--- old/src/hotspot/share/gc/parallel/psCompactionManager.hpp	2019-11-11 11:10:34.833081893 +0100
+++ new/src/hotspot/share/gc/parallel/psCompactionManager.hpp	2019-11-11 11:10:34.401079750 +0100
@@ -28,6 +28,7 @@
 #include "gc/shared/taskqueue.hpp"
 #include "memory/allocation.hpp"
 #include "utilities/stack.hpp"
+#include "psParallelCompact.hpp"
 
 class MutableSpace;
 class PSOldGen;
@@ -77,6 +78,7 @@
 private:
   OverflowTaskQueue<oop, mtGC>        _marking_stack;
   ObjArrayTaskQueue             _objarray_stack;
+  size_t                        _shadow_record;
 
   // Is there a way to reuse the _marking_stack for the
   // saving empty regions?  For now just create a different
@@ -85,6 +87,14 @@
 
   static ParMarkBitMap* _mark_bitmap;
 
+  // The shadow region array, we use it in a LIFO fashion, so
+  // that we can reuse shadow regions for better data locality
+  // and utilization
+  static GrowableArray<size_t>* _shadow_region_array;
+
+  // This Monitor provides mutual exclusive access of _shadow_region_array
+  static Monitor*               _shadow_region_monitor;
+
   Action _action;
 
   HeapWord* _last_query_beg;
@@ -109,6 +119,14 @@
   // marking stack and overflow stack directly.
 
  public:
+  static size_t  acquire_shadow_region(PSParallelCompact::RegionData* region_ptr);
+  static void    release_shadow_region(size_t shadow_region);
+  static void    enqueue_shadow_region(size_t shadow_region);
+  static void    dequeue_shadow_region();
+  inline size_t  shadow_record() { return _shadow_record; }
+  inline void    set_shadow_record(size_t record) { _shadow_record = record; }
+  inline size_t  next_shadow_record(size_t workers) { _shadow_record += workers; return shadow_record(); }
+
   void reset_bitmap_query_cache() {
     _last_query_beg = NULL;
     _last_query_obj = NULL;