mm: fix lumpy reclaim lru handling at isolate_lru_pages

At lumpy reclaim, a page failed to be taken by __isolate_lru_page() can be
pushed back to "src" list by list_move().  But the page may not be from
"src" list.  This pushes the page back to wrong LRU.  And list_move()
itself is unnecessary because the page is not on top of LRU.  Then, leave
it as it is if __isolate_lru_page() fails.

Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -929,18 +929,10 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			/* Check that we have not crossed a zone boundary. */
 			if (unlikely(page_zone_id(cursor_page) != zone_id))
 				continue;
-			switch (__isolate_lru_page(cursor_page, mode, file)) {
-			case 0:
+			if (__isolate_lru_page(cursor_page, mode, file) == 0) {
 				list_move(&cursor_page->lru, dst);
 				nr_taken++;
 				scan++;
-				break;
-
-			case -EBUSY:
-				/* else it is being freed elsewhere */
-				list_move(&cursor_page->lru, src);
-			default:
-				break;	/* ! on LRU or wrong list */
 			}
 		}
 	}