--- old/src/share/vm/memory/filemap.hpp	2016-09-06 18:50:38.520881444 -0400
+++ new/src/share/vm/memory/filemap.hpp	2016-09-06 18:50:37.692834160 -0400
@@ -252,10 +252,21 @@
   bool is_in_shared_region(const void* p, int idx) NOT_CDS_RETURN_(false);
   void print_shared_spaces() NOT_CDS_RETURN;
 
+  // The ro+rw+md+mc spaces size
+  static size_t core_spaces_size() {
+    return align_size_up((SharedReadOnlySize + SharedReadWriteSize +
+                          SharedMiscDataSize + SharedMiscCodeSize),
+                          os::vm_allocation_granularity());
+  }
+  // The estimated optional space size. Only the portion containning data is 
+  // written out to the archive and mapped at runtime. There is no memory waste
+  // due to unused portion in optional space.
+  static size_t optional_space_size() {
+    return core_spaces_size(); 
+  }
+  // Total shared_spaces size includes the ro, rw, md, mc and od spaces
   static size_t shared_spaces_size() {
-    return align_size_up(SharedReadOnlySize + SharedReadWriteSize +
-                         SharedMiscDataSize + SharedMiscCodeSize,
-                         os::vm_allocation_granularity());
+    return core_spaces_size() + optional_space_size();
   }
 
   // Stop CDS sharing and unmap CDS regions.