migrate: don't account swapcache as shmem

commit 99a15e21d96f6857dafab1e5167e5e8183215c9c upstream.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/mm/migrate.c b/mm/migrate.c
index 0e39f94b2d9c8b2e5273b45a2a9382c07c25fb8b..aaca868fb114b84b22f422591e1fb3cac149783e 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -314,7 +314,7 @@ 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);
        }