1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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  *
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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  24 
  25 #ifndef SHARE_GC_G1_G1SURVRATEGROUP_HPP
  26 #define SHARE_GC_G1_G1SURVRATEGROUP_HPP
  27 
  28 #include "gc/g1/g1Predictions.hpp"
  29 #include "utilities/numberSeq.hpp"
  30 
  31 // A survivor rate group tracks survival ratios of objects allocated in the
  32 // heap regions associated to a set of regions (a "space", i.e. eden or survivor)
  33 // on a time basis to predict future survival rates of regions of the same "age".
  34 //
  35 // Every time a new heap region associated with a survivor rate group is retired
  36 // (i.e. the time basis), it gets associated the next "age" entry in that group.
  37 //
  38 // During garbage collection G1 keeps track how much of total data is copied out
  39 // of a heap region (i.e. survives), to update the survivor rate predictor of that age.
  40 //
  41 // This information is used to predict, given a particular age of a heap region,
  42 // how much of its contents will likely survive to determine young generation sizes.
  43 //
  44 // The age index associated with a heap region is incremented from 0 (retired first)
  45 // to N (retired just before the GC).
  46 //
  47 // To avoid copying around data all the time when the total amount of regions in
  48 // a survivor rate group changes, this class organizes the arrays containing the
  49 // predictors in reverse chronological order as returned by age_in_group(). I.e.
  50 // index 0 contains the rate information for the region retired most recently.
  51 class G1SurvRateGroup : public CHeapObj<mtGC> {
  52   size_t  _stats_arrays_length;
  53   double* _accum_surv_rate_pred;
  54   double  _last_pred;
  55   TruncatedSeq** _surv_rate_predictors;
  56 
  57   size_t _num_added_regions;   // The number of regions in this survivor rate group.
  58 
  59   void fill_in_last_surv_rates();
  60   void finalize_predictions(const G1Predictions& predictor);
  61 
  62 public:
  63   static const int InvalidAgeIndex = -1;
  64   static bool is_valid_age_index(int age) { return age >= 0; }
  65 
  66   G1SurvRateGroup();
  67   void reset();
  68   void start_adding_regions();
  69   void stop_adding_regions();
  70   void record_surviving_words(int age_in_group, double surv_rate);
  71   void all_surviving_words_recorded(const G1Predictions& predictor, bool update_predictors);
  72 
  73   double accum_surv_rate_pred(int age) const {
  74     assert(_stats_arrays_length > 0, "invariant" );
  75     assert(is_valid_age_index(age), "must be");
  76     if ((size_t)age < _stats_arrays_length)
  77       return _accum_surv_rate_pred[age];
  78     else {
  79       double diff = (double)(age - _stats_arrays_length + 1);
  80       return _accum_surv_rate_pred[_stats_arrays_length - 1] + diff * _last_pred;
  81     }
  82   }
  83 
  84   double surv_rate_pred(G1Predictions const& predictor, int age) const {
  85     assert(is_valid_age_index(age), "must be");
  86 
  87     age = MIN2(age, (int)_stats_arrays_length - 1);
  88 
  89     return predictor.predict_in_unit_interval(_surv_rate_predictors[age]);
  90   }
  91 
  92   int next_age_index() {
  93     return (int)++_num_added_regions;
  94   }
  95 
  96   int age_in_group(int age_index) const {
  97     int result = (int)(_num_added_regions - age_index);
  98     assert(is_valid_age_index(result), "invariant" );
  99     return result;
 100   }
 101 };
 102 
 103 #endif // SHARE_GC_G1_G1SURVRATEGROUP_HPP