mm: migrate: one less atomic operation

migrate_page_move_mapping() drops a reference from the old page after
unfreezing its counter.  Both operations can be merged into a single
atomic operation by directly unfreezing to one less reference.

The same applies to migrate_huge_page_move_mapping().

Signed-off-by: Jacobo Giralt <jacobo.giralt@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 6 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 177aca424a0..594dc375d0f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -269,12 +269,12 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 
         radix_tree_replace_slot(pslot, newpage);
 
-        page_unfreeze_refs(page, expected_count);
         /*
-         * Drop cache reference from old page.
+         * Drop cache reference from old page by unfreezing
+         * to one less reference.
          * We know this isn't the last reference.
          */
-        __put_page(page);
+        page_unfreeze_refs(page, expected_count - 1);
 
         /*
          * If moved to a different zone then also account
@@ -334,9 +334,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 
         radix_tree_replace_slot(pslot, newpage);
 
-        page_unfreeze_refs(page, expected_count);
-
-        __put_page(page);
+        page_unfreeze_refs(page, expected_count - 1);
 
         spin_unlock_irq(&mapping->tree_lock);
         return 0;