--- a/src/hotspot/share/gc/g1/g1DirtyCardQueue.cpp	Fri Nov 22 16:26:35 2019 -0800
+++ b/src/hotspot/share/gc/g1/g1DirtyCardQueue.cpp	Fri Nov 22 17:03:55 2019 -0800
@@ -41,6 +41,7 @@
 #include "runtime/safepoint.hpp"
 #include "runtime/thread.inline.hpp"
 #include "runtime/threadSMR.hpp"
+#include "utilities/quickSort.hpp"
 
 G1DirtyCardQueue::G1DirtyCardQueue(G1DirtyCardQueueSet* qset) :
   // Dirty card queues are always active, so we create them with their
@@ -226,21 +227,127 @@
   return result;
 }
 
+class G1RefineBufferedCards : public StackObj {
+  BufferNode* const _node;
+  CardTable::CardValue** const _node_buffer;
+  const size_t _node_buffer_size;
+  const uint _worker_id;
+  size_t* _total_refined_cards;
+  G1RemSet* const _g1rs;
+
+  static inline int compare_card(const CardTable::CardValue* p1,
+                                 const CardTable::CardValue* p2) {
+    return p2 - p1;
+  }
+
+  // Sorts the cards from start_index to _node_buffer_size in *decreasing*
+  // address order. Tests showed that this order is preferable to not sorting
+  // or increasing address order.
+  void sort_cards(size_t start_index) {
+    QuickSort::sort(&_node_buffer[start_index],
+                    _node_buffer_size - start_index,
+                    compare_card,
+                    false);
+  }
+
+  // Returns the index to the first clean card in the buffer.
+  size_t clean_cards() {
+    const size_t start = _node->index();
+    assert(start <= _node_buffer_size, "invariant");
+
+    // Two-fingered compaction algorithm similar to the filtering mechanism in
+    // SATBMarkQueue. The main difference is that clean_card_before_refine()
+    // could change the buffer element in-place.
+    // We don't check for SuspendibleThreadSet::should_yield(), because
+    // cleaning and redirtying the cards is fast.
+    CardTable::CardValue** src = &_node_buffer[start];
+    CardTable::CardValue** dst = &_node_buffer[_node_buffer_size];
+    assert(src <= dst, "invariant");
+    for ( ; src < dst; ++src) {
+      // Search low to high for a card to keep.
+      if (_g1rs->clean_card_before_refine(src)) {
+        // Found keeper.  Search high to low for a card to discard.
+        while (src < --dst) {
+          if (!_g1rs->clean_card_before_refine(dst)) {
+            *dst = *src;         // Replace discard with keeper.
+            break;
+          }
+        }
+        // If discard search failed (src == dst), the outer loop will also end.
+      }
+    }
+
+    // dst points to the first retained clean card, or the end of the buffer
+    // if all the cards were discarded.
+    const size_t first_clean = dst - _node_buffer;
+    assert(first_clean >= start && first_clean <= _node_buffer_size, "invariant");
+    // Discarded cards are considered as refined.
+    *_total_refined_cards += first_clean - start;
+    return first_clean;
+  }
+
+  bool refine_cleaned_cards(size_t start_index) {
+    bool result = true;
+    size_t i = start_index;
+    for ( ; i < _node_buffer_size; ++i) {
+      if (SuspendibleThreadSet::should_yield()) {
+        redirty_unrefined_cards(i);
+        result = false;
+        break;
+      }
+      _g1rs->refine_card_concurrently(_node_buffer[i], _worker_id);
+    }
+    _node->set_index(i);
+    *_total_refined_cards += i - start_index;
+    return result;
+  }
+
+  void redirty_unrefined_cards(size_t start) {
+    for ( ; start < _node_buffer_size; ++start) {
+      *_node_buffer[start] = G1CardTable::dirty_card_val();
+    }
+  }
+
+public:
+  G1RefineBufferedCards(BufferNode* node,
+                        size_t node_buffer_size,
+                        uint worker_id,
+                        size_t* total_refined_cards) :
+    _node(node),
+    _node_buffer(reinterpret_cast<CardTable::CardValue**>(BufferNode::make_buffer_from_node(node))),
+    _node_buffer_size(node_buffer_size),
+    _worker_id(worker_id),
+    _total_refined_cards(total_refined_cards),
+    _g1rs(G1CollectedHeap::heap()->rem_set()) {}
+
+  bool refine() {
+    size_t first_clean_index = clean_cards();
+    if (first_clean_index == _node_buffer_size) {
+      _node->set_index(first_clean_index);
+      return true;
+    }
+    // This fence serves two purposes. First, the cards must be cleaned
+    // before processing the contents. Second, we can't proceed with
+    // processing a region until after the read of the region's top in
+    // collect_and_clean_cards(), for synchronization with possibly concurrent
+    // humongous object allocation (see comment at the StoreStore fence before
+    // setting the regions' tops in humongous allocation path).
+    // It's okay that reading region's top and reading region's type were racy
+    // wrto each other. We need both set, in any order, to proceed.
+    OrderAccess::fence();
+    sort_cards(first_clean_index);
+    return refine_cleaned_cards(first_clean_index);
+  }
+};
+
 bool G1DirtyCardQueueSet::refine_buffer(BufferNode* node,
                                         uint worker_id,
                                         size_t* total_refined_cards) {
-  G1RemSet* rem_set = G1CollectedHeap::heap()->rem_set();
-  size_t size = buffer_size();
-  void** buffer = BufferNode::make_buffer_from_node(node);
-  size_t i = node->index();
-  assert(i <= size, "invariant");
-  for ( ; (i < size) && !SuspendibleThreadSet::should_yield(); ++i) {
-    CardTable::CardValue* cp = static_cast<CardTable::CardValue*>(buffer[i]);
-    rem_set->refine_card_concurrently(cp, worker_id);
-  }
-  *total_refined_cards += (i - node->index());
-  node->set_index(i);
-  return i == size;
+  G1RefineBufferedCards buffered_cards(node,
+                                       buffer_size(),
+                                       worker_id,
+                                       total_refined_cards);
+  return buffered_cards.refine();
 }
 
 #ifndef ASSERT