From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760354AbaGYM3k (ORCPT ); Fri, 25 Jul 2014 08:29:40 -0400 Received: from cantor2.suse.de ([195.135.220.15]:39963 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760182AbaGYM3i (ORCPT ); Fri, 25 Jul 2014 08:29:38 -0400 Date: Fri, 25 Jul 2014 13:29:33 +0100 From: Mel Gorman To: Vlastimil Babka Cc: linux-mm@kvack.org, Andrew Morton , David Rientjes , linux-kernel@vger.kernel.org, Minchan Kim , Joonsoo Kim , Michal Nazarewicz , Christoph Lameter , Rik van Riel , Naoya Horiguchi , Zhang Yanfei Subject: Re: [PATCH V4 06/15] mm, compaction: reduce zone checking frequency in the migration scanner Message-ID: <20140725122933.GA10819@suse.de> References: <1405518503-27687-1-git-send-email-vbabka@suse.cz> <1405518503-27687-7-git-send-email-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1405518503-27687-7-git-send-email-vbabka@suse.cz> 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 Wed, Jul 16, 2014 at 03:48:14PM +0200, Vlastimil Babka wrote: > The unification of the migrate and free scanner families of function has > highlighted a difference in how the scanners ensure they only isolate pages > of the intended zone. This is important for taking zone lock or lru lock of > the correct zone. Due to nodes overlapping, it is however possible to > encounter a different zone within the range of the zone being compacted. > > The free scanner, since its inception by commit 748446bb6b ("mm: compaction: > memory compaction core"), has been checking the zone of the first valid page > in a pageblock, and skipping the whole pageblock if the zone does not match. > > This checking was completely missing from the migration scanner at first, and > later added by commit dc9086004b ("mm: compaction: check for overlapping > nodes during isolation for migration") in a reaction to a bug report. > But the zone comparison in migration scanner is done once per a single scanned > page, which is more defensive and thus more costly than a check per pageblock. > > This patch unifies the checking done in both scanners to once per pageblock, > through a new pageblock_within_zone() function, which also includes pfn_valid() > checks. It is more defensive than the current free scanner checks, as it checks > both the first and last page of the pageblock, but less defensive by the > migration scanner per-page checks. It assumes that node overlapping may result > (on some architecture) in a boundary between two nodes falling into the middle > of a pageblock, but that there cannot be a node0 node1 node0 interleaving > within a single pageblock. > > The result is more code being shared and a bit less per-page CPU cost in the > migration scanner. > > Reported-by: Naoya Horiguchi > Signed-off-by: Vlastimil Babka Acked-by: Mel Gorman -- Mel Gorman SUSE Labs