vmscan: fix get_scan_ratio() comment

Fix the old comment on the scan ratio calculations.
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -1389,9 +1389,9 @@ static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
 	file_prio = 200 - sc->swappiness;
 
 	/*
-	 *                  anon       recent_rotated[0]
-	 * %anon = 100 * ----------- / ----------------- * IO cost
-	 *               anon + file      rotate_sum
+	 * The amount of pressure on anon vs file pages is inversely
+	 * proportional to the fraction of recently scanned pages on
+	 * each list that were recently referenced and in active use.
 	 */
 	ap = (anon_prio + 1) * (zone->recent_scanned[0] + 1);
 	ap /= zone->recent_rotated[0] + 1;