On Fri, 21 May 2021 11:28:26 +0100 Mel Gorman wrote:

/*
 * Calculate and set new high and batch values for all per-cpu pagesets of a
- * zone based on the zone's size.
+ * zone based on the zone's size and the percpu_pagelist_high_fraction sysctl.
 */

It is the comment fitting zone_highsize() more.

static void zone_set_pageset_high_and_batch(struct zone *zone, int cpu_online)
{
	int new_high, new_batch;

+	if (!percpu_pagelist_high_fraction) {
+		new_high = zone_highsize(zone, low_wmark_pages(zone), cpu_online);
+	} else {
+		new_high = zone_highsize(zone,
+			zone_managed_pages(zone) / percpu_pagelist_high_fraction,
+			cpu_online);
+	}
+

Nit, move percpu_pagelist_high_fraction into zone_highsize() instead of
cluttering up here because

+The batch value of each per cpu pagelist remains the same regardless of the
+value of the high fraction so allocation latencies are unaffected.