view src/share/vm/gc_implementation/g1/g1HotCardCache.hpp @ 20543:e7d0505c8a30

8059758: Footprint regressions with JDK-8038423 Summary: Changes in JDK-8038423 always initialize (zero out) virtual memory used for auxiliary data structures. This causes a footprint regression for G1 in startup benchmarks. This is because they do not touch that memory at all, so the operating system does not actually commit these pages. The fix is to, if the initialization value of the data structures matches the default value of just committed memory (=0), do not do anything. Reviewed-by: jwilhelm, brutisso
author tschatzl
date Fri, 10 Oct 2014 15:51:58 +0200
parents 1f1d373cd044
children
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/*
 * Copyright (c) 2013, 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_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP
#define SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP

#include "gc_implementation/g1/g1_globals.hpp"
#include "gc_implementation/g1/g1CardCounts.hpp"
#include "memory/allocation.hpp"
#include "runtime/safepoint.hpp"
#include "runtime/thread.inline.hpp"
#include "utilities/globalDefinitions.hpp"

class DirtyCardQueue;
class G1CollectedHeap;
class G1RemSet;
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;

  // The card cache table
  jbyte**      _hot_cache;

  int          _hot_cache_size;
  int          _n_hot;
  int          _hot_cache_idx;

  int          _hot_cache_par_chunk_size;
  volatile int _hot_cache_par_claimed_idx;

  bool         _use_cache;

  G1CardCounts _card_counts;

  bool default_use_cache() const {
    return (G1ConcRSLogCacheSize > 0);
  }

 public:
  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(uint worker_i, G1RemSet* g1rs, DirtyCardQueue* into_cset_dcq);

  // 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");
    _hot_cache_idx = 0; _n_hot = 0;
  }

  bool hot_cache_is_empty() { return _n_hot == 0; }

  // 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);
};

#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP