vmscan: avoid multiplication overflow in shrink_zone()

Local variable `scan' can overflow on zones which are larger than

(2G * 4k) / 100 = 80GB.

Making it 64-bit on 64-bit will fix that up.

Cc: KOSAKI Motohiro <[e-mail]>
Cc: Wu Fengguang <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Lee Schermerhorn <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/vmscan.c

···
 
 	for_each_evictable_lru(l) {
 		int file = is_file_lru(l);
-		int scan;
+		unsigned long scan;
 
 		scan = zone_nr_pages(zone, sc, l);
 		if (priority) {