diff -r 4ebc2e2fb97c -r 71c04702a3d5 src/hotspot/share/gc/g1/g1HotCardCache.hpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/g1/g1HotCardCache.hpp	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,147 @@
+/*
+ * Copyright (c) 2013, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_VM_GC_G1_G1HOTCARDCACHE_HPP
+#define SHARE_VM_GC_G1_G1HOTCARDCACHE_HPP
+
+#include "gc/g1/g1CardCounts.hpp"
+#include "gc/g1/g1_globals.hpp"
+#include "memory/allocation.hpp"
+#include "runtime/safepoint.hpp"
+#include "runtime/thread.hpp"
+#include "utilities/globalDefinitions.hpp"
+
+class CardTableEntryClosure;
+class DirtyCardQueue;
+class G1CollectedHeap;
+class HeapRegion;
+
+// An evicting cache of cards that have been logged by the G1 post
+// write barrier. Placing a card in the cache delays the refinement
+// of the card until the card is evicted, or the cache is drained
+// during the next evacuation pause.
+//
+// The first thing the G1 post write barrier does is to check whether
+// the card containing the updated pointer is already dirty and, if
+// so, skips the remaining code in the barrier.
+//
+// Delaying the refinement of a card will make the card fail the
+// first is_dirty check in the write barrier, skipping the remainder
+// of the write barrier.
+//
+// This can significantly reduce the overhead of the write barrier
+// code, increasing throughput.
+
+class G1HotCardCache: public CHeapObj<mtGC> {
+
+  G1CollectedHeap*  _g1h;
+
+  bool              _use_cache;
+
+  G1CardCounts      _card_counts;
+
+
+  // The card cache table
+  jbyte**           _hot_cache;
+
+  size_t            _hot_cache_size;
+
+  size_t            _hot_cache_par_chunk_size;
+
+  // Avoids false sharing when concurrently updating _hot_cache_idx or
+  // _hot_cache_par_claimed_idx. These are never updated at the same time
+  // thus it's not necessary to separate them as well
+  char _pad_before[DEFAULT_CACHE_LINE_SIZE];
+
+  volatile size_t _hot_cache_idx;
+
+  volatile size_t _hot_cache_par_claimed_idx;
+
+  char _pad_after[DEFAULT_CACHE_LINE_SIZE];
+
+  // The number of cached cards a thread claims when flushing the cache
+  static const int ClaimChunkSize = 32;
+
+ public:
+  static bool default_use_cache() {
+    return (G1ConcRSLogCacheSize > 0);
+  }
+
+  G1HotCardCache(G1CollectedHeap* g1h);
+  ~G1HotCardCache();
+
+  void initialize(G1RegionToSpaceMapper* card_counts_storage);
+
+  bool use_cache() { return _use_cache; }
+
+  void set_use_cache(bool b) {
+    _use_cache = (b ? default_use_cache() : false);
+  }
+
+  // Returns the card to be refined or NULL.
+  //
+  // Increments the count for given the card. if the card is not 'hot',
+  // it is returned for immediate refining. Otherwise the card is
+  // added to the hot card cache.
+  // If there is enough room in the hot card cache for the card we're
+  // adding, NULL is returned and no further action in needed.
+  // If we evict a card from the cache to make room for the new card,
+  // the evicted card is then returned for refinement.
+  jbyte* insert(jbyte* card_ptr);
+
+  // Refine the cards that have delayed as a result of
+  // being in the cache.
+  void drain(CardTableEntryClosure* cl, uint worker_i);
+
+  // Set up for parallel processing of the cards in the hot cache
+  void reset_hot_cache_claimed_index() {
+    _hot_cache_par_claimed_idx = 0;
+  }
+
+  // Resets the hot card cache and discards the entries.
+  void reset_hot_cache() {
+    assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
+    assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");
+    if (default_use_cache()) {
+        reset_hot_cache_internal();
+    }
+  }
+
+  // Zeros the values in the card counts table for entire committed heap
+  void reset_card_counts();
+
+  // Zeros the values in the card counts table for the given region
+  void reset_card_counts(HeapRegion* hr);
+
+ private:
+  void reset_hot_cache_internal() {
+    assert(_hot_cache != NULL, "Logic");
+    _hot_cache_idx = 0;
+    for (size_t i = 0; i < _hot_cache_size; i++) {
+      _hot_cache[i] = NULL;
+    }
+  }
+};
+
+#endif // SHARE_VM_GC_G1_G1HOTCARDCACHE_HPP