1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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).
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  24 
  25 #ifndef SHARE_VM_GC_G1_G1COLLECTORPOLICY_HPP
  26 #define SHARE_VM_GC_G1_G1COLLECTORPOLICY_HPP
  27 
  28 #include "gc/g1/collectionSetChooser.hpp"
  29 #include "gc/g1/g1CollectorState.hpp"
  30 #include "gc/g1/g1GCPhaseTimes.hpp"
  31 #include "gc/g1/g1InCSetState.hpp"
  32 #include "gc/g1/g1MMUTracker.hpp"
  33 #include "gc/g1/g1Predictions.hpp"
  34 #include "gc/shared/collectorPolicy.hpp"
  35 
  36 // A G1CollectorPolicy makes policy decisions that determine the
  37 // characteristics of the collector.  Examples include:
  38 //   * choice of collection set.
  39 //   * when to collect.
  40 
  41 class HeapRegion;
  42 class CollectionSetChooser;
  43 
  44 // TraceYoungGenTime collects data on _both_ young and mixed evacuation pauses
  45 // (the latter may contain non-young regions - i.e. regions that are
  46 // technically in old) while TraceOldGenTime collects data about full GCs.
  47 class TraceYoungGenTimeData : public CHeapObj<mtGC> {
  48  private:
  49   unsigned  _young_pause_num;
  50   unsigned  _mixed_pause_num;
  51 
  52   NumberSeq _all_stop_world_times_ms;
  53   NumberSeq _all_yield_times_ms;
  54 
  55   NumberSeq _total;
  56   NumberSeq _other;
  57   NumberSeq _root_region_scan_wait;
  58   NumberSeq _parallel;
  59   NumberSeq _ext_root_scan;
  60   NumberSeq _satb_filtering;
  61   NumberSeq _update_rs;
  62   NumberSeq _scan_rs;
  63   NumberSeq _obj_copy;
  64   NumberSeq _termination;
  65   NumberSeq _parallel_other;
  66   NumberSeq _clear_ct;
  67 
  68   void print_summary(const char* str, const NumberSeq* seq) const;
  69   void print_summary_sd(const char* str, const NumberSeq* seq) const;
  70 
  71 public:
  72    TraceYoungGenTimeData() : _young_pause_num(0), _mixed_pause_num(0) {};
  73   void record_start_collection(double time_to_stop_the_world_ms);
  74   void record_yield_time(double yield_time_ms);
  75   void record_end_collection(double pause_time_ms, G1GCPhaseTimes* phase_times);
  76   void increment_young_collection_count();
  77   void increment_mixed_collection_count();
  78   void print() const;
  79 };
  80 
  81 class TraceOldGenTimeData : public CHeapObj<mtGC> {
  82  private:
  83   NumberSeq _all_full_gc_times;
  84 
  85  public:
  86   void record_full_collection(double full_gc_time_ms);
  87   void print() const;
  88 };
  89 
  90 // There are three command line options related to the young gen size:
  91 // NewSize, MaxNewSize and NewRatio (There is also -Xmn, but that is
  92 // just a short form for NewSize==MaxNewSize). G1 will use its internal
  93 // heuristics to calculate the actual young gen size, so these options
  94 // basically only limit the range within which G1 can pick a young gen
  95 // size. Also, these are general options taking byte sizes. G1 will
  96 // internally work with a number of regions instead. So, some rounding
  97 // will occur.
  98 //
  99 // If nothing related to the the young gen size is set on the command
 100 // line we should allow the young gen to be between G1NewSizePercent
 101 // and G1MaxNewSizePercent of the heap size. This means that every time
 102 // the heap size changes, the limits for the young gen size will be
 103 // recalculated.
 104 //
 105 // If only -XX:NewSize is set we should use the specified value as the
 106 // minimum size for young gen. Still using G1MaxNewSizePercent of the
 107 // heap as maximum.
 108 //
 109 // If only -XX:MaxNewSize is set we should use the specified value as the
 110 // maximum size for young gen. Still using G1NewSizePercent of the heap
 111 // as minimum.
 112 //
 113 // If -XX:NewSize and -XX:MaxNewSize are both specified we use these values.
 114 // No updates when the heap size changes. There is a special case when
 115 // NewSize==MaxNewSize. This is interpreted as "fixed" and will use a
 116 // different heuristic for calculating the collection set when we do mixed
 117 // collection.
 118 //
 119 // If only -XX:NewRatio is set we should use the specified ratio of the heap
 120 // as both min and max. This will be interpreted as "fixed" just like the
 121 // NewSize==MaxNewSize case above. But we will update the min and max
 122 // every time the heap size changes.
 123 //
 124 // NewSize and MaxNewSize override NewRatio. So, NewRatio is ignored if it is
 125 // combined with either NewSize or MaxNewSize. (A warning message is printed.)
 126 class G1YoungGenSizer : public CHeapObj<mtGC> {
 127 private:
 128   enum SizerKind {
 129     SizerDefaults,
 130     SizerNewSizeOnly,
 131     SizerMaxNewSizeOnly,
 132     SizerMaxAndNewSize,
 133     SizerNewRatio
 134   };
 135   SizerKind _sizer_kind;
 136   uint _min_desired_young_length;
 137   uint _max_desired_young_length;
 138   bool _adaptive_size;
 139   uint calculate_default_min_length(uint new_number_of_heap_regions);
 140   uint calculate_default_max_length(uint new_number_of_heap_regions);
 141 
 142   // Update the given values for minimum and maximum young gen length in regions
 143   // given the number of heap regions depending on the kind of sizing algorithm.
 144   void recalculate_min_max_young_length(uint number_of_heap_regions, uint* min_young_length, uint* max_young_length);
 145 
 146 public:
 147   G1YoungGenSizer();
 148   // Calculate the maximum length of the young gen given the number of regions
 149   // depending on the sizing algorithm.
 150   uint max_young_length(uint number_of_heap_regions);
 151 
 152   void heap_size_changed(uint new_number_of_heap_regions);
 153   uint min_desired_young_length() {
 154     return _min_desired_young_length;
 155   }
 156   uint max_desired_young_length() {
 157     return _max_desired_young_length;
 158   }
 159   
 160   bool adaptive_young_list_length() const {
 161     return _adaptive_size;
 162   }
 163 };
 164 
 165 class G1CollectorPolicy: public CollectorPolicy {
 166  private:
 167   G1Predictions _predictor;
 168 
 169   double get_new_prediction(TruncatedSeq const* seq) const;
 170 
 171   // either equal to the number of parallel threads, if ParallelGCThreads
 172   // has been set, or 1 otherwise
 173   int _parallel_gc_threads;
 174 
 175   // The number of GC threads currently active.
 176   uintx _no_of_gc_threads;
 177 
 178   G1MMUTracker* _mmu_tracker;
 179 
 180   void initialize_alignments();
 181   void initialize_flags();
 182 
 183   CollectionSetChooser* _collectionSetChooser;
 184 
 185   double _full_collection_start_sec;
 186   uint   _cur_collection_pause_used_regions_at_start;
 187 
 188   // These exclude marking times.
 189   TruncatedSeq* _recent_gc_times_ms;
 190 
 191   TruncatedSeq* _concurrent_mark_remark_times_ms;
 192   TruncatedSeq* _concurrent_mark_cleanup_times_ms;
 193 
 194   TraceYoungGenTimeData _trace_young_gen_time_data;
 195   TraceOldGenTimeData   _trace_old_gen_time_data;
 196 
 197   double _stop_world_start;
 198 
 199   uint _young_list_target_length;
 200   uint _young_list_fixed_length;
 201 
 202   // The max number of regions we can extend the eden by while the GC
 203   // locker is active. This should be >= _young_list_target_length;
 204   uint _young_list_max_length;
 205 
 206   SurvRateGroup* _short_lived_surv_rate_group;
 207   SurvRateGroup* _survivor_surv_rate_group;
 208   // add here any more surv rate groups
 209 
 210   double _gc_overhead_perc;
 211 
 212   double _reserve_factor;
 213   uint   _reserve_regions;
 214 
 215   enum PredictionConstants {
 216     TruncatedSeqLength = 10,
 217     NumPrevPausesForHeuristics = 10
 218   };
 219 
 220   TruncatedSeq* _alloc_rate_ms_seq;
 221   double        _prev_collection_pause_end_ms;
 222 
 223   TruncatedSeq* _rs_length_diff_seq;
 224   TruncatedSeq* _cost_per_card_ms_seq;
 225   TruncatedSeq* _cost_scan_hcc_seq;
 226   TruncatedSeq* _young_cards_per_entry_ratio_seq;
 227   TruncatedSeq* _mixed_cards_per_entry_ratio_seq;
 228   TruncatedSeq* _cost_per_entry_ms_seq;
 229   TruncatedSeq* _mixed_cost_per_entry_ms_seq;
 230   TruncatedSeq* _cost_per_byte_ms_seq;
 231   TruncatedSeq* _constant_other_time_ms_seq;
 232   TruncatedSeq* _young_other_cost_per_region_ms_seq;
 233   TruncatedSeq* _non_young_other_cost_per_region_ms_seq;
 234 
 235   TruncatedSeq* _pending_cards_seq;
 236   TruncatedSeq* _rs_lengths_seq;
 237 
 238   TruncatedSeq* _cost_per_byte_ms_during_cm_seq;
 239 
 240   G1YoungGenSizer* _young_gen_sizer;
 241 
 242   uint _eden_cset_region_length;
 243   uint _survivor_cset_region_length;
 244   uint _old_cset_region_length;
 245 
 246   void init_cset_region_lengths(uint eden_cset_region_length,
 247                                 uint survivor_cset_region_length);
 248 
 249   uint eden_cset_region_length() const     { return _eden_cset_region_length;     }
 250   uint survivor_cset_region_length() const { return _survivor_cset_region_length; }
 251   uint old_cset_region_length() const      { return _old_cset_region_length;      }
 252 
 253   uint _free_regions_at_end_of_collection;
 254 
 255   size_t _recorded_rs_lengths;
 256   size_t _max_rs_lengths;
 257 
 258   size_t _rs_lengths_prediction;
 259 
 260 #ifndef PRODUCT
 261   bool verify_young_ages(HeapRegion* head, SurvRateGroup *surv_rate_group);
 262 #endif // PRODUCT
 263 
 264   void adjust_concurrent_refinement(double update_rs_time,
 265                                     double update_rs_processed_buffers,
 266                                     double goal_ms);
 267 
 268   uintx no_of_gc_threads() { return _no_of_gc_threads; }
 269   void set_no_of_gc_threads(uintx v) { _no_of_gc_threads = v; }
 270 
 271   double _pause_time_target_ms;
 272 
 273   size_t _pending_cards;
 274 
 275 public:
 276   G1Predictions& predictor() { return _predictor; }
 277 
 278   // Accessors
 279 
 280   void set_region_eden(HeapRegion* hr, int young_index_in_cset) {
 281     hr->set_eden();
 282     hr->install_surv_rate_group(_short_lived_surv_rate_group);
 283     hr->set_young_index_in_cset(young_index_in_cset);
 284   }
 285 
 286   void set_region_survivor(HeapRegion* hr, int young_index_in_cset) {
 287     assert(hr->is_survivor(), "pre-condition");
 288     hr->install_surv_rate_group(_survivor_surv_rate_group);
 289     hr->set_young_index_in_cset(young_index_in_cset);
 290   }
 291 
 292 #ifndef PRODUCT
 293   bool verify_young_ages();
 294 #endif // PRODUCT
 295 
 296   void record_max_rs_lengths(size_t rs_lengths) {
 297     _max_rs_lengths = rs_lengths;
 298   }
 299 
 300   size_t predict_rs_length_diff() const;
 301 
 302   double predict_alloc_rate_ms() const;
 303 
 304   double predict_cost_per_card_ms() const;
 305 
 306   double predict_scan_hcc_ms() const;
 307 
 308   double predict_rs_update_time_ms(size_t pending_cards) const;
 309 
 310   double predict_young_cards_per_entry_ratio() const;
 311 
 312   double predict_mixed_cards_per_entry_ratio() const;
 313 
 314   size_t predict_young_card_num(size_t rs_length) const;
 315 
 316   size_t predict_non_young_card_num(size_t rs_length) const;
 317 
 318   double predict_rs_scan_time_ms(size_t card_num) const;
 319 
 320   double predict_mixed_rs_scan_time_ms(size_t card_num) const;
 321 
 322   double predict_object_copy_time_ms_during_cm(size_t bytes_to_copy) const;
 323 
 324   double predict_object_copy_time_ms(size_t bytes_to_copy) const;
 325 
 326   double predict_constant_other_time_ms() const;
 327 
 328   double predict_young_other_time_ms(size_t young_num) const;
 329 
 330   double predict_non_young_other_time_ms(size_t non_young_num) const;
 331 
 332   double predict_base_elapsed_time_ms(size_t pending_cards) const;
 333   double predict_base_elapsed_time_ms(size_t pending_cards,
 334                                       size_t scanned_cards) const;
 335   size_t predict_bytes_to_copy(HeapRegion* hr) const;
 336   double predict_region_elapsed_time_ms(HeapRegion* hr, bool for_young_gc) const;
 337 
 338   void set_recorded_rs_lengths(size_t rs_lengths);
 339 
 340   uint cset_region_length() const       { return young_cset_region_length() +
 341                                            old_cset_region_length(); }
 342   uint young_cset_region_length() const { return eden_cset_region_length() +
 343                                            survivor_cset_region_length(); }
 344 
 345   double predict_survivor_regions_evac_time() const;
 346 
 347   bool should_update_surv_rate_group_predictors() {
 348     return collector_state()->last_gc_was_young() && !collector_state()->in_marking_window();
 349   }
 350 
 351   void cset_regions_freed() {
 352     bool update = should_update_surv_rate_group_predictors();
 353 
 354     _short_lived_surv_rate_group->all_surviving_words_recorded(update);
 355     _survivor_surv_rate_group->all_surviving_words_recorded(update);
 356   }
 357 
 358   G1MMUTracker* mmu_tracker() {
 359     return _mmu_tracker;
 360   }
 361 
 362   const G1MMUTracker* mmu_tracker() const {
 363     return _mmu_tracker;
 364   }
 365 
 366   double max_pause_time_ms() const {
 367     return _mmu_tracker->max_gc_time() * 1000.0;
 368   }
 369 
 370   double predict_remark_time_ms() const;
 371 
 372   double predict_cleanup_time_ms() const;
 373 
 374   // Returns an estimate of the survival rate of the region at yg-age
 375   // "yg_age".
 376   double predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) const;
 377 
 378   double predict_yg_surv_rate(int age) const;
 379 
 380   double accum_yg_surv_rate_pred(int age) const;
 381 
 382 protected:
 383   virtual double average_time_ms(G1GCPhaseTimes::GCParPhases phase) const;
 384   virtual double other_time_ms(double pause_time_ms) const;
 385 
 386   double young_other_time_ms() const;
 387   double non_young_other_time_ms() const;
 388   double constant_other_time_ms(double pause_time_ms) const;
 389 
 390 private:
 391   // Statistics kept per GC stoppage, pause or full.
 392   TruncatedSeq* _recent_prev_end_times_for_all_gcs_sec;
 393 
 394   // Add a new GC of the given duration and end time to the record.
 395   void update_recent_gc_times(double end_time_sec, double elapsed_ms);
 396 
 397   // The head of the list (via "next_in_collection_set()") representing the
 398   // current collection set. Set from the incrementally built collection
 399   // set at the start of the pause.
 400   HeapRegion* _collection_set;
 401 
 402   // The number of bytes in the collection set before the pause. Set from
 403   // the incrementally built collection set at the start of an evacuation
 404   // pause, and incremented in finalize_old_cset_part() when adding old regions
 405   // (if any) to the collection set.
 406   size_t _collection_set_bytes_used_before;
 407 
 408   // The number of bytes copied during the GC.
 409   size_t _bytes_copied_during_gc;
 410 
 411   // The associated information that is maintained while the incremental
 412   // collection set is being built with young regions. Used to populate
 413   // the recorded info for the evacuation pause.
 414 
 415   enum CSetBuildType {
 416     Active,             // We are actively building the collection set
 417     Inactive            // We are not actively building the collection set
 418   };
 419 
 420   CSetBuildType _inc_cset_build_state;
 421 
 422   // The head of the incrementally built collection set.
 423   HeapRegion* _inc_cset_head;
 424 
 425   // The tail of the incrementally built collection set.
 426   HeapRegion* _inc_cset_tail;
 427 
 428   // The number of bytes in the incrementally built collection set.
 429   // Used to set _collection_set_bytes_used_before at the start of
 430   // an evacuation pause.
 431   size_t _inc_cset_bytes_used_before;
 432 
 433   // Used to record the highest end of heap region in collection set
 434   HeapWord* _inc_cset_max_finger;
 435 
 436   // The RSet lengths recorded for regions in the CSet. It is updated
 437   // by the thread that adds a new region to the CSet. We assume that
 438   // only one thread can be allocating a new CSet region (currently,
 439   // it does so after taking the Heap_lock) hence no need to
 440   // synchronize updates to this field.
 441   size_t _inc_cset_recorded_rs_lengths;
 442 
 443   // A concurrent refinement thread periodically samples the young
 444   // region RSets and needs to update _inc_cset_recorded_rs_lengths as
 445   // the RSets grow. Instead of having to synchronize updates to that
 446   // field we accumulate them in this field and add it to
 447   // _inc_cset_recorded_rs_lengths_diffs at the start of a GC.
 448   ssize_t _inc_cset_recorded_rs_lengths_diffs;
 449 
 450   // The predicted elapsed time it will take to collect the regions in
 451   // the CSet. This is updated by the thread that adds a new region to
 452   // the CSet. See the comment for _inc_cset_recorded_rs_lengths about
 453   // MT-safety assumptions.
 454   double _inc_cset_predicted_elapsed_time_ms;
 455 
 456   // See the comment for _inc_cset_recorded_rs_lengths_diffs.
 457   double _inc_cset_predicted_elapsed_time_ms_diffs;
 458 
 459   // Stash a pointer to the g1 heap.
 460   G1CollectedHeap* _g1;
 461 
 462   G1GCPhaseTimes* _phase_times;
 463 
 464   // The ratio of gc time to elapsed time, computed over recent pauses.
 465   double _recent_avg_pause_time_ratio;
 466 
 467   double recent_avg_pause_time_ratio() const {
 468     return _recent_avg_pause_time_ratio;
 469   }
 470 
 471   // This set of variables tracks the collector efficiency, in order to
 472   // determine whether we should initiate a new marking.
 473   double _cur_mark_stop_world_time_ms;
 474   double _mark_remark_start_sec;
 475   double _mark_cleanup_start_sec;
 476 
 477   void update_young_list_max_and_target_length();
 478   void update_young_list_max_and_target_length(size_t rs_lengths);
 479 
 480   // Update the young list target length either by setting it to the
 481   // desired fixed value or by calculating it using G1's pause
 482   // prediction model. If no rs_lengths parameter is passed, predict
 483   // the RS lengths using the prediction model, otherwise use the
 484   // given rs_lengths as the prediction.
 485   void update_young_list_target_length();
 486   void update_young_list_target_length(size_t rs_lengths);
 487 
 488   // Calculate and return the minimum desired young list target
 489   // length. This is the minimum desired young list length according
 490   // to the user's inputs.
 491   uint calculate_young_list_desired_min_length(uint base_min_length) const;
 492 
 493   // Calculate and return the maximum desired young list target
 494   // length. This is the maximum desired young list length according
 495   // to the user's inputs.
 496   uint calculate_young_list_desired_max_length() const;
 497 
 498   // Calculate and return the maximum young list target length that
 499   // can fit into the pause time goal. The parameters are: rs_lengths
 500   // represent the prediction of how large the young RSet lengths will
 501   // be, base_min_length is the already existing number of regions in
 502   // the young list, min_length and max_length are the desired min and
 503   // max young list length according to the user's inputs.
 504   uint calculate_young_list_target_length(size_t rs_lengths,
 505                                           uint base_min_length,
 506                                           uint desired_min_length,
 507                                           uint desired_max_length) const;
 508 
 509   uint bounded_young_list_target_length(size_t rs_lengths) const;
 510 
 511   void update_rs_lengths_prediction();
 512   void update_rs_lengths_prediction(size_t prediction);
 513 
 514   // Calculate and return chunk size (in number of regions) for parallel
 515   // concurrent mark cleanup.
 516   uint calculate_parallel_work_chunk_size(uint n_workers, uint n_regions) const;
 517 
 518   // Check whether a given young length (young_length) fits into the
 519   // given target pause time and whether the prediction for the amount
 520   // of objects to be copied for the given length will fit into the
 521   // given free space (expressed by base_free_regions).  It is used by
 522   // calculate_young_list_target_length().
 523   bool predict_will_fit(uint young_length, double base_time_ms,
 524                         uint base_free_regions, double target_pause_time_ms) const;
 525 
 526   // Calculate the minimum number of old regions we'll add to the CSet
 527   // during a mixed GC.
 528   uint calc_min_old_cset_length() const;
 529 
 530   // Calculate the maximum number of old regions we'll add to the CSet
 531   // during a mixed GC.
 532   uint calc_max_old_cset_length() const;
 533 
 534   // Returns the given amount of uncollected reclaimable space
 535   // as a percentage of the current heap capacity.
 536   double reclaimable_bytes_perc(size_t reclaimable_bytes) const;
 537 
 538 public:
 539 
 540   G1CollectorPolicy();
 541 
 542   virtual G1CollectorPolicy* as_g1_policy() { return this; }
 543 
 544   G1CollectorState* collector_state() const;
 545 
 546   G1GCPhaseTimes* phase_times() const { return _phase_times; }
 547 
 548   // Check the current value of the young list RSet lengths and
 549   // compare it against the last prediction. If the current value is
 550   // higher, recalculate the young list target length prediction.
 551   void revise_young_list_target_length_if_necessary();
 552 
 553   // This should be called after the heap is resized.
 554   void record_new_heap_size(uint new_number_of_regions);
 555 
 556   void init();
 557 
 558   virtual void note_gc_start(uint num_active_workers);
 559 
 560   // Create jstat counters for the policy.
 561   virtual void initialize_gc_policy_counters();
 562 
 563   virtual HeapWord* mem_allocate_work(size_t size,
 564                                       bool is_tlab,
 565                                       bool* gc_overhead_limit_was_exceeded);
 566 
 567   // This method controls how a collector handles one or more
 568   // of its generations being fully allocated.
 569   virtual HeapWord* satisfy_failed_allocation(size_t size,
 570                                               bool is_tlab);
 571 
 572   bool need_to_start_conc_mark(const char* source, size_t alloc_word_size = 0);
 573 
 574   // Record the start and end of an evacuation pause.
 575   void record_collection_pause_start(double start_time_sec);
 576   void record_collection_pause_end(double pause_time_ms, size_t cards_scanned);
 577 
 578   // Record the start and end of a full collection.
 579   void record_full_collection_start();
 580   void record_full_collection_end();
 581 
 582   // Must currently be called while the world is stopped.
 583   void record_concurrent_mark_init_end(double mark_init_elapsed_time_ms);
 584 
 585   // Record start and end of remark.
 586   void record_concurrent_mark_remark_start();
 587   void record_concurrent_mark_remark_end();
 588 
 589   // Record start, end, and completion of cleanup.
 590   void record_concurrent_mark_cleanup_start();
 591   void record_concurrent_mark_cleanup_end();
 592   void record_concurrent_mark_cleanup_completed();
 593 
 594   // Records the information about the heap size for reporting in
 595   // print_detailed_heap_transition
 596   void record_heap_size_info_at_start(bool full);
 597 
 598   // Print heap sizing transition (with less and more detail).
 599 
 600   void print_detailed_heap_transition() const;
 601 
 602   virtual void print_phases(double pause_time_sec);
 603 
 604   void record_stop_world_start();
 605   void record_concurrent_pause();
 606 
 607   // Record how much space we copied during a GC. This is typically
 608   // called when a GC alloc region is being retired.
 609   void record_bytes_copied_during_gc(size_t bytes) {
 610     _bytes_copied_during_gc += bytes;
 611   }
 612 
 613   // The amount of space we copied during a GC.
 614   size_t bytes_copied_during_gc() const {
 615     return _bytes_copied_during_gc;
 616   }
 617 
 618   size_t collection_set_bytes_used_before() const {
 619     return _collection_set_bytes_used_before;
 620   }
 621 
 622   // Determine whether there are candidate regions so that the
 623   // next GC should be mixed. The two action strings are used
 624   // in the ergo output when the method returns true or false.
 625   bool next_gc_should_be_mixed(const char* true_action_str,
 626                                const char* false_action_str) const;
 627 
 628   // Choose a new collection set.  Marks the chosen regions as being
 629   // "in_collection_set", and links them together.  The head and number of
 630   // the collection set are available via access methods.
 631   double finalize_young_cset_part(double target_pause_time_ms);
 632   virtual void finalize_old_cset_part(double time_remaining_ms);
 633 
 634   // The head of the list (via "next_in_collection_set()") representing the
 635   // current collection set.
 636   HeapRegion* collection_set() { return _collection_set; }
 637 
 638   void clear_collection_set() { _collection_set = NULL; }
 639 
 640   // Add old region "hr" to the CSet.
 641   void add_old_region_to_cset(HeapRegion* hr);
 642 
 643   // Incremental CSet Support
 644 
 645   // The head of the incrementally built collection set.
 646   HeapRegion* inc_cset_head() { return _inc_cset_head; }
 647 
 648   // The tail of the incrementally built collection set.
 649   HeapRegion* inc_set_tail() { return _inc_cset_tail; }
 650 
 651   // Initialize incremental collection set info.
 652   void start_incremental_cset_building();
 653 
 654   // Perform any final calculations on the incremental CSet fields
 655   // before we can use them.
 656   void finalize_incremental_cset_building();
 657 
 658   void clear_incremental_cset() {
 659     _inc_cset_head = NULL;
 660     _inc_cset_tail = NULL;
 661   }
 662 
 663   // Stop adding regions to the incremental collection set
 664   void stop_incremental_cset_building() { _inc_cset_build_state = Inactive; }
 665 
 666   // Add information about hr to the aggregated information for the
 667   // incrementally built collection set.
 668   void add_to_incremental_cset_info(HeapRegion* hr, size_t rs_length);
 669 
 670   // Update information about hr in the aggregated information for
 671   // the incrementally built collection set.
 672   void update_incremental_cset_info(HeapRegion* hr, size_t new_rs_length);
 673 
 674 private:
 675   // Update the incremental cset information when adding a region
 676   // (should not be called directly).
 677   void add_region_to_incremental_cset_common(HeapRegion* hr);
 678 
 679 public:
 680   // Add hr to the LHS of the incremental collection set.
 681   void add_region_to_incremental_cset_lhs(HeapRegion* hr);
 682 
 683   // Add hr to the RHS of the incremental collection set.
 684   void add_region_to_incremental_cset_rhs(HeapRegion* hr);
 685 
 686 #ifndef PRODUCT
 687   void print_collection_set(HeapRegion* list_head, outputStream* st);
 688 #endif // !PRODUCT
 689 
 690   // This sets the initiate_conc_mark_if_possible() flag to start a
 691   // new cycle, as long as we are not already in one. It's best if it
 692   // is called during a safepoint when the test whether a cycle is in
 693   // progress or not is stable.
 694   bool force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause);
 695 
 696   // This is called at the very beginning of an evacuation pause (it
 697   // has to be the first thing that the pause does). If
 698   // initiate_conc_mark_if_possible() is true, and the concurrent
 699   // marking thread has completed its work during the previous cycle,
 700   // it will set during_initial_mark_pause() to so that the pause does
 701   // the initial-mark work and start a marking cycle.
 702   void decide_on_conc_mark_initiation();
 703 
 704   // If an expansion would be appropriate, because recent GC overhead had
 705   // exceeded the desired limit, return an amount to expand by.
 706   virtual size_t expansion_amount() const;
 707 
 708   // Print tracing information.
 709   void print_tracing_info() const;
 710 
 711   // Print stats on young survival ratio
 712   void print_yg_surv_rate_info() const;
 713 
 714   void finished_recalculating_age_indexes(bool is_survivors) {
 715     if (is_survivors) {
 716       _survivor_surv_rate_group->finished_recalculating_age_indexes();
 717     } else {
 718       _short_lived_surv_rate_group->finished_recalculating_age_indexes();
 719     }
 720     // do that for any other surv rate groups
 721   }
 722 
 723   size_t young_list_target_length() const { return _young_list_target_length; }
 724 
 725   bool is_young_list_full() const;
 726 
 727   bool can_expand_young_list() const;
 728 
 729   uint young_list_max_length() const {
 730     return _young_list_max_length;
 731   }
 732 
 733   bool adaptive_young_list_length() const {
 734     return _young_gen_sizer->adaptive_young_list_length();
 735   }
 736 
 737 private:
 738   //
 739   // Survivor regions policy.
 740   //
 741 
 742   // Current tenuring threshold, set to 0 if the collector reaches the
 743   // maximum amount of survivors regions.
 744   uint _tenuring_threshold;
 745 
 746   // The limit on the number of regions allocated for survivors.
 747   uint _max_survivor_regions;
 748 
 749   // For reporting purposes.
 750   // The value of _heap_bytes_before_gc is also used to calculate
 751   // the cost of copying.
 752 
 753   size_t _eden_used_bytes_before_gc;         // Eden occupancy before GC
 754   size_t _survivor_used_bytes_before_gc;     // Survivor occupancy before GC
 755   size_t _old_used_bytes_before_gc;          // Old occupancy before GC
 756   size_t _heap_used_bytes_before_gc;         // Heap occupancy before GC
 757   size_t _metaspace_used_bytes_before_gc;    // Metaspace occupancy before GC
 758 
 759   size_t _eden_capacity_bytes_before_gc;     // Eden capacity before GC
 760   size_t _heap_capacity_bytes_before_gc;     // Heap capacity before GC
 761 
 762   // The amount of survivor regions after a collection.
 763   uint _recorded_survivor_regions;
 764   // List of survivor regions.
 765   HeapRegion* _recorded_survivor_head;
 766   HeapRegion* _recorded_survivor_tail;
 767 
 768   ageTable _survivors_age_table;
 769 
 770 public:
 771   uint tenuring_threshold() const { return _tenuring_threshold; }
 772 
 773   static const uint REGIONS_UNLIMITED = (uint) -1;
 774 
 775   uint max_regions(InCSetState dest) const {
 776     switch (dest.value()) {
 777       case InCSetState::Young:
 778         return _max_survivor_regions;
 779       case InCSetState::Old:
 780         return REGIONS_UNLIMITED;
 781       default:
 782         assert(false, "Unknown dest state: " CSETSTATE_FORMAT, dest.value());
 783         break;
 784     }
 785     // keep some compilers happy
 786     return 0;
 787   }
 788 
 789   void note_start_adding_survivor_regions() {
 790     _survivor_surv_rate_group->start_adding_regions();
 791   }
 792 
 793   void note_stop_adding_survivor_regions() {
 794     _survivor_surv_rate_group->stop_adding_regions();
 795   }
 796 
 797   void record_survivor_regions(uint regions,
 798                                HeapRegion* head,
 799                                HeapRegion* tail) {
 800     _recorded_survivor_regions = regions;
 801     _recorded_survivor_head    = head;
 802     _recorded_survivor_tail    = tail;
 803   }
 804 
 805   uint recorded_survivor_regions() const {
 806     return _recorded_survivor_regions;
 807   }
 808 
 809   void record_age_table(ageTable* age_table) {
 810     _survivors_age_table.merge(age_table);
 811   }
 812 
 813   void update_max_gc_locker_expansion();
 814 
 815   // Calculates survivor space parameters.
 816   void update_survivors_policy();
 817 
 818   virtual void post_heap_initialize();
 819 };
 820 
 821 #endif // SHARE_VM_GC_G1_G1COLLECTORPOLICY_HPP