diff -r 4d193fe22b76 -r 6719a2e727c0 hotspot/src/share/vm/gc_implementation/g1/concurrentMark.hpp
--- a/hotspot/src/share/vm/gc_implementation/g1/concurrentMark.hpp	Thu Apr 28 15:29:18 2011 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/concurrentMark.hpp	Fri Apr 29 12:40:49 2011 -0400
@@ -316,6 +316,19 @@
   void setEmpty()   { _index = 0; clear_overflow(); }
 };
 
+class ForceOverflowSettings VALUE_OBJ_CLASS_SPEC {
+private:
+#ifndef PRODUCT
+  uintx _num_remaining;
+  bool _force;
+#endif // !defined(PRODUCT)
+
+public:
+  void init() PRODUCT_RETURN;
+  void update() PRODUCT_RETURN;
+  bool should_force() PRODUCT_RETURN_( return false; );
+};
+
 // this will enable a variety of different statistics per GC task
 #define _MARKING_STATS_       0
 // this will enable the higher verbose levels
@@ -462,6 +475,9 @@
 
   WorkGang* _parallel_workers;
 
+  ForceOverflowSettings _force_overflow_conc;
+  ForceOverflowSettings _force_overflow_stw;
+
   void weakRefsWork(bool clear_all_soft_refs);
 
   void swapMarkBitMaps();
@@ -470,7 +486,7 @@
   // task local ones; should be called during initial mark.
   void reset();
   // It resets all the marking data structures.
-  void clear_marking_state();
+  void clear_marking_state(bool clear_overflow = true);
 
   // It should be called to indicate which phase we're in (concurrent
   // mark or remark) and how many threads are currently active.
@@ -547,6 +563,22 @@
   void enter_first_sync_barrier(int task_num);
   void enter_second_sync_barrier(int task_num);
 
+  ForceOverflowSettings* force_overflow_conc() {
+    return &_force_overflow_conc;
+  }
+
+  ForceOverflowSettings* force_overflow_stw() {
+    return &_force_overflow_stw;
+  }
+
+  ForceOverflowSettings* force_overflow() {
+    if (concurrent()) {
+      return force_overflow_conc();
+    } else {
+      return force_overflow_stw();
+    }
+  }
+
 public:
   // Manipulation of the global mark stack.
   // Notice that the first mark_stack_push is CAS-based, whereas the