mm: compaction: avoid fragmentation score calculation for empty zones

There is no need to calculate the fragmentation score for empty zones.

Link: https://lkml.kernel.org/r/100331ad9d274a9725e687b00d85d75d7e4a17c7.1673342761.git.baolin.wang@linux.alibaba.comSigned-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/compaction.c

@@ -2025,6 +2025,8 @@ static unsigned int fragmentation_score_node(pg_data_t *pgdat)
 		struct zone *zone;
 
 		zone = &pgdat->node_zones[zoneid];
+		if (!populated_zone(zone))
+			continue;
 		score += fragmentation_score_zone_weighted(zone);
 	}