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.
24 *
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
41 void ShenandoahArguments::initialize() {
42 #if !(defined AARCH64 || defined AMD64 || defined IA32 || defined PPC64 || defined RISCV64)
43 vm_exit_during_initialization("Shenandoah GC is not supported on this platform.");
44 #endif
45
46 #if 0 // leave this block as stepping stone for future platforms
47 log_warning(gc)("Shenandoah GC is not fully supported on this platform:");
48 log_warning(gc)(" concurrent modes are not supported, only STW cycles are enabled;");
49 log_warning(gc)(" arch-specific barrier code is not implemented, disabling barriers;");
50
51 FLAG_SET_DEFAULT(ShenandoahGCHeuristics, "passive");
52
53 FLAG_SET_DEFAULT(ShenandoahSATBBarrier, false);
54 FLAG_SET_DEFAULT(ShenandoahLoadRefBarrier, false);
55 FLAG_SET_DEFAULT(ShenandoahCASBarrier, false);
56 FLAG_SET_DEFAULT(ShenandoahCardBarrier, false);
57 FLAG_SET_DEFAULT(ShenandoahCloneBarrier, false);
58
59 FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
60 #endif
61 if (UseLargePages) {
62 size_t large_page_size = os::large_page_size();
63 if ((align_up(MaxHeapSize, large_page_size) / large_page_size) < ShenandoahHeapRegion::MIN_NUM_REGIONS) {
64 warning("Large pages size (%zuK) is too large to afford page-sized regions, disabling uncommit",
65 os::large_page_size() / K);
66 FLAG_SET_DEFAULT(ShenandoahUncommit, false);
67 }
68 }
69
70 // Enable NUMA by default. While Shenandoah is not NUMA-aware, enabling NUMA makes
71 // storage allocation code NUMA-aware.
72 if (FLAG_IS_DEFAULT(UseNUMA)) {
73 FLAG_SET_DEFAULT(UseNUMA, true);
74 }
75
76 // We use this as the time period for tracking minimum mutator utilization (MMU).
77 // In generational mode, the MMU is used as a signal to adjust the size of the
78 // young generation.
79 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
80 FLAG_SET_DEFAULT(GCPauseIntervalMillis, 5000);
81 }
82
83 // Set up default number of concurrent threads. We want to have cycles complete fast
84 // enough, but we also do not want to steal too much CPU from the concurrently running
85 // application. Using 1/4 of available threads for concurrent GC seems a good
86 // compromise here.
87 bool ergo_conc = FLAG_IS_DEFAULT(ConcGCThreads);
88 if (ergo_conc) {
89 FLAG_SET_DEFAULT(ConcGCThreads, MAX2(1, os::initial_active_processor_count() / 4));
90 }
91
92 if (ConcGCThreads == 0) {
93 vm_exit_during_initialization("Shenandoah expects ConcGCThreads > 0, check -XX:ConcGCThreads=#");
94 }
95
96 // Set up default number of parallel threads. We want to have decent pauses performance
97 // which would use parallel threads, but we also do not want to do too many threads
98 // that will overwhelm the OS scheduler. Using 1/2 of available threads seems to be a fair
99 // compromise here. Due to implementation constraints, it should not be lower than
100 // the number of concurrent threads.
101 bool ergo_parallel = FLAG_IS_DEFAULT(ParallelGCThreads);
102 if (ergo_parallel) {
103 FLAG_SET_DEFAULT(ParallelGCThreads, MAX2(1, os::initial_active_processor_count() / 2));
104 }
105
106 if (ParallelGCThreads == 0) {
107 vm_exit_during_initialization("Shenandoah expects ParallelGCThreads > 0, check -XX:ParallelGCThreads=#");
108 }
109
110 // Make sure ergonomic decisions do not break the thread count invariants.
111 // This may happen when user overrides one of the flags, but not the other.
112 // When that happens, we want to adjust the setting that was set ergonomically.
113 if (ParallelGCThreads < ConcGCThreads) {
114 if (ergo_conc && !ergo_parallel) {
115 FLAG_SET_DEFAULT(ConcGCThreads, ParallelGCThreads);
116 } else if (!ergo_conc && ergo_parallel) {
117 FLAG_SET_DEFAULT(ParallelGCThreads, ConcGCThreads);
118 } else if (ergo_conc && ergo_parallel) {
119 // Should not happen, check the ergonomic computation above. Fail with relevant error.
120 vm_exit_during_initialization("Shenandoah thread count ergonomic error");
121 } else {
122 // User settings error, report and ask user to rectify.
123 vm_exit_during_initialization("Shenandoah expects ConcGCThreads <= ParallelGCThreads, check -XX:ParallelGCThreads, -XX:ConcGCThreads");
124 }
125 }
126
127 // Disable support for dynamic number of GC threads. We do not let the runtime
128 // heuristics to misjudge how many threads we need during the heavy concurrent phase
129 // or a GC pause.
130 if (UseDynamicNumberOfGCThreads) {
131 if (FLAG_IS_CMDLINE(UseDynamicNumberOfGCThreads)) {
132 warning("Shenandoah does not support UseDynamicNumberOfGCThreads, disabling");
133 }
134 FLAG_SET_DEFAULT(UseDynamicNumberOfGCThreads, false);
135 }
136
137 if (ShenandoahRegionSampling && FLAG_IS_DEFAULT(PerfDataMemorySize)) {
138 // When sampling is enabled, max out the PerfData memory to get more
139 // Shenandoah data in, including Matrix.
140 FLAG_SET_DEFAULT(PerfDataMemorySize, 2048*K);
141 }
142
143 #ifdef COMPILER2
144 // Shenandoah cares more about pause times, rather than raw throughput.
145 if (FLAG_IS_DEFAULT(UseCountedLoopSafepoints)) {
146 FLAG_SET_DEFAULT(UseCountedLoopSafepoints, true);
147 if (FLAG_IS_DEFAULT(LoopStripMiningIter)) {
148 FLAG_SET_DEFAULT(LoopStripMiningIter, 1000);
149 }
150 }
151 #ifdef ASSERT
152 // C2 barrier verification is only reliable when all default barriers are enabled
153 if (ShenandoahVerifyOptoBarriers &&
154 (!FLAG_IS_DEFAULT(ShenandoahSATBBarrier) ||
155 !FLAG_IS_DEFAULT(ShenandoahLoadRefBarrier) ||
156 !FLAG_IS_DEFAULT(ShenandoahCASBarrier) ||
157 !FLAG_IS_DEFAULT(ShenandoahCloneBarrier)
158 )) {
159 warning("Unusual barrier configuration, disabling C2 barrier verification");
160 FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
161 }
162 #else
163 guarantee(!ShenandoahVerifyOptoBarriers, "Should be disabled");
164 #endif // ASSERT
165 #endif // COMPILER2
166
167 // Record more information about previous cycles for improved debugging pleasure
168 if (FLAG_IS_DEFAULT(LogEventsBufferEntries)) {
169 FLAG_SET_DEFAULT(LogEventsBufferEntries, 250);
170 }
171
172 if ((InitialHeapSize == MaxHeapSize) && ShenandoahUncommit) {
173 log_info(gc)("Min heap equals to max heap, disabling ShenandoahUncommit");
174 FLAG_SET_DEFAULT(ShenandoahUncommit, false);
175 }
176
177 // If class unloading is disabled, no unloading for concurrent cycles as well.
178 if (!ClassUnloading) {
179 FLAG_SET_DEFAULT(ClassUnloadingWithConcurrentMark, false);
180 }
181
182 // TLAB sizing policy makes resizing decisions before each GC cycle. It averages
183 // historical data, assigning more recent data the weight according to TLABAllocationWeight.
184 // Current default is good for generational collectors that run frequent young GCs.
185 // With Shenandoah, GC cycles are much less frequent, so we need we need sizing policy
186 // to converge faster over smaller number of resizing decisions.
187 if (FLAG_IS_DEFAULT(TLABAllocationWeight)) {
188 FLAG_SET_DEFAULT(TLABAllocationWeight, 90);
189 }
190
191 if (GCCardSizeInBytes < ShenandoahMinCardSizeInBytes) {
192 vm_exit_during_initialization(
193 err_msg("GCCardSizeInBytes ( %u ) must be >= %u\n", GCCardSizeInBytes, (unsigned int) ShenandoahMinCardSizeInBytes));
194 }
195
196 FullGCForwarding::initialize_flags(MaxHeapSize);
197 }
198
199 size_t ShenandoahArguments::conservative_max_heap_alignment() {
200 size_t align = ShenandoahMaxRegionSize;
201 if (UseLargePages) {
202 align = MAX2(align, os::large_page_size());
203 }
204 return align;
205 }
206
207 void ShenandoahArguments::initialize_alignments() {
208 CardTable::initialize_card_size();
209
210 // Need to setup sizes early to get correct alignments.
211 MaxHeapSize = ShenandoahHeapRegion::setup_sizes(MaxHeapSize);
212
213 // This is expected by our algorithm for ShenandoahHeap::heap_region_containing().
214 size_t align = ShenandoahHeapRegion::region_size_bytes();
215 if (UseLargePages) {
216 align = MAX2(align, os::large_page_size());
217 }
218 SpaceAlignment = align;
219 HeapAlignment = align;
220 }
221
222 CollectedHeap* ShenandoahArguments::create_heap() {
223 if (strcmp(ShenandoahGCMode, "generational") != 0) {
224 // Not generational
225 return new ShenandoahHeap(new ShenandoahCollectorPolicy());
226 } else {
227 return new ShenandoahGenerationalHeap(new ShenandoahCollectorPolicy());
228 }
229 }