diff -r d4ddf19c2624 -r bd9dba789919 src/hotspot/share/gc/g1/g1RemSet.hpp
--- a/src/hotspot/share/gc/g1/g1RemSet.hpp	Fri Nov 22 16:26:35 2019 -0800
+++ b/src/hotspot/share/gc/g1/g1RemSet.hpp	Fri Nov 22 17:03:55 2019 -0800
@@ -113,10 +113,17 @@
                                    G1GCPhaseTimes::GCParPhases coderoots_phase,
                                    G1GCPhaseTimes::GCParPhases objcopy_phase);
 
-  // Refine the card corresponding to "card_ptr". Safe to be called concurrently
-  // to the mutator.
-  void refine_card_concurrently(CardValue* card_ptr,
-                                uint worker_id);
+  // Two methods for concurrent refinement support, executed concurrently to
+  // the mutator:
+  // Cleans the card at "*card_ptr_addr" before refinement, returns true iff the
+  // card needs later refinement. Note that "*card_ptr_addr" could be updated to
+  // a different card due to use of hot card cache.
+  bool clean_card_before_refine(CardValue** const card_ptr_addr);
+  // Refine the region corresponding to "card_ptr". Must be called after
+  // being filtered by clean_card_before_refine(), and after proper
+  // fence/synchronization.
+  void refine_card_concurrently(CardValue* const card_ptr,
+                                const uint worker_id);
 
   // Print accumulated summary info from the start of the VM.
   void print_summary_info();