[PATCH 28/97] mm/compaction: disallow high-order page for migration target

From: Mel Gorman
Date: Thu Aug 28 2014 - 15:05:52 EST

From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

commit 7d348b9ea64db0a315d777ce7d4b06697f946503 upstream.

Purpose of compaction is to get a high order page. Currently, if we
find high-order page while searching migration target page, we break it
to order-0 pages and use them as migration target. It is contrary to
purpose of compaction, so disallow high-order page to be used for
migration target.

Additionally, clean-up logic in suitable_migration_target() to simplify
the code. There is no functional changes from this clean-up.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
mm/compaction.c | 15 +++------------
1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 4885387..5e48834 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -217,21 +217,12 @@ static inline bool compact_trylock_irqsave(spinlock_t *lock,
/* Returns true if the page is within a block suitable for migration to */
static bool suitable_migration_target(struct page *page)
- int migratetype = get_pageblock_migratetype(page);
- /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
- if (migratetype == MIGRATE_RESERVE)
- return false;
- if (is_migrate_isolate(migratetype))
- return false;
- /* If the page is a large free page, then allow migration */
+ /* If the page is a large free page, then disallow migration */
if (PageBuddy(page) && page_order(page) >= pageblock_order)
- return true;
+ return false;

/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
- if (migrate_async_suitable(migratetype))
+ if (migrate_async_suitable(get_pageblock_migratetype(page)))
return true;

/* Otherwise skip the block */

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