1 /*
2 * Copyright (c) 2021, Amazon.com, Inc. 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.
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 *
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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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_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP
26 #define SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP
27
28
29 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
30
31 class ShenandoahCollectionSet;
32 class ShenandoahHeapRegion;
33 class ShenandoahOldGeneration;
34
35 class ShenandoahOldHeuristics : public ShenandoahHeuristics {
36
37 private:
38
39 static uint NOT_FOUND;
40
41 // After final marking of the old generation, this heuristic will select
42 // a set of candidate regions to be included in subsequent mixed collections.
43 // The regions are sorted into a `_region_data` array (declared in base
44 // class) in decreasing order of garbage. The heuristic will give priority
45 // to regions containing more garbage.
46
47 // The following members are used to keep track of which candidate regions
48 // have yet to be added to a mixed collection. There is also some special
49 // handling for pinned regions, described further below.
50
51 // Pinned regions may not be included in the collection set. Any old regions
52 // which were pinned at the time when old regions were added to the mixed
53 // collection will have been skipped. These regions are still contain garbage,
54 // so we want to include them at the start of the list of candidates for the
55 // _next_ mixed collection cycle. This variable is the index of the _first_
56 // old region which is pinned when the mixed collection set is formed.
57 uint _first_pinned_candidate;
58
59 // This is the index of the last region which is above the garbage threshold.
60 // No regions after this will be considered for inclusion in a mixed collection
61 // set.
62 uint _last_old_collection_candidate;
63
64 // This index points to the first candidate in line to be added to the mixed
65 // collection set. It is updated as regions are added to the collection set.
66 uint _next_old_collection_candidate;
67
68 // This is the last index in the array of old regions which were active at
69 // the end of old final mark.
70 uint _last_old_region;
71
72 // This can be the 'static' or 'adaptive' heuristic.
73 ShenandoahHeuristics* _trigger_heuristic;
74
75 // Flag is set when promotion failure is detected (by gc thread), and cleared when
76 // old generation collection begins (by control thread).
77 volatile bool _promotion_failed;
78
79 // Keep a pointer to our generation that we can use without down casting a protected member from the base class.
80 ShenandoahOldGeneration* _old_generation;
81
82 protected:
83 virtual void choose_collection_set_from_regiondata(ShenandoahCollectionSet* set, RegionData* data, size_t data_size,
84 size_t free) override;
85
86 public:
87 ShenandoahOldHeuristics(ShenandoahOldGeneration* generation, ShenandoahHeuristics* trigger_heuristic);
88
89 virtual void choose_collection_set(ShenandoahCollectionSet* collection_set, ShenandoahOldHeuristics* old_heuristics) override;
90
91 // Prepare for evacuation of old-gen regions by capturing the mark results of a recently completed concurrent mark pass.
92 void prepare_for_old_collections();
93
94 // Return true iff the collection set is primed with at least one old-gen region.
95 bool prime_collection_set(ShenandoahCollectionSet* set);
96
97 // How many old-collection candidates have not yet been processed?
98 uint unprocessed_old_collection_candidates();
99
100 // How many old or hidden collection candidates have not yet been processed?
101 uint last_old_collection_candidate_index();
102
103 // Return the next old-collection candidate in order of decreasing amounts of garbage. (We process most-garbage regions
104 // first.) This does not consume the candidate. If the candidate is selected for inclusion in a collection set, then
105 // the candidate is consumed by invoking consume_old_collection_candidate().
106 ShenandoahHeapRegion* next_old_collection_candidate();
107
108 // Adjust internal state to reflect that one fewer old-collection candidate remains to be processed.
109 void consume_old_collection_candidate();
110
111 // How many old-collection regions were identified at the end of the most recent old-gen mark to require their
112 // unmarked objects to be coalesced and filled?
113 uint last_old_region_index() const;
114
115 // Fill in buffer with all of the old-collection regions that were identified at the end of the most recent old-gen
116 // mark to require their unmarked objects to be coalesced and filled. The buffer array must have at least
117 // last_old_region_index() entries, or memory may be corrupted when this function overwrites the
118 // end of the array.
119 unsigned int get_coalesce_and_fill_candidates(ShenandoahHeapRegion** buffer);
120
121 // If a GLOBAL gc occurs, it will collect the entire heap which invalidates any collection candidates being
122 // held by this heuristic for supplying mixed collections.
123 void abandon_collection_candidates();
124
125 // Notify the heuristic of promotion failures. The promotion attempt will be skipped and the object will
126 // be evacuated into the young generation. The collection should complete normally, but we want to schedule
127 // an old collection as soon as possible.
128 void handle_promotion_failure();
129
130 virtual void record_cycle_start() override;
131
132 virtual void record_cycle_end() override;
133
134 virtual bool should_start_gc() override;
135
136 virtual bool should_degenerate_cycle() override;
137
138 virtual void record_success_concurrent(bool abbreviated) override;
139
140 virtual void record_success_degenerated() override;
141
142 virtual void record_success_full() override;
143
144 virtual void record_allocation_failure_gc() override;
145
146 virtual void record_requested_gc() override;
147
148 virtual void reset_gc_learning() override;
149
150 virtual bool can_unload_classes() override;
151
152 virtual bool can_unload_classes_normal() override;
153
154 virtual bool should_unload_classes() override;
155
156 virtual const char* name() override;
157
158 virtual bool is_diagnostic() override;
159
160 virtual bool is_experimental() override;
161
162 private:
163 void slide_pinned_regions_to_front();
164 };
165
166 #endif // SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP