migrate: don't account swapcache as shmem

swapcache will reach the below code path in migrate_page_move_mapping,
and swapcache is accounted as NR_FILE_PAGES but it's not accounted as
NR_SHMEM.

Hugh pointed out we must use PageSwapCache instead of comparing
mapping to &swapper_space, to avoid build failure with CONFIG_SWAP=n.

Signed-off-by: Andrea Arcangeli <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/migrate.c b/mm/migrate.c
index e4a5c912983df5352d701bce82fb691160c2e657..666e4e677414e6d790de715761e395116441e6c4 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -288,7 +288,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
         */
        __dec_zone_page_state(page, NR_FILE_PAGES);
        __inc_zone_page_state(newpage, NR_FILE_PAGES);
-       if (PageSwapBacked(page)) {
+       if (!PageSwapCache(page) && PageSwapBacked(page)) {
                __dec_zone_page_state(page, NR_SHMEM);
                __inc_zone_page_state(newpage, NR_SHMEM);
        }