[PATCH 2/5] mm/compaction: do not call suitable_migration_target() on every page

[Joonsoo Kim]

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@xxxxxxx>

diff --git a/mm/compaction.c b/mm/compaction.c
index bbe1260..0d821a2 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -245,6 +245,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 	unsigned long nr_strict_required = end_pfn - blockpfn;
 	unsigned long flags;
 	bool locked = false;
+	bool checked_pageblock = false;
 
 	cursor = pfn_to_page(blockpfn);
 
@@ -275,8 +276,16 @@ 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))
-- 
1.7.9.5

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