/*

 * Copyright (c) 2016, 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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 */

#include "precompiled.hpp"

#include "gc/g1/g1CollectedHeap.hpp"

#include "gc/g1/g1HeapSizingPolicy.hpp"

#include "gc/g1/g1Analytics.hpp"

#include "logging/log.hpp"

#include "runtime/globals.hpp"

#include "utilities/debug.hpp"

#include "utilities/globalDefinitions.hpp"

void G1HeapSizingPolicy::clear_ratio_check_data() {

  _ratio_over_threshold_count = 0;

  _ratio_over_threshold_sum = 0.0;

  _pauses_since_start = 0;

}

size_t G1HeapSizingPolicy::expansion_amount() {

  double recent_gc_overhead = _analytics->recent_avg_pause_time_ratio() * 100.0;

  double last_gc_overhead = _analytics->last_pause_time_ratio() * 100.0;

  assert(GCTimeRatio > 0,

         "we should have set it to a default value set_g1_gc_flags() "

         "if a user set it to 0");

  const double gc_overhead_percent = 100.0 * (1.0 / (1.0 + GCTimeRatio));

  double threshold = gc_overhead_percent;

  size_t expand_bytes = 0;

  // If the heap is at less than half its maximum size, scale the threshold down,

  // to a limit of 1. Thus the smaller the heap is, the more likely it is to expand,

  // though the scaling code will likely keep the increase small.

    threshold = MAX2(threshold, 1.0);

  }

  // If the last GC time ratio is over the threshold, increment the count of

  // times it has been exceeded, and add this ratio to the sum of exceeded

  // ratios.

  if (last_gc_overhead > threshold) {

    _ratio_over_threshold_count++;

    _ratio_over_threshold_sum += last_gc_overhead;

  }

  // Check if we've had enough GC time ratio checks that were over the

  // threshold to trigger an expansion. We'll also expand if we've

  // reached the end of the history buffer and the average of all entries

  // is still over the threshold. This indicates a smaller number of GCs were

  // long enough to make the average exceed the threshold.

  bool filled_history_buffer = _pauses_since_start == _num_prev_pauses_for_heuristics;

  if ((_ratio_over_threshold_count == MinOverThresholdForGrowth) ||

      (filled_history_buffer && (recent_gc_overhead > threshold))) {

    size_t min_expand_bytes = HeapRegion::GrainBytes;

    size_t uncommitted_bytes = reserved_bytes - committed_bytes;

    size_t expand_bytes_via_pct =

      uncommitted_bytes * G1ExpandByPercentOfAvailable / 100;

    double scale_factor = 1.0;

    // If the current size is less than 1/4 of the Initial heap size, expand

    // by half of the delta between the current and Initial sizes. IE, grow

    // back quickly.

    //

    // Otherwise, take the current size, or G1ExpandByPercentOfAvailable % of

    // the available expansion space, whichever is smaller, as the base

    // expansion size. Then possibly scale this size according to how much the

    // threshold has (on average) been exceeded by. If the delta is small

    // (less than the StartScaleDownAt value), scale the size down linearly, but

    // not by less than MinScaleDownFactor. If the delta is large (greater than

    // the StartScaleUpAt value), scale up, but adding no more than MaxScaleUpFactor

    // times the base size. The scaling will be linear in the range from

    // StartScaleUpAt to (StartScaleUpAt + ScaleUpRange). In other words,

    // ScaleUpRange sets the rate of scaling up.

    if (committed_bytes < InitialHeapSize / 4) {

      expand_bytes = (InitialHeapSize - committed_bytes) / 2;

    } else {

      double const MinScaleDownFactor = 0.2;

      double const MaxScaleUpFactor = 2;

      double const StartScaleDownAt = gc_overhead_percent;

      double const StartScaleUpAt = gc_overhead_percent * 1.5;

      double const ScaleUpRange = gc_overhead_percent * 2.0;

      double ratio_delta;

      if (filled_history_buffer) {

        ratio_delta = recent_gc_overhead - threshold;

      } else {

        ratio_delta = (_ratio_over_threshold_sum/_ratio_over_threshold_count) - threshold;

      }

      expand_bytes = MIN2(expand_bytes_via_pct, committed_bytes);

      if (ratio_delta < StartScaleDownAt) {

        scale_factor = ratio_delta / StartScaleDownAt;

        scale_factor = MAX2(scale_factor, MinScaleDownFactor);

      } else if (ratio_delta > StartScaleUpAt) {

        scale_factor = 1 + ((ratio_delta - StartScaleUpAt) / ScaleUpRange);

        scale_factor = MIN2(scale_factor, MaxScaleUpFactor);

      }

    }

    log_debug(gc, ergo, heap)("Attempt heap expansion (recent GC overhead higher than threshold after GC) "

                              "recent GC overhead: %1.2f %% threshold: %1.2f %% uncommitted: " SIZE_FORMAT "B base expansion amount and scale: " SIZE_FORMAT "B (%1.2f%%)",

                              recent_gc_overhead, threshold, uncommitted_bytes, expand_bytes, scale_factor * 100);

    expand_bytes = static_cast<size_t>(expand_bytes * scale_factor);

    // Ensure the expansion size is at least the minimum growth amount

    // and at most the remaining uncommitted byte size.

    expand_bytes = MAX2(expand_bytes, min_expand_bytes);

    expand_bytes = MIN2(expand_bytes, uncommitted_bytes);

    clear_ratio_check_data();

  } else {

    // An expansion was not triggered. If we've started counting, increment

    // the number of checks we've made in the current window.  If we've

    // reached the end of the window without resizing, clear the counters to

    // start again the next time we see a ratio above the threshold.

    if (_ratio_over_threshold_count > 0) {

      _pauses_since_start++;

      if (_pauses_since_start > _num_prev_pauses_for_heuristics) {

        clear_ratio_check_data();

      }

    }

  }

  return expand_bytes;

}