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 "gc/g1/g1Policy.hpp"
30 #include "logging/log.hpp"
31 #include "runtime/globals.hpp"
32 #include "utilities/debug.hpp"
33 #include "utilities/globalDefinitions.hpp"
34
35 G1HeapSizingPolicy* G1HeapSizingPolicy::create(const G1CollectedHeap* g1h, const G1Analytics* analytics) {
36 return new G1HeapSizingPolicy(g1h, analytics);
37 }
38
39 G1HeapSizingPolicy::G1HeapSizingPolicy(const G1CollectedHeap* g1h, const G1Analytics* analytics) :
40 _g1h(g1h),
41 _analytics(analytics),
42 _num_prev_pauses_for_heuristics(analytics->number_of_recorded_pause_times()),
43 _minimum_desired_bytes_after_last_cm(MinHeapSize) {
44
45 assert(MinOverThresholdForGrowth < _num_prev_pauses_for_heuristics, "Threshold must be less than %u", _num_prev_pauses_for_heuristics);
46 clear_ratio_check_data();
47 }
48
49 void G1HeapSizingPolicy::clear_ratio_check_data() {
50 _ratio_over_threshold_count = 0;
51 _ratio_over_threshold_sum = 0.0;
52 _pauses_since_start = 0;
53 }
54
55 size_t G1HeapSizingPolicy::expansion_amount_after_young_collection() {
56 double recent_gc_overhead = _analytics->recent_avg_pause_time_ratio() * 100.0;
57 double last_gc_overhead = _analytics->last_pause_time_ratio() * 100.0;
58 assert(GCTimeRatio > 0,
59 "we should have set it to a default value set_g1_gc_flags() "
60 "if a user set it to 0");
61 const double gc_overhead_percent = 100.0 * (1.0 / (1.0 + GCTimeRatio));
62
63 double threshold = gc_overhead_percent;
64 size_t expand_bytes = 0;
65
66 // If the heap is at less than half its maximum size, scale the threshold down,
67 // to a limit of 1. Thus the smaller the heap is, the more likely it is to expand,
68 // though the scaling code will likely keep the increase small.
69 if (_g1h->capacity() <= _g1h->max_capacity() / 2) {
70 threshold *= (double)_g1h->capacity() / (double)(_g1h->max_capacity() / 2);
71 threshold = MAX2(threshold, 1.0);
72 }
73
74 // If the last GC time ratio is over the threshold, increment the count of
75 // times it has been exceeded, and add this ratio to the sum of exceeded
76 // ratios.
77 if (last_gc_overhead > threshold) {
78 _ratio_over_threshold_count++;
79 _ratio_over_threshold_sum += last_gc_overhead;
80 }
81
82 // Check if we've had enough GC time ratio checks that were over the
83 // threshold to trigger an expansion. We'll also expand if we've
84 // reached the end of the history buffer and the average of all entries
85 // is still over the threshold. This indicates a smaller number of GCs were
86 // long enough to make the average exceed the threshold.
87 bool filled_history_buffer = _pauses_since_start == _num_prev_pauses_for_heuristics;
88 if ((_ratio_over_threshold_count == MinOverThresholdForGrowth) ||
89 (filled_history_buffer && (recent_gc_overhead > threshold))) {
90 size_t min_expand_bytes = HeapRegion::GrainBytes;
91 size_t reserved_bytes = _g1h->max_capacity();
92 size_t committed_bytes = _g1h->capacity();
93 size_t uncommitted_bytes = reserved_bytes - committed_bytes;
94 size_t expand_bytes_via_pct =
95 uncommitted_bytes * G1ExpandByPercentOfAvailable / 100;
96 double scale_factor = 1.0;
97
98 // If the current size is less than 1/4 of the Initial heap size, expand
99 // by half of the delta between the current and Initial sizes. IE, grow
100 // back quickly.
101 //
102 // Otherwise, take the current size, or G1ExpandByPercentOfAvailable % of
103 // the available expansion space, whichever is smaller, as the base
104 // expansion size. Then possibly scale this size according to how much the
105 // threshold has (on average) been exceeded by. If the delta is small
106 // (less than the StartScaleDownAt value), scale the size down linearly, but
107 // not by less than MinScaleDownFactor. If the delta is large (greater than
108 // the StartScaleUpAt value), scale up, but adding no more than MaxScaleUpFactor
109 // times the base size. The scaling will be linear in the range from
110 // StartScaleUpAt to (StartScaleUpAt + ScaleUpRange). In other words,
111 // ScaleUpRange sets the rate of scaling up.
112 if (committed_bytes < InitialHeapSize / 4) {
113 expand_bytes = (InitialHeapSize - committed_bytes) / 2;
114 } else {
115 double const MinScaleDownFactor = 0.2;
116 double const MaxScaleUpFactor = 2;
117 double const StartScaleDownAt = gc_overhead_percent;
118 double const StartScaleUpAt = gc_overhead_percent * 1.5;
119 double const ScaleUpRange = gc_overhead_percent * 2.0;
120
121 double ratio_delta;
122 if (filled_history_buffer) {
123 ratio_delta = recent_gc_overhead - threshold;
124 } else {
125 ratio_delta = (_ratio_over_threshold_sum/_ratio_over_threshold_count) - threshold;
126 }
127
128 expand_bytes = MIN2(expand_bytes_via_pct, committed_bytes);
129 if (ratio_delta < StartScaleDownAt) {
130 scale_factor = ratio_delta / StartScaleDownAt;
131 scale_factor = MAX2(scale_factor, MinScaleDownFactor);
132 } else if (ratio_delta > StartScaleUpAt) {
133 scale_factor = 1 + ((ratio_delta - StartScaleUpAt) / ScaleUpRange);
134 scale_factor = MIN2(scale_factor, MaxScaleUpFactor);
135 }
136 }
137
138 log_debug(gc, ergo, heap)("Attempt heap expansion (recent GC overhead higher than threshold after GC) "
139 "recent GC overhead: %1.2f %% threshold: %1.2f %% uncommitted: " SIZE_FORMAT "B base expansion amount and scale: " SIZE_FORMAT "B (%1.2f%%)",
140 recent_gc_overhead, threshold, uncommitted_bytes, expand_bytes, scale_factor * 100);
141
142 expand_bytes = static_cast<size_t>(expand_bytes * scale_factor);
143
144 // Ensure the expansion size is at least the minimum growth amount
145 // and at most the remaining uncommitted byte size.
146 expand_bytes = MAX2(expand_bytes, min_expand_bytes);
147 expand_bytes = MIN2(expand_bytes, uncommitted_bytes);
148
149 clear_ratio_check_data();
150 } else {
151 // An expansion was not triggered. If we've started counting, increment
152 // the number of checks we've made in the current window. If we've
153 // reached the end of the window without resizing, clear the counters to
154 // start again the next time we see a ratio above the threshold.
155 if (_ratio_over_threshold_count > 0) {
156 _pauses_since_start++;
157 if (_pauses_since_start > _num_prev_pauses_for_heuristics) {
158 clear_ratio_check_data();
159 }
160 }
161 }
162
163 return expand_bytes;
164 }
165
166 size_t G1HeapSizingPolicy::expansion_amount_after_concurrent_mark() {
167 size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
168 _minimum_desired_bytes_after_last_cm = _g1h->policy()->minimum_desired_bytes_after_concurrent_mark(cur_used_bytes);
169
170 return _minimum_desired_bytes_after_last_cm > _g1h->capacity() ?
171 _minimum_desired_bytes_after_last_cm - _g1h->capacity() : 0;
172 }
173
174 size_t G1HeapSizingPolicy::shrink_amount_after_mixed_collections() {
175 size_t shrink_bytes = 0;
176 const size_t capacity_after_gc = _g1h->capacity();
177 const size_t used_after_gc = capacity_after_gc - _g1h->unused_committed_regions_in_bytes();
178
179 const double maximum_free_percentage = (double) MaxHeapFreeRatio / 100.0;
180 const double minimum_used_percentage = 1.0 - maximum_free_percentage;
181
182 double used_after_gc_d = (double) used_after_gc;
183 double maximum_desired_capacity_d = used_after_gc_d / minimum_used_percentage;
184 // Let's make sure that they are both under the max heap size, which
185 // by default will make them fit into a size_t.
186 double desired_capacity_upper_bound = (double) MaxHeapSize;
187 maximum_desired_capacity_d = MIN2(maximum_desired_capacity_d,
188 desired_capacity_upper_bound);
189 // We can now safely turn them into size_t's.
190 size_t maximum_desired_capacity = (size_t) maximum_desired_capacity_d;
191
192 // soft_max_capacity can be smaller
193 maximum_desired_capacity = MIN2(maximum_desired_capacity, _g1h->soft_max_capacity());
194
195 // Make sure not less than _minimum_desired_bytes_after_last_cm
196 maximum_desired_capacity = MAX2(maximum_desired_capacity, _minimum_desired_bytes_after_last_cm);
197
198 if (capacity_after_gc > maximum_desired_capacity) {
199 shrink_bytes = capacity_after_gc - maximum_desired_capacity;
200 }
201
202 return shrink_bytes;
203 }