--- a/src/hotspot/share/gc/z/zCollectedHeap.cpp	Thu Apr 25 08:55:49 2019 +0200
+++ b/src/hotspot/share/gc/z/zCollectedHeap.cpp	Thu Apr 25 08:55:49 2019 +0200
@@ -100,6 +100,10 @@
   return _heap.used();
 }
 
+size_t ZCollectedHeap::unused() const {
+  return _heap.unused();
+}
+
 bool ZCollectedHeap::is_maximal_no_gc() const {
   // Not supported
   ShouldNotReachHere();