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
57 // After final marking of the old generation, this heuristic will select
58 // a set of candidate regions to be included in subsequent mixed collections.
59 // The regions are sorted into a `_region_data` array (declared in base
60 // class) in decreasing order of garbage. The heuristic will give priority
61 // to regions containing more garbage.
62
63 // The following members are used to keep track of which candidate regions
64 // have yet to be added to a mixed collection. There is also some special
65 // handling for pinned regions, described further below.
66
67 // Pinned regions may not be included in the collection set. Any old regions
68 // which were pinned at the time when old regions were added to the mixed
69 // collection will have been skipped. These regions are still contain garbage,
70 // so we want to include them at the start of the list of candidates for the
71 // _next_ mixed collection cycle. This variable is the index of the _first_
72 // old region which is pinned when the mixed collection set is formed.
73 uint _first_pinned_candidate;
74
75 // This is the index of the last region which is above the garbage threshold.
76 // No regions after this will be considered for inclusion in a mixed collection
77 // set.
78 uint _last_old_collection_candidate;
79
80 // This index points to the first candidate in line to be added to the mixed
81 // collection set. It is updated as regions are added to the collection set.
82 uint _next_old_collection_candidate;
83
84 // This is the last index in the array of old regions which were active at
85 // the end of old final mark.
86 uint _last_old_region;
87
88 // How much live data must be evacuated from within the unprocessed mixed evacuation candidates?
89 size_t _live_bytes_in_unprocessed_candidates;
90
91 // Keep a pointer to our generation that we can use without down casting a protected member from the base class.
92 ShenandoahOldGeneration* _old_generation;
93
94 // Flags are set when promotion failure is detected (by gc thread), and cleared when
95 // old generation collection begins (by control thread). Flags are set and cleared at safepoints.
96 bool _cannot_expand_trigger;
97 bool _fragmentation_trigger;
98 bool _growth_trigger;
99
100 // Motivation for a fragmentation_trigger
101 double _fragmentation_density;
102 size_t _fragmentation_first_old_region;
103 size_t _fragmentation_last_old_region;
104
105 // Compare by live is used to prioritize compaction of old-gen regions. With old-gen compaction, the goal is
106 // to tightly pack long-lived objects into available regions. In most cases, there has not been an accumulation
107 // of garbage within old-gen regions. The more likely opportunity will be to combine multiple sparsely populated
108 // old-gen regions which may have been promoted in place into a smaller number of densely packed old-gen regions.
109 // This improves subsequent allocation efficiency and reduces the likelihood of allocation failure (including
110 // humongous allocation failure) due to fragmentation of the available old-gen allocation pool
111 static int compare_by_live(RegionData a, RegionData b);
112
113 static int compare_by_index(RegionData a, RegionData b);
114
115 // Set the fragmentation trigger if old-gen memory has become fragmented.
116 void set_trigger_if_old_is_fragmented(size_t first_old_region, size_t last_old_region,
117 size_t old_region_count, size_t num_regions);
118
119 // Set the overgrowth trigger if old-gen memory has grown beyond a particular threshold.
120 void set_trigger_if_old_is_overgrown();
121
122 protected:
123 void choose_collection_set_from_regiondata(ShenandoahCollectionSet* set, RegionData* data, size_t data_size, size_t free) override;
124
125 public:
126 explicit ShenandoahOldHeuristics(ShenandoahOldGeneration* generation, ShenandoahGenerationalHeap* gen_heap);
127
128 // Prepare for evacuation of old-gen regions by capturing the mark results of a recently completed concurrent mark pass.
129 void prepare_for_old_collections();
130
131 // Return true iff the collection set is primed with at least one old-gen region.
132 bool prime_collection_set(ShenandoahCollectionSet* set);
133
134 // How many old-collection candidates have not yet been processed?
135 uint unprocessed_old_collection_candidates() const;
136
137 // How much live memory must be evacuated from within old-collection candidates that have not yet been processed?
138 size_t unprocessed_old_collection_candidates_live_memory() const;
139
140 void set_unprocessed_old_collection_candidates_live_memory(size_t initial_live);
141
142 void decrease_unprocessed_old_collection_candidates_live_memory(size_t evacuated_live);
143
144 // How many old or hidden collection candidates have not yet been processed?
145 uint last_old_collection_candidate_index() const;
146
147 // Return the next old-collection candidate in order of decreasing amounts of garbage. (We process most-garbage regions
148 // first.) This does not consume the candidate. If the candidate is selected for inclusion in a collection set, then
149 // the candidate is consumed by invoking consume_old_collection_candidate().
150 ShenandoahHeapRegion* next_old_collection_candidate();
151
152 // Adjust internal state to reflect that one fewer old-collection candidate remains to be processed.
153 void consume_old_collection_candidate();
154
155 // Fill in buffer with all the old-collection regions that were identified at the end of the most recent old-gen
156 // mark to require their unmarked objects to be coalesced and filled. The buffer array must have at least
157 // last_old_region_index() entries, or memory may be corrupted when this function overwrites the
158 // end of the array.
159 unsigned int get_coalesce_and_fill_candidates(ShenandoahHeapRegion** buffer);
160
161 // True if there are old regions that need to be filled.
162 bool has_coalesce_and_fill_candidates() const { return coalesce_and_fill_candidates_count() > 0; }
163
164 // Return the number of old regions that need to be filled.
165 size_t coalesce_and_fill_candidates_count() const { return _last_old_region - _next_old_collection_candidate; }
166
167 // If a GLOBAL gc occurs, it will collect the entire heap which invalidates any collection candidates being
168 // held by this heuristic for supplying mixed collections.
169 void abandon_collection_candidates();
170
171 void trigger_cannot_expand() { _cannot_expand_trigger = true; };
172
173 inline void get_fragmentation_trigger_reason_for_log_message(double &density, size_t &first_index, size_t &last_index) {
174 density = _fragmentation_density;
175 first_index = _fragmentation_first_old_region;
176 last_index = _fragmentation_last_old_region;
177 }
178
179 void clear_triggers();
180
181 // Check whether conditions merit the start of old GC. Set appropriate trigger if so.
182 void evaluate_triggers(size_t first_old_region, size_t last_old_region, size_t old_region_count, size_t num_regions);
183
184 void record_cycle_end() override;
185
186 bool should_start_gc() override;
187
188 // Returns true if the old generation needs to prepare for marking, or continue marking.
189 bool should_resume_old_cycle();
190
191 void record_success_concurrent() override;
192
193 void record_success_degenerated() override;
194
195 void record_success_full() override;
196
197 const char* name() override;
198
199 bool is_diagnostic() override;
200
201 bool is_experimental() override;
202
203 private:
204 void slide_pinned_regions_to_front();
205 bool all_candidates_are_pinned();
206 };
207
208 #endif // SHARE_GC_SHENANDOAH_HEURISTICS_SHENANDOAHOLDHEURISTICS_HPP