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/globalDefinitions.hpp" 32 33 void G1HeapSizingPolicy::clear_ratio_check_data() { 34 _ratio_over_threshold_count = 0; 35 _ratio_over_threshold_sum = 0.0; 36 _pauses_since_start = 0; 37 } 38 39 size_t G1HeapSizingPolicy::expansion_amount() { 40 double recent_gc_overhead = _analytics->recent_avg_pause_time_ratio() * 100.0; 41 double last_gc_overhead = _analytics->last_pause_time_ratio() * 100.0; 42 assert(GCTimeRatio > 0, 43 "we should have set it to a default value set_g1_gc_flags() " 44 "if a user set it to 0"); 45 const double gc_overhead_perc = 100.0 * (1.0 / (1.0 + GCTimeRatio)); 46 47 double threshold = gc_overhead_perc; 48 size_t expand_bytes = 0; 49 50 // If the heap is at less than half its maximum size, scale the threshold down, 51 // to a limit of 1. Thus the smaller the heap is, the more likely it is to expand, 52 // though the scaling code will likely keep the increase small. 53 if (_g1->capacity() <= _g1->max_capacity() / 2) { 54 threshold *= (double)_g1->capacity() / (double)(_g1->max_capacity() / 2); 55 threshold = MAX2(threshold, 1.0); 56 } 57 58 // If the last GC time ratio is over the threshold, increment the count of 59 // times it has been exceeded, and add this ratio to the sum of exceeded 60 // ratios. 61 if (last_gc_overhead > threshold) { 62 _ratio_over_threshold_count++; 63 _ratio_over_threshold_sum += last_gc_overhead; 64 } 65 66 // Check if we've had enough GC time ratio checks that were over the 67 // threshold to trigger an expansion. We'll also expand if we've 68 // reached the end of the history buffer and the average of all entries 69 // is still over the threshold. This indicates a smaller number of GCs were 70 // long enough to make the average exceed the threshold. 71 bool filled_history_buffer = _pauses_since_start == NumPrevPausesForHeuristics; 72 if ((_ratio_over_threshold_count == MinOverThresholdForGrowth) || 73 (filled_history_buffer && (recent_gc_overhead > threshold))) { 74 size_t min_expand_bytes = HeapRegion::GrainBytes; 75 size_t reserved_bytes = _g1->max_capacity(); 76 size_t committed_bytes = _g1->capacity(); 77 size_t uncommitted_bytes = reserved_bytes - committed_bytes; 78 size_t expand_bytes_via_pct = 79 uncommitted_bytes * G1ExpandByPercentOfAvailable / 100; 80 double scale_factor = 1.0; 81 82 // If the current size is less than 1/4 of the Initial heap size, expand 83 // by half of the delta between the current and Initial sizes. IE, grow 84 // back quickly. 85 // 86 // Otherwise, take the current size, or G1ExpandByPercentOfAvailable % of 87 // the available expansion space, whichever is smaller, as the base 88 // expansion size. Then possibly scale this size according to how much the 89 // threshold has (on average) been exceeded by. If the delta is small 90 // (less than the StartScaleDownAt value), scale the size down linearly, but 91 // not by less than MinScaleDownFactor. If the delta is large (greater than 92 // the StartScaleUpAt value), scale up, but adding no more than MaxScaleUpFactor 93 // times the base size. The scaling will be linear in the range from 94 // StartScaleUpAt to (StartScaleUpAt + ScaleUpRange). In other words, 95 // ScaleUpRange sets the rate of scaling up. 96 if (committed_bytes < InitialHeapSize / 4) { 97 expand_bytes = (InitialHeapSize - committed_bytes) / 2; 98 } else { 99 double const MinScaleDownFactor = 0.2; 100 double const MaxScaleUpFactor = 2; 101 double const StartScaleDownAt = gc_overhead_perc; 102 double const StartScaleUpAt = gc_overhead_perc * 1.5; 103 double const ScaleUpRange = gc_overhead_perc * 2.0; 104 105 double ratio_delta; 106 if (filled_history_buffer) { 107 ratio_delta = recent_gc_overhead - threshold; 108 } else { 109 ratio_delta = (_ratio_over_threshold_sum/_ratio_over_threshold_count) - threshold; 110 } 111 112 expand_bytes = MIN2(expand_bytes_via_pct, committed_bytes); 113 if (ratio_delta < StartScaleDownAt) { 114 scale_factor = ratio_delta / StartScaleDownAt; 115 scale_factor = MAX2(scale_factor, MinScaleDownFactor); 116 } else if (ratio_delta > StartScaleUpAt) { 117 scale_factor = 1 + ((ratio_delta - StartScaleUpAt) / ScaleUpRange); 118 scale_factor = MIN2(scale_factor, MaxScaleUpFactor); 119 } 120 } 121 122 log_debug(gc, ergo, heap)("Attempt heap expansion (recent GC overhead higher than threshold after GC) " 123 "recent GC overhead: %1.2f %% threshold: %1.2f %% uncommitted: " SIZE_FORMAT "B base expansion amount and scale: " SIZE_FORMAT "B (%1.2f%%)", 124 recent_gc_overhead, threshold, uncommitted_bytes, expand_bytes, scale_factor * 100); 125 126 expand_bytes = static_cast<size_t>(expand_bytes * scale_factor); 127 128 // Ensure the expansion size is at least the minimum growth amount 129 // and at most the remaining uncommitted byte size. 130 expand_bytes = MAX2(expand_bytes, min_expand_bytes); 131 expand_bytes = MIN2(expand_bytes, uncommitted_bytes); 132 133 clear_ratio_check_data(); 134 } else { 135 // An expansion was not triggered. If we've started counting, increment 136 // the number of checks we've made in the current window. If we've 137 // reached the end of the window without resizing, clear the counters to 138 // start again the next time we see a ratio above the threshold. 139 if (_ratio_over_threshold_count > 0) { 140 _pauses_since_start++; 141 if (_pauses_since_start > NumPrevPausesForHeuristics) { 142 clear_ratio_check_data(); 143 } 144 } 145 } 146 147 return expand_bytes; 148 }