From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752061Ab0CSKKf (ORCPT ); Fri, 19 Mar 2010 06:10:35 -0400 Received: from gir.skynet.ie ([193.1.99.77]:49108 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750947Ab0CSKKe (ORCPT ); Fri, 19 Mar 2010 06:10:34 -0400 Date: Fri, 19 Mar 2010 10:10:16 +0000 From: Mel Gorman To: KOSAKI Motohiro Cc: Andrew Morton , Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , David Rientjes , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 10/11] Direct compact when a high-order allocation fails Message-ID: <20100319101016.GS12388@csn.ul.ie> References: <1268412087-13536-11-git-send-email-mel@csn.ul.ie> <20100319152105.8772.A69D9226@jp.fujitsu.com> <20100319152516.8778.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100319152516.8778.A69D9226@jp.fujitsu.com> 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 On Fri, Mar 19, 2010 at 03:31:27PM +0900, KOSAKI Motohiro wrote: > > Viewpoint 1. Unnecessary IO > > > > isolate_pages() for lumpy reclaim frequently grab very young page. it is often > > still dirty. then, pageout() is called much. > > > > Unfortunately, page size grained io is _very_ inefficient. it can makes lots disk > > seek and kill disk io bandwidth. > > > > > > Viewpoint 2. Unevictable pages > > > > isolate_pages() for lumpy reclaim can pick up unevictable page. it is obviously > > undroppable. so if the zone have plenty mlocked pages (it is not rare case on > > server use case), lumpy reclaim can become very useless. > > > > > > Viewpoint 3. GFP_ATOMIC allocation failure > > > > Obviously lumpy reclaim can't help GFP_ATOMIC issue. > > > > > > Viewpoint 4. reclaim latency > > > > reclaim latency directly affect page allocation latency. so if lumpy reclaim with > > much pageout io is slow (often it is), it affect page allocation latency and can > > reduce end user experience. > > Viewpoint 5. end user surprising > > lumpy reclaim can makes swap-out even though the system have lots free > memory. end users very surprised it and they can think it is bug. > > Also, this swap activity easyly confuse that an administrator decide when > install more memory into the system. > Compaction in this case is a lot less surprising. If there is enough free memory, compaction will trigger automatically without any reclaim. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab