thp: scale nr_rotated to balance memory pressure

Make sure we scale up nr_rotated when we encounter a referenced
transparent huge page.  This ensures pageout scanning balance is not
distorted when there are huge pages on the LRU.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -1276,7 +1276,8 @@ putback_lru_pages(struct zone *zone, struct scan_control *sc,
 		add_page_to_lru_list(zone, page, lru);
 		if (is_active_lru(lru)) {
 			int file = is_file_lru(lru);
-			reclaim_stat->recent_rotated[file]++;
+			int numpages = hpage_nr_pages(page);
+			reclaim_stat->recent_rotated[file] += numpages;
 		}
 		if (!pagevec_add(&pvec, page)) {
 			spin_unlock_irq(&zone->lru_lock);
@@ -1552,7 +1553,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 		}
 
 		if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
-			nr_rotated++;
+			nr_rotated += hpage_nr_pages(page);
 			/*
 			 * Identify referenced, file-backed active pages and
 			 * give them one more trip around the active list. So