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 21 * questions. 22 * 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 G1CardTableEntryClosure; 36 class G1CollectedHeap; 37 class HeapRegion; 38 39 // An evicting cache of cards that have been logged by the G1 post 40 // write barrier. Placing a card in the cache delays the refinement 41 // of the card until the card is evicted, or the cache is drained 42 // during the next evacuation pause. 43 // 44 // The first thing the G1 post write barrier does is to check whether 45 // the card containing the updated pointer is already dirty and, if 46 // so, skips the remaining code in the barrier. 47 // 48 // Delaying the refinement of a card will make the card fail the 49 // first is_dirty check in the write barrier, skipping the remainder 50 // of the write barrier. 51 // 52 // This can significantly reduce the overhead of the write barrier 53 // code, increasing throughput. 54 55 class G1HotCardCache: public CHeapObj<mtGC> { 56 57 G1CollectedHeap* _g1h; 58 59 bool _use_cache; 60 61 G1CardCounts _card_counts; 62 63 64 // The card cache table 65 jbyte** _hot_cache; 66 67 size_t _hot_cache_size; 68 69 size_t _hot_cache_par_chunk_size; 70 71 // Avoids false sharing when concurrently updating _hot_cache_idx or 72 // _hot_cache_par_claimed_idx. These are never updated at the same time 73 // thus it's not necessary to separate them as well 74 char _pad_before[DEFAULT_CACHE_LINE_SIZE]; 75 76 volatile size_t _hot_cache_idx; 77 78 volatile size_t _hot_cache_par_claimed_idx; 79 80 char _pad_after[DEFAULT_CACHE_LINE_SIZE]; 81 82 // The number of cached cards a thread claims when flushing the cache 83 static const int ClaimChunkSize = 32; 84 85 public: 86 static bool default_use_cache() { 87 return (G1ConcRSLogCacheSize > 0); 88 } 89 90 G1HotCardCache(G1CollectedHeap* g1h); 91 ~G1HotCardCache(); 92 93 void initialize(G1RegionToSpaceMapper* card_counts_storage); 94 95 bool use_cache() { return _use_cache; } 96 97 void set_use_cache(bool b) { 98 _use_cache = (b ? default_use_cache() : false); 99 } 100 101 // Returns the card to be refined or NULL. 102 // 103 // Increments the count for given the card. if the card is not 'hot', 104 // it is returned for immediate refining. Otherwise the card is 105 // added to the hot card cache. 106 // If there is enough room in the hot card cache for the card we're 107 // adding, NULL is returned and no further action in needed. 108 // If we evict a card from the cache to make room for the new card, 109 // the evicted card is then returned for refinement. 110 jbyte* insert(jbyte* card_ptr); 111 112 // Refine the cards that have delayed as a result of 113 // being in the cache. 114 void drain(G1CardTableEntryClosure* cl, uint worker_i); 115 116 // Set up for parallel processing of the cards in the hot cache 117 void reset_hot_cache_claimed_index() { 118 _hot_cache_par_claimed_idx = 0; 119 } 120 121 // Resets the hot card cache and discards the entries. 122 void reset_hot_cache() { 123 assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint"); 124 assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread"); 125 if (default_use_cache()) { 126 reset_hot_cache_internal(); 127 } 128 } 129 130 // Zeros the values in the card counts table for the given region 131 void reset_card_counts(HeapRegion* hr); 132 133 private: 134 void reset_hot_cache_internal() { 135 assert(_hot_cache != NULL, "Logic"); 136 _hot_cache_idx = 0; 137 for (size_t i = 0; i < _hot_cache_size; i++) { 138 _hot_cache[i] = NULL; 139 } 140 } 141 }; 142 143 #endif // SHARE_GC_G1_G1HOTCARDCACHE_HPP