--- a/src/hotspot/share/gc/z/zCollectedHeap.hpp	Thu Apr 25 08:55:49 2019 +0200
+++ b/src/hotspot/share/gc/z/zCollectedHeap.hpp	Thu Apr 25 08:55:49 2019 +0200
@@ -69,6 +69,7 @@
   virtual size_t max_capacity() const;
   virtual size_t capacity() const;
   virtual size_t used() const;
+  virtual size_t unused() const;
 
   virtual bool is_maximal_no_gc() const;
   virtual bool is_in(const void* p) const;