--- a/hotspot/src/share/vm/gc_implementation/g1/g1MMUTracker.cpp	Wed Jun 09 13:53:58 2010 -0400
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1MMUTracker.cpp	Thu Jun 10 08:27:35 2010 -0700
@@ -81,20 +81,24 @@
 
   remove_expired_entries(end);
   if (_no_entries == QueueLength) {
-    // OK, right now when we fill up we bomb out
-    // there are a few ways of dealing with this "gracefully"
+    // OK, we've filled up the queue. There are a few ways
+    // of dealing with this "gracefully"
     //   increase the array size (:-)
     //   remove the oldest entry (this might allow more GC time for
-    //     the time slice than what's allowed)
+    //     the time slice than what's allowed) - this is what we
+    //     currently do
     //   consolidate the two entries with the minimum gap between them
     //     (this might allow less GC time than what's allowed)
-    guarantee(NOT_PRODUCT(ScavengeALot ||) G1UseFixedWindowMMUTracker,
-              "array full, currently we can't recover unless +G1UseFixedWindowMMUTracker");
+
     // In the case where ScavengeALot is true, such overflow is not
     // uncommon; in such cases, we can, without much loss of precision
     // or performance (we are GC'ing most of the time anyway!),
-    // simply overwrite the oldest entry in the tracker: this
-    // is also the behaviour when G1UseFixedWindowMMUTracker is enabled.
+    // simply overwrite the oldest entry in the tracker.
+
+    if (G1PolicyVerbose > 1) {
+      warning("MMU Tracker Queue overflow. Replacing earliest entry.");
+    }
+
     _head_index = trim_index(_head_index + 1);
     assert(_head_index == _tail_index, "Because we have a full circular buffer");
     _tail_index = trim_index(_tail_index + 1);