--- old/src/hotspot/share/gc/g1/g1CollectionSet.cpp	2018-11-27 18:26:12.512012368 +0100
+++ new/src/hotspot/share/gc/g1/g1CollectionSet.cpp	2018-11-27 18:26:12.088010266 +0100
@@ -26,6 +26,7 @@
 #include "gc/g1/g1CollectedHeap.inline.hpp"
 #include "gc/g1/g1CollectionSet.hpp"
 #include "gc/g1/g1CollectorState.hpp"
+#include "gc/g1/g1ParScanThreadState.hpp"
 #include "gc/g1/g1Policy.hpp"
 #include "gc/g1/heapRegion.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
@@ -104,6 +105,8 @@
 
 void G1CollectionSet::initialize_optional(uint max_length) {
   assert(_optional_regions == NULL, "Already initialized");
+  assert(_optional_region_length == 0, "Already initialized");
+  assert(_optional_region_max_length == 0, "Already initialized");
   _optional_region_max_length = max_length;
   _optional_regions = NEW_C_HEAP_ARRAY(HeapRegion*, _optional_region_max_length, mtGC);
 }
@@ -449,6 +452,7 @@
 }
 
 bool G1CollectionSet::optional_is_full() {
+  assert(_optional_region_length <= _optional_region_max_length, "Invariant");
   return _optional_region_length == _optional_region_max_length;
 }
 
@@ -630,6 +634,7 @@
     // chooser in reverse order to maintain the old order.
     HeapRegion* hr = _cset->remove_last_optional_region();
     assert(hr != NULL, "Should be valid region left");
+    _pset->free_unused_optional_region(hr);
     g1h->old_set_add(hr);
     g1h->clear_in_cset(hr);
     hr->set_index_in_opt_cset(InvalidCSetIndex);