From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753050AbaGHVx5 (ORCPT ); Tue, 8 Jul 2014 17:53:57 -0400 Received: from mail-qa0-f46.google.com ([209.85.216.46]:45104 "EHLO mail-qa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750951AbaGHVxz (ORCPT ); Tue, 8 Jul 2014 17:53:55 -0400 Date: Tue, 8 Jul 2014 17:53:51 -0400 From: Tejun Heo To: Vivek Goyal Cc: lizefan@huawei.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, hannes@cmpxchg.org, mhocko@suse.cz, axboe@kernel.dk Subject: Re: [PATCH v2 6/6] blkcg, memcg: make blkcg depend on memcg on the default hierarchy Message-ID: <20140708215351.GJ4979@htj.dyndns.org> References: <1403917392-32555-1-git-send-email-tj@kernel.org> <1403917392-32555-7-git-send-email-tj@kernel.org> <20140628114907.GA10829@htj.dyndns.org> <20140708194226.GA18382@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140708194226.GA18382@redhat.com> 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 Hello, Vivek. On Tue, Jul 08, 2014 at 03:42:26PM -0400, Vivek Goyal wrote: > I have couple questions about new semantics. Following is my > understanding. Is it right? > > - So after this change one can not use blkio controller on unified > hiearchy if memory controller is mounted on some other hierarchy > and is not available for mounting unified hiearchy. Hmmm? No, the only behavior which changes is when both blkcg and memcg are mounted on the unified hierarchy. Nothing else changes. The dependency behavior kicks in iff memcg is available on the unified hierarchy. > - If blkio controller is enabled on unified hiearchy (memory controller > implicitly enabled), then one can't mount memory controller on other > hierarchies without first disabling blkio controller on unified hiearchy. Yes, blkio needs to be disabled to the root for memcg to be able to become free. This is an extra restriction but I don't think it's anything drastic. Once a controller starts being actively used on any hierarchy, nothing has been guaranteed about when the controller would become free again even if the whole hierarchy is reduced to the root. Thanks. -- tejun