diff -r 9a7135d0a309 -r 7386b3a385ac src/share/vm/memory/generation.hpp
--- a/src/share/vm/memory/generation.hpp	Tue Dec 17 05:07:06 2019 +0000
+++ b/src/share/vm/memory/generation.hpp	Tue Dec 17 05:26:57 2019 +0000
@@ -168,6 +168,7 @@
   virtual size_t capacity() const = 0;  // The maximum number of object bytes the
                                         // generation can currently hold.
   virtual size_t used() const = 0;      // The number of used bytes in the gen.
+  virtual size_t used_stable() const;   // The number of used bytes for memory monitoring tools.
   virtual size_t free() const = 0;      // The number of free bytes in the gen.
 
   // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.