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(const G1CollectedHeap* g1, const G1Analytics* analytics) : 35 _g1(g1), 36 _analytics(analytics), 37 _num_prev_pauses_for_heuristics(analytics->number_of_recorded_pause_times()) { 38 assert(MinOverThresholdForGrowth < _num_prev_pauses_for_heuristics, "Threshold must be less than %u", _num_prev_pauses_for_heuristics); 39 clear_ratio_check_data(); 40 } 41 42 void G1HeapSizingPolicy::clear_ratio_check_data() { 43 _ratio_over_threshold_count = 0; 44 _ratio_over_threshold_sum = 0.0; 45 _pauses_since_start = 0; 46 } 47 48 size_t G1HeapSizingPolicy::expansion_amount() { 49 double recent_gc_overhead = _analytics->recent_avg_pause_time_ratio() * 100.0; 50 double last_gc_overhead = _analytics->last_pause_time_ratio() * 100.0; 51 assert(GCTimeRatio > 0, 52 "we should have set it to a default value set_g1_gc_flags() " 53 "if a user set it to 0"); 54 const double gc_overhead_percent = 100.0 * (1.0 / (1.0 + GCTimeRatio)); 55 56 double threshold = gc_overhead_percent; 57 size_t expand_bytes = 0; 58 59 // If the heap is at less than half its maximum size, scale the threshold down, 60 // to a limit of 1. Thus the smaller the heap is, the more likely it is to expand, 61 // though the scaling code will likely keep the increase small. 62 if (_g1->capacity() <= _g1->max_capacity() / 2) { 63 threshold *= (double)_g1->capacity() / (double)(_g1->max_capacity() / 2); 64 threshold = MAX2(threshold, 1.0); 65 } 66 67 // If the last GC time ratio is over the threshold, increment the count of 68 // times it has been exceeded, and add this ratio to the sum of exceeded 69 // ratios. 70 if (last_gc_overhead > threshold) { 71 _ratio_over_threshold_count++; 72 _ratio_over_threshold_sum += last_gc_overhead; 73 } 74 75 // Check if we've had enough GC time ratio checks that were over the 76 // threshold to trigger an expansion. We'll also expand if we've 77 // reached the end of the history buffer and the average of all entries 78 // is still over the threshold. This indicates a smaller number of GCs were 79 // long enough to make the average exceed the threshold. 80 bool filled_history_buffer = _pauses_since_start == _num_prev_pauses_for_heuristics; 81 if ((_ratio_over_threshold_count == MinOverThresholdForGrowth) || 82 (filled_history_buffer && (recent_gc_overhead > threshold))) { 83 size_t min_expand_bytes = HeapRegion::GrainBytes; 84 size_t reserved_bytes = _g1->max_capacity(); 85 size_t committed_bytes = _g1->capacity(); 86 size_t uncommitted_bytes = reserved_bytes - committed_bytes; 87 size_t expand_bytes_via_pct = 88 uncommitted_bytes * G1ExpandByPercentOfAvailable / 100; 89 double scale_factor = 1.0; 90 91 // If the current size is less than 1/4 of the Initial heap size, expand 92 // by half of the delta between the current and Initial sizes. IE, grow 93 // back quickly. 94 // 95 // Otherwise, take the current size, or G1ExpandByPercentOfAvailable % of 96 // the available expansion space, whichever is smaller, as the base 97 // expansion size. Then possibly scale this size according to how much the 98 // threshold has (on average) been exceeded by. If the delta is small 99 // (less than the StartScaleDownAt value), scale the size down linearly, but 100 // not by less than MinScaleDownFactor. If the delta is large (greater than 101 // the StartScaleUpAt value), scale up, but adding no more than MaxScaleUpFactor 102 // times the base size. The scaling will be linear in the range from 103 // StartScaleUpAt to (StartScaleUpAt + ScaleUpRange). In other words, 104 // ScaleUpRange sets the rate of scaling up. 105 if (committed_bytes < InitialHeapSize / 4) { 106 expand_bytes = (InitialHeapSize - committed_bytes) / 2; 107 } else { 108 double const MinScaleDownFactor = 0.2; 109 double const MaxScaleUpFactor = 2; 110 double const StartScaleDownAt = gc_overhead_percent; 111 double const StartScaleUpAt = gc_overhead_percent * 1.5; 112 double const ScaleUpRange = gc_overhead_percent * 2.0; 113 114 double ratio_delta; 115 if (filled_history_buffer) { 116 ratio_delta = recent_gc_overhead - threshold; 117 } else { 118 ratio_delta = (_ratio_over_threshold_sum/_ratio_over_threshold_count) - threshold; 119 } 120 121 expand_bytes = MIN2(expand_bytes_via_pct, committed_bytes); 122 if (ratio_delta < StartScaleDownAt) { 123 scale_factor = ratio_delta / StartScaleDownAt; 124 scale_factor = MAX2(scale_factor, MinScaleDownFactor); 125 } else if (ratio_delta > StartScaleUpAt) { 126 scale_factor = 1 + ((ratio_delta - StartScaleUpAt) / ScaleUpRange); 127 scale_factor = MIN2(scale_factor, MaxScaleUpFactor); 128 } 129 } 130 131 log_debug(gc, ergo, heap)("Attempt heap expansion (recent GC overhead higher than threshold after GC) " 132 "recent GC overhead: %1.2f %% threshold: %1.2f %% uncommitted: " SIZE_FORMAT "B base expansion amount and scale: " SIZE_FORMAT "B (%1.2f%%)", 133 recent_gc_overhead, threshold, uncommitted_bytes, expand_bytes, scale_factor * 100); 134 135 expand_bytes = static_cast<size_t>(expand_bytes * scale_factor); 136 137 // Ensure the expansion size is at least the minimum growth amount 138 // and at most the remaining uncommitted byte size. 139 expand_bytes = MAX2(expand_bytes, min_expand_bytes); 140 expand_bytes = MIN2(expand_bytes, uncommitted_bytes); 141 142 clear_ratio_check_data(); 143 } else { 144 // An expansion was not triggered. If we've started counting, increment 145 // the number of checks we've made in the current window. If we've 146 // reached the end of the window without resizing, clear the counters to 147 // start again the next time we see a ratio above the threshold. 148 if (_ratio_over_threshold_count > 0) { 149 _pauses_since_start++; 150 if (_pauses_since_start > _num_prev_pauses_for_heuristics) { 151 clear_ratio_check_data(); 152 } 153 } 154 } 155 156 return expand_bytes; 157 }