diff -r caf5eb7dd4a7 -r 882756847a04 hotspot/src/share/vm/memory/genRemSet.cpp
--- a/hotspot/src/share/vm/memory/genRemSet.cpp	Fri Aug 31 16:39:35 2012 -0700
+++ b/hotspot/src/share/vm/memory/genRemSet.cpp	Sat Sep 01 13:25:18 2012 -0400
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -23,6 +23,7 @@
  */
 
 #include "precompiled.hpp"
+#include "classfile/classLoaderData.hpp"
 #include "memory/cardTableRS.hpp"
 #include "memory/genRemSet.hpp"
 
@@ -39,3 +40,43 @@
     return (0); // Make Windows compiler happy
   }
 }
+
+class HasAccumulatedModifiedOopsClosure : public KlassClosure {
+  bool _found;
+ public:
+  HasAccumulatedModifiedOopsClosure() : _found(false) {}
+  void do_klass(Klass* klass) {
+    if (_found) {
+      return;
+    }
+
+    if (klass->has_accumulated_modified_oops()) {
+      _found = true;
+    }
+  }
+  bool found() {
+    return _found;
+  }
+};
+
+bool KlassRemSet::mod_union_is_clear() {
+  HasAccumulatedModifiedOopsClosure closure;
+  ClassLoaderDataGraph::classes_do(&closure);
+
+  return !closure.found();
+}
+
+
+class ClearKlassModUnionClosure : public KlassClosure {
+ public:
+  void do_klass(Klass* klass) {
+    if (klass->has_accumulated_modified_oops()) {
+      klass->clear_accumulated_modified_oops();
+    }
+  }
+};
+
+void KlassRemSet::clear_mod_union() {
+  ClearKlassModUnionClosure closure;
+  ClassLoaderDataGraph::classes_do(&closure);
+}