Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755243AbaFKCq2 (ORCPT ); Tue, 10 Jun 2014 22:46:28 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:35530 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751634AbaFKCq1 (ORCPT ); Tue, 10 Jun 2014 22:46:27 -0400 X-IronPort-AV: E=Sophos;i="5.00,686,1396972800"; d="scan'208";a="31740728" Message-ID: <5397C2BA.5030808@cn.fujitsu.com> Date: Wed, 11 Jun 2014 10:45:14 +0800 From: Zhang Yanfei User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131030 Thunderbird/17.0.10 MIME-Version: 1.0 To: Vlastimil Babka CC: David Rientjes , , , Andrew Morton , Greg Thelen , Minchan Kim , Mel Gorman , Joonsoo Kim , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel Subject: Re: [PATCH 01/10] mm, compaction: do not recheck suitable_migration_target under lock References: <1402305982-6928-1-git-send-email-vbabka@suse.cz> In-Reply-To: <1402305982-6928-1-git-send-email-vbabka@suse.cz> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.225.89] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/09/2014 05:26 PM, 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 > Cc: Minchan Kim > Cc: Mel Gorman > Cc: Joonsoo Kim > Cc: Michal Nazarewicz > Cc: Naoya Horiguchi > Cc: Christoph Lameter > Cc: Rik van Riel > Cc: David Rientjes > --- > I suggest folding mm-compactionc-isolate_freepages_block-small-tuneup.patch into this > > mm/compaction.c | 13 ------------- > 1 file changed, 13 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 5175019..b73b182 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -276,7 +276,6 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, > struct page *cursor, *valid_page = NULL; > unsigned long flags; > bool locked = false; > - bool checked_pageblock = false; > > cursor = pfn_to_page(blockpfn); > > @@ -307,18 +306,6 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, > if (!locked) > break; > > - /* Recheck this is a suitable migration target under lock */ > - if (!strict && !checked_pageblock) { > - /* > - * We need to check suitability of pageblock only once > - * and this isolate_freepages_block() is called with > - * pageblock range, so just check once is sufficient. > - */ > - checked_pageblock = true; > - if (!suitable_migration_target(page)) > - break; > - } > - > /* Recheck this is a buddy page under lock */ > if (!PageBuddy(page)) > goto isolate_fail; > -- Thanks. Zhang Yanfei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/