1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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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 /*
36 * This heuristic is responsible for choosing a set of candidates for inclusion
37 * in mixed collections. These candidates are chosen when marking of the old
38 * generation is complete. Note that this list of candidates may live through
39 * several mixed collections.
40 *
41 * This heuristic is also responsible for triggering old collections. It has its
42 * own collection of triggers to decide whether to start an old collection. It does
43 * _not_ use any of the functionality from the adaptive heuristics for triggers.
44 * It also does not use any of the functionality from the heuristics base classes
45 * to choose the collection set. For these reasons, it does not extend from
46 * ShenandoahGenerationalHeuristics.
47 */
48 class ShenandoahOldHeuristics : public ShenandoahHeuristics {
49
50 private:
51
52 static uint NOT_FOUND;
53
54 // After final marking of the old generation, this heuristic will select
55 // a set of candidate regions to be included in subsequent mixed collections.
56 // The regions are sorted into a `_region_data` array (declared in base
57 // class) in decreasing order of garbage. The heuristic will give priority
58 // to regions containing more garbage.
59
60 // The following members are used to keep track of which candidate regions
61 // have yet to be added to a mixed collection. There is also some special
62 // handling for pinned regions, described further below.
63
64 // Pinned regions may not be included in the collection set. Any old regions
65 // which were pinned at the time when old regions were added to the mixed
66 // collection will have been skipped. These regions are still contain garbage,
67 // so we want to include them at the start of the list of candidates for the
68 // _next_ mixed collection cycle. This variable is the index of the _first_
69 // old region which is pinned when the mixed collection set is formed.
70 uint _first_pinned_candidate;
71
72 // This is the index of the last region which is above the garbage threshold.
73 // No regions after this will be considered for inclusion in a mixed collection
74 // set.
75 uint _last_old_collection_candidate;
76
77 // This index points to the first candidate in line to be added to the mixed
78 // collection set. It is updated as regions are added to the collection set.
79 uint _next_old_collection_candidate;
80
81 // This is the last index in the array of old regions which were active at
82 // the end of old final mark.
83 uint _last_old_region;
84
85 // How much live data must be evacuated from within the unprocessed mixed evacuation candidates?
86 size_t _live_bytes_in_unprocessed_candidates;
87
88 // Keep a pointer to our generation that we can use without down casting a protected member from the base class.
89 ShenandoahOldGeneration* _old_generation;
90
91 // Flags are set when promotion failure is detected (by gc thread), and cleared when
92 // old generation collection begins (by control thread). Flags are set and cleared at safepoints.
93 bool _cannot_expand_trigger;
94 bool _fragmentation_trigger;
95 bool _growth_trigger;
96
97 // Motivation for a fragmentation_trigger
98 double _fragmentation_density;
99 size_t _fragmentation_first_old_region;
100 size_t _fragmentation_last_old_region;
101
102 // Compare by live is used to prioritize compaction of old-gen regions. With old-gen compaction, the goal is
103 // to tightly pack long-lived objects into available regions. In most cases, there has not been an accumulation
104 // of garbage within old-gen regions. The more likely opportunity will be to combine multiple sparsely populated
105 // old-gen regions which may have been promoted in place into a smaller number of densely packed old-gen regions.
106 // This improves subsequent allocation efficiency and reduces the likelihood of allocation failure (including
107 // humongous allocation failure) due to fragmentation of the available old-gen allocation pool
108 static int compare_by_live(RegionData a, RegionData b);
109
110 static int compare_by_index(RegionData a, RegionData b);
111
112 protected:
113 void choose_collection_set_from_regiondata(ShenandoahCollectionSet* set, RegionData* data, size_t data_size, size_t free) override;
114
115 public:
116 explicit ShenandoahOldHeuristics(ShenandoahOldGeneration* generation);
117
118 // Prepare for evacuation of old-gen regions by capturing the mark results of a recently completed concurrent mark pass.
119 void prepare_for_old_collections();
120
121 // Return true iff the collection set is primed with at least one old-gen region.
122 bool prime_collection_set(ShenandoahCollectionSet* set);
123
124 // How many old-collection candidates have not yet been processed?
125 uint unprocessed_old_collection_candidates() const;
126
127 // How much live memory must be evacuated from within old-collection candidates that have not yet been processed?
128 size_t unprocessed_old_collection_candidates_live_memory() const;
129
130 void set_unprocessed_old_collection_candidates_live_memory(size_t initial_live);
131
132 void decrease_unprocessed_old_collection_candidates_live_memory(size_t evacuated_live);
133
134 // How many old or hidden collection candidates have not yet been processed?
135 uint last_old_collection_candidate_index() const;
136
137 // Return the next old-collection candidate in order of decreasing amounts of garbage. (We process most-garbage regions
138 // first.) This does not consume the candidate. If the candidate is selected for inclusion in a collection set, then
139 // the candidate is consumed by invoking consume_old_collection_candidate().
140 ShenandoahHeapRegion* next_old_collection_candidate();
141
142 // Adjust internal state to reflect that one fewer old-collection candidate remains to be processed.
143 void consume_old_collection_candidate();
144
145 // Fill in buffer with all the old-collection regions that were identified at the end of the most recent old-gen
146 // mark to require their unmarked objects to be coalesced and filled. The buffer array must have at least
147 // last_old_region_index() entries, or memory may be corrupted when this function overwrites the
148 // end of the array.
149 unsigned int get_coalesce_and_fill_candidates(ShenandoahHeapRegion** buffer);
150
151 // True if there are old regions that need to be filled.
152 bool has_coalesce_and_fill_candidates() const { return coalesce_and_fill_candidates_count() > 0; }
153
154 // Return the number of old regions that need to be filled.
155 size_t coalesce_and_fill_candidates_count() const { return _last_old_region - _next_old_collection_candidate; }
156
157 // If a GLOBAL gc occurs, it will collect the entire heap which invalidates any collection candidates being
158 // held by this heuristic for supplying mixed collections.
159 void abandon_collection_candidates();
160
161 void trigger_cannot_expand() { _cannot_expand_trigger = true; };
162
163 inline void trigger_old_is_fragmented(double density, size_t first_old_index, size_t last_old_index) {
164 _fragmentation_trigger = true;
165 _fragmentation_density = density;
166 _fragmentation_first_old_region = first_old_index;
167 _fragmentation_last_old_region = last_old_index;
168 }
169 void trigger_old_has_grown() { _growth_trigger = true; }
170
171 inline void get_fragmentation_trigger_reason_for_log_message(double &density, size_t &first_index, size_t &last_index) {
172 density = _fragmentation_density;
173 first_index = _fragmentation_first_old_region;
174 last_index = _fragmentation_last_old_region;
175 }
176
177 void clear_triggers();
178
179 void record_cycle_end() override;
180
181 bool should_start_gc() override;
182
183 void record_success_concurrent(bool abbreviated) override;
184
185 void record_success_degenerated() override;
186
187 void record_success_full() override;
188
189 const char* name() override;
190
191 bool is_diagnostic() override;
192
193 bool is_experimental() override;
194
195 private:
196 void slide_pinned_regions_to_front();
197 bool all_candidates_are_pinned();
198 };
199
200 #endif // SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP