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 <aarcange@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index e4a5c912983d..666e4e677414 100644
--- 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);
         }