Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757331Ab0FQLlV (ORCPT ); Thu, 17 Jun 2010 07:41:21 -0400 Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:54800 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752553Ab0FQLlU (ORCPT ); Thu, 17 Jun 2010 07:41:20 -0400 Message-ID: <4C1A09DF.9070809@kernel.dk> Date: Thu, 17 Jun 2010 13:41:19 +0200 From: Jens Axboe MIME-Version: 1.0 To: Richard Kennedy CC: Peter Zijlstra , Andrew Morton , Wu Fengguang , lkml , linux-mm Subject: Re: [RFC PATCH] mm: let the bdi_writeout fraction respond more quickly References: <1276523894.1980.85.camel@castor.rsk> <1276526681.1980.89.camel@castor.rsk> <1276714466.1745.625.camel@laptop> <1276774796.1978.11.camel@castor.rsk> In-Reply-To: <1276774796.1978.11.camel@castor.rsk> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1764 Lines: 46 On 2010-06-17 13:39, Richard Kennedy wrote: > On Wed, 2010-06-16 at 20:54 +0200, Peter Zijlstra wrote: >> On Mon, 2010-06-14 at 15:44 +0100, Richard Kennedy wrote: >>>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c >>>> index 2fdda90..315dd04 100644 >>>> --- a/mm/page-writeback.c >>>> +++ b/mm/page-writeback.c >>>> @@ -144,7 +144,7 @@ static int calc_period_shift(void) >>>> else >>>> dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) / >>>> 100; >>>> - return 2 + ilog2(dirty_total - 1); >>>> + return ilog2(dirty_total - 1) - 4; >>>> } >> >> IIRC I suggested similar things in the past and all we needed to do was >> find people doing the measurements on different bits of hardware or so.. >> >> I don't have any problems with the approach, all we need to make sure is >> that we never return 0 or a negative number (possibly ensure a minimum >> positive shift value). > > Yep that sounds reasonable. would minimum shift of 4 be ok ? > > something like > > max ( (ilog2(dirty_total - 1)- 4) , 4); > > Unfortunately volunteers don't seem to be leaping out of the woodwork, > maybe Andrew could be persuaded to try this in his tree for a while and > see if any one squeaks ? I'm pretty sure that most volunteers are curious what to actually test, so they shy away from it. If you added a good explanation of an easy way to test the before and after, then it would be more approachable. I'll give it a spin here. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/