1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_GC_G1_G1COLLECTIONSET_HPP
26 #define SHARE_GC_G1_G1COLLECTIONSET_HPP
27
28 #include "utilities/debug.hpp"
29 #include "utilities/globalDefinitions.hpp"
30
31 class G1CollectedHeap;
32 class G1CollectionSetCandidates;
33 class G1CollectorState;
34 class G1GCPhaseTimes;
35 class G1ParScanThreadStateSet;
36 class G1Policy;
37 class G1SurvivorRegions;
38 class HeapRegion;
39 class HeapRegionClosure;
40
41 // The collection set.
42 //
43 // The set of regions that are evacuated during an evacuation pause.
44 //
45 // At the end of a collection, before freeing the collection set, this set
46 // contains all regions that were evacuated during this collection:
47 //
48 // - survivor regions from the last collection (if any)
49 // - eden regions allocated by the mutator
50 // - old gen regions evacuated during mixed gc
51 //
52 // This set is built incrementally at mutator time as regions are retired, and
53 // if this had been a mixed gc, some additional (during gc) incrementally added
54 // old regions from the collection set candidates built during the concurrent
55 // cycle.
56 //
57 // A more detailed overview of how the collection set changes over time follows:
58 //
59 // 0) at the end of GC the survivor regions are added to this collection set.
60 // 1) the mutator incrementally adds eden regions as they retire
61 //
62 // ----- gc starts
63 //
64 // 2) prepare (finalize) young regions of the collection set for collection
65 // - relabel the survivors as eden
66 // - finish up the incremental building that happened at mutator time
67 //
68 // iff this is a young-only collection:
69 //
70 // a3) evacuate the current collection set in one "initial evacuation" phase
71 //
72 // iff this is a mixed collection:
73 //
74 // b3) calculate the set of old gen regions we may be able to collect in this
75 // collection from the list of collection set candidates.
76 // - one part is added to the current collection set
77 // - the remainder regions are labeled as optional, and NOT yet added to the
78 // collection set.
79 // b4) evacuate the current collection set in the "initial evacuation" phase
80 // b5) evacuate the optional regions in the "optional evacuation" phase. This is
81 // done in increments (or rounds).
82 // b5-1) add a few of the optional regions to the current collection set
83 // b5-2) evacuate only these newly added optional regions. For this mechanism we
84 // reuse the incremental collection set building infrastructure (used also at
85 // mutator time).
86 // b5-3) repeat from b5-1 until the policy determines we are done
87 //
88 // all collections
89 //
90 // 6) free the collection set (contains all regions now; empties collection set
91 // afterwards)
92 // 7) add survivors to this collection set
93 //
94 // ----- gc ends
95 //
96 // goto 1)
97 //
98 // Examples of how the collection set might look over time:
99 //
100 // Legend:
101 // S = survivor, E = eden, O = old.
102 // |xxxx| = increment (with increment markers), containing four regions
103 //
104 // |SSSS| ... after step 0), with four survivor regions
105 // |SSSSEE| ... at step 1), after retiring two eden regions
106 // |SSSSEEEE| ... after step 1), after retiring four eden regions
107 // |EEEEEEEE| ... after step 2)
108 //
109 // iff this is a young-only collection
110 //
111 // EEEEEEEE|| ... after step a3), after initial evacuation phase
112 // || ... after step 6)
113 // |SS| ... after step 7), with two survivor regions
114 //
115 // iff this is a mixed collection
116 //
117 // |EEEEEEEEOOOO| ... after step b3), added four regions to be
118 // evacuated in the "initial evacuation" phase
119 // EEEEEEEEOOOO|| ... after step b4), incremental part is empty
120 // after evacuation
121 // EEEEEEEEOOOO|OO| ... after step b5.1), added two regions to be
122 // evacuated in the first round of the
123 // "optional evacuation" phase
124 // EEEEEEEEOOOOOO|O| ... after step b5.1), added one region to be
125 // evacuated in the second round of the
126 // "optional evacuation" phase
127 // EEEEEEEEOOOOOOO|| ... after step b5), the complete collection set.
128 // || ... after step b6)
129 // |SSS| ... after step 7), with three survivor regions
130 //
131 class G1CollectionSet {
132 G1CollectedHeap* _g1h;
133 G1Policy* _policy;
134
135 // All old gen collection set candidate regions for the current mixed phase.
136 G1CollectionSetCandidates* _candidates;
137
138 uint _eden_region_length;
139 uint _survivor_region_length;
140 uint _old_region_length;
141
142 // The actual collection set as a set of region indices.
143 // All entries in _collection_set_regions below _collection_set_cur_length are
144 // assumed to be part of the collection set.
145 // We assume that at any time there is at most only one writer and (one or more)
146 // concurrent readers. This means we are good with using storestore and loadload
147 // barriers on the writer and reader respectively only.
148 uint* _collection_set_regions;
149 volatile size_t _collection_set_cur_length;
150 size_t _collection_set_max_length;
151
152 // When doing mixed collections we can add old regions to the collection set, which
153 // will be collected only if there is enough time. We call these optional regions.
154 // This member records the current number of regions that are of that type that
155 // correspond to the first x entries in the collection set candidates.
156 uint _num_optional_regions;
157
158 // The number of bytes in the collection set before the pause. Set from
159 // the incrementally built collection set at the start of an evacuation
160 // pause, and updated as more regions are added to the collection set.
161 size_t _bytes_used_before;
162
163 // The number of cards in the remembered set in the collection set. Set from
164 // the incrementally built collection set at the start of an evacuation
165 // pause, and updated as more regions are added to the collection set.
166 size_t _recorded_rs_lengths;
167
168 enum CSetBuildType {
169 Active, // We are actively building the collection set
170 Inactive // We are not actively building the collection set
171 };
172
173 CSetBuildType _inc_build_state;
174 size_t _inc_part_start;
175
176 // The associated information that is maintained while the incremental
177 // collection set is being built with *young* regions. Used to populate
178 // the recorded info for the evacuation pause.
179
180 // The number of bytes in the incrementally built collection set.
181 // Used to set _collection_set_bytes_used_before at the start of
182 // an evacuation pause.
183 size_t _inc_bytes_used_before;
184
185 // The RSet lengths recorded for regions in the CSet. It is updated
186 // by the thread that adds a new region to the CSet. We assume that
187 // only one thread can be allocating a new CSet region (currently,
188 // it does so after taking the Heap_lock) hence no need to
189 // synchronize updates to this field.
190 size_t _inc_recorded_rs_lengths;
191
192 // A concurrent refinement thread periodically samples the young
193 // region RSets and needs to update _inc_recorded_rs_lengths as
194 // the RSets grow. Instead of having to synchronize updates to that
195 // field we accumulate them in this field and add it to
196 // _inc_recorded_rs_lengths_diffs at the start of a GC.
197 ssize_t _inc_recorded_rs_lengths_diffs;
198
199 // The predicted elapsed time it will take to collect the regions in
200 // the CSet. This is updated by the thread that adds a new region to
201 // the CSet. See the comment for _inc_recorded_rs_lengths about
202 // MT-safety assumptions.
203 double _inc_predicted_elapsed_time_ms;
204
205 // See the comment for _inc_recorded_rs_lengths_diffs.
206 double _inc_predicted_elapsed_time_ms_diffs;
207
208 void set_recorded_rs_lengths(size_t rs_lengths);
209
210 G1CollectorState* collector_state();
211 G1GCPhaseTimes* phase_times();
212
213 void verify_young_cset_indices() const NOT_DEBUG_RETURN;
214
215 double predict_region_elapsed_time_ms(HeapRegion* hr);
216
217 // Update the incremental collection set information when adding a region.
218 void add_young_region_common(HeapRegion* hr);
219
220 // Add old region "hr" to the collection set.
221 void add_old_region(HeapRegion* hr);
222 void free_optional_regions();
223
224 // Add old region "hr" to optional collection set.
225 void add_optional_region(HeapRegion* hr);
226
227 void move_candidates_to_collection_set(uint num_regions);
228
229 // Finalize the young part of the initial collection set. Relabel survivor regions
230 // as Eden and calculate a prediction on how long the evacuation of all young regions
231 // will take.
232 double finalize_young_part(double target_pause_time_ms);
233 // Perform any final calculations on the incremental collection set fields before we
234 // can use them.
235 void finalize_incremental_building();
236
237 // Select the old regions of the initial collection set and determine how many optional
238 // regions we might be able to evacuate in this pause.
239 void finalize_old_part(double time_remaining_ms);
240 public:
241 G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy);
242 ~G1CollectionSet();
243
244 // Initializes the collection set giving the maximum possible length of the collection set.
245 void initialize(uint max_region_length);
246
247 void clear_candidates();
248
249 void set_candidates(G1CollectionSetCandidates* candidates) {
250 assert(_candidates == NULL, "Trying to replace collection set candidates.");
251 _candidates = candidates;
252 }
253 G1CollectionSetCandidates* candidates() { return _candidates; }
254
255 void init_region_lengths(uint eden_cset_region_length,
256 uint survivor_cset_region_length);
257
258 uint region_length() const { return young_region_length() +
259 old_region_length(); }
260 uint young_region_length() const { return eden_region_length() +
261 survivor_region_length(); }
262
263 uint eden_region_length() const { return _eden_region_length; }
264 uint survivor_region_length() const { return _survivor_region_length; }
265 uint old_region_length() const { return _old_region_length; }
266 uint optional_region_length() const { return _num_optional_regions; }
267
268 // Reset the contents of the collection set.
269 void clear();
270
271 // Incremental collection set support
272
273 // Initialize incremental collection set info.
274 void start_incremental_building();
275 // Start a new collection set increment.
276 void update_incremental_marker() { _inc_build_state = Active; _inc_part_start = _collection_set_cur_length; }
277 // Stop adding regions to the current collection set increment.
278 void stop_incremental_building() { _inc_build_state = Inactive; }
279
280 // Iterate over the current collection set increment applying the given HeapRegionClosure
281 // from a starting position determined by the given worker id.
282 void iterate_incremental_part_from(HeapRegionClosure* cl, uint worker_id, uint total_workers) const;
283
284 // Iterate over the entire collection set (all increments calculated so far), applying
285 // the given HeapRegionClosure on all of them.
286 void iterate(HeapRegionClosure* cl) const;
287
288 void iterate_optional(HeapRegionClosure* cl) const;
289
290 size_t recorded_rs_lengths() { return _recorded_rs_lengths; }
291
292 size_t bytes_used_before() const {
293 return _bytes_used_before;
294 }
295
296 void reset_bytes_used_before() {
297 _bytes_used_before = 0;
298 }
299
300 // Finalize the initial collection set consisting of all young regions potentially a
301 // few old gen regions.
302 void finalize_initial_collection_set(double target_pause_time_ms);
303 // Finalize the next collection set from the set of available optional old gen regions.
304 bool finalize_optional_for_evacuation(double remaining_pause_time);
305 // Abandon (clean up) optional collection set regions that were not evacuated in this
306 // pause.
307 void abandon_optional_collection_set(G1ParScanThreadStateSet* pss);
308
309 // Update information about hr in the aggregated information for
310 // the incrementally built collection set.
311 void update_young_region_prediction(HeapRegion* hr, size_t new_rs_length);
312
313 // Add eden region to the collection set.
314 void add_eden_region(HeapRegion* hr);
315
316 // Add survivor region to the collection set.
317 void add_survivor_regions(HeapRegion* hr);
318
319 #ifndef PRODUCT
320 bool verify_young_ages();
321
322 void print(outputStream* st);
323 #endif // !PRODUCT
324 };
325
326 #endif // SHARE_GC_G1_G1COLLECTIONSET_HPP