mm: remove return value of putback_lru_pages()

putback_lru_page() never can fail.  So it doesn't matter count of "the
number of pages put back".

In addition, users of this functions don't use return value.

Let's remove unnecessary code.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-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>
diff --git a/mm/migrate.c b/mm/migrate.c
index d3f3f7f..5938db5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -58,23 +58,18 @@
 /*
  * Add isolated pages on the list back to the LRU under page lock
  * to avoid leaking evictable pages back onto unevictable list.
- *
- * returns the number of pages put back.
  */
-int putback_lru_pages(struct list_head *l)
+void putback_lru_pages(struct list_head *l)
 {
 	struct page *page;
 	struct page *page2;
-	int count = 0;
 
 	list_for_each_entry_safe(page, page2, l, lru) {
 		list_del(&page->lru);
 		dec_zone_page_state(page, NR_ISOLATED_ANON +
 				page_is_file_cache(page));
 		putback_lru_page(page);
-		count++;
 	}
-	return count;
 }
 
 /*