mm: test PageSwapBacked in lumpy reclaim

Lumpy reclaim does well to stop at a PageAnon when there's no swap, but
better is to stop at any PageSwapBacked, which includes shmem/tmpfs too.
Signed-off-by: NHugh Dickins <hughd@google.com>
Reviewed-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -1166,7 +1166,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			 * anon page which don't already have a swap slot is
 			 * pointless.
 			 */
-			if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
+			if (nr_swap_pages <= 0 && PageSwapBacked(cursor_page) &&
 			    !PageSwapCache(cursor_page))
 				break;