From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934378Ab0KQEcH (ORCPT ); Tue, 16 Nov 2010 23:32:07 -0500 Received: from mga01.intel.com ([192.55.52.88]:47880 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933941Ab0KQEcD (ORCPT ); Tue, 16 Nov 2010 23:32:03 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.59,209,1288594800"; d="scan'208";a="858411811" Message-Id: <20101117042850.482907860@intel.com> User-Agent: quilt/0.48-1 Date: Wed, 17 Nov 2010 12:27:30 +0800 From: Wu Fengguang To: Andrew Morton CC: Jan Kara , Wu Fengguang CC: Christoph Hellwig CC: Dave Chinner CC: "Theodore Ts'o" CC: Chris Mason CC: Peter Zijlstra CC: Mel Gorman CC: Rik van Riel CC: KOSAKI Motohiro Cc: linux-mm Cc: Cc: LKML Subject: [PATCH 10/13] writeback: make reasonable gap between the dirty/background thresholds References: <20101117042720.033773013@intel.com> Content-Disposition: inline; filename=writeback-fix-oversize-background-thresh.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The change is virtually a no-op for the majority users that use the default 10/20 background/dirty ratios. For others don't know why they are setting background ratio close enough to dirty ratio. Someone must set background ratio equal to dirty ratio, but no one seems to notice or complain that it's then silently halved under the hood.. Signed-off-by: Wu Fengguang --- mm/page-writeback.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) --- linux-next.orig/mm/page-writeback.c 2010-11-15 13:12:50.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-11-15 13:13:42.000000000 +0800 @@ -403,8 +403,15 @@ void global_dirty_limits(unsigned long * else background = (dirty_background_ratio * available_memory) / 100; - if (background >= dirty) - background = dirty / 2; + /* + * Ensure at least 1/4 gap between background and dirty thresholds, so + * that when dirty throttling starts at (background + dirty)/2, it's at + * the entrance of bdi soft throttle threshold, so as to avoid being + * hard throttled. + */ + if (background > dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT) + background = dirty - dirty * 2 / BDI_SOFT_DIRTY_LIMIT; + tsk = current; if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { background += background / 4;