--- a/hotspot/src/share/vm/gc_implementation/g1/g1AllocRegion.hpp	Thu Aug 11 11:36:29 2011 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1AllocRegion.hpp	Fri Aug 12 11:31:06 2011 -0400
@@ -36,7 +36,7 @@
 
 // A class that holds a region that is active in satisfying allocation
 // requests, potentially issued in parallel. When the active region is
-// full it will be retired it replaced with a new one. The
+// full it will be retired and replaced with a new one. The
 // implementation assumes that fast-path allocations will be lock-free
 // and a lock will need to be taken when the active region needs to be
 // replaced.
@@ -57,13 +57,22 @@
   // correct use of init() and release()).
   HeapRegion* _alloc_region;
 
+  // It keeps track of the distinct number of regions that are used
+  // for allocation in the active interval of this object, i.e.,
+  // between a call to init() and a call to release(). The count
+  // mostly includes regions that are freshly allocated, as well as
+  // the region that is re-used using the set() method. This count can
+  // be used in any heuristics that might want to bound how many
+  // distinct regions this object can used during an active interval.
+  size_t _count;
+
   // When we set up a new active region we save its used bytes in this
   // field so that, when we retire it, we can calculate how much space
   // we allocated in it.
   size_t _used_bytes_before;
 
-  // Specifies whether the allocate calls will do BOT updates or not.
-  bool _bot_updates;
+  // When true, indicates that allocate calls should do BOT updates.
+  const bool _bot_updates;
 
   // Useful for debugging and tracing.
   const char* _name;
@@ -127,6 +136,8 @@
     return (_alloc_region == _dummy_region) ? NULL : _alloc_region;
   }
 
+  size_t count() { return _count; }
+
   // The following two are the building blocks for the allocation method.
 
   // First-level allocation: Should be called without holding a
@@ -153,6 +164,12 @@
   // Should be called before we start using this object.
   void init();
 
+  // This can be used to set the active region to a specific
+  // region. (Use Example: we try to retain the last old GC alloc
+  // region that we've used during a GC and we can use set() to
+  // re-instate it at the beginning of the next GC.)
+  void set(HeapRegion* alloc_region);
+
   // Should be called when we want to release the active region which
   // is returned after it's been retired.
   HeapRegion* release();