1 /*
2 * Copyright (c) 2015, 2019, 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 #include "precompiled.hpp"
25 #include "gc/z/zCollectedHeap.hpp"
26 #include "gc/z/zDirector.hpp"
27 #include "gc/z/zHeap.inline.hpp"
28 #include "gc/z/zStat.hpp"
29 #include "gc/z/zUtils.hpp"
30 #include "logging/log.hpp"
31
32 const double ZDirector::one_in_1000 = 3.290527;
33
34 ZDirector::ZDirector() :
35 _metronome(ZStatAllocRate::sample_hz) {
36 set_name("ZDirector");
37 create_and_start();
38 }
39
40 void ZDirector::sample_allocation_rate() const {
41 // Sample allocation rate. This is needed by rule_allocation_rate()
42 // below to estimate the time we have until we run out of memory.
43 const double bytes_per_second = ZStatAllocRate::sample_and_reset();
44
45 log_debug(gc, alloc)("Allocation Rate: %.3fMB/s, Avg: %.3f(+/-%.3f)MB/s",
46 bytes_per_second / M,
47 ZStatAllocRate::avg() / M,
48 ZStatAllocRate::avg_sd() / M);
49 }
50
51 bool ZDirector::rule_timer() const {
52 if (ZCollectionInterval == 0) {
53 // Rule disabled
54 return false;
55 }
56
57 // Perform GC if timer has expired.
58 const double time_since_last_gc = ZStatCycle::time_since_last();
59 const double time_until_gc = ZCollectionInterval - time_since_last_gc;
60
61 log_debug(gc, director)("Rule: Timer, Interval: %us, TimeUntilGC: %.3fs",
62 ZCollectionInterval, time_until_gc);
63
64 return time_until_gc <= 0;
65 }
66
67 bool ZDirector::rule_warmup() const {
68 if (ZStatCycle::is_warm()) {
69 // Rule disabled
70 return false;
71 }
72
73 // Perform GC if heap usage passes 10/20/30% and no other GC has been
74 // performed yet. This allows us to get some early samples of the GC
75 // duration, which is needed by the other rules.
76 const size_t max_capacity = ZHeap::heap()->soft_max_capacity();
77 const size_t used = ZHeap::heap()->used();
78 const double used_threshold_percent = (ZStatCycle::nwarmup_cycles() + 1) * 0.1;
79 const size_t used_threshold = max_capacity * used_threshold_percent;
80
81 log_debug(gc, director)("Rule: Warmup %.0f%%, Used: " SIZE_FORMAT "MB, UsedThreshold: " SIZE_FORMAT "MB",
82 used_threshold_percent * 100, used / M, used_threshold / M);
83
84 return used >= used_threshold;
85 }
86
87 bool ZDirector::rule_allocation_rate() const {
88 if (!ZStatCycle::is_normalized_duration_trustable()) {
89 // Rule disabled
90 return false;
91 }
92
93 // Perform GC if the estimated max allocation rate indicates that we
94 // will run out of memory. The estimated max allocation rate is based
95 // on the moving average of the sampled allocation rate plus a safety
96 // margin based on variations in the allocation rate and unforeseen
97 // allocation spikes.
98
99 // Calculate amount of free memory available to Java threads. Note that
100 // the heap reserve is not available to Java threads and is therefore not
101 // considered part of the free memory.
102 const size_t max_capacity = ZHeap::heap()->soft_max_capacity();
103 const size_t max_reserve = ZHeap::heap()->max_reserve();
104 const size_t used = ZHeap::heap()->used();
105 const size_t free_with_reserve = max_capacity - MIN2(max_capacity, used);
106 const size_t free = free_with_reserve - MIN2(free_with_reserve, max_reserve);
107
108 // Calculate time until OOM given the max allocation rate and the amount
109 // of free memory. The allocation rate is a moving average and we multiply
110 // that with an allocation spike tolerance factor to guard against unforeseen
111 // phase changes in the allocate rate. We then add ~3.3 sigma to account for
112 // the allocation rate variance, which means the probability is 1 in 1000
113 // that a sample is outside of the confidence interval.
114 const double max_alloc_rate = (ZStatAllocRate::avg() * ZAllocationSpikeTolerance) + (ZStatAllocRate::avg_sd() * one_in_1000);
115 const double time_until_oom = free / (max_alloc_rate + 1.0); // Plus 1.0B/s to avoid division by zero
116
117 // Calculate max duration of a GC cycle. The duration of GC is a moving
118 // average, we add ~3.3 sigma to account for the GC duration variance.
119 const AbsSeq& duration_of_gc = ZStatCycle::normalized_duration();
120 const double max_duration_of_gc = duration_of_gc.davg() + (duration_of_gc.dsd() * one_in_1000);
121
122 // Calculate time until GC given the time until OOM and max duration of GC.
123 // We also deduct the sample interval, so that we don't overshoot the target
124 // time and end up starting the GC too late in the next interval.
125 const double sample_interval = 1.0 / ZStatAllocRate::sample_hz;
126 const double time_until_gc = time_until_oom - max_duration_of_gc - sample_interval;
127
128 log_debug(gc, director)("Rule: Allocation Rate, MaxAllocRate: %.3fMB/s, Free: " SIZE_FORMAT "MB, MaxDurationOfGC: %.3fs, TimeUntilGC: %.3fs",
129 max_alloc_rate / M, free / M, max_duration_of_gc, time_until_gc);
130
131 return time_until_gc <= 0;
132 }
133
134 bool ZDirector::rule_proactive() const {
135 if (!ZProactive || !ZStatCycle::is_warm()) {
136 // Rule disabled
137 return false;
138 }
139
140 // Perform GC if the impact of doing so, in terms of application throughput
141 // reduction, is considered acceptable. This rule allows us to keep the heap
142 // size down and allow reference processing to happen even when we have a lot
143 // of free space on the heap.
144
145 // Only consider doing a proactive GC if the heap usage has grown by at least
146 // 10% of the max capacity since the previous GC, or more than 5 minutes has
147 // passed since the previous GC. This helps avoid superfluous GCs when running
148 // applications with very low allocation rate.
149 const size_t used_after_last_gc = ZStatHeap::used_at_relocate_end();
150 const size_t used_increase_threshold = ZHeap::heap()->soft_max_capacity() * 0.10; // 10%
151 const size_t used_threshold = used_after_last_gc + used_increase_threshold;
152 const size_t used = ZHeap::heap()->used();
153 const double time_since_last_gc = ZStatCycle::time_since_last();
154 const double time_since_last_gc_threshold = 5 * 60; // 5 minutes
155 if (used < used_threshold && time_since_last_gc < time_since_last_gc_threshold) {
156 // Don't even consider doing a proactive GC
157 log_debug(gc, director)("Rule: Proactive, UsedUntilEnabled: " SIZE_FORMAT "MB, TimeUntilEnabled: %.3fs",
158 (used_threshold - used) / M,
159 time_since_last_gc_threshold - time_since_last_gc);
160 return false;
161 }
162
163 const double assumed_throughput_drop_during_gc = 0.50; // 50%
164 const double acceptable_throughput_drop = 0.01; // 1%
165 const AbsSeq& duration_of_gc = ZStatCycle::normalized_duration();
166 const double max_duration_of_gc = duration_of_gc.davg() + (duration_of_gc.dsd() * one_in_1000);
167 const double acceptable_gc_interval = max_duration_of_gc * ((assumed_throughput_drop_during_gc / acceptable_throughput_drop) - 1.0);
168 const double time_until_gc = acceptable_gc_interval - time_since_last_gc;
169
170 log_debug(gc, director)("Rule: Proactive, AcceptableGCInterval: %.3fs, TimeSinceLastGC: %.3fs, TimeUntilGC: %.3fs",
171 acceptable_gc_interval, time_since_last_gc, time_until_gc);
172
173 return time_until_gc <= 0;
174 }
175
176 bool ZDirector::rule_high_usage() const {
177 // Perform GC if the amount of free memory is 5% or less. This is a preventive
178 // meassure in the case where the application has a very low allocation rate,
179 // such that the allocation rate rule doesn't trigger, but the amount of free
180 // memory is still slowly but surely heading towards zero. In this situation,
181 // we start a GC cycle to avoid a potential allocation stall later.
182
183 // Calculate amount of free memory available to Java threads. Note that
184 // the heap reserve is not available to Java threads and is therefore not
185 // considered part of the free memory.
186 const size_t max_capacity = ZHeap::heap()->soft_max_capacity();
187 const size_t max_reserve = ZHeap::heap()->max_reserve();
188 const size_t used = ZHeap::heap()->used();
189 const size_t free_with_reserve = max_capacity - used;
190 const size_t free = free_with_reserve - MIN2(free_with_reserve, max_reserve);
191 const double free_percent = percent_of(free, max_capacity);
192
193 log_debug(gc, director)("Rule: High Usage, Free: " SIZE_FORMAT "MB(%.1f%%)",
194 free / M, free_percent);
195
196 return free_percent <= 5.0;
197 }
198
199 GCCause::Cause ZDirector::make_gc_decision() const {
200 // Rule 0: Timer
201 if (rule_timer()) {
202 return GCCause::_z_timer;
203 }
204
205 // Rule 1: Warmup
206 if (rule_warmup()) {
207 return GCCause::_z_warmup;
208 }
209
210 // Rule 2: Allocation rate
211 if (rule_allocation_rate()) {
212 return GCCause::_z_allocation_rate;
213 }
214
215 // Rule 3: Proactive
216 if (rule_proactive()) {
217 return GCCause::_z_proactive;
218 }
219
220 // Rule 4: High usage
221 if (rule_high_usage()) {
222 return GCCause::_z_high_usage;
223 }
224
225 // No GC
226 return GCCause::_no_gc;
227 }
228
229 void ZDirector::run_service() {
230 // Main loop
231 while (_metronome.wait_for_tick()) {
232 sample_allocation_rate();
233 const GCCause::Cause cause = make_gc_decision();
234 if (cause != GCCause::_no_gc) {
235 ZCollectedHeap::heap()->collect(cause);
236 }
237 }
238 }
239
240 void ZDirector::stop_service() {
241 _metronome.stop();
242 }
--- EOF ---