Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754653Ab0GGJue (ORCPT ); Wed, 7 Jul 2010 05:50:34 -0400 Received: from gir.skynet.ie ([193.1.99.77]:39959 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754178Ab0GGJu1 (ORCPT ); Wed, 7 Jul 2010 05:50:27 -0400 Date: Wed, 7 Jul 2010 10:50:10 +0100 From: Mel Gorman To: Wu Fengguang Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Chris Mason , Nick Piggin , Rik van Riel , Johannes Weiner , Christoph Hellwig , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Andrea Arcangeli , Jan Kara Subject: Re: [PATCH 12/14] vmscan: Do not writeback pages in direct reclaim Message-ID: <20100707095010.GK13780@csn.ul.ie> References: <1277811288-5195-1-git-send-email-mel@csn.ul.ie> <1277811288-5195-13-git-send-email-mel@csn.ul.ie> <20100702125155.69c02f85.akpm@linux-foundation.org> <20100705134949.GC13780@csn.ul.ie> <20100707050338.GA5039@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100707050338.GA5039@localhost> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1744 Lines: 40 On Wed, Jul 07, 2010 at 01:03:38PM +0800, Wu Fengguang wrote: > Hi Mel, > > > Second, using systemtap, I was able to see that file-backed dirty > > pages have a tendency to be near the end of the LRU even though they > > are a small percentage of the overall pages in the LRU. I'm hoping > > to figure out why this is as it would make avoiding writeback a lot > > less controversial. > > Your intuitions are correct -- the current background writeback logic > fails to write elder inodes first. Under heavy loads the background > writeback job may run for ever, totally ignoring the time order of > inode->dirtied_when. This is probably why you see lots of dirty pages > near the end of LRU. > Possible. In a mail to Christoph, I asserted that writeback of elder inodes was happening first but I obviously could be mistaken. > Here is an old patch for fixing this. Sorry for being late. I'll > pick up and refresh the patch series ASAP. (I made a mistake last > year to post too many patches at one time. I'll break them up into > more manageable pieces.) > > [PATCH 31/45] writeback: sync old inodes first in background writeback > > I'll check it out as an alternative to forward-flushing based on the amount of dirty pages encountered during scanning. Thanks. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/