--- a/src/hotspot/share/gc/parallel/psParallelCompact.cpp	Sun Jun 10 12:58:38 2018 +0300
+++ b/src/hotspot/share/gc/parallel/psParallelCompact.cpp	Mon Jun 11 12:09:57 2018 +0200
@@ -2112,7 +2112,10 @@
 
     ReferenceProcessorStats stats;
     ReferenceProcessorPhaseTimes pt(&_gc_timer, ref_processor()->max_num_queues());
+
     if (ref_processor()->processing_is_mt()) {
+      ref_processor()->set_active_mt_degree(active_gc_threads);
+
       RefProcTaskExecutor task_executor;
       stats = ref_processor()->process_discovered_references(
         is_alive_closure(), &mark_and_push_closure, &follow_stack_closure,