--- kernel/kern/zalloc.h	2018/04/24 18:26:07	1.1.1.1
+++ kernel/kern/zalloc.h	2018/04/24 18:32:26	1.1.1.2
@@ -101,6 +101,9 @@ typedef struct zone {
 	struct zone_free_space *
 			free_space;	/* where to get new elements from */
 	struct zone *	next_zone;	/* Link for all-zones list */
+#if DIAGNOSTIC
+	vm_offset_t	lowest, highest;
+#endif
 } *zone_t;
 
 #define		ZONE_NULL	((zone_t) 0)