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>

diff --git a/mm/migrate.c b/mm/migrate.c
index 177aca424a069ac1ae1b44d48a8e6d992cd42a4d..594dc375d0f96923ca9654dea0cd20bafb0f37f2 100644 (file)
--- 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;