HPA: Track dirty stats.

include/jemalloc/internal/psset.h

@@ -29,6 +29,8 @@ struct psset_bin_stats_s {
 	size_t npageslabs;
 	/* Of them, how many pages are active? */
 	size_t nactive;
+	/* And how many are dirty? */
+	size_t ndirty;
 };
 
 typedef struct psset_stats_s psset_stats_t;