7078465: G1: Don't use the undefined value (-1) for the G1 old memory pool max size

Reviewed-by: johnc, brutisso

src/share/vm/gc_implementation/g1/g1MonitoringSupport.hpp

@@ -89,16 +89,15 @@ class G1CollectedHeap;
 //
 // * Min Capacity
 //
-//    We set this to 0 for all spaces. We could consider setting the old
-//    min capacity to the min capacity of the heap (see 7078465).
+//    We set this to 0 for all spaces.
 //
 // * Max Capacity
 //
 //    For jstat, we set the max capacity of all spaces to heap_capacity,
-//    given that we don't always have a reasonably upper bound on how big
-//    each space can grow. For the memory pools, we actually make the max
-//    capacity undefined. We could consider setting the old max capacity
-//    to the max capacity of the heap (see 7078465).
+//    given that we don't always have a reasonable upper bound on how big
+//    each space can grow. For the memory pools, we make the max
+//    capacity undefined with the exception of the old memory pool for
+//    which we make the max capacity same as the max heap capacity.
 //
 // If we had more accurate occupancy / capacity information per
 // region set the above calculations would be greatly simplified and

src/share/vm/services/g1MemoryPool.hpp

@@ -101,7 +101,7 @@ public:
     return _g1mm->old_space_used();
   }
   size_t max_size() const {
-    return _undefined_max;
+    return _g1mm->old_gen_max();
   }
   MemoryUsage get_memory_usage();
 };