From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753648AbYJGLEk (ORCPT ); Tue, 7 Oct 2008 07:04:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752832AbYJGLEb (ORCPT ); Tue, 7 Oct 2008 07:04:31 -0400 Received: from e28smtp01.in.ibm.com ([59.145.155.1]:41241 "EHLO e28esmtp01.in.ibm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752781AbYJGLEb (ORCPT ); Tue, 7 Oct 2008 07:04:31 -0400 Message-ID: <48EB4236.1060100@linux.vnet.ibm.com> Date: Tue, 07 Oct 2008 16:34:22 +0530 From: Balbir Singh Reply-To: balbir@linux.vnet.ibm.com Organization: IBM User-Agent: Thunderbird 2.0.0.17 (X11/20080925) MIME-Version: 1.0 To: Michael Rubin CC: Andrew Morton , Andrea Righi , menage@google.com, kamezawa.hiroyu@jp.fujitsu.com, dave@linux.vnet.ibm.com, chlunde@ping.uio.no, dpshah@google.com, eric.rannaud@gmail.com, fernando@oss.ntt.co.jp, agk@sourceware.org, m.innocenti@cineca.it, s-uchida@ap.jp.nec.com, ryov@valinux.co.jp, matt@bluehost.com, dradford@bluehost.com, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] [PATCH -mm 0/2] memcg: per cgroup dirty_ratio References: <1221232192-13553-1-git-send-email-righi.andrea@gmail.com> <20080912131816.e0cfac7a.akpm@linux-foundation.org> <532480950809221641y3471267esff82a14be8056586@mail.gmail.com> In-Reply-To: <532480950809221641y3471267esff82a14be8056586@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michael Rubin wrote: > On Fri, Sep 12, 2008 at 1:18 PM, Andrew Morton > wrote: >> One thing to think about please: Michael Rubin is hitting problems with >> the existing /proc/sys/vm/dirty-ratio. Its present granularity of 1% >> is just too coarse for really large machines, and as >> memory-size/disk-speed ratios continue to increase, this will just get >> worse. > > Re-sending since I top-posted before. Never again. Also adding more > thoughts on a byte based interface. > > Currently the problem we are hitting is that we cannot specify pdflush > to have background limits less than 1% of memory. I am currently > finishing up a patch right now that adds a dirty_ratio_millis > interface. I hope to submit the patch to LKML by the end of the week. > > The idea is that we don't want to break backwards compatibility and we > also don't want to have two conflicting knobs in the sysctl or > /proc/sys/vm/ space. I thought adding a new knob for those who want to > specify finer grained functionality was a compromise. So the patch has > a vm_dirty_ratio and a vm_dirty_ratio_millis interface. The first to > specify 0-100% and the second to specify .0 to .999%. > > So to represent 0.125% of RAM we set > vm_dirty_ratio = 0 > vm_dirty_ratio_millis = 125 > > The same for the background_ratio. > > I would also prefer using a bytes interface but I am not sure how to > offer that without either removing the legacy interface of the ratios > or by offering a concurrent interface that might be confusing such as > when users are looking at the old one and not aware of a new one. > Just provide a vm_dirty_ration_in_bytes interface and keep it in sync with vm_dirty_ratio (they are just two representations of the same internal value) and for higher resolution propose that users use the bytes interface. -- Balbir