mm/compaction: disallow high-order page for migration target

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@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index b6ab771..9a03fdb 100644 (file)
--- 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 */