From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f45.google.com (mail-wg0-f45.google.com [74.125.82.45]) by kanga.kvack.org (Postfix) with ESMTP id 60E7B6B0038 for ; Mon, 9 Jun 2014 05:26:36 -0400 (EDT) Received: by mail-wg0-f45.google.com with SMTP id m15so5375948wgh.28 for ; Mon, 09 Jun 2014 02:26:35 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id gu6si10606899wib.18.2014.06.09.02.26.33 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 09 Jun 2014 02:26:34 -0700 (PDT) From: Vlastimil Babka Subject: [PATCH 01/10] mm, compaction: do not recheck suitable_migration_target under lock Date: Mon, 9 Jun 2014 11:26:13 +0200 Message-Id: <1402305982-6928-1-git-send-email-vbabka@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Greg Thelen , Vlastimil Babka , Minchan Kim , Mel Gorman , Joonsoo Kim , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel 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 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; -- 1.8.4.5 -- 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