mm/compaction: do not call suitable_migration_target() on every page

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@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 9a03fdb..3a18285 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -244,6 +244,7 @@ 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);
 
@@ -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))