mm/vmscan.c: fix recent_rotated history

Johannes pointed out that after commit 886cf190 ("mm: move
recent_rotated pages calculation to shrink_inactive_list()") we lost all
zone_reclaim_stat::recent_rotated history.

This fixes it.

Link: http://lkml.kernel.org/r/155905972210.26456.11178359431724024112.stgit@localhost.localdomain
Fixes: 886cf190 ("mm: move recent_rotated pages calculation to shrink_inactive_list()")
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reported-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -1953,8 +1953,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	if (global_reclaim(sc))
 		__count_vm_events(item, nr_reclaimed);
 	__count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
-	reclaim_stat->recent_rotated[0] = stat.nr_activate[0];
-	reclaim_stat->recent_rotated[1] = stat.nr_activate[1];
+	reclaim_stat->recent_rotated[0] += stat.nr_activate[0];
+	reclaim_stat->recent_rotated[1] += stat.nr_activate[1];
 
 	move_pages_to_lru(lruvec, &page_list);