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
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
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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 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
31
32 class ShenandoahCollectionSet;
33 class ShenandoahHeapRegion;
34 class ShenandoahOldGeneration;
35
36 /*
37 * This heuristic is responsible for choosing a set of candidates for inclusion
38 * in mixed collections. These candidates are chosen when marking of the old
39 * generation is complete. Note that this list of candidates may live through
40 * several mixed collections.
41 *
42 * This heuristic is also responsible for triggering old collections. It has its
43 * own collection of triggers to decide whether to start an old collection. It does
44 * _not_ use any of the functionality from the adaptive heuristics for triggers.
45 * It also does not use any of the functionality from the heuristics base classes
46 * to choose the collection set. For these reasons, it does not extend from
47 * ShenandoahGenerationalHeuristics.
48 */
49 class ShenandoahOldHeuristics : public ShenandoahHeuristics {
50
51 private:
52
53 static uint NOT_FOUND;
54
55 ShenandoahGenerationalHeap* _heap;
56 ShenandoahOldGeneration* _old_gen;
57
58 // After final marking of the old generation, this heuristic will select
59 // a set of candidate regions to be included in subsequent mixed collections.
60 // The regions are sorted into a `_region_data` array (declared in base
61 // class) in decreasing order of garbage. The heuristic will give priority
62 // to regions containing more garbage.
63
64 // The following members are used to keep track of which candidate regions
65 // have yet to be added to a mixed collection. There is also some special
66 // handling for pinned regions, described further below.
67
68 // Pinned regions may not be included in the collection set. Any old regions
69 // which were pinned at the time when old regions were added to the mixed
70 // collection will have been skipped. These regions are still contain garbage,
71 // so we want to include them at the start of the list of candidates for the
72 // _next_ mixed collection cycle. This variable is the index of the _first_
73 // old region which is pinned when the mixed collection set is formed.
74 uint _first_pinned_candidate;
75
76 // This is the index of the last region which is above the garbage threshold.
77 // No regions after this will be considered for inclusion in a mixed collection
78 // set.
79 uint _last_old_collection_candidate;
80
81 // This index points to the first candidate in line to be added to the mixed
82 // collection set. It is updated as regions are added to the collection set.
83 uint _next_old_collection_candidate;
84
85 // This is the last index in the array of old regions which were active at
86 // the end of old final mark.
87 uint _last_old_region;
88
89 // How much live data must be evacuated from within the unprocessed mixed evacuation candidates?
90 size_t _live_bytes_in_unprocessed_candidates;
91
92 // Keep a pointer to our generation that we can use without down casting a protected member from the base class.
93 ShenandoahOldGeneration* _old_generation;
94
95 // Flags are set when promotion failure is detected (by gc thread), and cleared when
96 // old generation collection begins (by control thread). Flags are set and cleared at safepoints.
97 bool _cannot_expand_trigger;
98 bool _fragmentation_trigger;
99 bool _growth_trigger;
100
101 // Motivation for a fragmentation_trigger
102 double _fragmentation_density;
103 size_t _fragmentation_first_old_region;
104 size_t _fragmentation_last_old_region;
105
106 // Compare by live is used to prioritize compaction of old-gen regions. With old-gen compaction, the goal is
107 // to tightly pack long-lived objects into available regions. In most cases, there has not been an accumulation
108 // of garbage within old-gen regions. The more likely opportunity will be to combine multiple sparsely populated
109 // old-gen regions which may have been promoted in place into a smaller number of densely packed old-gen regions.
110 // This improves subsequent allocation efficiency and reduces the likelihood of allocation failure (including
111 // humongous allocation failure) due to fragmentation of the available old-gen allocation pool
112 static int compare_by_live(RegionData a, RegionData b);
113
114 static int compare_by_index(RegionData a, RegionData b);
115
116 // Set the fragmentation trigger if old-gen memory has become fragmented.
117 void set_trigger_if_old_is_fragmented(size_t first_old_region, size_t last_old_region,
118 size_t old_region_count, size_t num_regions);
119
120 // Set the overgrowth trigger if old-gen memory has grown beyond a particular threshold.
121 void set_trigger_if_old_is_overgrown();
122
123 protected:
124 void choose_collection_set_from_regiondata(ShenandoahCollectionSet* set, RegionData* data, size_t data_size, size_t free) override;
125
126 public:
127 explicit ShenandoahOldHeuristics(ShenandoahOldGeneration* generation, ShenandoahGenerationalHeap* gen_heap);
128
129 // Prepare for evacuation of old-gen regions by capturing the mark results of a recently completed concurrent mark pass.
130 void prepare_for_old_collections();
131
132 // Return true iff the collection set is primed with at least one old-gen region.
133 bool prime_collection_set(ShenandoahCollectionSet* set);
134
135 // How many old-collection candidates have not yet been processed?
136 uint unprocessed_old_collection_candidates() const;
137
138 // How much live memory must be evacuated from within old-collection candidates that have not yet been processed?
139 size_t unprocessed_old_collection_candidates_live_memory() const;
140
141 void set_unprocessed_old_collection_candidates_live_memory(size_t initial_live);
142
143 void decrease_unprocessed_old_collection_candidates_live_memory(size_t evacuated_live);
144
145 // How many old or hidden collection candidates have not yet been processed?
146 uint last_old_collection_candidate_index() const;
147
148 // Return the next old-collection candidate in order of decreasing amounts of garbage. (We process most-garbage regions
149 // first.) This does not consume the candidate. If the candidate is selected for inclusion in a collection set, then
150 // the candidate is consumed by invoking consume_old_collection_candidate().
151 ShenandoahHeapRegion* next_old_collection_candidate();
152
153 // Adjust internal state to reflect that one fewer old-collection candidate remains to be processed.
154 void consume_old_collection_candidate();
155
156 // Fill in buffer with all the old-collection regions that were identified at the end of the most recent old-gen
157 // mark to require their unmarked objects to be coalesced and filled. The buffer array must have at least
158 // last_old_region_index() entries, or memory may be corrupted when this function overwrites the
159 // end of the array.
160 unsigned int get_coalesce_and_fill_candidates(ShenandoahHeapRegion** buffer);
161
162 // True if there are old regions that need to be filled.
163 bool has_coalesce_and_fill_candidates() const { return coalesce_and_fill_candidates_count() > 0; }
164
165 // Return the number of old regions that need to be filled.
166 size_t coalesce_and_fill_candidates_count() const { return _last_old_region - _next_old_collection_candidate; }
167
168 // If a GLOBAL gc occurs, it will collect the entire heap which invalidates any collection candidates being
169 // held by this heuristic for supplying mixed collections.
170 void abandon_collection_candidates();
171
172 void trigger_cannot_expand() { _cannot_expand_trigger = true; };
173
174 inline void get_fragmentation_trigger_reason_for_log_message(double &density, size_t &first_index, size_t &last_index) {
175 density = _fragmentation_density;
176 first_index = _fragmentation_first_old_region;
177 last_index = _fragmentation_last_old_region;
178 }
179
180 void clear_triggers();
181
182 // Check whether conditions merit the start of old GC. Set appropriate trigger if so.
183 void evaluate_triggers(size_t first_old_region, size_t last_old_region, size_t old_region_count, size_t num_regions);
184
185 void record_cycle_end() override;
186
187 bool should_start_gc() override;
188
189 void record_success_concurrent() override;
190
191 void record_success_degenerated() override;
192
193 void record_success_full() override;
194
195 const char* name() override;
196
197 bool is_diagnostic() override;
198
199 bool is_experimental() override;
200
201 private:
202 void slide_pinned_regions_to_front();
203 bool all_candidates_are_pinned();
204 };
205
206 #endif // SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP