1 /*
2 * Copyright (c) 2018, 2022, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
4 * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
5 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
6 *
7 * This code is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License version 2 only, as
9 * published by the Free Software Foundation.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
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25 */
26
27 #include "gc/shared/fullGCForwarding.hpp"
28 #include "gc/shared/gcArguments.hpp"
29 #include "gc/shared/tlab_globals.hpp"
30 #include "gc/shared/workerPolicy.hpp"
31 #include "gc/shenandoah/shenandoahArguments.hpp"
32 #include "gc/shenandoah/shenandoahCardTable.hpp"
33 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
34 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
35 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
36 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
37 #include "runtime/globals_extension.hpp"
38 #include "runtime/java.hpp"
39 #include "utilities/defaultStream.hpp"
40 #include "utilities/powerOfTwo.hpp"
41
42 void ShenandoahArguments::initialize() {
43 #if !(defined AARCH64 || defined AMD64 || defined PPC64 || defined RISCV64)
44 vm_exit_during_initialization("Shenandoah GC is not supported on this platform.");
45 #endif
46
47 #if 0 // leave this block as stepping stone for future platforms
48 log_warning(gc)("Shenandoah GC is not fully supported on this platform:");
49 log_warning(gc)(" concurrent modes are not supported, only STW cycles are enabled;");
50 log_warning(gc)(" arch-specific barrier code is not implemented, disabling barriers;");
51
52 FLAG_SET_DEFAULT(ShenandoahGCHeuristics, "passive");
53
54 FLAG_SET_DEFAULT(ShenandoahSATBBarrier, false);
55 FLAG_SET_DEFAULT(ShenandoahLoadRefBarrier, false);
56 FLAG_SET_DEFAULT(ShenandoahCASBarrier, false);
57 FLAG_SET_DEFAULT(ShenandoahCardBarrier, false);
58 FLAG_SET_DEFAULT(ShenandoahCloneBarrier, false);
59
60 FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
61 #endif
62 if (UseLargePages) {
63 size_t large_page_size = os::large_page_size();
64 if ((align_up(MaxHeapSize, large_page_size) / large_page_size) < ShenandoahHeapRegion::MIN_NUM_REGIONS) {
65 warning("Large pages size (%zuK) is too large to afford page-sized regions, disabling uncommit",
66 os::large_page_size() / K);
67 FLAG_SET_DEFAULT(ShenandoahUncommit, false);
68 }
69 }
70
71 // Enable NUMA by default. While Shenandoah is not NUMA-aware, enabling NUMA makes
72 // storage allocation code NUMA-aware.
73 if (FLAG_IS_DEFAULT(UseNUMA)) {
74 FLAG_SET_DEFAULT(UseNUMA, true);
75 }
76
77 // We use this as the time period for tracking minimum mutator utilization (MMU).
78 // In generational mode, the MMU is used as a signal to adjust the size of the
79 // young generation.
80 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
81 FLAG_SET_DEFAULT(GCPauseIntervalMillis, 5000);
82 }
83
84 // Set up default number of concurrent threads. We want to have cycles complete fast
85 // enough, but we also do not want to steal too much CPU from the concurrently running
86 // application. Using 1/4 of available threads for concurrent GC seems a good
87 // compromise here.
88 bool ergo_conc = FLAG_IS_DEFAULT(ConcGCThreads);
89 if (ergo_conc) {
90 FLAG_SET_DEFAULT(ConcGCThreads, MAX2(1, os::initial_active_processor_count() / 4));
91 }
92
93 if (ConcGCThreads == 0) {
94 vm_exit_during_initialization("Shenandoah expects ConcGCThreads > 0, check -XX:ConcGCThreads=#");
95 }
96
97 // Set up default number of parallel threads. We want to have decent pauses performance
98 // which would use parallel threads, but we also do not want to do too many threads
99 // that will overwhelm the OS scheduler. Using 1/2 of available threads seems to be a fair
100 // compromise here. Due to implementation constraints, it should not be lower than
101 // the number of concurrent threads.
102 bool ergo_parallel = FLAG_IS_DEFAULT(ParallelGCThreads);
103 if (ergo_parallel) {
104 FLAG_SET_DEFAULT(ParallelGCThreads, MAX2(1, os::initial_active_processor_count() / 2));
105 }
106
107 if (ParallelGCThreads == 0) {
108 vm_exit_during_initialization("Shenandoah expects ParallelGCThreads > 0, check -XX:ParallelGCThreads=#");
109 }
110
111 // Make sure ergonomic decisions do not break the thread count invariants.
112 // This may happen when user overrides one of the flags, but not the other.
113 // When that happens, we want to adjust the setting that was set ergonomically.
114 if (ParallelGCThreads < ConcGCThreads) {
115 if (ergo_conc && !ergo_parallel) {
116 FLAG_SET_DEFAULT(ConcGCThreads, ParallelGCThreads);
117 } else if (!ergo_conc && ergo_parallel) {
118 FLAG_SET_DEFAULT(ParallelGCThreads, ConcGCThreads);
119 } else if (ergo_conc && ergo_parallel) {
120 // Should not happen, check the ergonomic computation above. Fail with relevant error.
121 vm_exit_during_initialization("Shenandoah thread count ergonomic error");
122 } else {
123 // User settings error, report and ask user to rectify.
124 vm_exit_during_initialization("Shenandoah expects ConcGCThreads <= ParallelGCThreads, check -XX:ParallelGCThreads, -XX:ConcGCThreads");
125 }
126 }
127
128 // Disable support for dynamic number of GC threads. We do not let the runtime
129 // heuristics to misjudge how many threads we need during the heavy concurrent phase
130 // or a GC pause.
131 if (UseDynamicNumberOfGCThreads) {
132 if (FLAG_IS_CMDLINE(UseDynamicNumberOfGCThreads)) {
133 warning("Shenandoah does not support UseDynamicNumberOfGCThreads, disabling");
134 }
135 FLAG_SET_DEFAULT(UseDynamicNumberOfGCThreads, false);
136 }
137
138 if (ShenandoahRegionSampling && FLAG_IS_DEFAULT(PerfDataMemorySize)) {
139 // When sampling is enabled, max out the PerfData memory to get more
140 // Shenandoah data in, including Matrix.
141 FLAG_SET_DEFAULT(PerfDataMemorySize, 2048*K);
142 }
143
144 #ifdef COMPILER2
145 // Shenandoah cares more about pause times, rather than raw throughput.
146 if (FLAG_IS_DEFAULT(UseCountedLoopSafepoints)) {
147 FLAG_SET_DEFAULT(UseCountedLoopSafepoints, true);
148 if (FLAG_IS_DEFAULT(LoopStripMiningIter)) {
149 FLAG_SET_DEFAULT(LoopStripMiningIter, 1000);
150 }
151 }
152 #ifdef ASSERT
153 // C2 barrier verification is only reliable when all default barriers are enabled
154 if (ShenandoahVerifyOptoBarriers &&
155 (!FLAG_IS_DEFAULT(ShenandoahSATBBarrier) ||
156 !FLAG_IS_DEFAULT(ShenandoahLoadRefBarrier) ||
157 !FLAG_IS_DEFAULT(ShenandoahCASBarrier) ||
158 !FLAG_IS_DEFAULT(ShenandoahCloneBarrier)
159 )) {
160 warning("Unusual barrier configuration, disabling C2 barrier verification");
161 FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
162 }
163 #else
164 guarantee(!ShenandoahVerifyOptoBarriers, "Should be disabled");
165 #endif // ASSERT
166 #endif // COMPILER2
167
168 // Record more information about previous cycles for improved debugging pleasure
169 if (FLAG_IS_DEFAULT(LogEventsBufferEntries)) {
170 FLAG_SET_DEFAULT(LogEventsBufferEntries, 250);
171 }
172
173 if ((InitialHeapSize == MaxHeapSize) && ShenandoahUncommit) {
174 log_info(gc)("Min heap equals to max heap, disabling ShenandoahUncommit");
175 FLAG_SET_DEFAULT(ShenandoahUncommit, false);
176 }
177
178 // If class unloading is disabled, no unloading for concurrent cycles as well.
179 if (!ClassUnloading) {
180 FLAG_SET_DEFAULT(ClassUnloadingWithConcurrentMark, false);
181 }
182
183 // TLAB sizing policy makes resizing decisions before each GC cycle. It averages
184 // historical data, assigning more recent data the weight according to TLABAllocationWeight.
185 // Current default is good for generational collectors that run frequent young GCs.
186 // With Shenandoah, GC cycles are much less frequent, so we need we need sizing policy
187 // to converge faster over smaller number of resizing decisions.
188 if (strcmp(ShenandoahGCMode, "generational") && FLAG_IS_DEFAULT(TLABAllocationWeight)) {
189 FLAG_SET_DEFAULT(TLABAllocationWeight, 90);
190 }
191 // In generational mode, let TLABAllocationWeight keeps its default value of 35.
192
193 if (GCCardSizeInBytes < ShenandoahMinCardSizeInBytes) {
194 vm_exit_during_initialization(
195 err_msg("GCCardSizeInBytes ( %u ) must be >= %u\n", GCCardSizeInBytes, (unsigned int) ShenandoahMinCardSizeInBytes));
196 }
197
198 // Gen shen does not support any ShenandoahGCHeuristics value except for the default "adaptive"
199 if ((strcmp(ShenandoahGCMode, "generational") == 0)
200 && strcmp(ShenandoahGCHeuristics, "adaptive") != 0) {
201 log_warning(gc)("Ignoring -XX:ShenandoahGCHeuristics input: %s, because generational shenandoah only"
202 " supports adaptive heuristics", ShenandoahGCHeuristics);
203 }
204
205 FullGCForwarding::initialize_flags(MaxHeapSize);
206 }
207
208 size_t ShenandoahArguments::conservative_max_heap_alignment() {
209 size_t align = next_power_of_2(ShenandoahMaxRegionSize);
210 if (UseLargePages) {
211 align = MAX2(align, os::large_page_size());
212 }
213 return align;
214 }
215
216 void ShenandoahArguments::initialize_alignments() {
217 CardTable::initialize_card_size();
218
219 // Need to setup sizes early to get correct alignments.
220 MaxHeapSize = ShenandoahHeapRegion::setup_sizes(MaxHeapSize);
221
222 // This is expected by our algorithm for ShenandoahHeap::heap_region_containing().
223 size_t align = ShenandoahHeapRegion::region_size_bytes();
224 if (UseLargePages) {
225 align = MAX2(align, os::large_page_size());
226 }
227 SpaceAlignment = align;
228 HeapAlignment = align;
229
230 if (FLAG_IS_DEFAULT(TLABSize)) {
231 TLABSize = MAX2(ShenandoahHeapRegion::region_size_bytes() / 256, (size_t) 32 * 1024);
232 }
233 }
234
235 CollectedHeap* ShenandoahArguments::create_heap() {
236 if (strcmp(ShenandoahGCMode, "generational") != 0) {
237 // Not generational
238 return new ShenandoahHeap(new ShenandoahCollectorPolicy());
239 } else {
240 return new ShenandoahGenerationalHeap(new ShenandoahCollectorPolicy());
241 }
242 }