From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753282Ab2AWP5w (ORCPT ); Mon, 23 Jan 2012 10:57:52 -0500 Received: from mail-iy0-f174.google.com ([209.85.210.174]:58496 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751454Ab2AWP5u (ORCPT ); Mon, 23 Jan 2012 10:57:50 -0500 Date: Mon, 23 Jan 2012 07:57:45 -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: <20120123155745.GD12652@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120123155216.GF25986@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 10:52:16AM -0500, Vivek Goyal wrote: > Atleast throttling rules should not disappear over elevator switch. They > are per device and not per IO scheduler. Think of losing nr_requests > settings just because elevator switch happened. > > Elevator switch can be low frequency but how would a user space know > that elevator switch failed that's why we lost our rules and now lets > put the rules back. It's simple - store all the policy rules before switching elevators and restore them afterwards regardless of success / failure. > I am not sure how would we justify this that because of ease of programming > in kernel, now user space is supposed to make sure that any programmed > rules are still there and reprogram the cgroup if rules are gone for > some reason. Sanity in trade off? -- tejun