From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933209Ab0HEQ3Z (ORCPT ); Thu, 5 Aug 2010 12:29:25 -0400 Received: from mga03.intel.com ([143.182.124.21]:19701 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760462Ab0HEQ3S (ORCPT ); Thu, 5 Aug 2010 12:29:18 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.55,323,1278313200"; d="scan'208";a="308628097" Message-Id: <20100805162433.105093335@intel.com> User-Agent: quilt/0.48-1 Date: Fri, 06 Aug 2010 00:10:54 +0800 From: Wu Fengguang To: Andrew Morton Cc: Wu Fengguang , LKML , Christoph Hellwig , Dave Chinner , Jens Axboe , Peter Zijlstra CC: Mel Gorman , Chris Mason , Jan Kara , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" Subject: [PATCH 03/13] writeback: add comment to the dirty limits functions References: <20100805161051.501816677@intel.com> Content-Disposition: inline; filename=dirty-limits-comment.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Document global_dirty_limits(), bdi_dirty_limit() and task_dirty_limit(). Cc: Christoph Hellwig Cc: Dave Chinner Cc: Jens Axboe Cc: Peter Zijlstra Signed-off-by: Wu Fengguang --- mm/page-writeback.c | 31 ++++++++++++++++++++++++++++--- 1 file changed, 28 insertions(+), 3 deletions(-) --- linux-next.orig/mm/page-writeback.c 2010-08-03 23:14:19.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-08-05 00:37:17.000000000 +0800 @@ -261,11 +261,18 @@ static inline void task_dirties_fraction } /* - * scale the dirty limit + * task_dirty_limit - scale down dirty throttling threshold for one task * * task specific dirty limit: * * dirty -= (dirty/8) * p_{t} + * + * To protect light/slow dirtying tasks from heavier/fast ones, we start + * throttling individual tasks before reaching the bdi dirty limit. + * Relatively low thresholds will be allocated to heavy dirtiers. So when + * dirty pages grow large, heavy dirtiers will be throttled first, which will + * effectively curb the growth of dirty pages. Light dirtiers with high enough + * dirty threshold may never get throttled. */ static unsigned long task_dirty_limit(struct task_struct *tsk, unsigned long bdi_dirty) @@ -390,6 +397,15 @@ unsigned long determine_dirtyable_memory return x + 1; /* Ensure that we never return 0 */ } +/** + * global_dirty_limits - background-writeback and dirty-throttling thresholds + * + * Calculate the dirty thresholds based on sysctl parameters + * - vm.dirty_background_ratio or vm.dirty_background_bytes + * - vm.dirty_ratio or vm.dirty_bytes + * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and + * runtime tasks. + */ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) { unsigned long background; @@ -424,8 +440,17 @@ void global_dirty_limits(unsigned long * *pdirty = dirty; } -unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, - unsigned long dirty) +/** + * bdi_dirty_limit - @bdi's share of dirty throttling threshold + * + * Allocate high/low dirty limits to fast/slow devices, in order to prevent + * - starving fast devices + * - piling up dirty pages (that will take long time to sync) on slow devices + * + * The bdi's share of dirty limit will be adapting to its throughput and + * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set. + */ +unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) { u64 bdi_dirty; long numerator, denominator;