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.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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).
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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
34class G1CardTableEntryClosure;
35class G1CollectedHeap;
36class 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
54class G1HotCardCache: public CHeapObj<mtGC> {
55public:
56 typedef CardTable::CardValue CardValue;
57
58private:
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 // The number of cached cards a thread claims when flushing the cache
85 static const int ClaimChunkSize = 32;
86
87 public:
88 static bool default_use_cache() {
89 return (G1ConcRSLogCacheSize > 0);
90 }
91
92 G1HotCardCache(G1CollectedHeap* g1h);
93 ~G1HotCardCache();
94
95 void initialize(G1RegionToSpaceMapper* card_counts_storage);
96
97 bool use_cache() { return _use_cache; }
98
99 void set_use_cache(bool b) {
100 _use_cache = (b ? default_use_cache() : false);
101 }
102
103 // Returns the card to be refined or NULL.
104 //
105 // Increments the count for given the card. if the card is not 'hot',
106 // it is returned for immediate refining. Otherwise the card is
107 // added to the hot card cache.
108 // If there is enough room in the hot card cache for the card we're
109 // adding, NULL is returned and no further action in needed.
110 // If we evict a card from the cache to make room for the new card,
111 // the evicted card is then returned for refinement.
112 CardValue* insert(CardValue* card_ptr);
113
114 // Refine the cards that have delayed as a result of
115 // being in the cache.
116 void drain(G1CardTableEntryClosure* cl, uint worker_i);
117
118 // Set up for parallel processing of the cards in the hot cache
119 void reset_hot_cache_claimed_index() {
120 _hot_cache_par_claimed_idx = 0;
121 }
122
123 // Resets the hot card cache and discards the entries.
124 void reset_hot_cache() {
125 assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
126 assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");
127 if (default_use_cache()) {
128 reset_hot_cache_internal();
129 }
130 }
131
132 // Zeros the values in the card counts table for the given region
133 void reset_card_counts(HeapRegion* hr);
134
135 private:
136 void reset_hot_cache_internal() {
137 assert(_hot_cache != NULL, "Logic");
138 _hot_cache_idx = 0;
139 for (size_t i = 0; i < _hot_cache_size; i++) {
140 _hot_cache[i] = NULL;
141 }
142 }
143};
144
145#endif // SHARE_GC_G1_G1HOTCARDCACHE_HPP
146