diff -r eb6ebd9816cf src/share/vm/gc/shenandoah/shenandoahCollectorPolicy.cpp
--- a/src/share/vm/gc/shenandoah/shenandoahCollectorPolicy.cpp	Thu Mar 30 15:13:50 2017 +0200
+++ b/src/share/vm/gc/shenandoah/shenandoahCollectorPolicy.cpp	Thu Mar 30 21:21:43 2017 +0200
@@ -73,6 +73,7 @@
 
   size_t _bytes_allocated_after_last_gc;
 
+  bool _cm_happened;
   uint _cancelled_cm_cycles_in_a_row;
   uint _successful_cm_cycles_in_a_row;
 
@@ -121,6 +122,7 @@
   }
 
   virtual void record_cm_success() {
+    _cm_happened = true;
     _cancelled_cm_cycles_in_a_row = 0;
     _successful_cm_cycles_in_a_row++;
   }
@@ -170,6 +172,7 @@
   _bytes_in_cset(0),
   _cancelled_cm_cycles_in_a_row(0),
   _successful_cm_cycles_in_a_row(0),
+  _cm_happened(false),
   _region_garbage(NULL),
   _region_garbage_size(0)
 {
@@ -436,6 +439,7 @@
 private:
   uintx _free_threshold;
   TruncatedSeq* _cset_history;
+  bool _cm_happened;
 
 public:
   AdaptiveHeuristics() :
@@ -684,12 +688,15 @@
 
   virtual ~PartialHeuristics() {}
 
-  bool should_start_concurrent_mark(size_t used, size_t capacity) const {
-    // Never do concurrent GCs.
-    return false;
+  bool update_refs_early() {
+    return true;
   }
 
   bool should_start_partial_gc() {
+    if (!ShenandoahHeuristics::_cm_happened) {
+      return false;
+    }
+
     ShenandoahHeap* heap = ShenandoahHeap::heap();
     size_t capacity = heap->capacity();
 
diff -r eb6ebd9816cf src/share/vm/gc/shenandoah/shenandoahHeap.cpp
--- a/src/share/vm/gc/shenandoah/shenandoahHeap.cpp	Thu Mar 30 15:13:50 2017 +0200
+++ b/src/share/vm/gc/shenandoah/shenandoahHeap.cpp	Thu Mar 30 21:21:43 2017 +0200
@@ -2637,6 +2637,7 @@
   set_evacuation_in_progress_at_safepoint(false);
   set_update_refs_in_progress(true);
   ensure_parsability(true);
+  connection_matrix()->clear_all();
   for (uint i = 0; i < _num_regions; i++) {
     ShenandoahHeapRegion* r = _ordered_regions->get(i);
     r->set_concurrent_iteration_safe_limit(r->top());
diff -r eb6ebd9816cf src/share/vm/gc/shenandoah/shenandoahOopClosures.inline.hpp
--- a/src/share/vm/gc/shenandoah/shenandoahOopClosures.inline.hpp	Thu Mar 30 15:13:50 2017 +0200
+++ b/src/share/vm/gc/shenandoah/shenandoahOopClosures.inline.hpp	Thu Mar 30 21:21:43 2017 +0200
@@ -34,7 +34,10 @@
 
 template <class T>
 inline void ShenandoahUpdateHeapRefsClosure::do_oop_nv(T* p) {
-  _heap->maybe_update_oop_ref(p);
+  oop obj = _heap->maybe_update_oop_ref(p);
+  if (! oopDesc::is_null(obj)) {
+    _heap->connection_matrix()->set_connected(p, obj);
+  }
 }
 
 #endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHOOPCLOSURES_INLINE_HPP
diff -r eb6ebd9816cf src/share/vm/gc/shenandoah/shenandoahPartialGC.cpp
--- a/src/share/vm/gc/shenandoah/shenandoahPartialGC.cpp	Thu Mar 30 15:13:50 2017 +0200
+++ b/src/share/vm/gc/shenandoah/shenandoahPartialGC.cpp	Thu Mar 30 21:21:43 2017 +0200
@@ -106,7 +106,7 @@
       ShenandoahHeapRegion* r = _root_regions->claim_next();
       while (r != NULL) {
         assert(r->is_root(), "must be root region");
-        r->oop_iterate(&cl);
+        _heap->marked_object_oop_iterate(r, &cl);
         r->set_root(false);
         if (check_and_handle_cancelled_gc()) return;
         r = _root_regions->claim_next();
@@ -299,6 +299,11 @@
       for (size_t i = 0; i < num_cset; i++) {
         ShenandoahHeapRegion* r = _heap->collection_set()->get(i);
         _heap->decrease_used(r->used());
+        HeapWord* bottom = r->bottom();
+        HeapWord* top = _heap->complete_top_at_mark_start(r->bottom());
+        if (top > bottom) {
+          _heap->complete_mark_bit_map()->clear_range_large(MemRegion(bottom, top));
+        }
         r->recycle();
         _heap->free_regions()->add_region(r);
       }
@@ -343,7 +348,7 @@
     if (UPDATE_MATRIX) {
 #ifdef ASSERT
       oop forw = ShenandoahBarrierSet::resolve_oop_static_not_null(obj);
-      assert(oopDesc::unsafe_equals(obj, forw) || _heap->cancelled_concgc(), "must not be evacuated");
+      assert(oopDesc::unsafe_equals(obj, forw) || _heap->cancelled_concgc(), "must not be evacuated: "PTR_FORMAT" -> "PTR_FORMAT, p2i(obj), p2i(forw));
 #endif
       _matrix->set_connected(p, obj);
     }