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 /*

  * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP

 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP

 #include "gc_implementation/g1/collectionSetChooser.hpp"

 #include "gc_implementation/g1/g1MMUTracker.hpp"

 #include "memory/collectorPolicy.hpp"

 // A G1CollectorPolicy makes policy decisions that determine the

 // characteristics of the collector.  Examples include:

 //   * choice of collection set.

 //   * when to collect.

 class HeapRegion;

 class CollectionSetChooser;

 // Yes, this is a bit unpleasant... but it saves replicating the same thing

 // over and over again and introducing subtle problems through small typos and

 // cutting and pasting mistakes. The macros below introduces a number

 // sequnce into the following two classes and the methods that access it.

 #define define_num_seq(name)                                                  \

 private:                                                                      \

   NumberSeq _all_##name##_times_ms;                                           \

 public:                                                                       \

   void record_##name##_time_ms(double ms) {                                   \

     _all_##name##_times_ms.add(ms);                                           \

   }                                                                           \

   NumberSeq* get_##name##_seq() {                                             \

     return &_all_##name##_times_ms;                                           \

   }

 class MainBodySummary;

 class PauseSummary: public CHeapObj {

   define_num_seq(total)

     define_num_seq(other)

 public:

   virtual MainBodySummary*    main_body_summary()    { return NULL; }

 };

 class MainBodySummary: public CHeapObj {

   define_num_seq(satb_drain) // optional

   define_num_seq(parallel) // parallel only

     define_num_seq(ext_root_scan)

     define_num_seq(mark_stack_scan)

     define_num_seq(update_rs)

     define_num_seq(scan_rs)

     define_num_seq(obj_copy)

     define_num_seq(termination) // parallel only

     define_num_seq(parallel_other) // parallel only

   define_num_seq(mark_closure)

   define_num_seq(clear_ct)

 };

 class Summary: public PauseSummary,

                public MainBodySummary {

 public:

   virtual MainBodySummary*    main_body_summary()    { return this; }

 };

 class G1CollectorPolicy: public CollectorPolicy {

 private:

   // The number of pauses during the execution.

   long _n_pauses;

   // either equal to the number of parallel threads, if ParallelGCThreads

   // has been set, or 1 otherwise

   int _parallel_gc_threads;

   enum SomePrivateConstants {

     NumPrevPausesForHeuristics = 10

   };

   G1MMUTracker* _mmu_tracker;

   void initialize_flags();

   void initialize_all() {

     initialize_flags();

     initialize_size_info();

     initialize_perm_generation(PermGen::MarkSweepCompact);

   }

   CollectionSetChooser* _collectionSetChooser;

   double _cur_collection_start_sec;

   size_t _cur_collection_pause_used_at_start_bytes;

   size_t _cur_collection_pause_used_regions_at_start;

   size_t _prev_collection_pause_used_at_end_bytes;

   double _cur_collection_par_time_ms;

   double _cur_satb_drain_time_ms;

   double _cur_clear_ct_time_ms;

   double _cur_ref_proc_time_ms;

   double _cur_ref_enq_time_ms;

 #ifndef PRODUCT

   // Card Table Count Cache stats

   double _min_clear_cc_time_ms;         // min

   double _max_clear_cc_time_ms;         // max

   double _cur_clear_cc_time_ms;         // clearing time during current pause

   double _cum_clear_cc_time_ms;         // cummulative clearing time

   jlong  _num_cc_clears;                // number of times the card count cache has been cleared

 #endif

   // Statistics for recent GC pauses.  See below for how indexed.

   TruncatedSeq* _recent_rs_scan_times_ms;

   // These exclude marking times.

   TruncatedSeq* _recent_pause_times_ms;

   TruncatedSeq* _recent_gc_times_ms;

   TruncatedSeq* _recent_CS_bytes_used_before;

   TruncatedSeq* _recent_CS_bytes_surviving;

   TruncatedSeq* _recent_rs_sizes;

   TruncatedSeq* _concurrent_mark_remark_times_ms;

   TruncatedSeq* _concurrent_mark_cleanup_times_ms;

   Summary*           _summary;

   NumberSeq* _all_pause_times_ms;

   NumberSeq* _all_full_gc_times_ms;

   double _stop_world_start;

   NumberSeq* _all_stop_world_times_ms;

   NumberSeq* _all_yield_times_ms;

   size_t     _region_num_young;

   size_t     _region_num_tenured;

   size_t     _prev_region_num_young;

   size_t     _prev_region_num_tenured;

   NumberSeq* _all_mod_union_times_ms;

   int        _aux_num;

   NumberSeq* _all_aux_times_ms;

   double*    _cur_aux_start_times_ms;

   double*    _cur_aux_times_ms;

   bool*      _cur_aux_times_set;

   double* _par_last_gc_worker_start_times_ms;

   double* _par_last_ext_root_scan_times_ms;

   double* _par_last_mark_stack_scan_times_ms;

   double* _par_last_update_rs_times_ms;

   double* _par_last_update_rs_processed_buffers;

   double* _par_last_scan_rs_times_ms;

   double* _par_last_obj_copy_times_ms;

   double* _par_last_termination_times_ms;

   double* _par_last_termination_attempts;

   double* _par_last_gc_worker_end_times_ms;

   double* _par_last_gc_worker_times_ms;

   // Each workers 'other' time i.e. the elapsed time of the parallel

   // phase of the pause minus the sum of the individual sub-phase

   // times for a given worker thread.

   double* _par_last_gc_worker_other_times_ms;

   // indicates whether we are in full young or partially young GC mode

   bool _full_young_gcs;

   // if true, then it tries to dynamically adjust the length of the

   // young list

   bool _adaptive_young_list_length;

   size_t _young_list_target_length;

   size_t _young_list_fixed_length;

   size_t _prev_eden_capacity; // used for logging

   // The max number of regions we can extend the eden by while the GC

   // locker is active. This should be >= _young_list_target_length;

   size_t _young_list_max_length;

   size_t _young_cset_length;

   bool   _last_young_gc_full;

   unsigned              _full_young_pause_num;

   unsigned              _partial_young_pause_num;

   bool                  _during_marking;

   bool                  _in_marking_window;

   bool                  _in_marking_window_im;

   SurvRateGroup*        _short_lived_surv_rate_group;

   SurvRateGroup*        _survivor_surv_rate_group;

   // add here any more surv rate groups

   double                _gc_overhead_perc;

   double _reserve_factor;

   size_t _reserve_regions;

   bool during_marking() {

     return _during_marking;

   }

   // <NEW PREDICTION>

 private:

   enum PredictionConstants {

     TruncatedSeqLength = 10

   };

   TruncatedSeq* _alloc_rate_ms_seq;

   double        _prev_collection_pause_end_ms;

   TruncatedSeq* _pending_card_diff_seq;

   TruncatedSeq* _rs_length_diff_seq;

   TruncatedSeq* _cost_per_card_ms_seq;

   TruncatedSeq* _fully_young_cards_per_entry_ratio_seq;

   TruncatedSeq* _partially_young_cards_per_entry_ratio_seq;

   TruncatedSeq* _cost_per_entry_ms_seq;

   TruncatedSeq* _partially_young_cost_per_entry_ms_seq;

   TruncatedSeq* _cost_per_byte_ms_seq;

   TruncatedSeq* _constant_other_time_ms_seq;

   TruncatedSeq* _young_other_cost_per_region_ms_seq;

   TruncatedSeq* _non_young_other_cost_per_region_ms_seq;

   TruncatedSeq* _pending_cards_seq;

   TruncatedSeq* _scanned_cards_seq;

   TruncatedSeq* _rs_lengths_seq;

   TruncatedSeq* _cost_per_byte_ms_during_cm_seq;

   TruncatedSeq* _young_gc_eff_seq;

   TruncatedSeq* _max_conc_overhead_seq;

   bool   _using_new_ratio_calculations;

   size_t _min_desired_young_length; // as set on the command line or default calculations

   size_t _max_desired_young_length; // as set on the command line or default calculations

   size_t _recorded_young_regions;

   size_t _recorded_non_young_regions;

   size_t _recorded_region_num;

   size_t _free_regions_at_end_of_collection;

   size_t _recorded_rs_lengths;

   size_t _max_rs_lengths;

   size_t _recorded_marked_bytes;

   size_t _recorded_young_bytes;

   size_t _predicted_pending_cards;

   size_t _predicted_cards_scanned;

   size_t _predicted_rs_lengths;

   size_t _predicted_bytes_to_copy;

   double _predicted_survival_ratio;

   double _predicted_rs_update_time_ms;

   double _predicted_rs_scan_time_ms;

   double _predicted_object_copy_time_ms;

   double _predicted_constant_other_time_ms;

   double _predicted_young_other_time_ms;

   double _predicted_non_young_other_time_ms;

   double _predicted_pause_time_ms;

   double _vtime_diff_ms;

   double _recorded_young_free_cset_time_ms;

   double _recorded_non_young_free_cset_time_ms;

   double _sigma;

   double _expensive_region_limit_ms;

   size_t _rs_lengths_prediction;

   size_t _known_garbage_bytes;

   double _known_garbage_ratio;

   double sigma() {

     return _sigma;

   }

   // A function that prevents us putting too much stock in small sample

   // sets.  Returns a number between 2.0 and 1.0, depending on the number

   // of samples.  5 or more samples yields one; fewer scales linearly from

   // 2.0 at 1 sample to 1.0 at 5.

   double confidence_factor(int samples) {

     if (samples > 4) return 1.0;

     else return  1.0 + sigma() * ((double)(5 - samples))/2.0;

   }

   double get_new_neg_prediction(TruncatedSeq* seq) {

     return seq->davg() - sigma() * seq->dsd();

   }

 #ifndef PRODUCT

   bool verify_young_ages(HeapRegion* head, SurvRateGroup *surv_rate_group);

 #endif // PRODUCT

   void adjust_concurrent_refinement(double update_rs_time,

                                     double update_rs_processed_buffers,

                                     double goal_ms);

   double _pause_time_target_ms;

   double _recorded_young_cset_choice_time_ms;

   double _recorded_non_young_cset_choice_time_ms;

   bool   _within_target;

   size_t _pending_cards;

   size_t _max_pending_cards;

 public:

   void set_region_short_lived(HeapRegion* hr) {

     hr->install_surv_rate_group(_short_lived_surv_rate_group);

   }

   void set_region_survivors(HeapRegion* hr) {

     hr->install_surv_rate_group(_survivor_surv_rate_group);

   }

 #ifndef PRODUCT

   bool verify_young_ages();

 #endif // PRODUCT

   double get_new_prediction(TruncatedSeq* seq) {

     return MAX2(seq->davg() + sigma() * seq->dsd(),

                 seq->davg() * confidence_factor(seq->num()));

   }

   size_t young_cset_length() {

     return _young_cset_length;

   }

   void record_max_rs_lengths(size_t rs_lengths) {

     _max_rs_lengths = rs_lengths;

   }

   size_t predict_pending_card_diff() {

     double prediction = get_new_neg_prediction(_pending_card_diff_seq);

     if (prediction < 0.00001)

       return 0;

     else

       return (size_t) prediction;

   }

   size_t predict_pending_cards() {

     size_t max_pending_card_num = _g1->max_pending_card_num();

     size_t diff = predict_pending_card_diff();

     size_t prediction;

     if (diff > max_pending_card_num)

       prediction = max_pending_card_num;

     else

       prediction = max_pending_card_num - diff;

     return prediction;

   }

   size_t predict_rs_length_diff() {

     return (size_t) get_new_prediction(_rs_length_diff_seq);

   }

   double predict_alloc_rate_ms() {

     return get_new_prediction(_alloc_rate_ms_seq);

   }

   double predict_cost_per_card_ms() {

     return get_new_prediction(_cost_per_card_ms_seq);

   }

   double predict_rs_update_time_ms(size_t pending_cards) {

     return (double) pending_cards * predict_cost_per_card_ms();

   }

   double predict_fully_young_cards_per_entry_ratio() {

     return get_new_prediction(_fully_young_cards_per_entry_ratio_seq);

   }

   double predict_partially_young_cards_per_entry_ratio() {

     if (_partially_young_cards_per_entry_ratio_seq->num() < 2)

       return predict_fully_young_cards_per_entry_ratio();

     else

       return get_new_prediction(_partially_young_cards_per_entry_ratio_seq);

   }

   size_t predict_young_card_num(size_t rs_length) {

     return (size_t) ((double) rs_length *

                      predict_fully_young_cards_per_entry_ratio());

   }

   size_t predict_non_young_card_num(size_t rs_length) {

     return (size_t) ((double) rs_length *

                      predict_partially_young_cards_per_entry_ratio());

   }

   double predict_rs_scan_time_ms(size_t card_num) {

     if (full_young_gcs())

       return (double) card_num * get_new_prediction(_cost_per_entry_ms_seq);

     else

       return predict_partially_young_rs_scan_time_ms(card_num);

   }

   double predict_partially_young_rs_scan_time_ms(size_t card_num) {

     if (_partially_young_cost_per_entry_ms_seq->num() < 3)

       return (double) card_num * get_new_prediction(_cost_per_entry_ms_seq);

     else

       return (double) card_num *

         get_new_prediction(_partially_young_cost_per_entry_ms_seq);

   }

   double predict_object_copy_time_ms_during_cm(size_t bytes_to_copy) {

     if (_cost_per_byte_ms_during_cm_seq->num() < 3)

       return 1.1 * (double) bytes_to_copy *

         get_new_prediction(_cost_per_byte_ms_seq);

     else

       return (double) bytes_to_copy *

         get_new_prediction(_cost_per_byte_ms_during_cm_seq);

   }

   double predict_object_copy_time_ms(size_t bytes_to_copy) {

     if (_in_marking_window && !_in_marking_window_im)

       return predict_object_copy_time_ms_during_cm(bytes_to_copy);

     else

       return (double) bytes_to_copy *

         get_new_prediction(_cost_per_byte_ms_seq);

   }

   double predict_constant_other_time_ms() {

     return get_new_prediction(_constant_other_time_ms_seq);

   }

   double predict_young_other_time_ms(size_t young_num) {

     return

       (double) young_num *

       get_new_prediction(_young_other_cost_per_region_ms_seq);

   }

   double predict_non_young_other_time_ms(size_t non_young_num) {

     return

       (double) non_young_num *

       get_new_prediction(_non_young_other_cost_per_region_ms_seq);

   }

   void check_if_region_is_too_expensive(double predicted_time_ms);

   double predict_young_collection_elapsed_time_ms(size_t adjustment);

   double predict_base_elapsed_time_ms(size_t pending_cards);

   double predict_base_elapsed_time_ms(size_t pending_cards,

                                       size_t scanned_cards);

   size_t predict_bytes_to_copy(HeapRegion* hr);

   double predict_region_elapsed_time_ms(HeapRegion* hr, bool young);

   void start_recording_regions();

   void record_cset_region_info(HeapRegion* hr, bool young);

   void record_non_young_cset_region(HeapRegion* hr);

   void set_recorded_young_regions(size_t n_regions);

   void set_recorded_young_bytes(size_t bytes);

   void set_recorded_rs_lengths(size_t rs_lengths);

   void set_predicted_bytes_to_copy(size_t bytes);

   void end_recording_regions();

   void record_vtime_diff_ms(double vtime_diff_ms) {

     _vtime_diff_ms = vtime_diff_ms;

   }

   void record_young_free_cset_time_ms(double time_ms) {

     _recorded_young_free_cset_time_ms = time_ms;

   }

   void record_non_young_free_cset_time_ms(double time_ms) {

     _recorded_non_young_free_cset_time_ms = time_ms;

   }

   double predict_young_gc_eff() {

     return get_new_neg_prediction(_young_gc_eff_seq);

   }

   double predict_survivor_regions_evac_time();

   // </NEW PREDICTION>

   void cset_regions_freed() {

     bool propagate = _last_young_gc_full && !_in_marking_window;

     _short_lived_surv_rate_group->all_surviving_words_recorded(propagate);

     _survivor_surv_rate_group->all_surviving_words_recorded(propagate);

     // also call it on any more surv rate groups

   }

   void set_known_garbage_bytes(size_t known_garbage_bytes) {

     _known_garbage_bytes = known_garbage_bytes;

     size_t heap_bytes = _g1->capacity();

     _known_garbage_ratio = (double) _known_garbage_bytes / (double) heap_bytes;

   }

   void decrease_known_garbage_bytes(size_t known_garbage_bytes) {

     guarantee( _known_garbage_bytes >= known_garbage_bytes, "invariant" );

     _known_garbage_bytes -= known_garbage_bytes;

     size_t heap_bytes = _g1->capacity();

     _known_garbage_ratio = (double) _known_garbage_bytes / (double) heap_bytes;

   }

   G1MMUTracker* mmu_tracker() {

     return _mmu_tracker;

   }

   double max_pause_time_ms() {

     return _mmu_tracker->max_gc_time() * 1000.0;

   }

   double predict_remark_time_ms() {

     return get_new_prediction(_concurrent_mark_remark_times_ms);

   }

   double predict_cleanup_time_ms() {

     return get_new_prediction(_concurrent_mark_cleanup_times_ms);

   }

   // Returns an estimate of the survival rate of the region at yg-age

   // "yg_age".

   double predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) {

     TruncatedSeq* seq = surv_rate_group->get_seq(age);

     if (seq->num() == 0)

       gclog_or_tty->print("BARF! age is %d", age);

     guarantee( seq->num() > 0, "invariant" );

     double pred = get_new_prediction(seq);

     if (pred > 1.0)

       pred = 1.0;

     return pred;

   }

   double predict_yg_surv_rate(int age) {

     return predict_yg_surv_rate(age, _short_lived_surv_rate_group);

   }

   double accum_yg_surv_rate_pred(int age) {

     return _short_lived_surv_rate_group->accum_surv_rate_pred(age);

   }

 private:

   void print_stats(int level, const char* str, double value);

   void print_stats(int level, const char* str, int value);

   void print_par_stats(int level, const char* str, double* data);

   void print_par_sizes(int level, const char* str, double* data);

   void check_other_times(int level,

                          NumberSeq* other_times_ms,

                          NumberSeq* calc_other_times_ms) const;

   void print_summary (PauseSummary* stats) const;

   void print_summary (int level, const char* str, NumberSeq* seq) const;

   void print_summary_sd (int level, const char* str, NumberSeq* seq) const;

   double avg_value (double* data);

   double max_value (double* data);

   double sum_of_values (double* data);

   double max_sum (double* data1, double* data2);

   int _last_satb_drain_processed_buffers;

   int _last_update_rs_processed_buffers;

   double _last_pause_time_ms;

   size_t _bytes_in_collection_set_before_gc;

   size_t _bytes_copied_during_gc;

   // Used to count used bytes in CS.

   friend class CountCSClosure;

   // Statistics kept per GC stoppage, pause or full.

   TruncatedSeq* _recent_prev_end_times_for_all_gcs_sec;

   // Add a new GC of the given duration and end time to the record.

   void update_recent_gc_times(double end_time_sec, double elapsed_ms);

   // The head of the list (via "next_in_collection_set()") representing the

   // current collection set. Set from the incrementally built collection

   // set at the start of the pause.

   HeapRegion* _collection_set;

   // The number of regions in the collection set. Set from the incrementally

   // built collection set at the start of an evacuation pause.

   size_t _collection_set_size;

   // The number of bytes in the collection set before the pause. Set from

   // the incrementally built collection set at the start of an evacuation

   // pause.

   size_t _collection_set_bytes_used_before;

   // The associated information that is maintained while the incremental

   // collection set is being built with young regions. Used to populate

   // the recorded info for the evacuation pause.

   enum CSetBuildType {

     Active,             // We are actively building the collection set

     Inactive            // We are not actively building the collection set

   };

   CSetBuildType _inc_cset_build_state;

   // The head of the incrementally built collection set.

   HeapRegion* _inc_cset_head;

   // The tail of the incrementally built collection set.

   HeapRegion* _inc_cset_tail;

   // The number of regions in the incrementally built collection set.

   // Used to set _collection_set_size at the start of an evacuation

   // pause.

   size_t _inc_cset_size;

   // Used as the index in the surving young words structure

   // which tracks the amount of space, for each young region,

   // that survives the pause.

   size_t _inc_cset_young_index;

   // The number of bytes in the incrementally built collection set.

   // Used to set _collection_set_bytes_used_before at the start of

   // an evacuation pause.

   size_t _inc_cset_bytes_used_before;

   // Used to record the highest end of heap region in collection set

   HeapWord* _inc_cset_max_finger;

   // The number of recorded used bytes in the young regions

   // of the collection set. This is the sum of the used() bytes

   // of retired young regions in the collection set.

   size_t _inc_cset_recorded_young_bytes;

   // The RSet lengths recorded for regions in the collection set

   // (updated by the periodic sampling of the regions in the

   // young list/collection set).

   size_t _inc_cset_recorded_rs_lengths;

   // The predicted elapsed time it will take to collect the regions

   // in the collection set (updated by the periodic sampling of the

   // regions in the young list/collection set).

   double _inc_cset_predicted_elapsed_time_ms;

   // The predicted bytes to copy for the regions in the collection

   // set (updated by the periodic sampling of the regions in the

   // young list/collection set).

   size_t _inc_cset_predicted_bytes_to_copy;

   // Stash a pointer to the g1 heap.

   G1CollectedHeap* _g1;

   // The average time in ms per collection pause, averaged over recent pauses.

   double recent_avg_time_for_pauses_ms();

   // The average time in ms for RS scanning, per pause, averaged

   // over recent pauses. (Note the RS scanning time for a pause

   // is itself an average of the RS scanning time for each worker

   // thread.)

   double recent_avg_time_for_rs_scan_ms();

   // The number of "recent" GCs recorded in the number sequences

   int number_of_recent_gcs();

   // The average survival ratio, computed by the total number of bytes

   // suriviving / total number of bytes before collection over the last

   // several recent pauses.

   double recent_avg_survival_fraction();

   // The survival fraction of the most recent pause; if there have been no

   // pauses, returns 1.0.

   double last_survival_fraction();

   // Returns a "conservative" estimate of the recent survival rate, i.e.,

   // one that may be higher than "recent_avg_survival_fraction".

   // This is conservative in several ways:

   //   If there have been few pauses, it will assume a potential high

   //     variance, and err on the side of caution.

   //   It puts a lower bound (currently 0.1) on the value it will return.

   //   To try to detect phase changes, if the most recent pause ("latest") has a

   //     higher-than average ("avg") survival rate, it returns that rate.

   // "work" version is a utility function; young is restricted to young regions.

   double conservative_avg_survival_fraction_work(double avg,

                                                  double latest);

   // The arguments are the two sequences that keep track of the number of bytes

   //   surviving and the total number of bytes before collection, resp.,

   //   over the last evereal recent pauses

   // Returns the survival rate for the category in the most recent pause.

   // If there have been no pauses, returns 1.0.

   double last_survival_fraction_work(TruncatedSeq* surviving,

                                      TruncatedSeq* before);

   // The arguments are the two sequences that keep track of the number of bytes

   //   surviving and the total number of bytes before collection, resp.,

   //   over the last several recent pauses

   // Returns the average survival ration over the last several recent pauses

   // If there have been no pauses, return 1.0

   double recent_avg_survival_fraction_work(TruncatedSeq* surviving,

                                            TruncatedSeq* before);

   double conservative_avg_survival_fraction() {

     double avg = recent_avg_survival_fraction();

     double latest = last_survival_fraction();

     return conservative_avg_survival_fraction_work(avg, latest);

   }

   // The ratio of gc time to elapsed time, computed over recent pauses.

   double _recent_avg_pause_time_ratio;

   double recent_avg_pause_time_ratio() {

     return _recent_avg_pause_time_ratio;

   }

   // Number of pauses between concurrent marking.

   size_t _pauses_btwn_concurrent_mark;

   // At the end of a pause we check the heap occupancy and we decide

   // whether we will start a marking cycle during the next pause. If

   // we decide that we want to do that, we will set this parameter to

   // true. So, this parameter will stay true between the end of a

   // pause and the beginning of a subsequent pause (not necessarily

   // the next one, see the comments on the next field) when we decide

   // that we will indeed start a marking cycle and do the initial-mark

   // work.

   volatile bool _initiate_conc_mark_if_possible;

   // If initiate_conc_mark_if_possible() is set at the beginning of a

   // pause, it is a suggestion that the pause should start a marking

   // cycle by doing the initial-mark work. However, it is possible

   // that the concurrent marking thread is still finishing up the

   // previous marking cycle (e.g., clearing the next marking

   // bitmap). If that is the case we cannot start a new cycle and

   // we'll have to wait for the concurrent marking thread to finish

   // what it is doing. In this case we will postpone the marking cycle

   // initiation decision for the next pause. When we eventually decide

   // to start a cycle, we will set _during_initial_mark_pause which

   // will stay true until the end of the initial-mark pause and it's

   // the condition that indicates that a pause is doing the

   // initial-mark work.

   volatile bool _during_initial_mark_pause;

   bool _should_revert_to_full_young_gcs;

   bool _last_full_young_gc;

   // This set of variables tracks the collector efficiency, in order to

   // determine whether we should initiate a new marking.

   double _cur_mark_stop_world_time_ms;

   double _mark_remark_start_sec;

   double _mark_cleanup_start_sec;

   double _mark_closure_time_ms;

   // Update the young list target length either by setting it to the

   // desired fixed value or by calculating it using G1's pause

   // prediction model. If no rs_lengths parameter is passed, predict

   // the RS lengths using the prediction model, otherwise use the

   // given rs_lengths as the prediction.

   void update_young_list_target_length(size_t rs_lengths = (size_t) -1);

   // Calculate and return the minimum desired young list target

   // length. This is the minimum desired young list length according

   // to the user's inputs.

   size_t calculate_young_list_desired_min_length(size_t base_min_length);

   // Calculate and return the maximum desired young list target

   // length. This is the maximum desired young list length according

   // to the user's inputs.

   size_t calculate_young_list_desired_max_length();

   // Calculate and return the maximum young list target length that

   // can fit into the pause time goal. The parameters are: rs_lengths

   // represent the prediction of how large the young RSet lengths will

   // be, base_min_length is the alreay existing number of regions in

   // the young list, min_length and max_length are the desired min and

   // max young list length according to the user's inputs.

   size_t calculate_young_list_target_length(size_t rs_lengths,

                                             size_t base_min_length,

                                             size_t desired_min_length,

                                             size_t desired_max_length);

   // Check whether a given young length (young_length) fits into the

   // given target pause time and whether the prediction for the amount

   // of objects to be copied for the given length will fit into the

   // given free space (expressed by base_free_regions).  It is used by

   // calculate_young_list_target_length().

   bool predict_will_fit(size_t young_length, double base_time_ms,

                         size_t base_free_regions, double target_pause_time_ms);

   // Count the number of bytes used in the CS.

   void count_CS_bytes_used();

   void update_young_list_size_using_newratio(size_t number_of_heap_regions);

 public:

   G1CollectorPolicy();

   virtual G1CollectorPolicy* as_g1_policy() { return this; }

   virtual CollectorPolicy::Name kind() {

     return CollectorPolicy::G1CollectorPolicyKind;

   }

   // Check the current value of the young list RSet lengths and

   // compare it against the last prediction. If the current value is

   // higher, recalculate the young list target length prediction.

   void revise_young_list_target_length_if_necessary();

   size_t bytes_in_collection_set() {

     return _bytes_in_collection_set_before_gc;

   }

   unsigned calc_gc_alloc_time_stamp() {

     return _all_pause_times_ms->num() + 1;

   }

   // This should be called after the heap is resized.

   void record_new_heap_size(size_t new_number_of_regions);

 public:

   void init();

   // Create jstat counters for the policy.

   virtual void initialize_gc_policy_counters();

   virtual HeapWord* mem_allocate_work(size_t size,

                                       bool is_tlab,

                                       bool* gc_overhead_limit_was_exceeded);

   // This method controls how a collector handles one or more

   // of its generations being fully allocated.

   virtual HeapWord* satisfy_failed_allocation(size_t size,

                                               bool is_tlab);

   BarrierSet::Name barrier_set_name() { return BarrierSet::G1SATBCTLogging; }

   GenRemSet::Name  rem_set_name()     { return GenRemSet::CardTable; }

   // The number of collection pauses so far.

   long n_pauses() const { return _n_pauses; }

   // Update the heuristic info to record a collection pause of the given

   // start time, where the given number of bytes were used at the start.

   // This may involve changing the desired size of a collection set.

   void record_stop_world_start();

   void record_collection_pause_start(double start_time_sec, size_t start_used);

   // Must currently be called while the world is stopped.

   void record_concurrent_mark_init_end(double

                                            mark_init_elapsed_time_ms);

   void record_mark_closure_time(double mark_closure_time_ms);

   void record_concurrent_mark_remark_start();

   void record_concurrent_mark_remark_end();

   void record_concurrent_mark_cleanup_start();

   void record_concurrent_mark_cleanup_end();

   void record_concurrent_mark_cleanup_completed();

   void record_concurrent_pause();

   void record_concurrent_pause_end();

   void record_collection_pause_end();

   void print_heap_transition();

   // Record the fact that a full collection occurred.

   void record_full_collection_start();

   void record_full_collection_end();

   void record_gc_worker_start_time(int worker_i, double ms) {

     _par_last_gc_worker_start_times_ms[worker_i] = ms;

   }

   void record_ext_root_scan_time(int worker_i, double ms) {

     _par_last_ext_root_scan_times_ms[worker_i] = ms;

   }

   void record_mark_stack_scan_time(int worker_i, double ms) {

     _par_last_mark_stack_scan_times_ms[worker_i] = ms;

   }

   void record_satb_drain_time(double ms) {

     assert(_g1->mark_in_progress(), "shouldn't be here otherwise");

     _cur_satb_drain_time_ms = ms;

   }

   void record_satb_drain_processed_buffers(int processed_buffers) {

     assert(_g1->mark_in_progress(), "shouldn't be here otherwise");

     _last_satb_drain_processed_buffers = processed_buffers;

   }

   void record_mod_union_time(double ms) {

     _all_mod_union_times_ms->add(ms);

   }

   void record_update_rs_time(int thread, double ms) {

     _par_last_update_rs_times_ms[thread] = ms;

   }

   void record_update_rs_processed_buffers (int thread,

                                            double processed_buffers) {

     _par_last_update_rs_processed_buffers[thread] = processed_buffers;

   }

   void record_scan_rs_time(int thread, double ms) {

     _par_last_scan_rs_times_ms[thread] = ms;

   }

   void reset_obj_copy_time(int thread) {

     _par_last_obj_copy_times_ms[thread] = 0.0;

   }

   void reset_obj_copy_time() {

     reset_obj_copy_time(0);

   }

   void record_obj_copy_time(int thread, double ms) {

     _par_last_obj_copy_times_ms[thread] += ms;

   }

   void record_termination(int thread, double ms, size_t attempts) {

     _par_last_termination_times_ms[thread] = ms;

     _par_last_termination_attempts[thread] = (double) attempts;

   }

   void record_gc_worker_end_time(int worker_i, double ms) {

     _par_last_gc_worker_end_times_ms[worker_i] = ms;

   }

   void record_pause_time_ms(double ms) {

     _last_pause_time_ms = ms;

   }

   void record_clear_ct_time(double ms) {

     _cur_clear_ct_time_ms = ms;

   }

   void record_par_time(double ms) {

     _cur_collection_par_time_ms = ms;

   }

   void record_aux_start_time(int i) {

     guarantee(i < _aux_num, "should be within range");

     _cur_aux_start_times_ms[i] = os::elapsedTime() * 1000.0;

   }

   void record_aux_end_time(int i) {

     guarantee(i < _aux_num, "should be within range");

     double ms = os::elapsedTime() * 1000.0 - _cur_aux_start_times_ms[i];

     _cur_aux_times_set[i] = true;

     _cur_aux_times_ms[i] += ms;

   }

   void record_ref_proc_time(double ms) {

     _cur_ref_proc_time_ms = ms;

   }

   void record_ref_enq_time(double ms) {

     _cur_ref_enq_time_ms = ms;

   }

 #ifndef PRODUCT

   void record_cc_clear_time(double ms) {

     if (_min_clear_cc_time_ms < 0.0 || ms <= _min_clear_cc_time_ms)

       _min_clear_cc_time_ms = ms;

     if (_max_clear_cc_time_ms < 0.0 || ms >= _max_clear_cc_time_ms)

       _max_clear_cc_time_ms = ms;

     _cur_clear_cc_time_ms = ms;

     _cum_clear_cc_time_ms += ms;

     _num_cc_clears++;

   }

 #endif

   // Record how much space we copied during a GC. This is typically

   // called when a GC alloc region is being retired.

   void record_bytes_copied_during_gc(size_t bytes) {

     _bytes_copied_during_gc += bytes;

   }

   // The amount of space we copied during a GC.

   size_t bytes_copied_during_gc() {

     return _bytes_copied_during_gc;

   }

   // Choose a new collection set.  Marks the chosen regions as being

   // "in_collection_set", and links them together.  The head and number of

   // the collection set are available via access methods.

   void choose_collection_set(double target_pause_time_ms);

   // The head of the list (via "next_in_collection_set()") representing the

   // current collection set.

   HeapRegion* collection_set() { return _collection_set; }

   void clear_collection_set() { _collection_set = NULL; }

   // The number of elements in the current collection set.

   size_t collection_set_size() { return _collection_set_size; }

   // Add "hr" to the CS.

   void add_to_collection_set(HeapRegion* hr);

   // Incremental CSet Support

   // The head of the incrementally built collection set.

   HeapRegion* inc_cset_head() { return _inc_cset_head; }

   // The tail of the incrementally built collection set.

   HeapRegion* inc_set_tail() { return _inc_cset_tail; }

   // The number of elements in the incrementally built collection set.

   size_t inc_cset_size() { return _inc_cset_size; }

   // Initialize incremental collection set info.

   void start_incremental_cset_building();

   void clear_incremental_cset() {

     _inc_cset_head = NULL;

     _inc_cset_tail = NULL;

   }

   // Stop adding regions to the incremental collection set

   void stop_incremental_cset_building() { _inc_cset_build_state = Inactive; }

   // Add/remove information about hr to the aggregated information

   // for the incrementally built collection set.

   void add_to_incremental_cset_info(HeapRegion* hr, size_t rs_length);

   void remove_from_incremental_cset_info(HeapRegion* hr);

   // Update information about hr in the aggregated information for

   // the incrementally built collection set.

   void update_incremental_cset_info(HeapRegion* hr, size_t new_rs_length);

 private:

   // Update the incremental cset information when adding a region

   // (should not be called directly).

   void add_region_to_incremental_cset_common(HeapRegion* hr);

 public:

   // Add hr to the LHS of the incremental collection set.

   void add_region_to_incremental_cset_lhs(HeapRegion* hr);

   // Add hr to the RHS of the incremental collection set.

   void add_region_to_incremental_cset_rhs(HeapRegion* hr);

 #ifndef PRODUCT

   void print_collection_set(HeapRegion* list_head, outputStream* st);

 #endif // !PRODUCT

   bool initiate_conc_mark_if_possible()       { return _initiate_conc_mark_if_possible;  }

   void set_initiate_conc_mark_if_possible()   { _initiate_conc_mark_if_possible = true;  }

   void clear_initiate_conc_mark_if_possible() { _initiate_conc_mark_if_possible = false; }

   bool during_initial_mark_pause()      { return _during_initial_mark_pause;  }

   void set_during_initial_mark_pause()  { _during_initial_mark_pause = true;  }

   void clear_during_initial_mark_pause(){ _during_initial_mark_pause = false; }

   // This sets the initiate_conc_mark_if_possible() flag to start a

   // new cycle, as long as we are not already in one. It's best if it

   // is called during a safepoint when the test whether a cycle is in

   // progress or not is stable.

   bool force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause);

   // This is called at the very beginning of an evacuation pause (it

   // has to be the first thing that the pause does). If

   // initiate_conc_mark_if_possible() is true, and the concurrent

   // marking thread has completed its work during the previous cycle,

   // it will set during_initial_mark_pause() to so that the pause does

   // the initial-mark work and start a marking cycle.

   void decide_on_conc_mark_initiation();

   // If an expansion would be appropriate, because recent GC overhead had

   // exceeded the desired limit, return an amount to expand by.

   size_t expansion_amount();

 #ifndef PRODUCT

   // Check any appropriate marked bytes info, asserting false if

   // something's wrong, else returning "true".

   bool assertMarkedBytesDataOK();

 #endif

   // Print tracing information.

   void print_tracing_info() const;

   // Print stats on young survival ratio

   void print_yg_surv_rate_info() const;

   void finished_recalculating_age_indexes(bool is_survivors) {

     if (is_survivors) {

       _survivor_surv_rate_group->finished_recalculating_age_indexes();

     } else {

       _short_lived_surv_rate_group->finished_recalculating_age_indexes();

     }

     // do that for any other surv rate groups

   }

   bool is_young_list_full() {

     size_t young_list_length = _g1->young_list()->length();

     size_t young_list_target_length = _young_list_target_length;

     return young_list_length >= young_list_target_length;

   }

   bool can_expand_young_list() {

     size_t young_list_length = _g1->young_list()->length();

     size_t young_list_max_length = _young_list_max_length;

     return young_list_length < young_list_max_length;

   }

   size_t young_list_max_length() {

     return _young_list_max_length;

   }

   void update_region_num(bool young);

   bool full_young_gcs() {

     return _full_young_gcs;

   }

   void set_full_young_gcs(bool full_young_gcs) {

     _full_young_gcs = full_young_gcs;

   }

   bool adaptive_young_list_length() {

     return _adaptive_young_list_length;

   }

   void set_adaptive_young_list_length(bool adaptive_young_list_length) {

     _adaptive_young_list_length = adaptive_young_list_length;

   }

   inline double get_gc_eff_factor() {

     double ratio = _known_garbage_ratio;

     double square = ratio * ratio;

     // square = square * square;

     double ret = square * 9.0 + 1.0;

 #if 0

     gclog_or_tty->print_cr("ratio = %1.2lf, ret = %1.2lf", ratio, ret);

 #endif // 0

     guarantee(0.0 <= ret && ret < 10.0, "invariant!");

     return ret;

   }

 private:

   //

   // Survivor regions policy.

   //

   // Current tenuring threshold, set to 0 if the collector reaches the

   // maximum amount of suvivors regions.

   int _tenuring_threshold;

   // The limit on the number of regions allocated for survivors.

   size_t _max_survivor_regions;

   // For reporting purposes.

   size_t _eden_bytes_before_gc;

   size_t _survivor_bytes_before_gc;

   size_t _capacity_before_gc;

   // The amount of survor regions after a collection.

   size_t _recorded_survivor_regions;

   // List of survivor regions.

   HeapRegion* _recorded_survivor_head;

   HeapRegion* _recorded_survivor_tail;

   ageTable _survivors_age_table;

 public:

   inline GCAllocPurpose

     evacuation_destination(HeapRegion* src_region, int age, size_t word_sz) {

       if (age < _tenuring_threshold && src_region->is_young()) {

         return GCAllocForSurvived;

       } else {

         return GCAllocForTenured;

       }

   }

   inline bool track_object_age(GCAllocPurpose purpose) {

     return purpose == GCAllocForSurvived;

   }

   static const size_t REGIONS_UNLIMITED = ~(size_t)0;

   size_t max_regions(int purpose);

   // The limit on regions for a particular purpose is reached.

   void note_alloc_region_limit_reached(int purpose) {

     if (purpose == GCAllocForSurvived) {

       _tenuring_threshold = 0;

     }

   }

   void note_start_adding_survivor_regions() {

     _survivor_surv_rate_group->start_adding_regions();

   }

   void note_stop_adding_survivor_regions() {

     _survivor_surv_rate_group->stop_adding_regions();

   }

   void record_survivor_regions(size_t      regions,

                                HeapRegion* head,

                                HeapRegion* tail) {

     _recorded_survivor_regions = regions;

     _recorded_survivor_head    = head;

     _recorded_survivor_tail    = tail;

   }

   size_t recorded_survivor_regions() {

     return _recorded_survivor_regions;

   }

   void record_thread_age_table(ageTable* age_table)

   {

     _survivors_age_table.merge_par(age_table);

   }

   void update_max_gc_locker_expansion();

   // Calculates survivor space parameters.

   void update_survivors_policy();

 };

 // This should move to some place more general...

 // If we have "n" measurements, and we've kept track of their "sum" and the

 // "sum_of_squares" of the measurements, this returns the variance of the

 // sequence.

 inline double variance(int n, double sum_of_squares, double sum) {

   double n_d = (double)n;

   double avg = sum/n_d;

   return (sum_of_squares - 2.0 * avg * sum + n_d * avg * avg) / n_d;

 }

 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP