diff -r d3a33953b936 -r e64383344f14 src/hotspot/share/gc/shared/satbMarkQueue.hpp
--- a/src/hotspot/share/gc/shared/satbMarkQueue.hpp	Wed Jun 26 09:06:32 2019 -0400
+++ b/src/hotspot/share/gc/shared/satbMarkQueue.hpp	Wed Jun 26 13:18:38 2019 -0400
@@ -27,6 +27,7 @@
 
 #include "gc/shared/ptrQueue.hpp"
 #include "memory/allocation.hpp"
+#include "memory/padded.hpp"
 
 class Thread;
 class Monitor;
@@ -93,7 +94,17 @@
 };
 
 class SATBMarkQueueSet: public PtrQueueSet {
+
+  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, 0);
+  PaddedEnd<BufferNode::Stack> _list;
+  volatile size_t _count_and_process_flag;
+  // These are rarely (if ever) changed, so same cache line as count.
+  size_t _process_completed_buffers_threshold;
   size_t _buffer_enqueue_threshold;
+  DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, 3 * sizeof(size_t));
+
+  BufferNode* get_completed_buffer();
+  void abandon_completed_buffers();
 
 #ifdef ASSERT
   void dump_active_states(bool expected_active);
@@ -102,15 +113,14 @@
 
 protected:
   SATBMarkQueueSet();
-  ~SATBMarkQueueSet() {}
+  ~SATBMarkQueueSet();
 
   template<typename Filter>
   void apply_filter(Filter filter, SATBMarkQueue* queue) {
     queue->apply_filter(filter);
   }
 
-  void initialize(Monitor* cbl_mon,
-                  BufferNode::Allocator* allocator,
+  void initialize(BufferNode::Allocator* allocator,
                   size_t process_completed_buffers_threshold,
                   uint buffer_enqueue_threshold_percentage);
 
@@ -132,6 +142,19 @@
   // buffer; the leading entries may be excluded due to filtering.
   bool apply_closure_to_completed_buffer(SATBBufferClosure* cl);
 
+  virtual void enqueue_completed_buffer(BufferNode* node);
+
+  // The number of buffers in the list.  Racy and not updated atomically
+  // with the set of completed buffers.
+  size_t completed_buffers_num() const {
+    return _count_and_process_flag >> 1;
+  }
+
+  // Return true if completed buffers should be processed.
+  bool process_completed_buffers() const {
+    return (_count_and_process_flag & 1) != 0;
+  }
+
 #ifndef PRODUCT
   // Helpful for debugging
   void print_all(const char* msg);