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 HeapRegionClaimer;
40 class HeapRegionClosure;
41
42 // The collection set.
43 //
44 // The set of regions that are evacuated during an evacuation pause.
45 //
46 // At the end of a collection, before freeing the collection set, this set
47 // contains all regions that were evacuated during this collection:
48 //
49 // - survivor regions from the last collection (if any)
50 // - eden regions allocated by the mutator
51 // - old gen regions evacuated during mixed gc
52 //
53 // This set is built incrementally at mutator time as regions are retired, and
54 // if this had been a mixed gc, some additional (during gc) incrementally added
55 // old regions from the collection set candidates built during the concurrent
56 // cycle.
57 //
58 // A more detailed overview of how the collection set changes over time follows:
59 //
60 // 0) at the end of GC the survivor regions are added to this collection set.
61 // 1) the mutator incrementally adds eden regions as they retire
62 //
63 // ----- gc starts
64 //
65 // 2) prepare (finalize) young regions of the collection set for collection
66 // - relabel the survivors as eden
67 // - finish up the incremental building that happened at mutator time
68 //
69 // iff this is a young-only collection:
70 //
71 // a3) evacuate the current collection set in one "initial evacuation" phase
72 //
73 // iff this is a mixed collection:
74 //
75 // b3) calculate the set of old gen regions we may be able to collect in this
76 // collection from the list of collection set candidates.
77 // - one part is added to the current collection set
78 // - the remainder regions are labeled as optional, and NOT yet added to the
79 // collection set.
80 // b4) evacuate the current collection set in the "initial evacuation" phase
81 // b5) evacuate the optional regions in the "optional evacuation" phase. This is
82 // done in increments (or rounds).
83 // b5-1) add a few of the optional regions to the current collection set
84 // b5-2) evacuate only these newly added optional regions. For this mechanism we
85 // reuse the incremental collection set building infrastructure (used also at
86 // mutator time).
87 // b5-3) repeat from b5-1 until the policy determines we are done
88 //
89 // all collections
90 //
91 // 6) free the collection set (contains all regions now; empties collection set
92 // afterwards)
93 // 7) add survivors to this collection set
94 //
95 // ----- gc ends
96 //
97 // goto 1)
98 //
99 // Examples of how the collection set might look over time:
100 //
101 // Legend:
102 // S = survivor, E = eden, O = old.
103 // |xxxx| = increment (with increment markers), containing four regions
104 //
105 // |SSSS| ... after step 0), with four survivor regions
106 // |SSSSEE| ... at step 1), after retiring two eden regions
107 // |SSSSEEEE| ... after step 1), after retiring four eden regions
108 // |EEEEEEEE| ... after step 2)
109 //
110 // iff this is a young-only collection
111 //
112 // EEEEEEEE|| ... after step a3), after initial evacuation phase
113 // || ... after step 6)
114 // |SS| ... after step 7), with two survivor regions
115 //
116 // iff this is a mixed collection
117 //
118 // |EEEEEEEEOOOO| ... after step b3), added four regions to be
119 // evacuated in the "initial evacuation" phase
120 // EEEEEEEEOOOO|| ... after step b4), incremental part is empty
121 // after evacuation
122 // EEEEEEEEOOOO|OO| ... after step b5.1), added two regions to be
123 // evacuated in the first round of the
124 // "optional evacuation" phase
125 // EEEEEEEEOOOOOO|O| ... after step b5.1), added one region to be
126 // evacuated in the second round of the
127 // "optional evacuation" phase
128 // EEEEEEEEOOOOOOO|| ... after step b5), the complete collection set.
129 // || ... after step b6)
130 // |SSS| ... after step 7), with three survivor regions
131 //
132 class G1CollectionSet {
133 G1CollectedHeap* _g1h;
134 G1Policy* _policy;
135
136 // All old gen collection set candidate regions for the current mixed phase.
137 G1CollectionSetCandidates* _candidates;
138
139 uint _eden_region_length;
140 uint _survivor_region_length;
141 uint _old_region_length;
142
143 // The actual collection set as a set of region indices.
144 // All entries in _collection_set_regions below _collection_set_cur_length are
145 // assumed to be part of the collection set.
146 // We assume that at any time there is at most only one writer and (one or more)
147 // concurrent readers. This means we are good with using storestore and loadload
148 // barriers on the writer and reader respectively only.
149 uint* _collection_set_regions;
150 volatile size_t _collection_set_cur_length;
151 size_t _collection_set_max_length;
152
153 // When doing mixed collections we can add old regions to the collection set, which
154 // will be collected only if there is enough time. We call these optional regions.
155 // This member records the current number of regions that are of that type that
156 // correspond to the first x entries in the collection set candidates.
157 uint _num_optional_regions;
158
159 // The number of bytes in the collection set before the pause. Set from
160 // the incrementally built collection set at the start of an evacuation
161 // pause, and updated as more regions are added to the collection set.
162 size_t _bytes_used_before;
163
164 // The number of cards in the remembered set in the collection set. Set from
165 // the incrementally built collection set at the start of an evacuation
166 // pause, and updated as more regions are added to the collection set.
167 size_t _recorded_rs_length;
168
169 enum CSetBuildType {
170 Active, // We are actively building the collection set
171 Inactive // We are not actively building the collection set
172 };
173
174 CSetBuildType _inc_build_state;
175 size_t _inc_part_start;
176
177 // Information about eden regions in the incremental collection set.
178 struct IncCollectionSetRegionStat {
179 // The predicted time without copy time that was added to total value
180 // for the collection set.
181 double _non_copy_time_ms;
182 // The remembered set length that was added to the total value
183 // for the collection set.
184 size_t _rs_length;
185 };
186
187 IncCollectionSetRegionStat* _inc_collection_set_stats;
188 // The associated information that is maintained while the incremental
189 // collection set is being built with *young* regions. Used to populate
190 // the recorded info for the evacuation pause.
191
192 // The number of bytes in the incrementally built collection set.
193 // Used to set _collection_set_bytes_used_before at the start of
194 // an evacuation pause.
195 size_t _inc_bytes_used_before;
196
197 // The RSet lengths recorded for regions in the CSet. It is updated
198 // by the thread that adds a new region to the CSet. We assume that
199 // only one thread can be allocating a new CSet region (currently,
200 // it does so after taking the Heap_lock) hence no need to
201 // synchronize updates to this field.
202 size_t _inc_recorded_rs_length;
203
204 // A concurrent refinement thread periodically samples the young
205 // region RSets and needs to update _inc_recorded_rs_length as
206 // the RSets grow. Instead of having to synchronize updates to that
207 // field we accumulate them in this field and add it to
208 // _inc_recorded_rs_length_diff at the start of a GC.
209 size_t _inc_recorded_rs_length_diff;
210
211 // The predicted elapsed time it will take to collect the regions in
212 // the CSet. This is updated by the thread that adds a new region to
213 // the CSet. See the comment for _inc_recorded_rs_length about
214 // MT-safety assumptions.
215 double _inc_predicted_non_copy_time_ms;
216
217 // See the comment for _inc_recorded_rs_length_diff.
218 double _inc_predicted_non_copy_time_ms_diff;
219
220 void set_recorded_rs_length(size_t rs_length);
221
222 G1CollectorState* collector_state() const;
223 G1GCPhaseTimes* phase_times();
224
225 void verify_young_cset_indices() const NOT_DEBUG_RETURN;
226
227 double predict_region_non_copy_time_ms(HeapRegion* hr) const;
228
229 // Update the incremental collection set information when adding a region.
230 void add_young_region_common(HeapRegion* hr);
231
232 // Add old region "hr" to the collection set.
233 void add_old_region(HeapRegion* hr);
234 void free_optional_regions();
235
236 // Add old region "hr" to optional collection set.
237 void add_optional_region(HeapRegion* hr);
238
239 void move_candidates_to_collection_set(uint num_regions);
240
241 // Finalize the young part of the initial collection set. Relabel survivor regions
242 // as Eden and calculate a prediction on how long the evacuation of all young regions
243 // will take.
244 double finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors);
245 // Perform any final calculations on the incremental collection set fields before we
246 // can use them.
247 void finalize_incremental_building();
248
249 // Select the old regions of the initial collection set and determine how many optional
250 // regions we might be able to evacuate in this pause.
251 void finalize_old_part(double time_remaining_ms);
252 public:
253 G1CollectionSet(G1CollectedHeap* g1h, G1Policy* policy);
254 ~G1CollectionSet();
255
256 // Initializes the collection set giving the maximum possible length of the collection set.
257 void initialize(uint max_region_length);
258
259 void clear_candidates();
260
261 void set_candidates(G1CollectionSetCandidates* candidates) {
262 assert(_candidates == NULL, "Trying to replace collection set candidates.");
263 _candidates = candidates;
264 }
265 G1CollectionSetCandidates* candidates() { return _candidates; }
266
267 void init_region_lengths(uint eden_cset_region_length,
268 uint survivor_cset_region_length);
269
270 uint region_length() const { return young_region_length() +
271 old_region_length(); }
272 uint young_region_length() const { return eden_region_length() +
273 survivor_region_length(); }
274
275 uint eden_region_length() const { return _eden_region_length; }
276 uint survivor_region_length() const { return _survivor_region_length; }
277 uint old_region_length() const { return _old_region_length; }
278 uint optional_region_length() const { return _num_optional_regions; }
279
280 // Reset the contents of the collection set.
281 void clear();
282
283 // Incremental collection set support
284
285 // Initialize incremental collection set info.
286 void start_incremental_building();
287 // Start a new collection set increment.
288 void update_incremental_marker() { _inc_build_state = Active; _inc_part_start = _collection_set_cur_length; }
289 // Stop adding regions to the current collection set increment.
290 void stop_incremental_building() { _inc_build_state = Inactive; }
291
292 // Iterate over the current collection set increment applying the given HeapRegionClosure
293 // from a starting position determined by the given worker id.
294 void iterate_incremental_part_from(HeapRegionClosure* cl, HeapRegionClaimer* hr_claimer, uint worker_id, uint total_workers) const;
295
296 // Returns the length of the current increment in number of regions.
297 size_t increment_length() const { return _collection_set_cur_length - _inc_part_start; }
298 // Returns the length of the whole current collection set in number of regions
299 size_t cur_length() const { return _collection_set_cur_length; }
300
301 // Iterate over the entire collection set (all increments calculated so far), applying
302 // the given HeapRegionClosure on all of them.
303 void iterate(HeapRegionClosure* cl) const;
304
305 void iterate_optional(HeapRegionClosure* cl) const;
306
307 size_t recorded_rs_length() { return _recorded_rs_length; }
308
309 size_t bytes_used_before() const {
310 return _bytes_used_before;
311 }
312
313 void reset_bytes_used_before() {
314 _bytes_used_before = 0;
315 }
316
317 // Finalize the initial collection set consisting of all young regions potentially a
318 // few old gen regions.
319 void finalize_initial_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor);
320 // Finalize the next collection set from the set of available optional old gen regions.
321 bool finalize_optional_for_evacuation(double remaining_pause_time);
322 // Abandon (clean up) optional collection set regions that were not evacuated in this
323 // pause.
324 void abandon_optional_collection_set(G1ParScanThreadStateSet* pss);
325
326 // Update information about hr in the aggregated information for
327 // the incrementally built collection set.
328 void update_young_region_prediction(HeapRegion* hr, size_t new_rs_length);
329
330 // Add eden region to the collection set.
331 void add_eden_region(HeapRegion* hr);
332
333 // Add survivor region to the collection set.
334 void add_survivor_regions(HeapRegion* hr);
335
336 #ifndef PRODUCT
337 bool verify_young_ages();
338
339 void print(outputStream* st);
340 #endif // !PRODUCT
341 };
342
343 #endif // SHARE_GC_G1_G1COLLECTIONSET_HPP