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 // Shenandoah relies on the object header bits (including the self-forwarded bit
48 // at markWord::self_fwd_mask_in_place) being preserved across monitor inflation,
49 // which only holds with UseObjectMonitorTable.
50 if (!UseObjectMonitorTable) {
51 if (FLAG_IS_CMDLINE(UseObjectMonitorTable)) {
52 vm_exit_during_initialization("Shenandoah requires UseObjectMonitorTable");
53 }
54 FLAG_SET_DEFAULT(UseObjectMonitorTable, true);
55 }
56
57 #if 0 // leave this block as stepping stone for future platforms
58 log_warning(gc)("Shenandoah GC is not fully supported on this platform:");
59 log_warning(gc)(" concurrent modes are not supported, only STW cycles are enabled;");
60 log_warning(gc)(" arch-specific barrier code is not implemented, disabling barriers;");
61
62 FLAG_SET_DEFAULT(ShenandoahGCHeuristics, "passive");
63
64 FLAG_SET_DEFAULT(ShenandoahSATBBarrier, false);
65 FLAG_SET_DEFAULT(ShenandoahLoadRefBarrier, false);
66 FLAG_SET_DEFAULT(ShenandoahCASBarrier, false);
67 FLAG_SET_DEFAULT(ShenandoahCardBarrier, false);
68 FLAG_SET_DEFAULT(ShenandoahCloneBarrier, false);
69
70 FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
71 #endif
72 if (UseLargePages) {
73 size_t large_page_size = os::large_page_size();
74 if ((align_up(MaxHeapSize, large_page_size) / large_page_size) < ShenandoahHeapRegion::MIN_NUM_REGIONS) {
75 warning("Large pages size (%zuK) is too large to afford page-sized regions, disabling uncommit",
76 os::large_page_size() / K);
77 FLAG_SET_DEFAULT(ShenandoahUncommit, false);
78 }
79 }
80
81 // Enable NUMA by default. While Shenandoah is not NUMA-aware, enabling NUMA makes
82 // storage allocation code NUMA-aware.
83 if (FLAG_IS_DEFAULT(UseNUMA)) {
84 FLAG_SET_DEFAULT(UseNUMA, true);
85 }
86
87 // We use this as the time period for tracking minimum mutator utilization (MMU).
88 // In generational mode, the MMU is used as a signal to adjust the size of the
89 // young generation.
90 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
91 FLAG_SET_DEFAULT(GCPauseIntervalMillis, 5000);
92 }
93
94 // Set up default number of concurrent threads. We want to have cycles complete fast
95 // enough, but we also do not want to steal too much CPU from the concurrently running
96 // application. Using 1/4 of available threads for concurrent GC seems a good
97 // compromise here.
98 bool ergo_conc = FLAG_IS_DEFAULT(ConcGCThreads);
99 if (ergo_conc) {
100 FLAG_SET_DEFAULT(ConcGCThreads, MAX2(1, os::initial_active_processor_count() / 4));
101 }
102
103 if (ConcGCThreads == 0) {
104 vm_exit_during_initialization("Shenandoah expects ConcGCThreads > 0, check -XX:ConcGCThreads=#");
105 }
106
107 // Set up default number of parallel threads. We want to have decent pauses performance
108 // which would use parallel threads, but we also do not want to do too many threads
109 // that will overwhelm the OS scheduler. Using 1/2 of available threads seems to be a fair
110 // compromise here. Due to implementation constraints, it should not be lower than
111 // the number of concurrent threads.
112 bool ergo_parallel = FLAG_IS_DEFAULT(ParallelGCThreads);
113 if (ergo_parallel) {
114 FLAG_SET_DEFAULT(ParallelGCThreads, MAX2(1, os::initial_active_processor_count() / 2));
115 }
116
117 if (ParallelGCThreads == 0) {
118 vm_exit_during_initialization("Shenandoah expects ParallelGCThreads > 0, check -XX:ParallelGCThreads=#");
119 }
120
121 // Make sure ergonomic decisions do not break the thread count invariants.
122 // This may happen when user overrides one of the flags, but not the other.
123 // When that happens, we want to adjust the setting that was set ergonomically.
124 if (ParallelGCThreads < ConcGCThreads) {
125 if (ergo_conc && !ergo_parallel) {
126 FLAG_SET_DEFAULT(ConcGCThreads, ParallelGCThreads);
127 } else if (!ergo_conc && ergo_parallel) {
128 FLAG_SET_DEFAULT(ParallelGCThreads, ConcGCThreads);
129 } else if (ergo_conc && ergo_parallel) {
130 // Should not happen, check the ergonomic computation above. Fail with relevant error.
131 vm_exit_during_initialization("Shenandoah thread count ergonomic error");
132 } else {
133 // User settings error, report and ask user to rectify.
134 vm_exit_during_initialization("Shenandoah expects ConcGCThreads <= ParallelGCThreads, check -XX:ParallelGCThreads, -XX:ConcGCThreads");
135 }
136 }
137
138 // Disable support for dynamic number of GC threads. We do not let the runtime
139 // heuristics to misjudge how many threads we need during the heavy concurrent phase
140 // or a GC pause.
141 if (UseDynamicNumberOfGCThreads) {
142 if (FLAG_IS_CMDLINE(UseDynamicNumberOfGCThreads)) {
143 warning("Shenandoah does not support UseDynamicNumberOfGCThreads, disabling");
144 }
145 FLAG_SET_DEFAULT(UseDynamicNumberOfGCThreads, false);
146 }
147
148 if (ShenandoahRegionSampling && FLAG_IS_DEFAULT(PerfDataMemorySize)) {
149 // When sampling is enabled, max out the PerfData memory to get more
150 // Shenandoah data in, including Matrix.
151 FLAG_SET_DEFAULT(PerfDataMemorySize, 2048*K);
152 }
153
154 #ifdef COMPILER2
155 // Shenandoah cares more about pause times, rather than raw throughput.
156 if (FLAG_IS_DEFAULT(UseCountedLoopSafepoints)) {
157 FLAG_SET_DEFAULT(UseCountedLoopSafepoints, true);
158 if (FLAG_IS_DEFAULT(LoopStripMiningIter)) {
159 FLAG_SET_DEFAULT(LoopStripMiningIter, 1000);
160 }
161 }
162 #ifdef ASSERT
163 // C2 barrier verification is only reliable when all default barriers are enabled
164 if (ShenandoahVerifyOptoBarriers &&
165 (!FLAG_IS_DEFAULT(ShenandoahSATBBarrier) ||
166 !FLAG_IS_DEFAULT(ShenandoahLoadRefBarrier) ||
167 !FLAG_IS_DEFAULT(ShenandoahCASBarrier) ||
168 !FLAG_IS_DEFAULT(ShenandoahCloneBarrier)
169 )) {
170 warning("Unusual barrier configuration, disabling C2 barrier verification");
171 FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
172 }
173 #else
174 guarantee(!ShenandoahVerifyOptoBarriers, "Should be disabled");
175 #endif // ASSERT
176 #endif // COMPILER2
177
178 // Record more information about previous cycles for improved debugging pleasure
179 if (FLAG_IS_DEFAULT(LogEventsBufferEntries)) {
180 FLAG_SET_DEFAULT(LogEventsBufferEntries, 250);
181 }
182
183 if ((InitialHeapSize == MaxHeapSize) && ShenandoahUncommit) {
184 log_info(gc)("Min heap equals to max heap, disabling ShenandoahUncommit");
185 FLAG_SET_DEFAULT(ShenandoahUncommit, false);
186 }
187
188 // If class unloading is disabled, no unloading for concurrent cycles as well.
189 if (!ClassUnloading) {
190 FLAG_SET_DEFAULT(ClassUnloadingWithConcurrentMark, false);
191 }
192
193 // TLAB sizing policy makes resizing decisions before each GC cycle. It averages
194 // historical data, assigning more recent data the weight according to TLABAllocationWeight.
195 // Current default is good for generational collectors that run frequent young GCs.
196 // With Shenandoah, GC cycles are much less frequent, so we need we need sizing policy
197 // to converge faster over smaller number of resizing decisions.
198 if (strcmp(ShenandoahGCMode, "generational") && FLAG_IS_DEFAULT(TLABAllocationWeight)) {
199 FLAG_SET_DEFAULT(TLABAllocationWeight, 90);
200 }
201 // In generational mode, let TLABAllocationWeight keeps its default value of 35.
202
203 if (GCCardSizeInBytes < ShenandoahMinCardSizeInBytes) {
204 vm_exit_during_initialization(
205 err_msg("GCCardSizeInBytes ( %u ) must be >= %u\n", GCCardSizeInBytes, (unsigned int) ShenandoahMinCardSizeInBytes));
206 }
207
208 // Gen shen does not support any ShenandoahGCHeuristics value except for the default "adaptive"
209 if ((strcmp(ShenandoahGCMode, "generational") == 0)
210 && strcmp(ShenandoahGCHeuristics, "adaptive") != 0) {
211 log_warning(gc)("Ignoring -XX:ShenandoahGCHeuristics input: %s, because generational shenandoah only"
212 " supports adaptive heuristics", ShenandoahGCHeuristics);
213 FLAG_SET_ERGO(ShenandoahGCHeuristics, "adaptive");
214 }
215
216 FullGCForwarding::initialize_flags(MaxHeapSize);
217 }
218
219 size_t ShenandoahArguments::conservative_max_heap_alignment() {
220 static_assert(is_power_of_2(ShenandoahHeapRegion::MAX_REGION_SIZE), "Max region size must be a power of 2.");
221 size_t align = ShenandoahHeapRegion::MAX_REGION_SIZE;
222 if (UseLargePages) {
223 align = MAX2(align, os::large_page_size());
224 }
225 return align;
226 }
227
228 void ShenandoahArguments::initialize_alignments() {
229 CardTable::initialize_card_size();
230
231 // Need to setup sizes early to get correct alignments.
232 MaxHeapSize = ShenandoahHeapRegion::setup_sizes(MaxHeapSize);
233
234 // This is expected by our algorithm for ShenandoahHeap::heap_region_containing().
235 size_t align = ShenandoahHeapRegion::region_size_bytes();
236 if (UseLargePages) {
237 align = MAX2(align, os::large_page_size());
238 }
239 SpaceAlignment = align;
240 HeapAlignment = align;
241
242 if (FLAG_IS_DEFAULT(TLABSize)) {
243 TLABSize = MAX2(ShenandoahHeapRegion::region_size_bytes() / 256, (size_t) 32 * 1024);
244 }
245 }
246
247 CollectedHeap* ShenandoahArguments::create_heap() {
248 if (strcmp(ShenandoahGCMode, "generational") != 0) {
249 // Not generational
250 return new ShenandoahHeap(new ShenandoahCollectorPolicy());
251 } else {
252 return new ShenandoahGenerationalHeap(new ShenandoahCollectorPolicy());
253 }
254 }