From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752910Ab1EJCpe (ORCPT ); Mon, 9 May 2011 22:45:34 -0400 Received: from mga09.intel.com ([134.134.136.24]:38354 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752417Ab1EJCpc (ORCPT ); Mon, 9 May 2011 22:45:32 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.64,344,1301900400"; d="scan'208";a="744819000" Date: Tue, 10 May 2011 10:45:28 +0800 From: Wu Fengguang To: Rik van Riel Cc: Jan Kara , Andrew Morton , LKML , Dave Chinner , Mel Gorman , Christoph Hellwig , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH 06/17] writeback: sync expired inodes first in background writeback Message-ID: <20110510024528.GD6758@localhost> References: <20110506030821.523093711@intel.com> <20110506031612.539339712@intel.com> <20110509160827.GS4122@quack.suse.cz> <4DC813CB.2040103@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4DC813CB.2040103@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 10, 2011 at 12:18:19AM +0800, Rik van Riel wrote: > On 05/09/2011 12:08 PM, Jan Kara wrote: > > > The age of pages in LRU is not necessarily related with the > > i_dirtied_when time stamp so I'm not sure how much this will help after all > > Not necessarily, but given that the inactive file list is a > FIFO list, I expect there will be decent correlation. > > > but it makes some sense from the data integrity point of view at least. You > > can add: > > Acked-by: Jan Kara > > Good point on the data integrity. Yeah, I added this good point to the changelog :) Thanks, Fengguang --- Subject: writeback: sync expired inodes first in background writeback Date: Wed Jul 21 20:11:53 CST 2010 A background flush work may run for ever. So it's reasonable for it to mimic the kupdate behavior of syncing old/expired inodes first. At each queue_io() time, first try enqueuing only newly expired inodes. If there are zero expired inodes to work with, then relax the rule and enqueue all dirty inodes. It at least makes sense from the data integrity point of view. This may also reduce the number of dirty pages encountered by page reclaim, eg. the pageout() calls. Normally older inodes contain older dirty pages, which are more close to the end of the LRU lists. So syncing older inodes first helps reducing the dirty pages reached by the page reclaim code. More background: as Mel put it, "it makes sense to write old pages first to reduce the chances page reclaim is initiating IO." Rik also presented the situation with a graph: LRU head [*] dirty page [ * * * * * * * * * * *] Ideally, most dirty pages should lie close to the LRU tail instead of LRU head. That requires the flusher thread to sync old/expired inodes first (as there are obvious correlations between inode age and page age), and to give fair opportunities to newly expired inodes rather than sticking with some large eldest inodes (as larger inodes have weaker correlations in the inode<=>page ages). This patch helps the flusher to meet both the above requirements. Side effects: it might reduce the batch size and hence reduce inode_wb_list_lock hold time, but in turn make the cluster-by-partition logic in the same function less effective on reducing disk seeks. v2: keep policy changes inside wb_writeback() and keep the wbc.older_than_this visibility as suggested by Dave. CC: Dave Chinner Acked-by: Jan Kara Acked-by: Rik van Riel Acked-by: Mel Gorman Signed-off-by: Wu Fengguang --- fs/fs-writeback.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) --- linux-next.orig/fs/fs-writeback.c 2011-05-05 23:30:25.000000000 +0800 +++ linux-next/fs/fs-writeback.c 2011-05-05 23:30:26.000000000 +0800 @@ -718,7 +718,7 @@ static long wb_writeback(struct bdi_writ if (work->for_background && !over_bground_thresh()) break; - if (work->for_kupdate) { + if (work->for_kupdate || work->for_background) { oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10); wbc.older_than_this = &oldest_jif; @@ -729,6 +729,7 @@ static long wb_writeback(struct bdi_writ wbc.pages_skipped = 0; wbc.inodes_cleaned = 0; +retry: trace_wbc_writeback_start(&wbc, wb->bdi); if (work->sb) __writeback_inodes_sb(work->sb, wb, &wbc); @@ -752,6 +753,19 @@ static long wb_writeback(struct bdi_writ if (wbc.inodes_cleaned) continue; /* + * background writeback will start with expired inodes, and + * if none is found, fallback to all inodes. This order helps + * reduce the number of dirty pages reaching the end of LRU + * lists and cause trouble to the page reclaim. + */ + if (work->for_background && + wbc.older_than_this && + list_empty(&wb->b_io) && + list_empty(&wb->b_more_io)) { + wbc.older_than_this = NULL; + goto retry; + } + /* * No more inodes for IO, bail */ if (!wbc.more_io)