mm, pagevec: release/reacquire lru_lock on pgdat change

With node-lru, the locking is based on the pgdat.  Previously it was
required that a pagevec drain released one zone lru_lock and acquired
another zone lru_lock on every zone change.  Now, it's only necessary if
the node changes.  The end-result is fewer lock release/acquires if the
pages are all on the same node but in different zones.

Link: http://lkml.kernel.org/r/1468588165-12461-4-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swap.c

@@ -179,26 +179,26 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
 	void *arg)
 {
 	int i;
-	struct zone *zone = NULL;
+	struct pglist_data *pgdat = NULL;
 	struct lruvec *lruvec;
 	unsigned long flags = 0;
 
 	for (i = 0; i < pagevec_count(pvec); i++) {
 		struct page *page = pvec->pages[i];
-		struct zone *pagezone = page_zone(page);
+		struct pglist_data *pagepgdat = page_pgdat(page);
 
-		if (pagezone != zone) {
-			if (zone)
-				spin_unlock_irqrestore(zone_lru_lock(zone), flags);
-			zone = pagezone;
-			spin_lock_irqsave(zone_lru_lock(zone), flags);
+		if (pagepgdat != pgdat) {
+			if (pgdat)
+				spin_unlock_irqrestore(&pgdat->lru_lock, flags);
+			pgdat = pagepgdat;
+			spin_lock_irqsave(&pgdat->lru_lock, flags);
 		}
 
-		lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
+		lruvec = mem_cgroup_page_lruvec(page, pgdat);
 		(*move_fn)(page, lruvec, arg);
 	}
-	if (zone)
-		spin_unlock_irqrestore(zone_lru_lock(zone), flags);
+	if (pgdat)
+		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
 	release_pages(pvec->pages, pvec->nr, pvec->cold);
 	pagevec_reinit(pvec);
 }