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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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/shenandoahAllocRequest.hpp"
30 #include "gc/shenandoah/shenandoahGeneration.hpp"
31 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
32 #include "gc/shenandoah/shenandoahScanRemembered.hpp"
33 #include "gc/shenandoah/shenandoahSharedVariables.hpp"
34
35 class ShenandoahHeapRegion;
36 class ShenandoahHeapRegionClosure;
37 class ShenandoahOldHeuristics;
38
39 class ShenandoahOldGeneration : public ShenandoahGeneration {
40 private:
41 ShenandoahHeapRegion** _coalesce_and_fill_region_array;
42 ShenandoahOldHeuristics* _old_heuristics;
43
44 // After determining the desired size of the old generation (see compute_old_generation_balance), this
45 // quantity represents the number of regions above (surplus) or below (deficit) that size.
46 // This value is computed prior to the actual exchange of any regions. A positive value represents
47 // a surplus of old regions which will be transferred from old _to_ young. A negative value represents
48 // a deficit of regions that will be replenished by a transfer _from_ young to old.
49 ssize_t _region_balance;
50
51 // Set when evacuation in the old generation fails. When this is set, the control thread will initiate a
52 // full GC instead of a futile degenerated cycle.
53 ShenandoahSharedFlag _failed_evacuation;
54
55 // Bytes reserved within old-gen to hold the results of promotion. This is separate from
56 // and in addition to the evacuation reserve for intra-generation evacuations (ShenandoahGeneration::_evacuation_reserve).
57 size_t _promoted_reserve;
58
59 // Bytes of old-gen memory expended on promotions. This may be modified concurrently
60 // by mutators and gc workers when promotion LABs are retired during evacuation. It
61 // is therefore always accessed through atomic operations. This is increased when a
62 // PLAB is allocated for promotions. The value is decreased by the amount of memory
63 // remaining in a PLAB when it is retired.
64 size_t _promoted_expended;
65
66 // Represents the quantity of live bytes we expect to promote in place during the next
67 // evacuation cycle. This value is used by the young heuristic to trigger mixed collections.
68 // It is also used when computing the optimum size for the old generation.
69 size_t _promotion_potential;
70
71 // When a region is selected to be promoted in place, the remaining free memory is filled
72 // in to prevent additional allocations (preventing premature promotion of newly allocated
73 // objects. This field records the total amount of padding used for such regions.
74 size_t _pad_for_promote_in_place;
75
76 // During construction of the collection set, we keep track of regions that are eligible
77 // for promotion in place. These fields track the count of those humongous and regular regions.
78 // This data is used to force the evacuation phase even when the collection set is otherwise
79 // empty.
80 size_t _promotable_humongous_regions;
81 size_t _promotable_regular_regions;
82
83 // True if old regions may be safely traversed by the remembered set scan.
84 bool _is_parseable;
85
86 bool coalesce_and_fill();
87
88 public:
89 ShenandoahOldGeneration(uint max_queues, size_t max_capacity, size_t soft_max_capacity);
90
91 virtual ShenandoahHeuristics* initialize_heuristics(ShenandoahMode* gc_mode) override;
92
93 const char* name() const override {
94 return "OLD";
95 }
96
97 ShenandoahOldHeuristics* heuristics() const override {
98 return _old_heuristics;
99 }
100
101 // See description in field declaration
102 void set_promoted_reserve(size_t new_val);
103 size_t get_promoted_reserve() const;
104
105 // The promotion reserve is increased when rebuilding the free set transfers a region to the old generation
106 void augment_promoted_reserve(size_t increment);
107
108 // This zeros out the expended promotion count after the promotion reserve is computed
109 void reset_promoted_expended();
110
111 // This is incremented when allocations are made to copy promotions into the old generation
112 size_t expend_promoted(size_t increment);
113
114 // This is used to return unused memory from a retired promotion LAB
115 size_t unexpend_promoted(size_t decrement);
116
117 // This is used on the allocation path to gate promotions that would exceed the reserve
118 size_t get_promoted_expended() const;
119
120 // Test if there is enough memory reserved for this promotion
121 bool can_promote(size_t requested_bytes) const {
122 size_t promotion_avail = get_promoted_reserve();
123 size_t promotion_expended = get_promoted_expended();
124 return promotion_expended + requested_bytes <= promotion_avail;
125 }
126
127 // Test if there is enough memory available in the old generation to accommodate this request.
128 // The request will be subject to constraints on promotion and evacuation reserves.
129 bool can_allocate(const ShenandoahAllocRequest& req) const;
130
131 // Updates the promotion expenditure tracking and configures whether the plab may be used
132 // for promotions and evacuations, or just evacuations.
133 void configure_plab_for_current_thread(const ShenandoahAllocRequest &req);
134
135 // See description in field declaration
136 void set_region_balance(ssize_t balance) { _region_balance = balance; }
137 ssize_t get_region_balance() const { return _region_balance; }
138 // See description in field declaration
139 void set_promotion_potential(size_t val) { _promotion_potential = val; };
140 size_t get_promotion_potential() const { return _promotion_potential; };
141
142 // See description in field declaration
143 void set_pad_for_promote_in_place(size_t pad) { _pad_for_promote_in_place = pad; }
144 size_t get_pad_for_promote_in_place() const { return _pad_for_promote_in_place; }
145
146 // See description in field declaration
147 void set_expected_humongous_region_promotions(size_t region_count) { _promotable_humongous_regions = region_count; }
148 void set_expected_regular_region_promotions(size_t region_count) { _promotable_regular_regions = region_count; }
149 bool has_in_place_promotions() const { return (_promotable_humongous_regions + _promotable_regular_regions) > 0; }
150
151 // Class unloading may render the card table offsets unusable, if they refer to unmarked objects
152 bool is_parseable() const { return _is_parseable; }
153 void set_parseable(bool parseable);
154
155 // This will signal the heuristic to trigger an old generation collection
156 void handle_failed_transfer();
157
158 // This will signal the control thread to run a full GC instead of a futile degenerated gc
159 void handle_failed_evacuation();
160
161 // This logs that an evacuation to the old generation has failed
162 void handle_failed_promotion(Thread* thread, size_t size);
163
164 // A successful evacuation re-dirties the cards and registers the object with the remembered set
165 void handle_evacuation(HeapWord* obj, size_t words, bool promotion);
166
167 // Clear the flag after it is consumed by the control thread
168 bool clear_failed_evacuation() {
169 return _failed_evacuation.try_unset();
170 }
171
172 // Transition to the next state after mixed evacuations have completed
173 void complete_mixed_evacuations();
174
175 // Abandon any future mixed collections. This is invoked when all old regions eligible for
176 // inclusion in a mixed evacuation are pinned. This should be rare.
177 void abandon_mixed_evacuations();
178
179 private:
180 RememberedScanner* _card_scan;
181
182 public:
183 RememberedScanner* card_scan() { return _card_scan; }
184
185 // Clear cards for given region
186 void clear_cards_for(ShenandoahHeapRegion* region);
187
188 // Mark card for this location as dirty
189 void mark_card_as_dirty(void* location);
190
191 void parallel_heap_region_iterate(ShenandoahHeapRegionClosure* cl) override;
192
193 void parallel_region_iterate_free(ShenandoahHeapRegionClosure* cl) override;
194
195 void heap_region_iterate(ShenandoahHeapRegionClosure* cl) override;
196
197 bool contains(ShenandoahHeapRegion* region) const override;
198 bool contains(oop obj) const override;
199
200 void set_concurrent_mark_in_progress(bool in_progress) override;
201 bool is_concurrent_mark_in_progress() override;
202
203 bool entry_coalesce_and_fill();
204 void prepare_for_mixed_collections_after_global_gc();
205 void prepare_gc() override;
206 void prepare_regions_and_collection_set(bool concurrent) override;
207 void record_success_concurrent(bool abbreviated) override;
208 void cancel_marking() override;
209
210 // Cancels old gc and transitions to the idle state
211 void cancel_gc();
212
213 // We leave the SATB barrier on for the entirety of the old generation
214 // marking phase. In some cases, this can cause a write to a perfectly
215 // reachable oop to enqueue a pointer that later becomes garbage (because
216 // it points at an object that is later chosen for the collection set). There are
217 // also cases where the referent of a weak reference ends up in the SATB
218 // and is later collected. In these cases the oop in the SATB buffer becomes
219 // invalid and the _next_ cycle will crash during its marking phase. To
220 // avoid this problem, we "purge" the SATB buffers during the final update
221 // references phase if (and only if) an old generation mark is in progress.
222 // At this stage we can safely determine if any of the oops in the SATB
223 // buffer belong to trashed regions (before they are recycled). As it
224 // happens, flushing a SATB queue also filters out oops which have already
225 // been marked - which is the case for anything that is being evacuated
226 // from the collection set.
227 //
228 // Alternatively, we could inspect the state of the heap and the age of the
229 // object at the barrier, but we reject this approach because it is likely
230 // the performance impact would be too severe.
231 void transfer_pointers_from_satb();
232
233 // True if there are old regions waiting to be selected for a mixed collection
234 bool has_unprocessed_collection_candidates();
235
236 bool is_doing_mixed_evacuations() const {
237 return state() == EVACUATING || state() == EVACUATING_AFTER_GLOBAL;
238 }
239
240 bool is_preparing_for_mark() const {
241 return state() == FILLING;
242 }
243
244 bool is_idle() const {
245 return state() == WAITING_FOR_BOOTSTRAP;
246 }
247
248 bool is_bootstrapping() const {
249 return state() == BOOTSTRAPPING;
250 }
251
252 // Amount of live memory (bytes) in regions waiting for mixed collections
253 size_t unprocessed_collection_candidates_live_memory();
254
255 // Abandon any regions waiting for mixed collections
256 void abandon_collection_candidates();
257
258 public:
259 enum State {
260 FILLING, WAITING_FOR_BOOTSTRAP, BOOTSTRAPPING, MARKING, EVACUATING, EVACUATING_AFTER_GLOBAL
261 };
262
263 #ifdef ASSERT
264 bool validate_waiting_for_bootstrap();
265 #endif
266
267 private:
268 State _state;
269
270 static const size_t FRACTIONAL_DENOMINATOR = 65536;
271
272 // During initialization of the JVM, we search for the correct old-gen size by initially performing old-gen
273 // collection when old-gen usage is 50% more (INITIAL_GROWTH_BEFORE_COMPACTION) than the initial old-gen size
274 // estimate (3.125% of heap). The next old-gen trigger occurs when old-gen grows 25% larger than its live
275 // memory at the end of the first old-gen collection. Then we trigger again when old-gen grows 12.5%
276 // more than its live memory at the end of the previous old-gen collection. Thereafter, we trigger each time
277 // old-gen grows more than 12.5% following the end of its previous old-gen collection.
278 static const size_t INITIAL_GROWTH_BEFORE_COMPACTION = FRACTIONAL_DENOMINATOR / 2; // 50.0%
279
280 // INITIAL_LIVE_FRACTION represents the initial guess of how large old-gen should be. We estimate that old-gen
281 // needs to consume 6.25% of the total heap size. And we "pretend" that we start out with this amount of live
282 // old-gen memory. The first old-collection trigger will occur when old-gen occupies 50% more than this initial
283 // approximation of the old-gen memory requirement, in other words when old-gen usage is 150% of 6.25%, which
284 // is 9.375% of the total heap size.
285 static const uint16_t INITIAL_LIVE_FRACTION = FRACTIONAL_DENOMINATOR / 16; // 6.25%
286
287 size_t _live_bytes_after_last_mark;
288
289 // How much growth in usage before we trigger old collection, per FRACTIONAL_DENOMINATOR (65_536)
290 size_t _growth_before_compaction;
291 const size_t _min_growth_before_compaction; // Default is 12.5%
292
293 void validate_transition(State new_state) NOT_DEBUG_RETURN;
294
295 public:
296 State state() const {
297 return _state;
298 }
299
300 const char* state_name() const {
301 return state_name(_state);
302 }
303
304 void transition_to(State new_state);
305
306 size_t get_live_bytes_after_last_mark() const;
307 void set_live_bytes_after_last_mark(size_t new_live);
308
309 size_t usage_trigger_threshold() const;
310
311 bool can_start_gc() {
312 return _state == WAITING_FOR_BOOTSTRAP;
313 }
314
315 static const char* state_name(State state);
316
317 };
318
319
320 #endif //SHARE_VM_GC_SHENANDOAH_SHENANDOAHOLDGENERATION_HPP