diff -r 70021dbed82b -r 9ee940f1de90 src/hotspot/share/gc/g1/g1CardTable.inline.hpp
--- a/src/hotspot/share/gc/g1/g1CardTable.inline.hpp	Fri Nov 29 11:28:39 2019 +0300
+++ b/src/hotspot/share/gc/g1/g1CardTable.inline.hpp	Fri Nov 29 10:20:14 2019 +0100
@@ -33,17 +33,21 @@
   return (uint)(card_idx >> (HeapRegion::LogOfHRGrainBytes - card_shift));
 }
 
-inline void G1CardTable::mark_clean_as_dirty(size_t card_index) {
+inline size_t G1CardTable::mark_clean_as_dirty(size_t card_index) {
   CardValue value = _byte_map[card_index];
   if (value == clean_card_val()) {
     _byte_map[card_index] = dirty_card_val();
+    return 1;
   }
+  return 0;
 }
 
-inline void G1CardTable::mark_region_dirty(size_t start_card_index, size_t num_cards) {
+inline size_t G1CardTable::mark_region_dirty(size_t start_card_index, size_t num_cards) {
   assert(is_aligned(start_card_index, sizeof(size_t)), "Start card index must be aligned.");
   assert(is_aligned(num_cards, sizeof(size_t)), "Number of cards to change must be evenly divisible.");
 
+  size_t result = 0;
+
   size_t const num_chunks = num_cards / sizeof(size_t);
 
   size_t* cur_word = (size_t*)&_byte_map[start_card_index];
@@ -52,6 +56,7 @@
     size_t value = *cur_word;
     if (value == WordAllClean) {
       *cur_word = WordAllDirty;
+      result += sizeof(value);
     } else if (value == WordAllDirty) {
       // do nothing.
     } else {
@@ -61,12 +66,15 @@
         CardValue value = *cur;
         if (value == clean_card_val()) {
           *cur = dirty_card_val();
+          result++;
         }
         cur++;
       }
     }
     cur_word++;
   }
+
+  return result;
 }
 
 inline void G1CardTable::mark_as_scanned(size_t start_card_index, size_t num_cards) {