1 /*
   2  * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  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  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "gc/g1/g1CollectedHeap.hpp"
  27 #include "gc/g1/g1HeapSizingPolicy.hpp"
  28 #include "gc/g1/g1Analytics.hpp"
  29 #include "logging/log.hpp"
  30 #include "runtime/globals.hpp"
  31 #include "utilities/debug.hpp"
  32 #include "utilities/globalDefinitions.hpp"
  33 
  34 G1HeapSizingPolicy* G1HeapSizingPolicy::create(const G1CollectedHeap* g1h, const G1Analytics* analytics) {
  35   return new G1HeapSizingPolicy(g1h, analytics);
  36 }
  37 
  38 G1HeapSizingPolicy::G1HeapSizingPolicy(const G1CollectedHeap* g1h, const G1Analytics* analytics) :
  39   _g1h(g1h),
  40   _analytics(analytics),
  41   _num_prev_pauses_for_heuristics(analytics->number_of_recorded_pause_times()) {
  42 
  43   assert(MinOverThresholdForGrowth < _num_prev_pauses_for_heuristics, "Threshold must be less than %u", _num_prev_pauses_for_heuristics);
  44   clear_ratio_check_data();
  45 }
  46 
  47 void G1HeapSizingPolicy::clear_ratio_check_data() {
  48   _ratio_over_threshold_count = 0;
  49   _ratio_over_threshold_sum = 0.0;
  50   _pauses_since_start = 0;
  51 }
  52 
  53 double G1HeapSizingPolicy::scale_with_heap(double pause_time_threshold) {
  54   double threshold = pause_time_threshold;
  55   // If the heap is at less than half its maximum size, scale the threshold down,
  56   // to a limit of 1%. Thus the smaller the heap is, the more likely it is to expand,
  57   // though the scaling code will likely keep the increase small.
  58   if (_g1h->capacity() <= _g1h->max_capacity() / 2) {
  59     threshold *= (double)_g1h->capacity() / (double)(_g1h->max_capacity() / 2);
  60     threshold = MAX2(threshold, 0.01);
  61   }
  62 
  63   return threshold;
  64 }
  65 
  66 size_t G1HeapSizingPolicy::expansion_amount() {
  67   assert(GCTimeRatio > 0, "must be");
  68 
  69   double long_term_pause_time_ratio = _analytics->long_term_pause_time_ratio();
  70   double short_term_pause_time_ratio = _analytics->short_term_pause_time_ratio();
  71   size_t expand_bytes = 0;
  72 
  73   if (_g1h->capacity() == _g1h->max_capacity()) {
  74     log_trace(gc, ergo, heap)("Cannot expand (heap already fully expanded) "
  75                               "long term GC overhead: %1.2f%%  committed: " SIZE_FORMAT "B",
  76                               long_term_pause_time_ratio * 100.0, _g1h->capacity());
  77 
  78     clear_ratio_check_data();
  79     return expand_bytes;
  80   }
  81 
  82   const double pause_time_threshold = 1.0 / (1.0 + GCTimeRatio);
  83 
  84   double threshold = scale_with_heap(pause_time_threshold);
  85 
  86   // If the last GC time ratio is over the threshold, increment the count of
  87   // times it has been exceeded, and add this ratio to the sum of exceeded
  88   // ratios.
  89   if (short_term_pause_time_ratio > threshold) {
  90     _ratio_over_threshold_count++;
  91     _ratio_over_threshold_sum += short_term_pause_time_ratio;
  92   }
  93   // Check if we've had enough GC time ratio checks that were over the
  94   // threshold to trigger an expansion. We'll also expand if we've
  95   // reached the end of the history buffer and the average of all entries
  96   // is still over the threshold. This indicates a smaller number of GCs were
  97   // long enough to make the average exceed the threshold.
  98   bool filled_history_buffer = _pauses_since_start == _num_prev_pauses_for_heuristics;
  99   if ((_ratio_over_threshold_count == MinOverThresholdForGrowth) ||
 100       (filled_history_buffer && (long_term_pause_time_ratio > threshold))) {
 101     size_t min_expand_bytes = HeapRegion::GrainBytes;
 102     size_t reserved_bytes = _g1h->max_capacity();
 103     size_t committed_bytes = _g1h->capacity();
 104     size_t uncommitted_bytes = reserved_bytes - committed_bytes;
 105     size_t expand_bytes_via_pct =
 106       uncommitted_bytes * G1ExpandByPercentOfAvailable / 100;
 107     double scale_factor = 1.0;
 108 
 109     // If the current size is less than 1/4 of the Initial heap size, expand
 110     // by half of the delta between the current and Initial sizes. IE, grow
 111     // back quickly.
 112     //
 113     // Otherwise, take the current size, or G1ExpandByPercentOfAvailable % of
 114     // the available expansion space, whichever is smaller, as the base
 115     // expansion size. Then possibly scale this size according to how much the
 116     // threshold has (on average) been exceeded by. If the delta is small
 117     // (less than the StartScaleDownAt value), scale the size down linearly, but
 118     // not by less than MinScaleDownFactor. If the delta is large (greater than
 119     // the StartScaleUpAt value), scale up, but adding no more than MaxScaleUpFactor
 120     // times the base size. The scaling will be linear in the range from
 121     // StartScaleUpAt to (StartScaleUpAt + ScaleUpRange). In other words,
 122     // ScaleUpRange sets the rate of scaling up.
 123     if (committed_bytes < InitialHeapSize / 4) {
 124       expand_bytes = (InitialHeapSize - committed_bytes) / 2;
 125     } else {
 126       double const MinScaleDownFactor = 0.2;
 127       double const MaxScaleUpFactor = 2;
 128       double const StartScaleDownAt = pause_time_threshold;
 129       double const StartScaleUpAt = pause_time_threshold * 1.5;
 130       double const ScaleUpRange = pause_time_threshold * 2.0;
 131 
 132       double ratio_delta;
 133       if (filled_history_buffer) {
 134         ratio_delta = long_term_pause_time_ratio - threshold;
 135       } else {
 136         ratio_delta = (_ratio_over_threshold_sum / _ratio_over_threshold_count) - threshold;
 137       }
 138 
 139       expand_bytes = MIN2(expand_bytes_via_pct, committed_bytes);
 140       if (ratio_delta < StartScaleDownAt) {
 141         scale_factor = ratio_delta / StartScaleDownAt;
 142         scale_factor = MAX2(scale_factor, MinScaleDownFactor);
 143       } else if (ratio_delta > StartScaleUpAt) {
 144         scale_factor = 1 + ((ratio_delta - StartScaleUpAt) / ScaleUpRange);
 145         scale_factor = MIN2(scale_factor, MaxScaleUpFactor);
 146       }
 147     }
 148 
 149     log_debug(gc, ergo, heap)("Attempt heap expansion (recent GC overhead higher than threshold after GC) "
 150                               "long term GC overhead: %1.2f%% threshold: %1.2f%% uncommitted: " SIZE_FORMAT "B "
 151                               "base expansion amount and scale: " SIZE_FORMAT "B (%1.2f%%)",
 152                               long_term_pause_time_ratio * 100.0, threshold * 100.0,
 153                               uncommitted_bytes, expand_bytes, scale_factor * 100.0);
 154 
 155     expand_bytes = static_cast<size_t>(expand_bytes * scale_factor);
 156 
 157     // Ensure the expansion size is at least the minimum growth amount
 158     // and at most the remaining uncommitted byte size.
 159     expand_bytes = MAX2(expand_bytes, min_expand_bytes);
 160     expand_bytes = MIN2(expand_bytes, uncommitted_bytes);
 161 
 162     clear_ratio_check_data();
 163   } else {
 164     // An expansion was not triggered. If we've started counting, increment
 165     // the number of checks we've made in the current window.  If we've
 166     // reached the end of the window without resizing, clear the counters to
 167     // start again the next time we see a ratio above the threshold.
 168     if (_ratio_over_threshold_count > 0) {
 169       _pauses_since_start++;
 170       if (_pauses_since_start > _num_prev_pauses_for_heuristics) {
 171         clear_ratio_check_data();
 172       }
 173     }
 174   }
 175 
 176   return expand_bytes;
 177 }