1 /*
2 * Copyright Amazon.com Inc. 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
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18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 */
24
25 #ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHOLDGENERATION_HPP
26 #define SHARE_VM_GC_SHENANDOAH_SHENANDOAHOLDGENERATION_HPP
27
28 #include "gc/shenandoah/heuristics/shenandoahOldHeuristics.hpp"
29 #include "gc/shenandoah/shenandoahGeneration.hpp"
30 #include "gc/shenandoah/shenandoahSharedVariables.hpp"
31
32 class ShenandoahHeapRegion;
33 class ShenandoahHeapRegionClosure;
34
35 class ShenandoahOldGeneration : public ShenandoahGeneration {
36 private:
37 ShenandoahHeapRegion** _coalesce_and_fill_region_array;
38 ShenandoahOldHeuristics* _old_heuristics;
39
40 // After determining the desired size of the old generation (see compute_old_generation_balance), this
41 // quantity represents the number of regions above (surplus) or below (deficit) that size.
42 // This value is computed prior to the actual exchange of any regions. A positive value represents
43 // a surplus of old regions which will be transferred from old _to_ young. A negative value represents
44 // a deficit of regions that will be replenished by a transfer _from_ young to old.
45 ssize_t _region_balance;
46
47 // Set when evacuation in the old generation fails. When this is set, the control thread will initiate a
48 // full GC instead of a futile degenerated cycle.
49 ShenandoahSharedFlag _failed_evacuation;
50
51 // Bytes reserved within old-gen to hold the results of promotion. This is separate from
52 // and in addition to the evacuation reserve for intra-generation evacuations (ShenandoahGeneration::_evacuation_reserve).
53 size_t _promoted_reserve;
54
55 // Bytes of old-gen memory expended on promotions. This may be modified concurrently
56 // by mutators and gc workers when promotion LABs are retired during evacuation. It
57 // is therefore always accessed through atomic operations. This is increased when a
58 // PLAB is allocated for promotions. The value is decreased by the amount of memory
59 // remaining in a PLAB when it is retired.
60 size_t _promoted_expended;
61
62 // Represents the quantity of live bytes we expect to promote in place during the next
63 // evacuation cycle. This value is used by the young heuristic to trigger mixed collections.
64 // It is also used when computing the optimum size for the old generation.
65 size_t _promotion_potential;
66
67 // When a region is selected to be promoted in place, the remaining free memory is filled
68 // in to prevent additional allocations (preventing premature promotion of newly allocated
69 // objects. This field records the total amount of padding used for such regions.
70 size_t _pad_for_promote_in_place;
71
72 // During construction of the collection set, we keep track of regions that are eligible
73 // for promotion in place. These fields track the count of those humongous and regular regions.
74 // This data is used to force the evacuation phase even when the collection set is otherwise
75 // empty.
76 size_t _promotable_humongous_regions;
77 size_t _promotable_regular_regions;
78
79 // True if old regions may be safely traversed by the remembered set scan.
80 bool _is_parseable;
81
82 bool coalesce_and_fill();
83
84 public:
85 ShenandoahOldGeneration(uint max_queues, size_t max_capacity, size_t soft_max_capacity);
86
87 virtual ShenandoahHeuristics* initialize_heuristics(ShenandoahMode* gc_mode) override;
88
89 const char* name() const override {
90 return "OLD";
91 }
92
93 ShenandoahOldHeuristics* heuristics() const override {
94 return _old_heuristics;
95 }
96
97 // See description in field declaration
98 void set_promoted_reserve(size_t new_val);
99 size_t get_promoted_reserve() const;
100
101 // The promotion reserve is increased when rebuilding the free set transfers a region to the old generation
102 void augment_promoted_reserve(size_t increment);
103
104 // This zeros out the expended promotion count after the promotion reserve is computed
105 void reset_promoted_expended();
106
107 // This is incremented when allocations are made to copy promotions into the old generation
108 size_t expend_promoted(size_t increment);
109
110 // This is used to return unused memory from a retired promotion LAB
111 size_t unexpend_promoted(size_t decrement);
112
113 // This is used on the allocation path to gate promotions that would exceed the reserve
114 size_t get_promoted_expended();
115
116 // See description in field declaration
117 void set_region_balance(ssize_t balance) { _region_balance = balance; }
118 ssize_t get_region_balance() const { return _region_balance; }
119 // See description in field declaration
120 void set_promotion_potential(size_t val) { _promotion_potential = val; };
121 size_t get_promotion_potential() const { return _promotion_potential; };
122
123 // See description in field declaration
124 void set_pad_for_promote_in_place(size_t pad) { _pad_for_promote_in_place = pad; }
125 size_t get_pad_for_promote_in_place() const { return _pad_for_promote_in_place; }
126
127 // See description in field declaration
128 void set_expected_humongous_region_promotions(size_t region_count) { _promotable_humongous_regions = region_count; }
129 void set_expected_regular_region_promotions(size_t region_count) { _promotable_regular_regions = region_count; }
130 bool has_in_place_promotions() const { return (_promotable_humongous_regions + _promotable_regular_regions) > 0; }
131
132 // Class unloading may render the card table offsets unusable, if they refer to unmarked objects
133 bool is_parseable() const { return _is_parseable; }
134 void set_parseable(bool parseable);
135
136 // This will signal the heuristic to trigger an old generation collection
137 void handle_failed_transfer();
138
139 // This will signal the control thread to run a full GC instead of a futile degenerated gc
140 void handle_failed_evacuation();
141
142 // This logs that an evacuation to the old generation has failed
143 void handle_failed_promotion(Thread* thread, size_t size);
144
145 // A successful evacuation re-dirties the cards and registers the object with the remembered set
146 void handle_evacuation(HeapWord* obj, size_t words, bool promotion);
147
148 // Clear the flag after it is consumed by the control thread
149 bool clear_failed_evacuation() {
150 return _failed_evacuation.try_unset();
151 }
152
153 // Transition to the next state after mixed evacuations have completed
154 void complete_mixed_evacuations();
155
156 // Abandon any future mixed collections. This is invoked when all old regions eligible for
157 // inclusion in a mixed evacuation are pinned. This should be rare.
158 void abandon_mixed_evacuations();
159
160 void parallel_heap_region_iterate(ShenandoahHeapRegionClosure* cl) override;
161
162 void parallel_region_iterate_free(ShenandoahHeapRegionClosure* cl) override;
163
164 void heap_region_iterate(ShenandoahHeapRegionClosure* cl) override;
165
166 bool contains(ShenandoahHeapRegion* region) const override;
167 bool contains(oop obj) const override;
168
169 void set_concurrent_mark_in_progress(bool in_progress) override;
170 bool is_concurrent_mark_in_progress() override;
171
172 bool entry_coalesce_and_fill();
173 void prepare_for_mixed_collections_after_global_gc();
174 void prepare_gc() override;
175 void prepare_regions_and_collection_set(bool concurrent) override;
176 void record_success_concurrent(bool abbreviated) override;
177 void cancel_marking() override;
178
179 // We leave the SATB barrier on for the entirety of the old generation
180 // marking phase. In some cases, this can cause a write to a perfectly
181 // reachable oop to enqueue a pointer that later becomes garbage (because
182 // it points at an object that is later chosen for the collection set). There are
183 // also cases where the referent of a weak reference ends up in the SATB
184 // and is later collected. In these cases the oop in the SATB buffer becomes
185 // invalid and the _next_ cycle will crash during its marking phase. To
186 // avoid this problem, we "purge" the SATB buffers during the final update
187 // references phase if (and only if) an old generation mark is in progress.
188 // At this stage we can safely determine if any of the oops in the SATB
189 // buffer belong to trashed regions (before they are recycled). As it
190 // happens, flushing a SATB queue also filters out oops which have already
191 // been marked - which is the case for anything that is being evacuated
192 // from the collection set.
193 //
194 // Alternatively, we could inspect the state of the heap and the age of the
195 // object at the barrier, but we reject this approach because it is likely
196 // the performance impact would be too severe.
197 void transfer_pointers_from_satb();
198
199 // True if there are old regions waiting to be selected for a mixed collection
200 bool has_unprocessed_collection_candidates();
201
202 bool is_doing_mixed_evacuations() const {
203 return state() == EVACUATING || state() == EVACUATING_AFTER_GLOBAL;
204 }
205
206 bool is_preparing_for_mark() const {
207 return state() == FILLING;
208 }
209
210 bool is_idle() const {
211 return state() == WAITING_FOR_BOOTSTRAP;
212 }
213
214 bool is_bootstrapping() const {
215 return state() == BOOTSTRAPPING;
216 }
217
218 // Amount of live memory (bytes) in regions waiting for mixed collections
219 size_t unprocessed_collection_candidates_live_memory();
220
221 // Abandon any regions waiting for mixed collections
222 void abandon_collection_candidates();
223
224 void maybe_trigger_collection(size_t first_old_region, size_t last_old_region, size_t old_region_count);
225 public:
226 enum State {
227 FILLING, WAITING_FOR_BOOTSTRAP, BOOTSTRAPPING, MARKING, EVACUATING, EVACUATING_AFTER_GLOBAL
228 };
229
230 #ifdef ASSERT
231 bool validate_waiting_for_bootstrap();
232 #endif
233
234 private:
235 State _state;
236
237 static const size_t FRACTIONAL_DENOMINATOR = 64536;
238
239 // During initialization of the JVM, we search for the correct old-gen size by initially performing old-gen
240 // collection when old-gen usage is 50% more (INITIAL_GROWTH_BEFORE_COMPACTION) than the initial old-gen size
241 // estimate (3.125% of heap). The next old-gen trigger occurs when old-gen grows 25% larger than its live
242 // memory at the end of the first old-gen collection. Then we trigger again when old-gen grows 12.5%
243 // more than its live memory at the end of the previous old-gen collection. Thereafter, we trigger each time
244 // old-gen grows more than 12.5% following the end of its previous old-gen collection.
245 static const size_t INITIAL_GROWTH_BEFORE_COMPACTION = FRACTIONAL_DENOMINATOR / 2; // 50.0%
246
247 // INITIAL_LIVE_FRACTION represents the initial guess of how large old-gen should be. We estimate that old-gen
248 // needs to consume 6.25% of the total heap size. And we "pretend" that we start out with this amount of live
249 // old-gen memory. The first old-collection trigger will occur when old-gen occupies 50% more than this initial
250 // approximation of the old-gen memory requirement, in other words when old-gen usage is 150% of 6.25%, which
251 // is 9.375% of the total heap size.
252 static const uint16_t INITIAL_LIVE_FRACTION = FRACTIONAL_DENOMINATOR / 16; // 6.25%
253
254 size_t _live_bytes_after_last_mark;
255
256 // How much growth in usage before we trigger old collection, per FRACTIONAL_DENOMINATOR (65_536)
257 size_t _growth_before_compaction;
258 const size_t _min_growth_before_compaction; // Default is 12.5%
259
260 void validate_transition(State new_state) NOT_DEBUG_RETURN;
261
262 public:
263 State state() const {
264 return _state;
265 }
266
267 const char* state_name() const {
268 return state_name(_state);
269 }
270
271 void transition_to(State new_state);
272
273 size_t get_live_bytes_after_last_mark() const;
274 void set_live_bytes_after_last_mark(size_t new_live);
275
276 size_t usage_trigger_threshold() const;
277
278 bool can_start_gc() {
279 return _state == WAITING_FOR_BOOTSTRAP;
280 }
281
282 static const char* state_name(State state);
283 };
284
285
286 #endif //SHARE_VM_GC_SHENANDOAH_SHENANDOAHOLDGENERATION_HPP