src/hotspot/share/gc/g1/g1SurvRateGroup.cpp

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#include "gc/g1/g1HeapRegion.hpp"
#include "gc/g1/g1Predictions.hpp"
#include "gc/g1/g1SurvRateGroup.hpp"
#include "logging/log.hpp"
#include "memory/allocation.hpp"

G1SurvRateGroup::G1SurvRateGroup() :
  _stats_arrays_length(0),
  _num_added_regions(0),
  _accum_surv_rate_pred(nullptr),
  _last_pred(0.0),
  _surv_rate_predictors(nullptr) {
  reset();
  start_adding_regions();
}

void G1SurvRateGroup::reset() {
  _last_pred = 0.0;
  // the following will set up the arrays with length 1
  _num_added_regions = 1;

  // The call to stop_adding_regions() will use "new" to refill
  // the _surv_rate_pred array, so we need to make sure to call
  // "delete".
  for (uint i = 0; i < _stats_arrays_length; ++i) {
    delete _surv_rate_predictors[i];
  }
  _stats_arrays_length = 0;

  stop_adding_regions();

  // Seed initial _surv_rate_pred and _accum_surv_rate_pred values
  guarantee(_stats_arrays_length == 1, "invariant" );

  _num_added_regions = 0;
}

void G1SurvRateGroup::start_adding_regions() {
  _num_added_regions = 0;
}

void G1SurvRateGroup::stop_adding_regions() {
  if (_num_added_regions > _stats_arrays_length) {
    _accum_surv_rate_pred = REALLOC_C_HEAP_ARRAY(double, _accum_surv_rate_pred, _num_added_regions, mtGC);
    _surv_rate_predictors = REALLOC_C_HEAP_ARRAY(TruncatedSeq*, _surv_rate_predictors, _num_added_regions, mtGC);

    for (uint i = _stats_arrays_length; i < _num_added_regions; ++i) {
      // Initialize predictors and accumulated survivor rate predictions.
      _surv_rate_predictors[i] = new TruncatedSeq(10);
      if (i == 0) {
        _surv_rate_predictors[i]->add(InitialSurvivorRate);
        _accum_surv_rate_pred[i] = InitialSurvivorRate;
      } else {
        // Assume that the prediction for the newly added regions is the same as the
        // ones at the (current) end of the array. Particularly predictions at the end
        // of this array fairly seldom get updated, so having a better initial value
        // that is at least somewhat related to the actual application is preferable.
        double next_pred = _surv_rate_predictors[i-1]->last();
        _surv_rate_predictors[i]->add(next_pred);
        _accum_surv_rate_pred[i] = _accum_surv_rate_pred[i-1] + next_pred;
      }
    }
    _last_pred = _surv_rate_predictors[_num_added_regions-1]->last();

    _stats_arrays_length = _num_added_regions;
  }
}

void G1SurvRateGroup::record_surviving_words(uint age, size_t surv_words) {
  assert(is_valid_age(age), "age is %u not between 0 and %u", age, _num_added_regions);

  double surv_rate = (double)surv_words / G1HeapRegion::GrainWords;
  _surv_rate_predictors[age]->add(surv_rate);
}

void G1SurvRateGroup::all_surviving_words_recorded(const G1Predictions& predictor, bool update_predictors) {
  if (update_predictors) {
    fill_in_last_surv_rates();
  }
  finalize_predictions(predictor);
}

double G1SurvRateGroup::accum_surv_rate_pred(uint age) const {
  assert(_stats_arrays_length > 0, "invariant" );
  double result;
  if (age < _stats_arrays_length) {
    result = _accum_surv_rate_pred[age];
  } else {
    double diff = (double)(age - _stats_arrays_length + 1);
    result = _accum_surv_rate_pred[_stats_arrays_length - 1] + diff * _last_pred;
  }
  assert(result <= (age + 1.0), "Accumulated survivor rate %.2f must be smaller than age+1 %u", result, age + 1);
  return result;
}

void G1SurvRateGroup::fill_in_last_surv_rates() {
  if (_num_added_regions > 0) { // conservative
    double surv_rate = _surv_rate_predictors[_num_added_regions-1]->last();
    for (uint i = _num_added_regions; i < _stats_arrays_length; ++i) {
      _surv_rate_predictors[i]->add(surv_rate);
    }
  }
}

void G1SurvRateGroup::finalize_predictions(const G1Predictions& predictor) {
  double accum = 0.0;
  double pred = 0.0;
  for (uint i = 0; i < _stats_arrays_length; ++i) {
    pred = predictor.predict_in_unit_interval(_surv_rate_predictors[i]);
    accum += pred;
    _accum_surv_rate_pred[i] = accum;
  }
  _last_pred = pred;
}