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 "memory/allocation.hpp"
30 #include "runtime/safepoint.hpp"
31 #include "runtime/thread.hpp"
32 #include "utilities/globalDefinitions.hpp"
33
34 class G1CardTableEntryClosure;
35 class G1CollectedHeap;
36 class HeapRegion;
37
38 // An evicting cache of cards that have been logged by the G1 post
39 // write barrier. Placing a card in the cache delays the refinement
40 // of the card until the card is evicted, or the cache is drained
41 // during the next evacuation pause.
42 //
43 // The first thing the G1 post write barrier does is to check whether
44 // the card containing the updated pointer is already dirty and, if
45 // so, skips the remaining code in the barrier.
46 //
47 // Delaying the refinement of a card will make the card fail the
48 // first is_dirty check in the write barrier, skipping the remainder
49 // of the write barrier.
50 //
51 // This can significantly reduce the overhead of the write barrier
52 // code, increasing throughput.
53
54 class G1HotCardCache: public CHeapObj<mtGC> {
55 public:
56 typedef CardTable::CardValue CardValue;
57
58 private:
59 G1CollectedHeap* _g1h;
60
61 bool _use_cache;
62
63 G1CardCounts _card_counts;
64
65
66 // The card cache table
67 CardValue** _hot_cache;
68
69 size_t _hot_cache_size;
70
71 size_t _hot_cache_par_chunk_size;
72
73 // Avoids false sharing when concurrently updating _hot_cache_idx or
74 // _hot_cache_par_claimed_idx. These are never updated at the same time
75 // thus it's not necessary to separate them as well
76 char _pad_before[DEFAULT_CACHE_LINE_SIZE];
77
78 volatile size_t _hot_cache_idx;
79
80 volatile size_t _hot_cache_par_claimed_idx;
81
82 char _pad_after[DEFAULT_CACHE_LINE_SIZE];
83
84 // Records whether insertion overflowed the hot card cache at least once. This
85 // avoids the need for a separate atomic counter of how many valid entries are
86 // in the HCC.
87 volatile bool _cache_wrapped_around;
88
89 // The number of cached cards a thread claims when flushing the cache
90 static const int ClaimChunkSize = 32;
91
92 public:
93 static bool default_use_cache() {
94 return (G1ConcRSLogCacheSize > 0);
95 }
96
97 G1HotCardCache(G1CollectedHeap* g1h);
98 ~G1HotCardCache();
99
100 void initialize(G1RegionToSpaceMapper* card_counts_storage);
101
102 bool use_cache() { return _use_cache; }
103
104 void set_use_cache(bool b) {
105 _use_cache = (b ? default_use_cache() : false);
106 }
107
108 // Returns the card to be refined or NULL.
109 //
110 // Increments the count for given the card. if the card is not 'hot',
111 // it is returned for immediate refining. Otherwise the card is
112 // added to the hot card cache.
113 // If there is enough room in the hot card cache for the card we're
114 // adding, NULL is returned and no further action in needed.
115 // If we evict a card from the cache to make room for the new card,
116 // the evicted card is then returned for refinement.
117 CardValue* insert(CardValue* card_ptr);
118
119 // Refine the cards that have delayed as a result of
120 // being in the cache.
121 void drain(G1CardTableEntryClosure* cl, uint worker_id);
122
123 // Set up for parallel processing of the cards in the hot cache
124 void reset_hot_cache_claimed_index() {
125 _hot_cache_par_claimed_idx = 0;
126 }
127
128 // Resets the hot card cache and discards the entries.
129 void reset_hot_cache() {
130 assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
131 assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");
132 if (default_use_cache()) {
133 reset_hot_cache_internal();
134 }
135 }
136
137 // Zeros the values in the card counts table for the given region
138 void reset_card_counts(HeapRegion* hr);
139
140 // Number of entries in the HCC.
141 size_t num_entries() const {
142 return _cache_wrapped_around ? _hot_cache_size : _hot_cache_idx + 1;
143 }
144 private:
145 void reset_hot_cache_internal() {
146 assert(_hot_cache != NULL, "Logic");
147 _hot_cache_idx = 0;
148 for (size_t i = 0; i < _hot_cache_size; i++) {
149 _hot_cache[i] = NULL;
150 }
151 _cache_wrapped_around = false;
152 }
153 };
154
155 #endif // SHARE_GC_G1_G1HOTCARDCACHE_HPP