks (e.g. reset > memory.low). > > Signed-off-by: Roman Gushchin > Cc: Vladimir Davydov > Cc: Tejun Heo > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: kernel-team@fb.com > Cc: cgroups@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org Acked-by: Johannes Weiner