diff -r 6a8ccac44f41 -r 54b3b351d6f9 src/share/vm/gc_implementation/g1/g1MarkSweep.cpp
--- a/src/share/vm/gc_implementation/g1/g1MarkSweep.cpp	Fri Sep 18 09:57:47 2009 -0700
+++ b/src/share/vm/gc_implementation/g1/g1MarkSweep.cpp	Wed Sep 23 23:56:15 2009 -0700
@@ -102,9 +102,14 @@
   GenMarkSweep::_marking_stack =
     new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);
 
-  size_t size = SystemDictionary::number_of_classes() * 2;
+  int size = SystemDictionary::number_of_classes() * 2;
   GenMarkSweep::_revisit_klass_stack =
-    new (ResourceObj::C_HEAP) GrowableArray<Klass*>((int)size, true);
+    new (ResourceObj::C_HEAP) GrowableArray<Klass*>(size, true);
+  // (#klass/k)^2 for k ~ 10 appears a better fit, but this will have to do
+  // for now until we have a chance to work out a more optimal setting.
+  GenMarkSweep::_revisit_mdo_stack =
+    new (ResourceObj::C_HEAP) GrowableArray<DataLayout*>(size*2, true);
+
 }
 
 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
@@ -141,13 +146,18 @@
   CodeCache::do_unloading(&GenMarkSweep::is_alive,
                                    &GenMarkSweep::keep_alive,
                                    purged_class);
-           GenMarkSweep::follow_stack();
+  GenMarkSweep::follow_stack();
 
   // Update subklass/sibling/implementor links of live klasses
   GenMarkSweep::follow_weak_klass_links();
   assert(GenMarkSweep::_marking_stack->is_empty(),
          "stack should be empty by now");
 
+  // Visit memoized MDO's and clear any unmarked weak refs
+  GenMarkSweep::follow_mdo_weak_refs();
+  assert(GenMarkSweep::_marking_stack->is_empty(), "just drained");
+
+
   // Visit symbol and interned string tables and delete unmarked oops
   SymbolTable::unlink(&GenMarkSweep::is_alive);
   StringTable::unlink(&GenMarkSweep::is_alive);