diff -r 1edb08142cea -r 47c20fc6a517 src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/g1/HeapRegion.java
--- a/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/g1/HeapRegion.java	Fri Nov 08 09:16:48 2019 +0100
+++ b/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/g1/HeapRegion.java	Fri Nov 08 10:01:13 2019 +0100
@@ -45,9 +45,12 @@
 // any of its fields but only iterate over it.
 
 public class HeapRegion extends CompactibleSpace implements LiveRegionsProvider {
-    // static int GrainBytes;
+    private static AddressField bottomField;
+    static private AddressField topField;
+    private static AddressField endField;
+    private static AddressField compactionTopField;
+
     static private CIntegerField grainBytesField;
-    static private AddressField topField;
     private static long typeFieldOffset;
     private static long pointerSize;
 
@@ -64,8 +67,12 @@
     static private synchronized void initialize(TypeDataBase db) {
         Type type = db.lookupType("HeapRegion");
 
+        bottomField = type.getAddressField("_bottom");
+        topField = type.getAddressField("_top");
+        endField = type.getAddressField("_end");
+        compactionTopField = type.getAddressField("_compaction_top");
+
         grainBytesField = type.getCIntegerField("GrainBytes");
-        topField = type.getAddressField("_top");
         typeFieldOffset = type.getField("_type").getOffset();
 
         pointerSize = db.lookupType("HeapRegion*").getSize();
@@ -82,9 +89,11 @@
         type = (HeapRegionType)VMObjectFactory.newObject(HeapRegionType.class, typeAddr);
     }
 
-    public Address top() {
-        return topField.getValue(addr);
-    }
+    public Address bottom()        { return bottomField.getValue(addr); }
+    public Address top()           { return topField.getValue(addr); }
+    public Address end()           { return endField.getValue(addr); }
+
+    public Address compactionTop() { return compactionTopField.getValue(addr); }
 
     @Override
     public List<MemRegion> getLiveRegions() {
@@ -93,12 +102,16 @@
         return res;
     }
 
-    @Override
+    /** Returns a subregion of the space containing all the objects in
+        the space. */
+    public MemRegion usedRegion() {
+        return new MemRegion(bottom(), end());
+    }
+
     public long used() {
         return top().minus(bottom());
     }
 
-    @Override
     public long free() {
         return end().minus(top());
     }