From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f171.google.com (mail-we0-f171.google.com [74.125.82.171]) by kanga.kvack.org (Postfix) with ESMTP id D25C06B0035 for ; Fri, 25 Jul 2014 08:24:03 -0400 (EDT) Received: by mail-we0-f171.google.com with SMTP id p10so4175211wes.16 for ; Fri, 25 Jul 2014 05:24:03 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id df4si17574908wjb.115.2014.07.25.05.24.02 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 25 Jul 2014 05:24:02 -0700 (PDT) Date: Fri, 25 Jul 2014 13:23:58 +0100 From: Mel Gorman Subject: Re: [PATCH V4 04/15] mm, compaction: do not recheck suitable_migration_target under lock Message-ID: <20140725122358.GY10819@suse.de> References: <1405518503-27687-1-git-send-email-vbabka@suse.cz> <1405518503-27687-5-git-send-email-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1405518503-27687-5-git-send-email-vbabka@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: linux-mm@kvack.org, Andrew Morton , David Rientjes , linux-kernel@vger.kernel.org, Joonsoo Kim , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel , Minchan Kim , Zhang Yanfei On Wed, Jul 16, 2014 at 03:48:12PM +0200, Vlastimil Babka wrote: > isolate_freepages_block() rechecks if the pageblock is suitable to be a target > for migration after it has taken the zone->lock. However, the check has been > optimized to occur only once per pageblock, and compact_checklock_irqsave() > might be dropping and reacquiring lock, which means somebody else might have > changed the pageblock's migratetype meanwhile. > > Furthermore, nothing prevents the migratetype to change right after > isolate_freepages_block() has finished isolating. Given how imperfect this is, > it's simpler to just rely on the check done in isolate_freepages() without > lock, and not pretend that the recheck under lock guarantees anything. It is > just a heuristic after all. > > Signed-off-by: Vlastimil Babka > Reviewed-by: Zhang Yanfei > Acked-by: Minchan Kim > Cc: Mel Gorman > Cc: Joonsoo Kim > Cc: Michal Nazarewicz > Cc: Naoya Horiguchi > Cc: Christoph Lameter > Cc: Rik van Riel > Acked-by: David Rientjes Acked-by: Mel Gorman -- Mel Gorman SUSE Labs -- 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