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 static void log_expansion(double short_term_pause_time_ratio,
67 double long_term_pause_time_ratio,
68 double threshold,
69 double pause_time_ratio,
70 bool fully_expanded,
71 size_t resize_bytes) {
72
73 log_debug(gc, ergo, heap)("Heap expansion: "
74 "short term pause time ratio %1.2f%% long term pause time ratio %1.2f%% "
75 "threshold %1.2f%% pause time ratio %1.2f%% fully expanded %s "
76 "resize by " SIZE_FORMAT "B",
77 short_term_pause_time_ratio * 100.0,
78 long_term_pause_time_ratio * 100.0,
79 threshold * 100.0,
80 pause_time_ratio * 100.0,
81 BOOL_TO_STR(fully_expanded),
82 resize_bytes);
83 }
84
85 size_t G1HeapSizingPolicy::expansion_amount() {
86 assert(GCTimeRatio > 0, "must be");
87
88 double long_term_pause_time_ratio = _analytics->long_term_pause_time_ratio();
89 double short_term_pause_time_ratio = _analytics->short_term_pause_time_ratio();
90 const double pause_time_threshold = 1.0 / (1.0 + GCTimeRatio);
91 double threshold = scale_with_heap(pause_time_threshold);
92
93 size_t expand_bytes = 0;
94
95 if (_g1h->capacity() == _g1h->max_capacity()) {
96 log_expansion(short_term_pause_time_ratio, long_term_pause_time_ratio,
97 threshold, pause_time_threshold, true, 0);
98 clear_ratio_check_data();
99 return expand_bytes;
100 }
101
102 // If the last GC time ratio is over the threshold, increment the count of
103 // times it has been exceeded, and add this ratio to the sum of exceeded
104 // ratios.
105 if (short_term_pause_time_ratio > threshold) {
106 _ratio_over_threshold_count++;
107 _ratio_over_threshold_sum += short_term_pause_time_ratio;
108 }
109
110 log_trace(gc, ergo, heap)("Heap expansion triggers: pauses since start: %u "
111 "num prev pauses for heuristics: %u "
112 "ratio over threshold count: %u",
113 _pauses_since_start,
114 _num_prev_pauses_for_heuristics,
115 _ratio_over_threshold_count);
116
117 // Check if we've had enough GC time ratio checks that were over the
118 // threshold to trigger an expansion. We'll also expand if we've
119 // reached the end of the history buffer and the average of all entries
120 // is still over the threshold. This indicates a smaller number of GCs were
121 // long enough to make the average exceed the threshold.
122 bool filled_history_buffer = _pauses_since_start == _num_prev_pauses_for_heuristics;
123 if ((_ratio_over_threshold_count == MinOverThresholdForGrowth) ||
124 (filled_history_buffer && (long_term_pause_time_ratio > threshold))) {
125 size_t min_expand_bytes = HeapRegion::GrainBytes;
126 size_t reserved_bytes = _g1h->max_capacity();
127 size_t committed_bytes = _g1h->capacity();
128 size_t uncommitted_bytes = reserved_bytes - committed_bytes;
129 size_t expand_bytes_via_pct =
130 uncommitted_bytes * G1ExpandByPercentOfAvailable / 100;
131 double scale_factor = 1.0;
132
133 // If the current size is less than 1/4 of the Initial heap size, expand
134 // by half of the delta between the current and Initial sizes. IE, grow
135 // back quickly.
136 //
137 // Otherwise, take the current size, or G1ExpandByPercentOfAvailable % of
138 // the available expansion space, whichever is smaller, as the base
139 // expansion size. Then possibly scale this size according to how much the
140 // threshold has (on average) been exceeded by. If the delta is small
141 // (less than the StartScaleDownAt value), scale the size down linearly, but
142 // not by less than MinScaleDownFactor. If the delta is large (greater than
143 // the StartScaleUpAt value), scale up, but adding no more than MaxScaleUpFactor
144 // times the base size. The scaling will be linear in the range from
145 // StartScaleUpAt to (StartScaleUpAt + ScaleUpRange). In other words,
146 // ScaleUpRange sets the rate of scaling up.
147 if (committed_bytes < InitialHeapSize / 4) {
148 expand_bytes = (InitialHeapSize - committed_bytes) / 2;
149 } else {
150 double const MinScaleDownFactor = 0.2;
151 double const MaxScaleUpFactor = 2;
152 double const StartScaleDownAt = pause_time_threshold;
153 double const StartScaleUpAt = pause_time_threshold * 1.5;
154 double const ScaleUpRange = pause_time_threshold * 2.0;
155
156 double ratio_delta;
157 if (filled_history_buffer) {
158 ratio_delta = long_term_pause_time_ratio - threshold;
159 } else {
160 ratio_delta = (_ratio_over_threshold_sum / _ratio_over_threshold_count) - threshold;
161 }
162
163 expand_bytes = MIN2(expand_bytes_via_pct, committed_bytes);
164 if (ratio_delta < StartScaleDownAt) {
165 scale_factor = ratio_delta / StartScaleDownAt;
166 scale_factor = MAX2(scale_factor, MinScaleDownFactor);
167 } else if (ratio_delta > StartScaleUpAt) {
168 scale_factor = 1 + ((ratio_delta - StartScaleUpAt) / ScaleUpRange);
169 scale_factor = MIN2(scale_factor, MaxScaleUpFactor);
170 }
171 }
172
173 expand_bytes = static_cast<size_t>(expand_bytes * scale_factor);
174
175 // Ensure the expansion size is at least the minimum growth amount
176 // and at most the remaining uncommitted byte size.
177 expand_bytes = clamp(expand_bytes, min_expand_bytes, uncommitted_bytes);
178
179 clear_ratio_check_data();
180 } else {
181 // An expansion was not triggered. If we've started counting, increment
182 // the number of checks we've made in the current window. If we've
183 // reached the end of the window without resizing, clear the counters to
184 // start again the next time we see a ratio above the threshold.
185 if (_ratio_over_threshold_count > 0) {
186 _pauses_since_start++;
187 if (_pauses_since_start > _num_prev_pauses_for_heuristics) {
188 clear_ratio_check_data();
189 }
190 }
191 }
192
193 log_expansion(short_term_pause_time_ratio, long_term_pause_time_ratio,
194 threshold, pause_time_threshold, false, expand_bytes);
195
196 return expand_bytes;
197 }