--- old/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	2018-11-15 14:43:19.482917278 +0100
+++ new/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	2018-11-15 14:43:19.042903716 +0100
@@ -1151,6 +1151,8 @@
 }
 
 void G1CollectedHeap::resize_heap_if_necessary() {
+  assert_at_safepoint_on_vm_thread();
+
   // Capacity, free and used after the GC counted as full regions to
   // include the waste in the following calculations.
   const size_t capacity_after_gc = capacity();
@@ -1973,6 +1975,7 @@
   switch (cause) {
     case GCCause::_gc_locker:               return GCLockerInvokesConcurrent;
     case GCCause::_g1_humongous_allocation: return true;
+    case GCCause::_g1_periodic_collection:  return G1PeriodicGCInvokesConcurrent;
     default:                                return is_user_requested_concurrent_full_gc(cause);
   }
 }