--- old/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/z/ZPage.java	2018-07-19 22:49:39.449540005 +0900
+++ new/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/z/ZPage.java	2018-07-19 22:49:39.242538607 +0900
@@ -35,6 +35,8 @@
 public class ZPage extends VMObject {
     private static CIntegerField typeField;
     private static long virtualFieldOffset;
+    private static CIntegerField topField;
+    private static CIntegerField refcountField;
     private static long forwardingFieldOffset;
 
     static {
@@ -46,6 +48,8 @@
 
         typeField = type.getCIntegerField("_type");
         virtualFieldOffset = type.getField("_virtual").getOffset();
+        topField = type.getCIntegerField("_top");
+        refcountField = type.getCIntegerField("_refcount");
         forwardingFieldOffset = type.getField("_forwarding").getOffset();
     }
 
@@ -65,10 +69,18 @@
         return (ZForwardingTable)VMObjectFactory.newObject(ZForwardingTable.class, addr.addOffsetTo(forwardingFieldOffset));
     }
 
-    private long start() {
+    public long start() {
         return virtual().start();
     }
 
+    public long top() {
+        return topField.getJLong(addr);
+    }
+
+    public int refcount() {
+        return topField.getJInt(addr);
+    }
+
     Address forward_object(Address from) {
         // Lookup address in forwarding table
         long from_offset = ZAddress.offset(from);