[Devel] [PATCH rh7 08/25] ms/mm/compaction: do not call suitable_migration_target() on every page

[Andrey Ryabinin]

From: Joonsoo Kim <iamjoonsoo.kim at lge.com>

suitable_migration_target() checks that pageblock is suitable for
migration target.  In isolate_freepages_block(), it is called on every
page and this is inefficient.  So make it called once per pageblock.

suitable_migration_target() also checks if page is highorder or not, but
it's criteria for highorder is pageblock order.  So calling it once
within pageblock range has no problem.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Acked-by: Vlastimil Babka <vbabka at suse.cz>
Cc: Mel Gorman <mgorman at suse.de>
Cc: Rik van Riel <riel at redhat.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit 01ead5340bcf5f3a1cd2452c75516d0ef4d908d7)
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/compaction.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 1faade458d38..c29883fe146d 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -247,6 +247,7 @@ 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);
 
@@ -278,8 +279,16 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 			break;
 
 		/* Recheck this is a suitable migration target under lock */
-		if (!strict && !suitable_migration_target(page))
-			break;
+		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))
-- 
2.13.6