From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wu Fengguang Subject: [PATCH 1/5] writeback: balanced_rate cannot exceed write bandwidth Date: Mon, 21 Nov 2011 21:03:43 +0800 Message-ID: <20111121131215.645601798@intel.com> References: <20111121130342.211953629@intel.com> Cc: Jan Kara , Wu Fengguang To: Return-path: Received: from mga14.intel.com ([143.182.124.37]:15513 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754026Ab1KUNPk (ORCPT ); Mon, 21 Nov 2011 08:15:40 -0500 cc: Peter Zijlstra CC: Christoph Hellwig cc: Andrew Morton Cc: LKML Content-Disposition: inline; filename=ref-bw-up-bound Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Add an upper limit to balanced_rate according to the below inequality. This filters out some rare but huge singular points, which at least enables more readable gnuplot figures. When there are N dd dirtiers, balanced_dirty_ratelimit = write_bw / N So it holds that balanced_dirty_ratelimit <= write_bw Signed-off-by: Wu Fengguang --- mm/page-writeback.c | 5 +++++ 1 file changed, 5 insertions(+) --- linux-next.orig/mm/page-writeback.c 2011-11-17 20:18:03.000000000 +0800 +++ linux-next/mm/page-writeback.c 2011-11-17 20:18:23.000000000 +0800 @@ -804,6 +804,11 @@ static void bdi_update_dirty_ratelimit(s */ balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, dirty_rate | 1); + /* + * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw + */ + if (unlikely(balanced_dirty_ratelimit > write_bw)) + balanced_dirty_ratelimit = write_bw; /* * We could safely do this and return immediately: