From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757601Ab1IAOUd (ORCPT ); Thu, 1 Sep 2011 10:20:33 -0400 Received: from cantor2.suse.de ([195.135.220.15]:40664 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757508Ab1IAOUb (ORCPT ); Thu, 1 Sep 2011 10:20:31 -0400 Date: Thu, 1 Sep 2011 15:20:27 +0100 From: Mel Gorman To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , Johannes Weiner , Rik van Riel Subject: Re: [PATCH 3/3] compaction accouting fix Message-ID: <20110901142027.GI14369@suse.de> References: <282a4531f23c5e35cfddf089f93559130b4bb660.1321112552.git.minchan.kim@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <282a4531f23c5e35cfddf089f93559130b4bb660.1321112552.git.minchan.kim@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 13, 2011 at 01:37:43AM +0900, Minchan Kim wrote: > I saw the following accouting of compaction during test of the series. s/accouting/accounting/ both here and in the subject. A nicer name the patch would have been "mm: compaction: Only update compact_blocks_moved if compaction was successful" > > compact_blocks_moved 251 > compact_pages_moved 44 > > It's very awkward to me although it's possbile because it means we try to compact 251 blocks > but it just migrated 44 pages. As further investigation, I found isolate_migratepages doesn't > isolate any pages but it returns ISOLATE_SUCCESS and then, it just increases compact_blocks_moved > but doesn't increased compact_pages_moved. > > This patch makes accouting of compaction works only in case of success of isolation. > compact_blocks_moved exists to indicate the rate compaction is scanning pageblocks. If compact_blocks_moved and compact_pages_moved are increasing at a similar rate for example, it could imply that compaction is doing a lot of scanning but is not necessarily useful work. It's not necessarily reflected by compact_fail because that counter is only updated for pages that were isolated from the LRU. I now recognise of course that "compact_blocks_moved" was an *awful* choice of name for this stat. -- Mel Gorman SUSE Labs