gc/shared/adaptiveSizePolicy.cpp

/*
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 * 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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#include "precompiled.hpp"
#include "gc/shared/adaptiveSizePolicy.hpp"
#include "gc/shared/gcCause.hpp"
#include "gc/shared/gcUtil.inline.hpp"
#include "gc/shared/softRefPolicy.hpp"
#include "logging/log.hpp"
#include "runtime/timer.hpp"

elapsedTimer AdaptiveSizePolicy::_minor_timer;
elapsedTimer AdaptiveSizePolicy::_major_timer;

// The throughput goal is implemented as
//      _throughput_goal = 1 - ( 1 / (1 + gc_cost_ratio))
// gc_cost_ratio is the ratio
//      application cost / gc cost
// For example a gc_cost_ratio of 4 translates into a
// throughput goal of .80

AdaptiveSizePolicy::AdaptiveSizePolicy(size_t init_eden_size,
                                       size_t init_promo_size,
                                       size_t init_survivor_size,
                                       double gc_pause_goal_sec,
                                       uint gc_cost_ratio) :
    _throughput_goal(1.0 - double(1.0 / (1.0 + (double) gc_cost_ratio))),
    _eden_size(init_eden_size),
    _promo_size(init_promo_size),
    _survivor_size(init_survivor_size),
    _gc_overhead_limit_exceeded(false),
    _print_gc_overhead_limit_would_be_exceeded(false),
    _gc_overhead_limit_count(0),
    _latest_minor_mutator_interval_seconds(0),
    _threshold_tolerance_percent(1.0 + ThresholdTolerance/100.0),
    _gc_pause_goal_sec(gc_pause_goal_sec),
    _young_gen_change_for_minor_throughput(0),
    _old_gen_change_for_major_throughput(0) {
  assert(AdaptiveSizePolicyGCTimeLimitThreshold > 0,
    "No opportunity to clear SoftReferences before GC overhead limit");
  _avg_minor_pause    =
    new AdaptivePaddedAverage(AdaptiveTimeWeight, PausePadding);
  _avg_minor_interval = new AdaptiveWeightedAverage(AdaptiveTimeWeight);
  _avg_minor_gc_cost  = new AdaptiveWeightedAverage(AdaptiveTimeWeight);
  _avg_major_gc_cost  = new AdaptiveWeightedAverage(AdaptiveTimeWeight);

  _avg_young_live     = new AdaptiveWeightedAverage(AdaptiveSizePolicyWeight);
  _avg_old_live       = new AdaptiveWeightedAverage(AdaptiveSizePolicyWeight);
  _avg_eden_live      = new AdaptiveWeightedAverage(AdaptiveSizePolicyWeight);

  _avg_survived       = new AdaptivePaddedAverage(AdaptiveSizePolicyWeight,
                                                  SurvivorPadding);
  _avg_pretenured     = new AdaptivePaddedNoZeroDevAverage(
                                                  AdaptiveSizePolicyWeight,
                                                  SurvivorPadding);

  _minor_pause_old_estimator =
    new LinearLeastSquareFit(AdaptiveSizePolicyWeight);
  _minor_pause_young_estimator =
    new LinearLeastSquareFit(AdaptiveSizePolicyWeight);
  _minor_collection_estimator =
    new LinearLeastSquareFit(AdaptiveSizePolicyWeight);
  _major_collection_estimator =
    new LinearLeastSquareFit(AdaptiveSizePolicyWeight);

  // Start the timers
  _minor_timer.start();

  _young_gen_policy_is_ready = false;
}

bool AdaptiveSizePolicy::tenuring_threshold_change() const {
  return decrement_tenuring_threshold_for_gc_cost() ||
         increment_tenuring_threshold_for_gc_cost() ||
         decrement_tenuring_threshold_for_survivor_limit();
}

void AdaptiveSizePolicy::minor_collection_begin() {
  // Update the interval time
  _minor_timer.stop();
  // Save most recent collection time
  _latest_minor_mutator_interval_seconds = _minor_timer.seconds();
  _minor_timer.reset();
  _minor_timer.start();
}

void AdaptiveSizePolicy::update_minor_pause_young_estimator(
    double minor_pause_in_ms) {
  double eden_size_in_mbytes = ((double)_eden_size)/((double)M);
  _minor_pause_young_estimator->update(eden_size_in_mbytes,
    minor_pause_in_ms);
}

void AdaptiveSizePolicy::minor_collection_end(GCCause::Cause gc_cause) {
  // Update the pause time.
  _minor_timer.stop();

  if (!GCCause::is_user_requested_gc(gc_cause) ||
      UseAdaptiveSizePolicyWithSystemGC) {
    double minor_pause_in_seconds = _minor_timer.seconds();
    double minor_pause_in_ms = minor_pause_in_seconds * MILLIUNITS;

    // Sample for performance counter
    _avg_minor_pause->sample(minor_pause_in_seconds);

    // Cost of collection (unit-less)
    double collection_cost = 0.0;
    if ((_latest_minor_mutator_interval_seconds > 0.0) &&
        (minor_pause_in_seconds > 0.0)) {
      double interval_in_seconds =
        _latest_minor_mutator_interval_seconds + minor_pause_in_seconds;
      collection_cost =
        minor_pause_in_seconds / interval_in_seconds;
      _avg_minor_gc_cost->sample(collection_cost);
      // Sample for performance counter
      _avg_minor_interval->sample(interval_in_seconds);
    }

    // The policy does not have enough data until at least some
    // young collections have been done.
    _young_gen_policy_is_ready =
      (_avg_minor_gc_cost->count() >= AdaptiveSizePolicyReadyThreshold);

    // Calculate variables used to estimate pause time vs. gen sizes
    double eden_size_in_mbytes = ((double)_eden_size) / ((double)M);
    update_minor_pause_young_estimator(minor_pause_in_ms);
    update_minor_pause_old_estimator(minor_pause_in_ms);

    log_trace(gc, ergo)("AdaptiveSizePolicy::minor_collection_end: minor gc cost: %f  average: %f",
                        collection_cost, _avg_minor_gc_cost->average());
    log_trace(gc, ergo)("  minor pause: %f minor period %f",
                        minor_pause_in_ms, _latest_minor_mutator_interval_seconds * MILLIUNITS);

    // Calculate variable used to estimate collection cost vs. gen sizes
    assert(collection_cost >= 0.0, "Expected to be non-negative");
    _minor_collection_estimator->update(eden_size_in_mbytes, collection_cost);
  }

  // Interval times use this timer to measure the mutator time.
  // Reset the timer after the GC pause.
  _minor_timer.reset();
  _minor_timer.start();
}

size_t AdaptiveSizePolicy::eden_increment(size_t cur_eden, uint percent_change) {
  size_t eden_heap_delta;
  eden_heap_delta = cur_eden / 100 * percent_change;
  return eden_heap_delta;
}

size_t AdaptiveSizePolicy::eden_increment(size_t cur_eden) {
  return eden_increment(cur_eden, YoungGenerationSizeIncrement);
}

size_t AdaptiveSizePolicy::eden_decrement(size_t cur_eden) {
  size_t eden_heap_delta = eden_increment(cur_eden) /
    AdaptiveSizeDecrementScaleFactor;
  return eden_heap_delta;
}

size_t AdaptiveSizePolicy::promo_increment(size_t cur_promo, uint percent_change) {
  size_t promo_heap_delta;
  promo_heap_delta = cur_promo / 100 * percent_change;
  return promo_heap_delta;
}

size_t AdaptiveSizePolicy::promo_increment(size_t cur_promo) {
  return promo_increment(cur_promo, TenuredGenerationSizeIncrement);
}

size_t AdaptiveSizePolicy::promo_decrement(size_t cur_promo) {
  size_t promo_heap_delta = promo_increment(cur_promo);
  promo_heap_delta = promo_heap_delta / AdaptiveSizeDecrementScaleFactor;
  return promo_heap_delta;
}

double AdaptiveSizePolicy::time_since_major_gc() const {
  _major_timer.stop();
  double result = _major_timer.seconds();
  _major_timer.start();
  return result;
}

// Linear decay of major gc cost
double AdaptiveSizePolicy::decaying_major_gc_cost() const {
  double major_interval = major_gc_interval_average_for_decay();
  double major_gc_cost_average = major_gc_cost();
  double decayed_major_gc_cost = major_gc_cost_average;
  if(time_since_major_gc() > 0.0) {
    decayed_major_gc_cost = major_gc_cost() *
      (((double) AdaptiveSizeMajorGCDecayTimeScale) * major_interval)
      / time_since_major_gc();
  }

  // The decayed cost should always be smaller than the
  // average cost but the vagaries of finite arithmetic could
  // produce a larger value in decayed_major_gc_cost so protect
  // against that.
  return MIN2(major_gc_cost_average, decayed_major_gc_cost);
}

// Use a value of the major gc cost that has been decayed
// by the factor
//
//      average-interval-between-major-gc * AdaptiveSizeMajorGCDecayTimeScale /
//        time-since-last-major-gc
//
// if the average-interval-between-major-gc * AdaptiveSizeMajorGCDecayTimeScale
// is less than time-since-last-major-gc.
//
// In cases where there are initial major gc's that
// are of a relatively high cost but no later major
// gc's, the total gc cost can remain high because
// the major gc cost remains unchanged (since there are no major
// gc's).  In such a situation the value of the unchanging
// major gc cost can keep the mutator throughput below
// the goal when in fact the major gc cost is becoming diminishingly
// small.  Use the decaying gc cost only to decide whether to
// adjust for throughput.  Using it also to determine the adjustment
// to be made for throughput also seems reasonable but there is
// no test case to use to decide if it is the right thing to do
// don't do it yet.

double AdaptiveSizePolicy::decaying_gc_cost() const {
  double decayed_major_gc_cost = major_gc_cost();
  double avg_major_interval = major_gc_interval_average_for_decay();
  if (UseAdaptiveSizeDecayMajorGCCost &&
      (AdaptiveSizeMajorGCDecayTimeScale > 0) &&
      (avg_major_interval > 0.00)) {
    double time_since_last_major_gc = time_since_major_gc();

    // Decay the major gc cost?
    if (time_since_last_major_gc >
        ((double) AdaptiveSizeMajorGCDecayTimeScale) * avg_major_interval) {

      // Decay using the time-since-last-major-gc
      decayed_major_gc_cost = decaying_major_gc_cost();
      log_trace(gc, ergo)("decaying_gc_cost: major interval average: %f  time since last major gc: %f",
                    avg_major_interval, time_since_last_major_gc);
      log_trace(gc, ergo)("  major gc cost: %f  decayed major gc cost: %f",
                    major_gc_cost(), decayed_major_gc_cost);
    }
  }
  double result = MIN2(1.0, decayed_major_gc_cost + minor_gc_cost());
  return result;
}


void AdaptiveSizePolicy::clear_generation_free_space_flags() {
  set_change_young_gen_for_min_pauses(0);
  set_change_old_gen_for_maj_pauses(0);

  set_change_old_gen_for_throughput(0);
  set_change_young_gen_for_throughput(0);
  set_decrease_for_footprint(0);
  set_decide_at_full_gc(0);
}

void AdaptiveSizePolicy::check_gc_overhead_limit(
                                          size_t young_live,
                                          size_t eden_live,
                                          size_t max_old_gen_size,
                                          size_t max_eden_size,
                                          bool   is_full_gc,
                                          GCCause::Cause gc_cause,
                                          SoftRefPolicy* soft_ref_policy) {

  // Ignore explicit GC's.  Exiting here does not set the flag and
  // does not reset the count.  Updating of the averages for system
  // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
  if (GCCause::is_user_requested_gc(gc_cause) ||
      GCCause::is_serviceability_requested_gc(gc_cause)) {
    return;
  }
  // eden_limit is the upper limit on the size of eden based on
  // the maximum size of the young generation and the sizes
  // of the survivor space.
  // The question being asked is whether the gc costs are high
  // and the space being recovered by a collection is low.
  // free_in_young_gen is the free space in the young generation
  // after a collection and promo_live is the free space in the old
  // generation after a collection.
  //
  // Use the minimum of the current value of the live in the
  // young gen or the average of the live in the young gen.
  // If the current value drops quickly, that should be taken
  // into account (i.e., don't trigger if the amount of free
  // space has suddenly jumped up).  If the current is much
  // higher than the average, use the average since it represents
  // the longer term behavior.
  const size_t live_in_eden =
    MIN2(eden_live, (size_t) avg_eden_live()->average());
  const size_t free_in_eden = max_eden_size > live_in_eden ?
    max_eden_size - live_in_eden : 0;
  const size_t free_in_old_gen = (size_t)(max_old_gen_size - avg_old_live()->average());
  const size_t total_free_limit = free_in_old_gen + free_in_eden;
  const size_t total_mem = max_old_gen_size + max_eden_size;
  const double mem_free_limit = total_mem * (GCHeapFreeLimit/100.0);
  const double mem_free_old_limit = max_old_gen_size * (GCHeapFreeLimit/100.0);
  const double mem_free_eden_limit = max_eden_size * (GCHeapFreeLimit/100.0);
  const double gc_cost_limit = GCTimeLimit/100.0;
  size_t promo_limit = (size_t)(max_old_gen_size - avg_old_live()->average());
  // But don't force a promo size below the current promo size. Otherwise,
  // the promo size will shrink for no good reason.
  promo_limit = MAX2(promo_limit, _promo_size);


  log_trace(gc, ergo)(
        "PSAdaptiveSizePolicy::check_gc_overhead_limit:"
        " promo_limit: " SIZE_FORMAT
        " max_eden_size: " SIZE_FORMAT
        " total_free_limit: " SIZE_FORMAT
        " max_old_gen_size: " SIZE_FORMAT
        " max_eden_size: " SIZE_FORMAT
        " mem_free_limit: " SIZE_FORMAT,
        promo_limit, max_eden_size, total_free_limit,
        max_old_gen_size, max_eden_size,
        (size_t) mem_free_limit);

  bool print_gc_overhead_limit_would_be_exceeded = false;
  if (is_full_gc) {
    if (gc_cost() > gc_cost_limit &&
      free_in_old_gen < (size_t) mem_free_old_limit &&
      free_in_eden < (size_t) mem_free_eden_limit) {
      // Collections, on average, are taking too much time, and
      //      gc_cost() > gc_cost_limit
      // we have too little space available after a full gc.
      //      total_free_limit < mem_free_limit
      // where
      //   total_free_limit is the free space available in
      //     both generations
      //   total_mem is the total space available for allocation
      //     in both generations (survivor spaces are not included
      //     just as they are not included in eden_limit).
      //   mem_free_limit is a fraction of total_mem judged to be an
      //     acceptable amount that is still unused.
      // The heap can ask for the value of this variable when deciding
      // whether to thrown an OutOfMemory error.
      // Note that the gc time limit test only works for the collections
      // of the young gen + tenured gen and not for collections of the
      // permanent gen.  That is because the calculation of the space
      // freed by the collection is the free space in the young gen +
      // tenured gen.
      // At this point the GC overhead limit is being exceeded.
      inc_gc_overhead_limit_count();
      if (UseGCOverheadLimit) {
        if (gc_overhead_limit_count() >=
            AdaptiveSizePolicyGCTimeLimitThreshold){
          // All conditions have been met for throwing an out-of-memory
          set_gc_overhead_limit_exceeded(true);
          // Avoid consecutive OOM due to the gc time limit by resetting
          // the counter.
          reset_gc_overhead_limit_count();
        } else {
          // The required consecutive collections which exceed the
          // GC time limit may or may not have been reached. We
          // are approaching that condition and so as not to
          // throw an out-of-memory before all SoftRef's have been
          // cleared, set _should_clear_all_soft_refs in CollectorPolicy.
          // The clearing will be done on the next GC.
          bool near_limit = gc_overhead_limit_near();
          if (near_limit) {
            soft_ref_policy->set_should_clear_all_soft_refs(true);
            log_trace(gc, ergo)("Nearing GC overhead limit, will be clearing all SoftReference");
          }
        }
      }
      // Set this even when the overhead limit will not
      // cause an out-of-memory.  Diagnostic message indicating
      // that the overhead limit is being exceeded is sometimes
      // printed.
      print_gc_overhead_limit_would_be_exceeded = true;

    } else {
      // Did not exceed overhead limits
      reset_gc_overhead_limit_count();
    }
  }

  if (UseGCOverheadLimit) {
    if (gc_overhead_limit_exceeded()) {
      log_trace(gc, ergo)("GC is exceeding overhead limit of " UINTX_FORMAT "%%", GCTimeLimit);
      reset_gc_overhead_limit_count();
    } else if (print_gc_overhead_limit_would_be_exceeded) {
      assert(gc_overhead_limit_count() > 0, "Should not be printing");
      log_trace(gc, ergo)("GC would exceed overhead limit of " UINTX_FORMAT "%% %d consecutive time(s)",
                          GCTimeLimit, gc_overhead_limit_count());
    }
  }
}
// Printing

bool AdaptiveSizePolicy::print() const {
  assert(UseAdaptiveSizePolicy, "UseAdaptiveSizePolicy need to be enabled.");

  if (!log_is_enabled(Debug, gc, ergo)) {
    return false;
  }

  // Print goal for which action is needed.
  char* action = NULL;
  bool change_for_pause = false;
  if ((change_old_gen_for_maj_pauses() ==
         decrease_old_gen_for_maj_pauses_true) ||
      (change_young_gen_for_min_pauses() ==
         decrease_young_gen_for_min_pauses_true)) {
    action = (char*) " *** pause time goal ***";
    change_for_pause = true;
  } else if ((change_old_gen_for_throughput() ==
               increase_old_gen_for_throughput_true) ||
            (change_young_gen_for_throughput() ==
               increase_young_gen_for_througput_true)) {
    action = (char*) " *** throughput goal ***";
  } else if (decrease_for_footprint()) {
    action = (char*) " *** reduced footprint ***";
  } else {
    // No actions were taken.  This can legitimately be the
    // situation if not enough data has been gathered to make
    // decisions.
    return false;
  }

  // Pauses
  // Currently the size of the old gen is only adjusted to
  // change the major pause times.
  char* young_gen_action = NULL;
  char* tenured_gen_action = NULL;

  char* shrink_msg = (char*) "(attempted to shrink)";
  char* grow_msg = (char*) "(attempted to grow)";
  char* no_change_msg = (char*) "(no change)";
  if (change_young_gen_for_min_pauses() ==
      decrease_young_gen_for_min_pauses_true) {
    young_gen_action = shrink_msg;
  } else if (change_for_pause) {
    young_gen_action = no_change_msg;
  }

  if (change_old_gen_for_maj_pauses() == decrease_old_gen_for_maj_pauses_true) {
    tenured_gen_action = shrink_msg;
  } else if (change_for_pause) {
    tenured_gen_action = no_change_msg;
  }

  // Throughput
  if (change_old_gen_for_throughput() == increase_old_gen_for_throughput_true) {
    assert(change_young_gen_for_throughput() ==
           increase_young_gen_for_througput_true,
           "Both generations should be growing");
    young_gen_action = grow_msg;
    tenured_gen_action = grow_msg;
  } else if (change_young_gen_for_throughput() ==
             increase_young_gen_for_througput_true) {
    // Only the young generation may grow at start up (before
    // enough full collections have been done to grow the old generation).
    young_gen_action = grow_msg;
    tenured_gen_action = no_change_msg;
  }

  // Minimum footprint
  if (decrease_for_footprint() != 0) {
    young_gen_action = shrink_msg;
    tenured_gen_action = shrink_msg;
  }

  log_debug(gc, ergo)("UseAdaptiveSizePolicy actions to meet %s", action);
  log_debug(gc, ergo)("                       GC overhead (%%)");
  log_debug(gc, ergo)("    Young generation:     %7.2f\t  %s",
                      100.0 * avg_minor_gc_cost()->average(), young_gen_action);
  log_debug(gc, ergo)("    Tenured generation:   %7.2f\t  %s",
                      100.0 * avg_major_gc_cost()->average(), tenured_gen_action);
  return true;
}

void AdaptiveSizePolicy::print_tenuring_threshold( uint new_tenuring_threshold_arg) const {
  // Tenuring threshold
  if (decrement_tenuring_threshold_for_survivor_limit()) {
    log_debug(gc, ergo)("Tenuring threshold: (attempted to decrease to avoid survivor space overflow) = %u", new_tenuring_threshold_arg);
  } else if (decrement_tenuring_threshold_for_gc_cost()) {
    log_debug(gc, ergo)("Tenuring threshold: (attempted to decrease to balance GC costs) = %u", new_tenuring_threshold_arg);
  } else if (increment_tenuring_threshold_for_gc_cost()) {
    log_debug(gc, ergo)("Tenuring threshold: (attempted to increase to balance GC costs) = %u", new_tenuring_threshold_arg);
  } else {
    assert(!tenuring_threshold_change(), "(no change was attempted)");
  }
}