From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752759Ab0ETLZN (ORCPT ); Thu, 20 May 2010 07:25:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39773 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751470Ab0ETLZK (ORCPT ); Thu, 20 May 2010 07:25:10 -0400 Message-ID: <4BF51B0A.1050901@redhat.com> Date: Thu, 20 May 2010 07:20:42 -0400 From: Larry Woodman Reply-To: lwoodman@redhat.com Organization: RedHat User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: LKML , linux-mm Subject: RFC: dirty_ratio back to 40% Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We've seen multiple performance regressions linked to the lower(20%) dirty_ratio. When performing enough IO to overwhelm the background flush daemons the percent of dirty pagecache memory quickly climbs to the new/lower dirty_ratio value of 20%. At that point all writing processes are forced to stop and write dirty pagecache pages back to disk. This causes performance regressions in several benchmarks as well as causing a noticeable overall sluggishness. We all know that the dirty_ratio is an integrity vs performance trade-off but the file system journaling will cover any devastating effects in the event of a system crash. Increasing the dirty_ratio to 40% will regain the performance loss seen in several benchmarks. Whats everyone think about this??? ------------------------------------------------------------------------ diff --git a/mm/page-writeback.c b/mm/page-writeback.c index ef27e73..645a462 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -78,7 +78,7 @@ int vm_highmem_is_dirtyable; /* * The generator of dirty data starts writeback at this percentage */ -int vm_dirty_ratio = 20; +int vm_dirty_ratio = 40; /* * vm_dirty_bytes starts at 0 (disabled) so that it is a function of