1 /*
   2  * Copyright (c) 2013, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  23  */
  24 
  25 #ifndef SHARE_GC_G1_G1HOTCARDCACHE_HPP
  26 #define SHARE_GC_G1_G1HOTCARDCACHE_HPP
  27 
  28 #include "gc/g1/g1CardCounts.hpp"
  29 #include "gc/g1/g1_globals.hpp"
  30 #include "memory/allocation.hpp"
  31 #include "runtime/safepoint.hpp"
  32 #include "runtime/thread.hpp"
  33 #include "utilities/globalDefinitions.hpp"
  34 
  35 class CardTableEntryClosure;
  36 class DirtyCardQueue;
  37 class G1CollectedHeap;
  38 class HeapRegion;
  39 
  40 // An evicting cache of cards that have been logged by the G1 post
  41 // write barrier. Placing a card in the cache delays the refinement
  42 // of the card until the card is evicted, or the cache is drained
  43 // during the next evacuation pause.
  44 //
  45 // The first thing the G1 post write barrier does is to check whether
  46 // the card containing the updated pointer is already dirty and, if
  47 // so, skips the remaining code in the barrier.
  48 //
  49 // Delaying the refinement of a card will make the card fail the
  50 // first is_dirty check in the write barrier, skipping the remainder
  51 // of the write barrier.
  52 //
  53 // This can significantly reduce the overhead of the write barrier
  54 // code, increasing throughput.
  55 
  56 class G1HotCardCache: public CHeapObj<mtGC> {
  57 
  58   G1CollectedHeap*  _g1h;
  59 
  60   bool              _use_cache;
  61 
  62   G1CardCounts      _card_counts;
  63 
  64 
  65   // The card cache table
  66   jbyte**           _hot_cache;
  67 
  68   size_t            _hot_cache_size;
  69 
  70   size_t            _hot_cache_par_chunk_size;
  71 
  72   // Avoids false sharing when concurrently updating _hot_cache_idx or
  73   // _hot_cache_par_claimed_idx. These are never updated at the same time
  74   // thus it's not necessary to separate them as well
  75   char _pad_before[DEFAULT_CACHE_LINE_SIZE];
  76 
  77   volatile size_t _hot_cache_idx;
  78 
  79   volatile size_t _hot_cache_par_claimed_idx;
  80 
  81   char _pad_after[DEFAULT_CACHE_LINE_SIZE];
  82 
  83   // The number of cached cards a thread claims when flushing the cache
  84   static const int ClaimChunkSize = 32;
  85 
  86  public:
  87   static bool default_use_cache() {
  88     return (G1ConcRSLogCacheSize > 0);
  89   }
  90 
  91   G1HotCardCache(G1CollectedHeap* g1h);
  92   ~G1HotCardCache();
  93 
  94   void initialize(G1RegionToSpaceMapper* card_counts_storage);
  95 
  96   bool use_cache() { return _use_cache; }
  97 
  98   void set_use_cache(bool b) {
  99     _use_cache = (b ? default_use_cache() : false);
 100   }
 101 
 102   // Returns the card to be refined or NULL.
 103   //
 104   // Increments the count for given the card. if the card is not 'hot',
 105   // it is returned for immediate refining. Otherwise the card is
 106   // added to the hot card cache.
 107   // If there is enough room in the hot card cache for the card we're
 108   // adding, NULL is returned and no further action in needed.
 109   // If we evict a card from the cache to make room for the new card,
 110   // the evicted card is then returned for refinement.
 111   jbyte* insert(jbyte* card_ptr);
 112 
 113   // Refine the cards that have delayed as a result of
 114   // being in the cache.
 115   void drain(CardTableEntryClosure* cl, uint worker_i);
 116 
 117   // Set up for parallel processing of the cards in the hot cache
 118   void reset_hot_cache_claimed_index() {
 119     _hot_cache_par_claimed_idx = 0;
 120   }
 121 
 122   // Resets the hot card cache and discards the entries.
 123   void reset_hot_cache() {
 124     assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
 125     assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");
 126     if (default_use_cache()) {
 127         reset_hot_cache_internal();
 128     }
 129   }
 130 
 131   // Zeros the values in the card counts table for the given region
 132   void reset_card_counts(HeapRegion* hr);
 133 
 134  private:
 135   void reset_hot_cache_internal() {
 136     assert(_hot_cache != NULL, "Logic");
 137     _hot_cache_idx = 0;
 138     for (size_t i = 0; i < _hot_cache_size; i++) {
 139       _hot_cache[i] = NULL;
 140     }
 141   }
 142 };
 143 
 144 #endif // SHARE_GC_G1_G1HOTCARDCACHE_HPP