From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753325Ab2AWQQ0 (ORCPT ); Mon, 23 Jan 2012 11:16:26 -0500 Received: from mail-gx0-f174.google.com ([209.85.161.174]:52648 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751690Ab2AWQQZ (ORCPT ); Mon, 23 Jan 2012 11:16:25 -0500 Date: Mon, 23 Jan 2012 08:16:19 -0800 From: Tejun Heo To: Vivek Goyal Cc: axboe@kernel.dk, ctalbott@google.com, rni@google.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 08/17] blkcg: shoot down blkio_groups on elevator switch Message-ID: <20120123161619.GE12652@google.com> References: <1327202725-3383-1-git-send-email-tj@kernel.org> <1327202725-3383-9-git-send-email-tj@kernel.org> <20120123152055.GD25986@redhat.com> <20120123153913.GB12652@google.com> <20120123155216.GF25986@redhat.com> <20120123155745.GD12652@google.com> <20120123161042.GG25986@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120123161042.GG25986@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 23, 2012 at 11:10:42AM -0500, Vivek Goyal wrote: > This does not work well in hierachical management/scenario. Think that > a user gets an upper limit of 10MB/s on a device and now user can manage > its own children groups and divide allocated 10MB/s in children the way > he wants. > > Now if root does the elevator switch, and saves all the rules (including > user's rules) and then restores back, these can very well race with > user's scripts of changing rules. If user changed a cgroup device rule > during elevator switch and after elevator switch root restored back > old rules, user's new rule will be lost leading to confusion. It simply doesn't matter. Just declare elvswitch and policy change reset blkcg configurations. If some people are crazy enough to switch elevators regularly with full system running and parallel configuration going on, let them deal with synchronizing their scripts. -- tejun