mm: munlock: batch NR_MLOCK zone state updates

Depending on previous batch which introduced batched isolation in
munlock_vma_range(), we can batch also the updates of NR_MLOCK page stats.
 After the whole pagevec is processed for page isolation, the stats are
updated only once with the number of successful isolations.  There were
however no measurable perfomance gains.

Signed-off-by: Vlastimil Babka <[email protected]>
Reviewed-by: Jörn Engel <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/mlock.c

@@ -241,6 +241,7 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
 {
 	int i;
 	int nr = pagevec_count(pvec);
+	int delta_munlocked = -nr;
 
 	/* Phase 1: page isolation */
 	spin_lock_irq(&zone->lru_lock);
@@ -251,9 +252,6 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
 			struct lruvec *lruvec;
 			int lru;
 
-			/* we have disabled interrupts */
-			__mod_zone_page_state(zone, NR_MLOCK, -1);
-
 			if (PageLRU(page)) {
 				lruvec = mem_cgroup_page_lruvec(page, zone);
 				lru = page_lru(page);
@@ -275,8 +273,10 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
 			 */
 			pvec->pages[i] = NULL;
 			put_page(page);
+			delta_munlocked++;
 		}
 	}
+	__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
 	spin_unlock_irq(&zone->lru_lock);
 
 	/* Phase 2: page munlock and putback */