1 /*
2 * Copyright (c) 2015, 2018, 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::is_first() const {
52 return ZStatPhaseCycle::ncycles() == 0;
53 }
54
55 bool ZDirector::is_warm() const {
56 return ZStatPhaseCycle::ncycles() >= 3;
57 }
58
59 bool ZDirector::rule_timer() const {
60 if (ZCollectionInterval == 0) {
61 // Rule disabled
62 return false;
63 }
64
65 // Perform GC if timer has expired.
66 const double time_since_last_gc = ZStatPhaseCycle::time_since_last();
67 const double time_until_gc = ZCollectionInterval - time_since_last_gc;
68
69 log_debug(gc, director)("Rule: Timer, Interval: %us, TimeUntilGC: %.3lfs",
70 ZCollectionInterval, time_until_gc);
71
72 return time_until_gc <= 0;
73 }
74
75 bool ZDirector::rule_warmup() const {
76 if (is_warm()) {
77 // Rule disabled
78 return false;
79 }
80
81 // Perform GC if heap usage passes 10/20/30% and no other GC has been
82 // performed yet. This allows us to get some early samples of the GC
83 // duration, which is needed by the other rules.
84 const size_t max_capacity = ZHeap::heap()->max_capacity();
85 const size_t used = ZHeap::heap()->used();
86 const double used_threshold_percent = (ZStatPhaseCycle::ncycles() + 1) * 0.1;
87 const size_t used_threshold = max_capacity * used_threshold_percent;
88
89 log_debug(gc, director)("Rule: Warmup %.0f%%, Used: " SIZE_FORMAT "MB, UsedThreshold: " SIZE_FORMAT "MB",
90 used_threshold_percent * 100, used / M, used_threshold / M);
91
92 return used >= used_threshold;
93 }
94
95 bool ZDirector::rule_allocation_rate() const {
96 if (is_first()) {
97 // Rule disabled
98 return false;
99 }
100
101 // Perform GC if the estimated max allocation rate indicates that we
102 // will run out of memory. The estimated max allocation rate is based
103 // on the moving average of the sampled allocation rate plus a safety
104 // margin based on variations in the allocation rate and unforseen
105 // allocation spikes.
106
107 // Calculate amount of free memory available to Java threads. Note that
108 // the heap reserve is not available to Java threads and is therefore not
109 // considered part of the free memory.
110 const size_t max_capacity = ZHeap::heap()->max_capacity();
111 const size_t max_reserve = ZHeap::heap()->max_reserve();
112 const size_t used = ZHeap::heap()->used();
113 const size_t free_with_reserve = max_capacity - used;
114 const size_t free = free_with_reserve - MIN2(free_with_reserve, max_reserve);
115
116 // Calculate time until OOM given the max allocation rate and the amount
117 // of free memory. The allocation rate is a moving average and we multiply
118 // that with an alllcation spike tolerance factor to guard against unforseen
119 // phase changes in the allocate rate. We then add ~3.3 sigma to account for
120 // the allocation rate variance, which means the probablility is 1 in 1000
121 // that a sample is outside of the confidence interval.
122 const double max_alloc_rate = (ZStatAllocRate::avg() * ZAllocationSpikeTolerance) + (ZStatAllocRate::avg_sd() * one_in_1000);
123 const double time_until_oom = free / (max_alloc_rate + 1.0); // Plus 1.0B/s to avoid division by zero
124
125 // Calculate max duration of a GC cycle. The duration of GC is a moving
126 // average, we add ~3.3 sigma to account for the GC duration variance.
127 const AbsSeq& duration_of_gc = ZStatPhaseCycle::duration();
128 const double max_duration_of_gc = duration_of_gc.davg() + (duration_of_gc.dsd() * one_in_1000);
129
130 // Calculate time until GC given the time until OOM and max duration of GC.
131 // We also deduct the sample interval, so that we don't overshoot the target
132 // time and end up starting the GC too late in the next interval.
133 const double sample_interval = 1.0 / ZStatAllocRate::sample_hz;
134 const double time_until_gc = time_until_oom - max_duration_of_gc - sample_interval;
135
136 log_debug(gc, director)("Rule: Allocation Rate, MaxAllocRate: %.3lfMB/s, Free: " SIZE_FORMAT "MB, MaxDurationOfGC: %.3lfs, TimeUntilGC: %.3lfs",
137 max_alloc_rate / M, free / M, max_duration_of_gc, time_until_gc);
138
139 return time_until_gc <= 0;
140 }
141
142 bool ZDirector::rule_proactive() const {
143 if (!is_warm()) {
144 // Rule disabled
145 return false;
146 }
147
148 // Perform GC if the impact of doing so, in terms of application throughput
149 // reduction, is considered acceptable. This rule allows us to keep the heap
150 // size down and allow reference processing to happen even when we have a lot
151 // of free space on the heap.
152
153 // Only consider doing a proactive GC if the heap usage has grown by at least
154 // 10% of the max capacity since the previous GC, or more than 5 minutes has
155 // passed since the previous GC. This helps avoid superfluous GCs when running
156 // applications with very low allocation rate.
157 const size_t used_after_last_gc = ZStatHeap::used_at_relocate_end();
158 const size_t used_increase_threshold = ZHeap::heap()->max_capacity() * 0.10; // 10%
159 const size_t used_threshold = used_after_last_gc + used_increase_threshold;
160 const size_t used = ZHeap::heap()->used();
161 const double time_since_last_gc = ZStatPhaseCycle::time_since_last();
162 const double time_since_last_gc_threshold = 5 * 60; // 5 minutes
163 if (used < used_threshold && time_since_last_gc < time_since_last_gc_threshold) {
164 // Don't even consider doing a proactive GC
165 return false;
166 }
167
168 const double assumed_throughput_drop_during_gc = 0.50; // 50%
169 const double acceptable_throughput_drop = 0.01; // 1%
170 const AbsSeq& duration_of_gc = ZStatPhaseCycle::duration();
171 const double max_duration_of_gc = duration_of_gc.davg() + (duration_of_gc.dsd() * one_in_1000);
172 const double acceptable_gc_interval = max_duration_of_gc * ((assumed_throughput_drop_during_gc / acceptable_throughput_drop) - 1.0);
173 const double time_until_gc = acceptable_gc_interval - time_since_last_gc;
174
175 log_debug(gc, director)("Rule: Proactive, AcceptableGCInterval: %.3lfs, TimeSinceLastGC: %.3lfs, TimeUntilGC: %.3lfs",
176 acceptable_gc_interval, time_since_last_gc, time_until_gc);
177
178 return time_until_gc <= 0;
179 }
180
181 GCCause::Cause ZDirector::make_gc_decision() const {
182 // Rule 0: Timer
183 if (rule_timer()) {
184 return GCCause::_z_timer;
185 }
186
187 // Rule 1: Warmup
188 if (rule_warmup()) {
189 return GCCause::_z_warmup;
190 }
191
192 // Rule 2: Allocation rate
193 if (rule_allocation_rate()) {
194 return GCCause::_z_allocation_rate;
195 }
196
197 // Rule 3: Proactive
198 if (rule_proactive()) {
199 return GCCause::_z_proactive;
200 }
201
202 // No GC
203 return GCCause::_no_gc;
204 }
205
206 void ZDirector::run_service() {
207 // Main loop
208 while (_metronome.wait_for_tick()) {
209 sample_allocation_rate();
210 const GCCause::Cause cause = make_gc_decision();
211 if (cause != GCCause::_no_gc) {
212 ZCollectedHeap::heap()->collect(cause);
213 }
214 }
215 }
216
217 void ZDirector::stop_service() {
218 _metronome.stop();
219 }