1 /*
   2  * Copyright (c) 2001, 2011, Oracle and/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
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP
  26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP
  27 
  28 #include "gc_implementation/g1/collectionSetChooser.hpp"
  29 #include "gc_implementation/g1/g1MMUTracker.hpp"
  30 #include "memory/collectorPolicy.hpp"
  31 
  32 // A G1CollectorPolicy makes policy decisions that determine the
  33 // characteristics of the collector.  Examples include:
  34 //   * choice of collection set.
  35 //   * when to collect.
  36 
  37 class HeapRegion;
  38 class CollectionSetChooser;
  39 
  40 // Yes, this is a bit unpleasant... but it saves replicating the same thing
  41 // over and over again and introducing subtle problems through small typos and
  42 // cutting and pasting mistakes. The macros below introduces a number
  43 // sequnce into the following two classes and the methods that access it.
  44 
  45 #define define_num_seq(name)                                                  \
  46 private:                                                                      \
  47   NumberSeq _all_##name##_times_ms;                                           \
  48 public:                                                                       \
  49   void record_##name##_time_ms(double ms) {                                   \
  50     _all_##name##_times_ms.add(ms);                                           \
  51   }                                                                           \
  52   NumberSeq* get_##name##_seq() {                                             \
  53     return &_all_##name##_times_ms;                                           \
  54   }
  55 
  56 class MainBodySummary;
  57 
  58 class PauseSummary: public CHeapObj {
  59   define_num_seq(total)
  60     define_num_seq(other)
  61 
  62 public:
  63   virtual MainBodySummary*    main_body_summary()    { return NULL; }
  64 };
  65 
  66 class MainBodySummary: public CHeapObj {
  67   define_num_seq(satb_drain) // optional
  68   define_num_seq(parallel) // parallel only
  69     define_num_seq(ext_root_scan)
  70     define_num_seq(mark_stack_scan)
  71     define_num_seq(update_rs)
  72     define_num_seq(scan_rs)
  73     define_num_seq(obj_copy)
  74     define_num_seq(termination) // parallel only
  75     define_num_seq(parallel_other) // parallel only
  76   define_num_seq(mark_closure)
  77   define_num_seq(clear_ct)  // parallel only
  78 };
  79 
  80 class Summary: public PauseSummary,
  81                public MainBodySummary {
  82 public:
  83   virtual MainBodySummary*    main_body_summary()    { return this; }
  84 };
  85 
  86 class G1CollectorPolicy: public CollectorPolicy {
  87 protected:
  88   // The number of pauses during the execution.
  89   long _n_pauses;
  90 
  91   // either equal to the number of parallel threads, if ParallelGCThreads
  92   // has been set, or 1 otherwise
  93   int _parallel_gc_threads;
  94 
  95   enum SomePrivateConstants {
  96     NumPrevPausesForHeuristics = 10
  97   };
  98 
  99   G1MMUTracker* _mmu_tracker;
 100 
 101   void initialize_flags();
 102 
 103   void initialize_all() {
 104     initialize_flags();
 105     initialize_size_info();
 106     initialize_perm_generation(PermGen::MarkSweepCompact);
 107   }
 108 
 109   virtual size_t default_init_heap_size() {
 110     // Pick some reasonable default.
 111     return 8*M;
 112   }
 113 
 114   double _cur_collection_start_sec;
 115   size_t _cur_collection_pause_used_at_start_bytes;
 116   size_t _cur_collection_pause_used_regions_at_start;
 117   size_t _prev_collection_pause_used_at_end_bytes;
 118   double _cur_collection_par_time_ms;
 119   double _cur_satb_drain_time_ms;
 120   double _cur_clear_ct_time_ms;
 121   bool   _satb_drain_time_set;
 122 
 123 #ifndef PRODUCT
 124   // Card Table Count Cache stats
 125   double _min_clear_cc_time_ms;         // min
 126   double _max_clear_cc_time_ms;         // max
 127   double _cur_clear_cc_time_ms;         // clearing time during current pause
 128   double _cum_clear_cc_time_ms;         // cummulative clearing time
 129   jlong  _num_cc_clears;                // number of times the card count cache has been cleared
 130 #endif
 131 
 132   // Statistics for recent GC pauses.  See below for how indexed.
 133   TruncatedSeq* _recent_rs_scan_times_ms;
 134 
 135   // These exclude marking times.
 136   TruncatedSeq* _recent_pause_times_ms;
 137   TruncatedSeq* _recent_gc_times_ms;
 138 
 139   TruncatedSeq* _recent_CS_bytes_used_before;
 140   TruncatedSeq* _recent_CS_bytes_surviving;
 141 
 142   TruncatedSeq* _recent_rs_sizes;
 143 
 144   TruncatedSeq* _concurrent_mark_remark_times_ms;
 145   TruncatedSeq* _concurrent_mark_cleanup_times_ms;
 146 
 147   Summary*           _summary;
 148 
 149   NumberSeq* _all_pause_times_ms;
 150   NumberSeq* _all_full_gc_times_ms;
 151   double _stop_world_start;
 152   NumberSeq* _all_stop_world_times_ms;
 153   NumberSeq* _all_yield_times_ms;
 154 
 155   size_t     _region_num_young;
 156   size_t     _region_num_tenured;
 157   size_t     _prev_region_num_young;
 158   size_t     _prev_region_num_tenured;
 159 
 160   NumberSeq* _all_mod_union_times_ms;
 161 
 162   int        _aux_num;
 163   NumberSeq* _all_aux_times_ms;
 164   double*    _cur_aux_start_times_ms;
 165   double*    _cur_aux_times_ms;
 166   bool*      _cur_aux_times_set;
 167 
 168   double* _par_last_gc_worker_start_times_ms;
 169   double* _par_last_ext_root_scan_times_ms;
 170   double* _par_last_mark_stack_scan_times_ms;
 171   double* _par_last_update_rs_times_ms;
 172   double* _par_last_update_rs_processed_buffers;
 173   double* _par_last_scan_rs_times_ms;
 174   double* _par_last_obj_copy_times_ms;
 175   double* _par_last_termination_times_ms;
 176   double* _par_last_termination_attempts;
 177   double* _par_last_gc_worker_end_times_ms;
 178   double* _par_last_gc_worker_times_ms;
 179 
 180   // indicates whether we are in full young or partially young GC mode
 181   bool _full_young_gcs;
 182 
 183   // if true, then it tries to dynamically adjust the length of the
 184   // young list
 185   bool _adaptive_young_list_length;
 186   size_t _young_list_min_length;
 187   size_t _young_list_target_length;
 188   size_t _young_list_fixed_length;
 189 
 190   // The max number of regions we can extend the eden by while the GC
 191   // locker is active. This should be >= _young_list_target_length;
 192   size_t _young_list_max_length;
 193 
 194   size_t _young_cset_length;
 195   bool   _last_young_gc_full;
 196 
 197   unsigned              _full_young_pause_num;
 198   unsigned              _partial_young_pause_num;
 199 
 200   bool                  _during_marking;
 201   bool                  _in_marking_window;
 202   bool                  _in_marking_window_im;
 203 
 204   SurvRateGroup*        _short_lived_surv_rate_group;
 205   SurvRateGroup*        _survivor_surv_rate_group;
 206   // add here any more surv rate groups
 207 
 208   double                _gc_overhead_perc;
 209 
 210   bool during_marking() {
 211     return _during_marking;
 212   }
 213 
 214   // <NEW PREDICTION>
 215 
 216 private:
 217   enum PredictionConstants {
 218     TruncatedSeqLength = 10
 219   };
 220 
 221   TruncatedSeq* _alloc_rate_ms_seq;
 222   double        _prev_collection_pause_end_ms;
 223 
 224   TruncatedSeq* _pending_card_diff_seq;
 225   TruncatedSeq* _rs_length_diff_seq;
 226   TruncatedSeq* _cost_per_card_ms_seq;
 227   TruncatedSeq* _fully_young_cards_per_entry_ratio_seq;
 228   TruncatedSeq* _partially_young_cards_per_entry_ratio_seq;
 229   TruncatedSeq* _cost_per_entry_ms_seq;
 230   TruncatedSeq* _partially_young_cost_per_entry_ms_seq;
 231   TruncatedSeq* _cost_per_byte_ms_seq;
 232   TruncatedSeq* _constant_other_time_ms_seq;
 233   TruncatedSeq* _young_other_cost_per_region_ms_seq;
 234   TruncatedSeq* _non_young_other_cost_per_region_ms_seq;
 235 
 236   TruncatedSeq* _pending_cards_seq;
 237   TruncatedSeq* _scanned_cards_seq;
 238   TruncatedSeq* _rs_lengths_seq;
 239 
 240   TruncatedSeq* _cost_per_byte_ms_during_cm_seq;
 241 
 242   TruncatedSeq* _young_gc_eff_seq;
 243 
 244   TruncatedSeq* _max_conc_overhead_seq;
 245 
 246   size_t _recorded_young_regions;
 247   size_t _recorded_non_young_regions;
 248   size_t _recorded_region_num;
 249 
 250   size_t _free_regions_at_end_of_collection;
 251 
 252   size_t _recorded_rs_lengths;
 253   size_t _max_rs_lengths;
 254 
 255   size_t _recorded_marked_bytes;
 256   size_t _recorded_young_bytes;
 257 
 258   size_t _predicted_pending_cards;
 259   size_t _predicted_cards_scanned;
 260   size_t _predicted_rs_lengths;
 261   size_t _predicted_bytes_to_copy;
 262 
 263   double _predicted_survival_ratio;
 264   double _predicted_rs_update_time_ms;
 265   double _predicted_rs_scan_time_ms;
 266   double _predicted_object_copy_time_ms;
 267   double _predicted_constant_other_time_ms;
 268   double _predicted_young_other_time_ms;
 269   double _predicted_non_young_other_time_ms;
 270   double _predicted_pause_time_ms;
 271 
 272   double _vtime_diff_ms;
 273 
 274   double _recorded_young_free_cset_time_ms;
 275   double _recorded_non_young_free_cset_time_ms;
 276 
 277   double _sigma;
 278   double _expensive_region_limit_ms;
 279 
 280   size_t _rs_lengths_prediction;
 281 
 282   size_t _known_garbage_bytes;
 283   double _known_garbage_ratio;
 284 
 285   double sigma() {
 286     return _sigma;
 287   }
 288 
 289   // A function that prevents us putting too much stock in small sample
 290   // sets.  Returns a number between 2.0 and 1.0, depending on the number
 291   // of samples.  5 or more samples yields one; fewer scales linearly from
 292   // 2.0 at 1 sample to 1.0 at 5.
 293   double confidence_factor(int samples) {
 294     if (samples > 4) return 1.0;
 295     else return  1.0 + sigma() * ((double)(5 - samples))/2.0;
 296   }
 297 
 298   double get_new_neg_prediction(TruncatedSeq* seq) {
 299     return seq->davg() - sigma() * seq->dsd();
 300   }
 301 
 302 #ifndef PRODUCT
 303   bool verify_young_ages(HeapRegion* head, SurvRateGroup *surv_rate_group);
 304 #endif // PRODUCT
 305 
 306   void adjust_concurrent_refinement(double update_rs_time,
 307                                     double update_rs_processed_buffers,
 308                                     double goal_ms);
 309 
 310 protected:
 311   double _pause_time_target_ms;
 312   double _recorded_young_cset_choice_time_ms;
 313   double _recorded_non_young_cset_choice_time_ms;
 314   bool   _within_target;
 315   size_t _pending_cards;
 316   size_t _max_pending_cards;
 317 
 318 public:
 319 
 320   void set_region_short_lived(HeapRegion* hr) {
 321     hr->install_surv_rate_group(_short_lived_surv_rate_group);
 322   }
 323 
 324   void set_region_survivors(HeapRegion* hr) {
 325     hr->install_surv_rate_group(_survivor_surv_rate_group);
 326   }
 327 
 328 #ifndef PRODUCT
 329   bool verify_young_ages();
 330 #endif // PRODUCT
 331 
 332   double get_new_prediction(TruncatedSeq* seq) {
 333     return MAX2(seq->davg() + sigma() * seq->dsd(),
 334                 seq->davg() * confidence_factor(seq->num()));
 335   }
 336 
 337   size_t young_cset_length() {
 338     return _young_cset_length;
 339   }
 340 
 341   void record_max_rs_lengths(size_t rs_lengths) {
 342     _max_rs_lengths = rs_lengths;
 343   }
 344 
 345   size_t predict_pending_card_diff() {
 346     double prediction = get_new_neg_prediction(_pending_card_diff_seq);
 347     if (prediction < 0.00001)
 348       return 0;
 349     else
 350       return (size_t) prediction;
 351   }
 352 
 353   size_t predict_pending_cards() {
 354     size_t max_pending_card_num = _g1->max_pending_card_num();
 355     size_t diff = predict_pending_card_diff();
 356     size_t prediction;
 357     if (diff > max_pending_card_num)
 358       prediction = max_pending_card_num;
 359     else
 360       prediction = max_pending_card_num - diff;
 361 
 362     return prediction;
 363   }
 364 
 365   size_t predict_rs_length_diff() {
 366     return (size_t) get_new_prediction(_rs_length_diff_seq);
 367   }
 368 
 369   double predict_alloc_rate_ms() {
 370     return get_new_prediction(_alloc_rate_ms_seq);
 371   }
 372 
 373   double predict_cost_per_card_ms() {
 374     return get_new_prediction(_cost_per_card_ms_seq);
 375   }
 376 
 377   double predict_rs_update_time_ms(size_t pending_cards) {
 378     return (double) pending_cards * predict_cost_per_card_ms();
 379   }
 380 
 381   double predict_fully_young_cards_per_entry_ratio() {
 382     return get_new_prediction(_fully_young_cards_per_entry_ratio_seq);
 383   }
 384 
 385   double predict_partially_young_cards_per_entry_ratio() {
 386     if (_partially_young_cards_per_entry_ratio_seq->num() < 2)
 387       return predict_fully_young_cards_per_entry_ratio();
 388     else
 389       return get_new_prediction(_partially_young_cards_per_entry_ratio_seq);
 390   }
 391 
 392   size_t predict_young_card_num(size_t rs_length) {
 393     return (size_t) ((double) rs_length *
 394                      predict_fully_young_cards_per_entry_ratio());
 395   }
 396 
 397   size_t predict_non_young_card_num(size_t rs_length) {
 398     return (size_t) ((double) rs_length *
 399                      predict_partially_young_cards_per_entry_ratio());
 400   }
 401 
 402   double predict_rs_scan_time_ms(size_t card_num) {
 403     if (full_young_gcs())
 404       return (double) card_num * get_new_prediction(_cost_per_entry_ms_seq);
 405     else
 406       return predict_partially_young_rs_scan_time_ms(card_num);
 407   }
 408 
 409   double predict_partially_young_rs_scan_time_ms(size_t card_num) {
 410     if (_partially_young_cost_per_entry_ms_seq->num() < 3)
 411       return (double) card_num * get_new_prediction(_cost_per_entry_ms_seq);
 412     else
 413       return (double) card_num *
 414         get_new_prediction(_partially_young_cost_per_entry_ms_seq);
 415   }
 416 
 417   double predict_object_copy_time_ms_during_cm(size_t bytes_to_copy) {
 418     if (_cost_per_byte_ms_during_cm_seq->num() < 3)
 419       return 1.1 * (double) bytes_to_copy *
 420         get_new_prediction(_cost_per_byte_ms_seq);
 421     else
 422       return (double) bytes_to_copy *
 423         get_new_prediction(_cost_per_byte_ms_during_cm_seq);
 424   }
 425 
 426   double predict_object_copy_time_ms(size_t bytes_to_copy) {
 427     if (_in_marking_window && !_in_marking_window_im)
 428       return predict_object_copy_time_ms_during_cm(bytes_to_copy);
 429     else
 430       return (double) bytes_to_copy *
 431         get_new_prediction(_cost_per_byte_ms_seq);
 432   }
 433 
 434   double predict_constant_other_time_ms() {
 435     return get_new_prediction(_constant_other_time_ms_seq);
 436   }
 437 
 438   double predict_young_other_time_ms(size_t young_num) {
 439     return
 440       (double) young_num *
 441       get_new_prediction(_young_other_cost_per_region_ms_seq);
 442   }
 443 
 444   double predict_non_young_other_time_ms(size_t non_young_num) {
 445     return
 446       (double) non_young_num *
 447       get_new_prediction(_non_young_other_cost_per_region_ms_seq);
 448   }
 449 
 450   void check_if_region_is_too_expensive(double predicted_time_ms);
 451 
 452   double predict_young_collection_elapsed_time_ms(size_t adjustment);
 453   double predict_base_elapsed_time_ms(size_t pending_cards);
 454   double predict_base_elapsed_time_ms(size_t pending_cards,
 455                                       size_t scanned_cards);
 456   size_t predict_bytes_to_copy(HeapRegion* hr);
 457   double predict_region_elapsed_time_ms(HeapRegion* hr, bool young);
 458 
 459     // for use by: calculate_young_list_target_length(rs_length)
 460   bool predict_will_fit(size_t young_region_num,
 461                         double base_time_ms,
 462                         size_t init_free_regions,
 463                         double target_pause_time_ms);
 464 
 465   void start_recording_regions();
 466   void record_cset_region_info(HeapRegion* hr, bool young);
 467   void record_non_young_cset_region(HeapRegion* hr);
 468 
 469   void set_recorded_young_regions(size_t n_regions);
 470   void set_recorded_young_bytes(size_t bytes);
 471   void set_recorded_rs_lengths(size_t rs_lengths);
 472   void set_predicted_bytes_to_copy(size_t bytes);
 473 
 474   void end_recording_regions();
 475 
 476   void record_vtime_diff_ms(double vtime_diff_ms) {
 477     _vtime_diff_ms = vtime_diff_ms;
 478   }
 479 
 480   void record_young_free_cset_time_ms(double time_ms) {
 481     _recorded_young_free_cset_time_ms = time_ms;
 482   }
 483 
 484   void record_non_young_free_cset_time_ms(double time_ms) {
 485     _recorded_non_young_free_cset_time_ms = time_ms;
 486   }
 487 
 488   double predict_young_gc_eff() {
 489     return get_new_neg_prediction(_young_gc_eff_seq);
 490   }
 491 
 492   double predict_survivor_regions_evac_time();
 493 
 494   // </NEW PREDICTION>
 495 
 496 public:
 497   void cset_regions_freed() {
 498     bool propagate = _last_young_gc_full && !_in_marking_window;
 499     _short_lived_surv_rate_group->all_surviving_words_recorded(propagate);
 500     _survivor_surv_rate_group->all_surviving_words_recorded(propagate);
 501     // also call it on any more surv rate groups
 502   }
 503 
 504   void set_known_garbage_bytes(size_t known_garbage_bytes) {
 505     _known_garbage_bytes = known_garbage_bytes;
 506     size_t heap_bytes = _g1->capacity();
 507     _known_garbage_ratio = (double) _known_garbage_bytes / (double) heap_bytes;
 508   }
 509 
 510   void decrease_known_garbage_bytes(size_t known_garbage_bytes) {
 511     guarantee( _known_garbage_bytes >= known_garbage_bytes, "invariant" );
 512 
 513     _known_garbage_bytes -= known_garbage_bytes;
 514     size_t heap_bytes = _g1->capacity();
 515     _known_garbage_ratio = (double) _known_garbage_bytes / (double) heap_bytes;
 516   }
 517 
 518   G1MMUTracker* mmu_tracker() {
 519     return _mmu_tracker;
 520   }
 521 
 522   double max_pause_time_ms() {
 523     return _mmu_tracker->max_gc_time() * 1000.0;
 524   }
 525 
 526   double predict_remark_time_ms() {
 527     return get_new_prediction(_concurrent_mark_remark_times_ms);
 528   }
 529 
 530   double predict_cleanup_time_ms() {
 531     return get_new_prediction(_concurrent_mark_cleanup_times_ms);
 532   }
 533 
 534   // Returns an estimate of the survival rate of the region at yg-age
 535   // "yg_age".
 536   double predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) {
 537     TruncatedSeq* seq = surv_rate_group->get_seq(age);
 538     if (seq->num() == 0)
 539       gclog_or_tty->print("BARF! age is %d", age);
 540     guarantee( seq->num() > 0, "invariant" );
 541     double pred = get_new_prediction(seq);
 542     if (pred > 1.0)
 543       pred = 1.0;
 544     return pred;
 545   }
 546 
 547   double predict_yg_surv_rate(int age) {
 548     return predict_yg_surv_rate(age, _short_lived_surv_rate_group);
 549   }
 550 
 551   double accum_yg_surv_rate_pred(int age) {
 552     return _short_lived_surv_rate_group->accum_surv_rate_pred(age);
 553   }
 554 
 555 protected:
 556   void print_stats(int level, const char* str, double value);
 557   void print_stats(int level, const char* str, int value);
 558 
 559   void print_par_stats(int level, const char* str, double* data);
 560   void print_par_sizes(int level, const char* str, double* data);
 561 
 562   void check_other_times(int level,
 563                          NumberSeq* other_times_ms,
 564                          NumberSeq* calc_other_times_ms) const;
 565 
 566   void print_summary (PauseSummary* stats) const;
 567 
 568   void print_summary (int level, const char* str, NumberSeq* seq) const;
 569   void print_summary_sd (int level, const char* str, NumberSeq* seq) const;
 570 
 571   double avg_value (double* data);
 572   double max_value (double* data);
 573   double sum_of_values (double* data);
 574   double max_sum (double* data1, double* data2);
 575 
 576   int _last_satb_drain_processed_buffers;
 577   int _last_update_rs_processed_buffers;
 578   double _last_pause_time_ms;
 579 
 580   size_t _bytes_in_collection_set_before_gc;
 581   size_t _bytes_copied_during_gc;
 582 
 583   // Used to count used bytes in CS.
 584   friend class CountCSClosure;
 585 
 586   // Statistics kept per GC stoppage, pause or full.
 587   TruncatedSeq* _recent_prev_end_times_for_all_gcs_sec;
 588 
 589   // We track markings.
 590   int _num_markings;
 591   double _mark_thread_startup_sec;       // Time at startup of marking thread
 592 
 593   // Add a new GC of the given duration and end time to the record.
 594   void update_recent_gc_times(double end_time_sec, double elapsed_ms);
 595 
 596   // The head of the list (via "next_in_collection_set()") representing the
 597   // current collection set. Set from the incrementally built collection
 598   // set at the start of the pause.
 599   HeapRegion* _collection_set;
 600 
 601   // The number of regions in the collection set. Set from the incrementally
 602   // built collection set at the start of an evacuation pause.
 603   size_t _collection_set_size;
 604 
 605   // The number of bytes in the collection set before the pause. Set from
 606   // the incrementally built collection set at the start of an evacuation
 607   // pause.
 608   size_t _collection_set_bytes_used_before;
 609 
 610   // The associated information that is maintained while the incremental
 611   // collection set is being built with young regions. Used to populate
 612   // the recorded info for the evacuation pause.
 613 
 614   enum CSetBuildType {
 615     Active,             // We are actively building the collection set
 616     Inactive            // We are not actively building the collection set
 617   };
 618 
 619   CSetBuildType _inc_cset_build_state;
 620 
 621   // The head of the incrementally built collection set.
 622   HeapRegion* _inc_cset_head;
 623 
 624   // The tail of the incrementally built collection set.
 625   HeapRegion* _inc_cset_tail;
 626 
 627   // The number of regions in the incrementally built collection set.
 628   // Used to set _collection_set_size at the start of an evacuation
 629   // pause.
 630   size_t _inc_cset_size;
 631 
 632   // Used as the index in the surving young words structure
 633   // which tracks the amount of space, for each young region,
 634   // that survives the pause.
 635   size_t _inc_cset_young_index;
 636 
 637   // The number of bytes in the incrementally built collection set.
 638   // Used to set _collection_set_bytes_used_before at the start of
 639   // an evacuation pause.
 640   size_t _inc_cset_bytes_used_before;
 641 
 642   // Used to record the highest end of heap region in collection set
 643   HeapWord* _inc_cset_max_finger;
 644 
 645   // The number of recorded used bytes in the young regions
 646   // of the collection set. This is the sum of the used() bytes
 647   // of retired young regions in the collection set.
 648   size_t _inc_cset_recorded_young_bytes;
 649 
 650   // The RSet lengths recorded for regions in the collection set
 651   // (updated by the periodic sampling of the regions in the
 652   // young list/collection set).
 653   size_t _inc_cset_recorded_rs_lengths;
 654 
 655   // The predicted elapsed time it will take to collect the regions
 656   // in the collection set (updated by the periodic sampling of the
 657   // regions in the young list/collection set).
 658   double _inc_cset_predicted_elapsed_time_ms;
 659 
 660   // The predicted bytes to copy for the regions in the collection
 661   // set (updated by the periodic sampling of the regions in the
 662   // young list/collection set).
 663   size_t _inc_cset_predicted_bytes_to_copy;
 664 
 665   // Info about marking.
 666   int _n_marks; // Sticky at 2, so we know when we've done at least 2.
 667 
 668   // The number of collection pauses at the end of the last mark.
 669   size_t _n_pauses_at_mark_end;
 670 
 671   // Stash a pointer to the g1 heap.
 672   G1CollectedHeap* _g1;
 673 
 674   // The average time in ms per collection pause, averaged over recent pauses.
 675   double recent_avg_time_for_pauses_ms();
 676 
 677   // The average time in ms for RS scanning, per pause, averaged
 678   // over recent pauses. (Note the RS scanning time for a pause
 679   // is itself an average of the RS scanning time for each worker
 680   // thread.)
 681   double recent_avg_time_for_rs_scan_ms();
 682 
 683   // The number of "recent" GCs recorded in the number sequences
 684   int number_of_recent_gcs();
 685 
 686   // The average survival ratio, computed by the total number of bytes
 687   // suriviving / total number of bytes before collection over the last
 688   // several recent pauses.
 689   double recent_avg_survival_fraction();
 690   // The survival fraction of the most recent pause; if there have been no
 691   // pauses, returns 1.0.
 692   double last_survival_fraction();
 693 
 694   // Returns a "conservative" estimate of the recent survival rate, i.e.,
 695   // one that may be higher than "recent_avg_survival_fraction".
 696   // This is conservative in several ways:
 697   //   If there have been few pauses, it will assume a potential high
 698   //     variance, and err on the side of caution.
 699   //   It puts a lower bound (currently 0.1) on the value it will return.
 700   //   To try to detect phase changes, if the most recent pause ("latest") has a
 701   //     higher-than average ("avg") survival rate, it returns that rate.
 702   // "work" version is a utility function; young is restricted to young regions.
 703   double conservative_avg_survival_fraction_work(double avg,
 704                                                  double latest);
 705 
 706   // The arguments are the two sequences that keep track of the number of bytes
 707   //   surviving and the total number of bytes before collection, resp.,
 708   //   over the last evereal recent pauses
 709   // Returns the survival rate for the category in the most recent pause.
 710   // If there have been no pauses, returns 1.0.
 711   double last_survival_fraction_work(TruncatedSeq* surviving,
 712                                      TruncatedSeq* before);
 713 
 714   // The arguments are the two sequences that keep track of the number of bytes
 715   //   surviving and the total number of bytes before collection, resp.,
 716   //   over the last several recent pauses
 717   // Returns the average survival ration over the last several recent pauses
 718   // If there have been no pauses, return 1.0
 719   double recent_avg_survival_fraction_work(TruncatedSeq* surviving,
 720                                            TruncatedSeq* before);
 721 
 722   double conservative_avg_survival_fraction() {
 723     double avg = recent_avg_survival_fraction();
 724     double latest = last_survival_fraction();
 725     return conservative_avg_survival_fraction_work(avg, latest);
 726   }
 727 
 728   // The ratio of gc time to elapsed time, computed over recent pauses.
 729   double _recent_avg_pause_time_ratio;
 730 
 731   double recent_avg_pause_time_ratio() {
 732     return _recent_avg_pause_time_ratio;
 733   }
 734 
 735   // Number of pauses between concurrent marking.
 736   size_t _pauses_btwn_concurrent_mark;
 737 
 738   size_t _n_marks_since_last_pause;
 739 
 740   // At the end of a pause we check the heap occupancy and we decide
 741   // whether we will start a marking cycle during the next pause. If
 742   // we decide that we want to do that, we will set this parameter to
 743   // true. So, this parameter will stay true between the end of a
 744   // pause and the beginning of a subsequent pause (not necessarily
 745   // the next one, see the comments on the next field) when we decide
 746   // that we will indeed start a marking cycle and do the initial-mark
 747   // work.
 748   volatile bool _initiate_conc_mark_if_possible;
 749 
 750   // If initiate_conc_mark_if_possible() is set at the beginning of a
 751   // pause, it is a suggestion that the pause should start a marking
 752   // cycle by doing the initial-mark work. However, it is possible
 753   // that the concurrent marking thread is still finishing up the
 754   // previous marking cycle (e.g., clearing the next marking
 755   // bitmap). If that is the case we cannot start a new cycle and
 756   // we'll have to wait for the concurrent marking thread to finish
 757   // what it is doing. In this case we will postpone the marking cycle
 758   // initiation decision for the next pause. When we eventually decide
 759   // to start a cycle, we will set _during_initial_mark_pause which
 760   // will stay true until the end of the initial-mark pause and it's
 761   // the condition that indicates that a pause is doing the
 762   // initial-mark work.
 763   volatile bool _during_initial_mark_pause;
 764 
 765   bool _should_revert_to_full_young_gcs;
 766   bool _last_full_young_gc;
 767 
 768   // This set of variables tracks the collector efficiency, in order to
 769   // determine whether we should initiate a new marking.
 770   double _cur_mark_stop_world_time_ms;
 771   double _mark_remark_start_sec;
 772   double _mark_cleanup_start_sec;
 773   double _mark_closure_time_ms;
 774 
 775   void   calculate_young_list_min_length();
 776   void   calculate_young_list_target_length();
 777   void   calculate_young_list_target_length(size_t rs_lengths);
 778 
 779 public:
 780 
 781   G1CollectorPolicy();
 782 
 783   virtual G1CollectorPolicy* as_g1_policy() { return this; }
 784 
 785   virtual CollectorPolicy::Name kind() {
 786     return CollectorPolicy::G1CollectorPolicyKind;
 787   }
 788 
 789   void check_prediction_validity();
 790 
 791   size_t bytes_in_collection_set() {
 792     return _bytes_in_collection_set_before_gc;
 793   }
 794 
 795   unsigned calc_gc_alloc_time_stamp() {
 796     return _all_pause_times_ms->num() + 1;
 797   }
 798 
 799 protected:
 800 
 801   // Count the number of bytes used in the CS.
 802   void count_CS_bytes_used();
 803 
 804   // Together these do the base cleanup-recording work.  Subclasses might
 805   // want to put something between them.
 806   void record_concurrent_mark_cleanup_end_work1(size_t freed_bytes,
 807                                                 size_t max_live_bytes);
 808   void record_concurrent_mark_cleanup_end_work2();
 809 
 810 public:
 811 
 812   virtual void init();
 813 
 814   // Create jstat counters for the policy.
 815   virtual void initialize_gc_policy_counters();
 816 
 817   virtual HeapWord* mem_allocate_work(size_t size,
 818                                       bool is_tlab,
 819                                       bool* gc_overhead_limit_was_exceeded);
 820 
 821   // This method controls how a collector handles one or more
 822   // of its generations being fully allocated.
 823   virtual HeapWord* satisfy_failed_allocation(size_t size,
 824                                               bool is_tlab);
 825 
 826   BarrierSet::Name barrier_set_name() { return BarrierSet::G1SATBCTLogging; }
 827 
 828   GenRemSet::Name  rem_set_name()     { return GenRemSet::CardTable; }
 829 
 830   // The number of collection pauses so far.
 831   long n_pauses() const { return _n_pauses; }
 832 
 833   // Update the heuristic info to record a collection pause of the given
 834   // start time, where the given number of bytes were used at the start.
 835   // This may involve changing the desired size of a collection set.
 836 
 837   virtual void record_stop_world_start();
 838 
 839   virtual void record_collection_pause_start(double start_time_sec,
 840                                              size_t start_used);
 841 
 842   // Must currently be called while the world is stopped.
 843   void record_concurrent_mark_init_end(double
 844                                            mark_init_elapsed_time_ms);
 845 
 846   void record_mark_closure_time(double mark_closure_time_ms);
 847 
 848   virtual void record_concurrent_mark_remark_start();
 849   virtual void record_concurrent_mark_remark_end();
 850 
 851   virtual void record_concurrent_mark_cleanup_start();
 852   virtual void record_concurrent_mark_cleanup_end(size_t freed_bytes,
 853                                                   size_t max_live_bytes);
 854   virtual void record_concurrent_mark_cleanup_completed();
 855 
 856   virtual void record_concurrent_pause();
 857   virtual void record_concurrent_pause_end();
 858 
 859   virtual void record_collection_pause_end();
 860   void print_heap_transition();
 861 
 862   // Record the fact that a full collection occurred.
 863   virtual void record_full_collection_start();
 864   virtual void record_full_collection_end();
 865 
 866   void record_gc_worker_start_time(int worker_i, double ms) {
 867     _par_last_gc_worker_start_times_ms[worker_i] = ms;
 868   }
 869 
 870   void record_ext_root_scan_time(int worker_i, double ms) {
 871     _par_last_ext_root_scan_times_ms[worker_i] = ms;
 872   }
 873 
 874   void record_mark_stack_scan_time(int worker_i, double ms) {
 875     _par_last_mark_stack_scan_times_ms[worker_i] = ms;
 876   }
 877 
 878   void record_satb_drain_time(double ms) {
 879     _cur_satb_drain_time_ms = ms;
 880     _satb_drain_time_set    = true;
 881   }
 882 
 883   void record_satb_drain_processed_buffers (int processed_buffers) {
 884     _last_satb_drain_processed_buffers = processed_buffers;
 885   }
 886 
 887   void record_mod_union_time(double ms) {
 888     _all_mod_union_times_ms->add(ms);
 889   }
 890 
 891   void record_update_rs_time(int thread, double ms) {
 892     _par_last_update_rs_times_ms[thread] = ms;
 893   }
 894 
 895   void record_update_rs_processed_buffers (int thread,
 896                                            double processed_buffers) {
 897     _par_last_update_rs_processed_buffers[thread] = processed_buffers;
 898   }
 899 
 900   void record_scan_rs_time(int thread, double ms) {
 901     _par_last_scan_rs_times_ms[thread] = ms;
 902   }
 903 
 904   void reset_obj_copy_time(int thread) {
 905     _par_last_obj_copy_times_ms[thread] = 0.0;
 906   }
 907 
 908   void reset_obj_copy_time() {
 909     reset_obj_copy_time(0);
 910   }
 911 
 912   void record_obj_copy_time(int thread, double ms) {
 913     _par_last_obj_copy_times_ms[thread] += ms;
 914   }
 915 
 916   void record_termination(int thread, double ms, size_t attempts) {
 917     _par_last_termination_times_ms[thread] = ms;
 918     _par_last_termination_attempts[thread] = (double) attempts;
 919   }
 920 
 921   void record_gc_worker_end_time(int worker_i, double ms) {
 922     _par_last_gc_worker_end_times_ms[worker_i] = ms;
 923   }
 924 
 925   void record_pause_time_ms(double ms) {
 926     _last_pause_time_ms = ms;
 927   }
 928 
 929   void record_clear_ct_time(double ms) {
 930     _cur_clear_ct_time_ms = ms;
 931   }
 932 
 933   void record_par_time(double ms) {
 934     _cur_collection_par_time_ms = ms;
 935   }
 936 
 937   void record_aux_start_time(int i) {
 938     guarantee(i < _aux_num, "should be within range");
 939     _cur_aux_start_times_ms[i] = os::elapsedTime() * 1000.0;
 940   }
 941 
 942   void record_aux_end_time(int i) {
 943     guarantee(i < _aux_num, "should be within range");
 944     double ms = os::elapsedTime() * 1000.0 - _cur_aux_start_times_ms[i];
 945     _cur_aux_times_set[i] = true;
 946     _cur_aux_times_ms[i] += ms;
 947   }
 948 
 949 #ifndef PRODUCT
 950   void record_cc_clear_time(double ms) {
 951     if (_min_clear_cc_time_ms < 0.0 || ms <= _min_clear_cc_time_ms)
 952       _min_clear_cc_time_ms = ms;
 953     if (_max_clear_cc_time_ms < 0.0 || ms >= _max_clear_cc_time_ms)
 954       _max_clear_cc_time_ms = ms;
 955     _cur_clear_cc_time_ms = ms;
 956     _cum_clear_cc_time_ms += ms;
 957     _num_cc_clears++;
 958   }
 959 #endif
 960 
 961   // Record how much space we copied during a GC. This is typically
 962   // called when a GC alloc region is being retired.
 963   void record_bytes_copied_during_gc(size_t bytes) {
 964     _bytes_copied_during_gc += bytes;
 965   }
 966 
 967   // The amount of space we copied during a GC.
 968   size_t bytes_copied_during_gc() {
 969     return _bytes_copied_during_gc;
 970   }
 971 
 972   // Choose a new collection set.  Marks the chosen regions as being
 973   // "in_collection_set", and links them together.  The head and number of
 974   // the collection set are available via access methods.
 975   virtual void choose_collection_set(double target_pause_time_ms) = 0;
 976 
 977   // The head of the list (via "next_in_collection_set()") representing the
 978   // current collection set.
 979   HeapRegion* collection_set() { return _collection_set; }
 980 
 981   void clear_collection_set() { _collection_set = NULL; }
 982 
 983   // The number of elements in the current collection set.
 984   size_t collection_set_size() { return _collection_set_size; }
 985 
 986   // Add "hr" to the CS.
 987   void add_to_collection_set(HeapRegion* hr);
 988 
 989   // Incremental CSet Support
 990 
 991   // The head of the incrementally built collection set.
 992   HeapRegion* inc_cset_head() { return _inc_cset_head; }
 993 
 994   // The tail of the incrementally built collection set.
 995   HeapRegion* inc_set_tail() { return _inc_cset_tail; }
 996 
 997   // The number of elements in the incrementally built collection set.
 998   size_t inc_cset_size() { return _inc_cset_size; }
 999 
1000   // Initialize incremental collection set info.
1001   void start_incremental_cset_building();
1002 
1003   void clear_incremental_cset() {
1004     _inc_cset_head = NULL;
1005     _inc_cset_tail = NULL;
1006   }
1007 
1008   // Stop adding regions to the incremental collection set
1009   void stop_incremental_cset_building() { _inc_cset_build_state = Inactive; }
1010 
1011   // Add/remove information about hr to the aggregated information
1012   // for the incrementally built collection set.
1013   void add_to_incremental_cset_info(HeapRegion* hr, size_t rs_length);
1014   void remove_from_incremental_cset_info(HeapRegion* hr);
1015 
1016   // Update information about hr in the aggregated information for
1017   // the incrementally built collection set.
1018   void update_incremental_cset_info(HeapRegion* hr, size_t new_rs_length);
1019 
1020 private:
1021   // Update the incremental cset information when adding a region
1022   // (should not be called directly).
1023   void add_region_to_incremental_cset_common(HeapRegion* hr);
1024 
1025 public:
1026   // Add hr to the LHS of the incremental collection set.
1027   void add_region_to_incremental_cset_lhs(HeapRegion* hr);
1028 
1029   // Add hr to the RHS of the incremental collection set.
1030   void add_region_to_incremental_cset_rhs(HeapRegion* hr);
1031 
1032 #ifndef PRODUCT
1033   void print_collection_set(HeapRegion* list_head, outputStream* st);
1034 #endif // !PRODUCT
1035 
1036   bool initiate_conc_mark_if_possible()       { return _initiate_conc_mark_if_possible;  }
1037   void set_initiate_conc_mark_if_possible()   { _initiate_conc_mark_if_possible = true;  }
1038   void clear_initiate_conc_mark_if_possible() { _initiate_conc_mark_if_possible = false; }
1039 
1040   bool during_initial_mark_pause()      { return _during_initial_mark_pause;  }
1041   void set_during_initial_mark_pause()  { _during_initial_mark_pause = true;  }
1042   void clear_during_initial_mark_pause(){ _during_initial_mark_pause = false; }
1043 
1044   // This sets the initiate_conc_mark_if_possible() flag to start a
1045   // new cycle, as long as we are not already in one. It's best if it
1046   // is called during a safepoint when the test whether a cycle is in
1047   // progress or not is stable.
1048   bool force_initial_mark_if_outside_cycle();
1049 
1050   // This is called at the very beginning of an evacuation pause (it
1051   // has to be the first thing that the pause does). If
1052   // initiate_conc_mark_if_possible() is true, and the concurrent
1053   // marking thread has completed its work during the previous cycle,
1054   // it will set during_initial_mark_pause() to so that the pause does
1055   // the initial-mark work and start a marking cycle.
1056   void decide_on_conc_mark_initiation();
1057 
1058   // If an expansion would be appropriate, because recent GC overhead had
1059   // exceeded the desired limit, return an amount to expand by.
1060   virtual size_t expansion_amount();
1061 
1062   // note start of mark thread
1063   void note_start_of_mark_thread();
1064 
1065   // The marked bytes of the "r" has changed; reclassify it's desirability
1066   // for marking.  Also asserts that "r" is eligible for a CS.
1067   virtual void note_change_in_marked_bytes(HeapRegion* r) = 0;
1068 
1069 #ifndef PRODUCT
1070   // Check any appropriate marked bytes info, asserting false if
1071   // something's wrong, else returning "true".
1072   virtual bool assertMarkedBytesDataOK() = 0;
1073 #endif
1074 
1075   // Print tracing information.
1076   void print_tracing_info() const;
1077 
1078   // Print stats on young survival ratio
1079   void print_yg_surv_rate_info() const;
1080 
1081   void finished_recalculating_age_indexes(bool is_survivors) {
1082     if (is_survivors) {
1083       _survivor_surv_rate_group->finished_recalculating_age_indexes();
1084     } else {
1085       _short_lived_surv_rate_group->finished_recalculating_age_indexes();
1086     }
1087     // do that for any other surv rate groups
1088   }
1089 
1090   bool is_young_list_full() {
1091     size_t young_list_length = _g1->young_list()->length();
1092     size_t young_list_target_length = _young_list_target_length;
1093     if (G1FixedEdenSize) {
1094       young_list_target_length -= _max_survivor_regions;
1095     }
1096     return young_list_length >= young_list_target_length;
1097   }
1098 
1099   bool can_expand_young_list() {
1100     size_t young_list_length = _g1->young_list()->length();
1101     size_t young_list_max_length = _young_list_max_length;
1102     if (G1FixedEdenSize) {
1103       young_list_max_length -= _max_survivor_regions;
1104     }
1105     return young_list_length < young_list_max_length;
1106   }
1107 
1108   void update_region_num(bool young);
1109 
1110   bool full_young_gcs() {
1111     return _full_young_gcs;
1112   }
1113   void set_full_young_gcs(bool full_young_gcs) {
1114     _full_young_gcs = full_young_gcs;
1115   }
1116 
1117   bool adaptive_young_list_length() {
1118     return _adaptive_young_list_length;
1119   }
1120   void set_adaptive_young_list_length(bool adaptive_young_list_length) {
1121     _adaptive_young_list_length = adaptive_young_list_length;
1122   }
1123 
1124   inline double get_gc_eff_factor() {
1125     double ratio = _known_garbage_ratio;
1126 
1127     double square = ratio * ratio;
1128     // square = square * square;
1129     double ret = square * 9.0 + 1.0;
1130 #if 0
1131     gclog_or_tty->print_cr("ratio = %1.2lf, ret = %1.2lf", ratio, ret);
1132 #endif // 0
1133     guarantee(0.0 <= ret && ret < 10.0, "invariant!");
1134     return ret;
1135   }
1136 
1137   //
1138   // Survivor regions policy.
1139   //
1140 protected:
1141 
1142   // Current tenuring threshold, set to 0 if the collector reaches the
1143   // maximum amount of suvivors regions.
1144   int _tenuring_threshold;
1145 
1146   // The limit on the number of regions allocated for survivors.
1147   size_t _max_survivor_regions;
1148 
1149   // For reporting purposes.
1150   size_t _eden_bytes_before_gc;
1151   size_t _survivor_bytes_before_gc;
1152   size_t _capacity_before_gc;
1153 
1154   // The amount of survor regions after a collection.
1155   size_t _recorded_survivor_regions;
1156   // List of survivor regions.
1157   HeapRegion* _recorded_survivor_head;
1158   HeapRegion* _recorded_survivor_tail;
1159 
1160   ageTable _survivors_age_table;
1161 
1162 public:
1163 
1164   inline GCAllocPurpose
1165     evacuation_destination(HeapRegion* src_region, int age, size_t word_sz) {
1166       if (age < _tenuring_threshold && src_region->is_young()) {
1167         return GCAllocForSurvived;
1168       } else {
1169         return GCAllocForTenured;
1170       }
1171   }
1172 
1173   inline bool track_object_age(GCAllocPurpose purpose) {
1174     return purpose == GCAllocForSurvived;
1175   }
1176 
1177   static const size_t REGIONS_UNLIMITED = ~(size_t)0;
1178 
1179   size_t max_regions(int purpose);
1180 
1181   // The limit on regions for a particular purpose is reached.
1182   void note_alloc_region_limit_reached(int purpose) {
1183     if (purpose == GCAllocForSurvived) {
1184       _tenuring_threshold = 0;
1185     }
1186   }
1187 
1188   void note_start_adding_survivor_regions() {
1189     _survivor_surv_rate_group->start_adding_regions();
1190   }
1191 
1192   void note_stop_adding_survivor_regions() {
1193     _survivor_surv_rate_group->stop_adding_regions();
1194   }
1195 
1196   void record_survivor_regions(size_t      regions,
1197                                HeapRegion* head,
1198                                HeapRegion* tail) {
1199     _recorded_survivor_regions = regions;
1200     _recorded_survivor_head    = head;
1201     _recorded_survivor_tail    = tail;
1202   }
1203 
1204   size_t recorded_survivor_regions() {
1205     return _recorded_survivor_regions;
1206   }
1207 
1208   void record_thread_age_table(ageTable* age_table)
1209   {
1210     _survivors_age_table.merge_par(age_table);
1211   }
1212 
1213   void calculate_max_gc_locker_expansion();
1214 
1215   // Calculates survivor space parameters.
1216   void calculate_survivors_policy();
1217 
1218 };
1219 
1220 // This encapsulates a particular strategy for a g1 Collector.
1221 //
1222 //      Start a concurrent mark when our heap size is n bytes
1223 //            greater then our heap size was at the last concurrent
1224 //            mark.  Where n is a function of the CMSTriggerRatio
1225 //            and the MinHeapFreeRatio.
1226 //
1227 //      Start a g1 collection pause when we have allocated the
1228 //            average number of bytes currently being freed in
1229 //            a collection, but only if it is at least one region
1230 //            full
1231 //
1232 //      Resize Heap based on desired
1233 //      allocation space, where desired allocation space is
1234 //      a function of survival rate and desired future to size.
1235 //
1236 //      Choose collection set by first picking all older regions
1237 //      which have a survival rate which beats our projected young
1238 //      survival rate.  Then fill out the number of needed regions
1239 //      with young regions.
1240 
1241 class G1CollectorPolicy_BestRegionsFirst: public G1CollectorPolicy {
1242   CollectionSetChooser* _collectionSetChooser;
1243   // If the estimated is less then desirable, resize if possible.
1244   void expand_if_possible(size_t numRegions);
1245 
1246   virtual void choose_collection_set(double target_pause_time_ms);
1247   virtual void record_collection_pause_start(double start_time_sec,
1248                                              size_t start_used);
1249   virtual void record_concurrent_mark_cleanup_end(size_t freed_bytes,
1250                                                   size_t max_live_bytes);
1251   virtual void record_full_collection_end();
1252 
1253 public:
1254   G1CollectorPolicy_BestRegionsFirst() {
1255     _collectionSetChooser = new CollectionSetChooser();
1256   }
1257   void record_collection_pause_end();
1258   // This is not needed any more, after the CSet choosing code was
1259   // changed to use the pause prediction work. But let's leave the
1260   // hook in just in case.
1261   void note_change_in_marked_bytes(HeapRegion* r) { }
1262 #ifndef PRODUCT
1263   bool assertMarkedBytesDataOK();
1264 #endif
1265 };
1266 
1267 // This should move to some place more general...
1268 
1269 // If we have "n" measurements, and we've kept track of their "sum" and the
1270 // "sum_of_squares" of the measurements, this returns the variance of the
1271 // sequence.
1272 inline double variance(int n, double sum_of_squares, double sum) {
1273   double n_d = (double)n;
1274   double avg = sum/n_d;
1275   return (sum_of_squares - 2.0 * avg * sum + n_d * avg * avg) / n_d;
1276 }
1277 
1278 // Local Variables: ***
1279 // c-indentation-style: gnu ***
1280 // End: ***
1281 
1282 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP