From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758137Ab0LMPOQ (ORCPT ); Mon, 13 Dec 2010 10:14:16 -0500 Received: from mga02.intel.com ([134.134.136.20]:60850 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754535Ab0LMPIu (ORCPT ); Mon, 13 Dec 2010 10:08:50 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.59,336,1288594800"; d="scan'208";a="583219906" Message-Id: <20101213150328.526742344@intel.com> User-Agent: quilt/0.48-1 Date: Mon, 13 Dec 2010 22:47:04 +0800 From: Wu Fengguang To: Andrew Morton CC: Jan Kara , Wu Fengguang CC: Christoph Hellwig CC: Trond Myklebust CC: Dave Chinner CC: "Theodore Ts'o" CC: Chris Mason CC: Peter Zijlstra CC: Mel Gorman CC: Rik van Riel CC: KOSAKI Motohiro CC: Greg Thelen CC: Minchan Kim Cc: linux-mm Cc: Cc: LKML Subject: [PATCH 18/35] writeback: start background writeback earlier References: <20101213144646.341970461@intel.com> Content-Disposition: inline; filename=writeback-kick-background-early.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It's possible for some one to suddenly eat lots of memory, leading to sudden drop of global dirty limit. So a dirtier task may get hard throttled immediately without some previous balance_dirty_pages() call to invoke background writeback. In this case we need to check for background writeback earlier in the loop to avoid stucking the application for very long time. This was not a problem before the IO-less balance_dirty_pages() because it will try to write something and then break out of the loop regardless of the global limit. Another scheme this check will help is, the dirty limit is too close to the background threshold, so that someone manages to jump directly into the pause threshold (background+dirty)/2. Signed-off-by: Wu Fengguang --- mm/page-writeback.c | 3 +++ 1 file changed, 3 insertions(+) --- linux-next.orig/mm/page-writeback.c 2010-12-13 21:46:16.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-12-13 21:46:17.000000000 +0800 @@ -748,6 +748,9 @@ static void balance_dirty_pages(struct a bdi_stat(bdi, BDI_WRITEBACK); } + if (unlikely(!writeback_in_progress(bdi))) + bdi_start_background_writeback(bdi); + bdi_update_bandwidth(bdi, start_time, bdi_dirty, bdi_thresh); /*