From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752135AbbASKFp (ORCPT ); Mon, 19 Jan 2015 05:05:45 -0500 Received: from cantor2.suse.de ([195.135.220.15]:50994 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751928AbbASKFm (ORCPT ); Mon, 19 Jan 2015 05:05:42 -0500 From: Vlastimil Babka To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , Minchan Kim , Mel Gorman , Joonsoo Kim , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel , David Rientjes Subject: [PATCH 1/5] mm, compaction: more robust check for scanners meeting Date: Mon, 19 Jan 2015 11:05:16 +0100 Message-Id: <1421661920-4114-2-git-send-email-vbabka@suse.cz> X-Mailer: git-send-email 2.1.2 In-Reply-To: <1421661920-4114-1-git-send-email-vbabka@suse.cz> References: <1421661920-4114-1-git-send-email-vbabka@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Compaction should finish when the migration and free scanner meet, i.e. they reach the same pageblock. Currently however, the test in compact_finished() simply just compares the exact pfns, which may yield a false negative when the free scanner position is in the middle of a pageblock and the migration scanner reaches the begining of the same pageblock. This hasn't been a problem until commit e14c720efdd7 ("mm, compaction: remember position within pageblock in free pages scanner") allowed the free scanner position to be in the middle of a pageblock between invocations. The hot-fix 1d5bfe1ffb5b ("mm, compaction: prevent infinite loop in compact_zone") prevented the issue by adding a special check in the migration scanner to satisfy the current detection of scanners meeting. However, the proper fix is to make the detection more robust. This patch introduces the compact_scanners_met() function that returns true when the free scanner position is in the same or lower pageblock than the migration scanner. The special case in isolate_migratepages() introduced by 1d5bfe1ffb5b is removed. Suggested-by: Joonsoo Kim 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 --- mm/compaction.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 546e571..5fdbdb8 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -803,6 +803,16 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn, #endif /* CONFIG_COMPACTION || CONFIG_CMA */ #ifdef CONFIG_COMPACTION /* + * Test whether the free scanner has reached the same or lower pageblock than + * the migration scanner, and compaction should thus terminate. + */ +static inline bool compact_scanners_met(struct compact_control *cc) +{ + return (cc->free_pfn >> pageblock_order) + <= (cc->migrate_pfn >> pageblock_order); +} + +/* * Based on information in the current compact_control, find blocks * suitable for isolating free pages from and then isolate them. */ @@ -1027,12 +1037,8 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone, } acct_isolated(zone, cc); - /* - * Record where migration scanner will be restarted. If we end up in - * the same pageblock as the free scanner, make the scanners fully - * meet so that compact_finished() terminates compaction. - */ - cc->migrate_pfn = (end_pfn <= cc->free_pfn) ? low_pfn : cc->free_pfn; + /* Record where migration scanner will be restarted. */ + cc->migrate_pfn = low_pfn; return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE; } @@ -1047,7 +1053,7 @@ static int compact_finished(struct zone *zone, struct compact_control *cc, return COMPACT_PARTIAL; /* Compaction run completes if the migrate and free scanner meet */ - if (cc->free_pfn <= cc->migrate_pfn) { + if (compact_scanners_met(cc)) { /* Let the next compaction start anew. */ zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn; zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn; @@ -1238,7 +1244,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc) * migrate_pages() may return -ENOMEM when scanners meet * and we want compact_finished() to detect it */ - if (err == -ENOMEM && cc->free_pfn > cc->migrate_pfn) { + if (err == -ENOMEM && !compact_scanners_met(cc)) { ret = COMPACT_PARTIAL; goto out; } -- 2.1.2