1 /*

     2  * Copyright (c) 2013, 2017, 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

    21  * questions.

    22  *

    23  */

    24 

    25 #ifndef SHARE_VM_GC_G1_G1HOTCARDCACHE_HPP

    26 #define SHARE_VM_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 entire committed heap

   132   void reset_card_counts();

   133 

   134   // Zeros the values in the card counts table for the given region

   135   void reset_card_counts(HeapRegion* hr);

   136 

   137  private:

   138   void reset_hot_cache_internal() {

   139     assert(_hot_cache != NULL, "Logic");

   140     _hot_cache_idx = 0;

   141     for (size_t i = 0; i < _hot_cache_size; i++) {

   142       _hot_cache[i] = NULL;

   143     }

   144   }

   145 };

   146 

   147 #endif // SHARE_VM_GC_G1_G1HOTCARDCACHE_HPP