From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 1FF066B006A for ; Wed, 7 Jul 2010 01:03:46 -0400 (EDT) Date: Wed, 7 Jul 2010 13:03:38 +0800 From: Wu Fengguang Subject: Re: [PATCH 12/14] vmscan: Do not writeback pages in direct reclaim Message-ID: <20100707050338.GA5039@localhost> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100705134949.GC13780@csn.ul.ie> Sender: owner-linux-mm@kvack.org To: Mel Gorman 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 List-ID: 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. 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 Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org