Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934782AbaFTPuP (ORCPT ); Fri, 20 Jun 2014 11:50:15 -0400 Received: from cantor2.suse.de ([195.135.220.15]:58804 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934253AbaFTPuK (ORCPT ); Fri, 20 Jun 2014 11:50:10 -0400 From: Vlastimil Babka To: linux-mm@kvack.org, Andrew Morton , David Rientjes Cc: Minchan Kim , Mel Gorman , Joonsoo Kim , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel , Zhang Yanfei , linux-kernel@vger.kernel.org, Vlastimil Babka Subject: [PATCH v3 03/13] mm, compaction: do not recheck suitable_migration_target under lock Date: Fri, 20 Jun 2014 17:49:33 +0200 Message-Id: <1403279383-5862-4-git-send-email-vbabka@suse.cz> X-Mailer: git-send-email 1.8.4.5 In-Reply-To: <1403279383-5862-1-git-send-email-vbabka@suse.cz> References: <1403279383-5862-1-git-send-email-vbabka@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- mm/compaction.c | 13 ------------- 1 file changed, 13 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 7c491d0..3064a7f 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; -- 1.8.4.5 -- 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/