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/gcArguments.hpp"
28 #include "gc/shared/tlab_globals.hpp"
29 #include "gc/shared/workerPolicy.hpp"
30 #include "gc/shenandoah/shenandoahArguments.hpp"
31 #include "gc/shenandoah/shenandoahCardTable.hpp"
32 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
33 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
36 #include "runtime/globals_extension.hpp"
37 #include "runtime/java.hpp"
38 #include "utilities/defaultStream.hpp"
39 #include "utilities/powerOfTwo.hpp"
40
41 void ShenandoahArguments::initialize() {
42 #if !(defined AARCH64 || defined AMD64 || defined PPC64 || defined RISCV64)
43 vm_exit_during_initialization("Shenandoah GC is not supported on this platform.");
44 #endif
45
46 // Shenandoah relies on the object header bits (including the self-forwarded bit
47 // at markWord::self_fwd_mask_in_place) being preserved across monitor inflation,
48 // which only holds with UseObjectMonitorTable.
49 if (!UseObjectMonitorTable) {
50 if (FLAG_IS_CMDLINE(UseObjectMonitorTable)) {
51 vm_exit_during_initialization("Shenandoah requires UseObjectMonitorTable");
52 }
53 FLAG_SET_DEFAULT(UseObjectMonitorTable, true);
54 }
55
56 #if 0 // leave this block as stepping stone for future platforms
57 log_warning(gc)("Shenandoah GC is not fully supported on this platform:");
58 log_warning(gc)(" concurrent modes are not supported, only STW cycles are enabled;");
59 log_warning(gc)(" arch-specific barrier code is not implemented, disabling barriers;");
60
61 FLAG_SET_DEFAULT(ShenandoahGCHeuristics, "passive");
62
63 FLAG_SET_DEFAULT(ShenandoahSATBBarrier, false);
64 FLAG_SET_DEFAULT(ShenandoahLoadRefBarrier, false);
65 FLAG_SET_DEFAULT(ShenandoahCardBarrier, false);
66 FLAG_SET_DEFAULT(ShenandoahCloneBarrier, false);
67
68 FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers, false);
69 #endif
70 if (UseLargePages) {
71 size_t large_page_size = os::large_page_size();
72 if ((align_up(MaxHeapSize, large_page_size) / large_page_size) < ShenandoahHeapRegion::MIN_NUM_REGIONS) {
73 warning("Large pages size (%zuK) is too large to afford page-sized regions, disabling uncommit",
74 os::large_page_size() / K);
75 FLAG_SET_DEFAULT(ShenandoahUncommit, false);
76 }
77 }
78
79 // Enable NUMA by default. While Shenandoah is not NUMA-aware, enabling NUMA makes
80 // storage allocation code NUMA-aware.
81 if (FLAG_IS_DEFAULT(UseNUMA)) {
82 FLAG_SET_DEFAULT(UseNUMA, true);
83 }
84
85 // We use this as the time period for tracking minimum mutator utilization (MMU).
86 // In generational mode, the MMU is used as a signal to adjust the size of the
87 // young generation.
88 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
89 FLAG_SET_DEFAULT(GCPauseIntervalMillis, 5000);
90 }
91
92 // Set up default number of concurrent threads. We want to have cycles complete fast
93 // enough, but we also do not want to steal too much CPU from the concurrently running
94 // application. Using 1/4 of available threads for concurrent GC seems a good
95 // compromise here.
96 bool ergo_conc = FLAG_IS_DEFAULT(ConcGCThreads);
97 if (ergo_conc) {
98 FLAG_SET_DEFAULT(ConcGCThreads, MAX2(1, os::initial_active_processor_count() / 4));
99 }
100
101 if (ConcGCThreads == 0) {
102 vm_exit_during_initialization("Shenandoah expects ConcGCThreads > 0, check -XX:ConcGCThreads=#");
103 }
104
105 // Set up default number of parallel threads. We want to have decent pauses performance
106 // which would use parallel threads, but we also do not want to do too many threads
107 // that will overwhelm the OS scheduler. Using 1/2 of available threads seems to be a fair
108 // compromise here. Due to implementation constraints, it should not be lower than
109 // the number of concurrent threads.
110 bool ergo_parallel = FLAG_IS_DEFAULT(ParallelGCThreads);
111 if (ergo_parallel) {
112 FLAG_SET_DEFAULT(ParallelGCThreads, MAX2(1, os::initial_active_processor_count() / 2));
113 }
114
115 if (ParallelGCThreads == 0) {
116 vm_exit_during_initialization("Shenandoah expects ParallelGCThreads > 0, check -XX:ParallelGCThreads=#");
117 }
118
119 // Make sure ergonomic decisions do not break the thread count invariants.
120 // This may happen when user overrides one of the flags, but not the other.
121 // When that happens, we want to adjust the setting that was set ergonomically.
122 if (ParallelGCThreads < ConcGCThreads) {
123 if (ergo_conc && !ergo_parallel) {
124 FLAG_SET_DEFAULT(ConcGCThreads, ParallelGCThreads);
125 } else if (!ergo_conc && ergo_parallel) {
126 FLAG_SET_DEFAULT(ParallelGCThreads, ConcGCThreads);
127 } else if (ergo_conc && ergo_parallel) {
128 // Should not happen, check the ergonomic computation above. Fail with relevant error.
129 vm_exit_during_initialization("Shenandoah thread count ergonomic error");
130 } else {
131 // User settings error, report and ask user to rectify.
132 vm_exit_during_initialization("Shenandoah expects ConcGCThreads <= ParallelGCThreads, check -XX:ParallelGCThreads, -XX:ConcGCThreads");
133 }
134 }
135
136 // Disable support for dynamic number of GC threads. We do not let the runtime
137 // heuristics to misjudge how many threads we need during the heavy concurrent phase
138 // or a GC pause.
139 if (UseDynamicNumberOfGCThreads) {
140 if (FLAG_IS_CMDLINE(UseDynamicNumberOfGCThreads)) {
141 warning("Shenandoah does not support UseDynamicNumberOfGCThreads, disabling");
142 }
143 FLAG_SET_DEFAULT(UseDynamicNumberOfGCThreads, false);
144 }
145
146 if (ShenandoahRegionSampling && FLAG_IS_DEFAULT(PerfDataMemorySize)) {
147 // When sampling is enabled, max out the PerfData memory to get more
148 // Shenandoah data in, including Matrix.
149 FLAG_SET_DEFAULT(PerfDataMemorySize, 2048*K);
150 }
151
152 #ifdef COMPILER2
153 // Shenandoah cares more about pause times, rather than raw throughput.
154 if (FLAG_IS_DEFAULT(UseCountedLoopSafepoints)) {
155 FLAG_SET_DEFAULT(UseCountedLoopSafepoints, true);
156 if (FLAG_IS_DEFAULT(LoopStripMiningIter)) {
157 FLAG_SET_DEFAULT(LoopStripMiningIter, 1000);
158 }
159 }
160 #endif // COMPILER2
161
162 // Record more information about previous cycles for improved debugging pleasure
163 if (FLAG_IS_DEFAULT(LogEventsBufferEntries)) {
164 FLAG_SET_DEFAULT(LogEventsBufferEntries, 250);
165 }
166
167 if ((InitialHeapSize == MaxHeapSize) && ShenandoahUncommit) {
168 log_info(gc)("Min heap equals to max heap, disabling ShenandoahUncommit");
169 FLAG_SET_DEFAULT(ShenandoahUncommit, false);
170 }
171
172 // If class unloading is disabled, no unloading for concurrent cycles as well.
173 if (!ClassUnloading) {
174 FLAG_SET_DEFAULT(ClassUnloadingWithConcurrentMark, false);
175 }
176
177 // TLAB sizing policy makes resizing decisions before each GC cycle. It averages
178 // historical data, assigning more recent data the weight according to TLABAllocationWeight.
179 // Current default is good for generational collectors that run frequent young GCs.
180 // With Shenandoah, GC cycles are much less frequent, so we need sizing policy
181 // to converge faster over smaller number of resizing decisions.
182 if (strcmp(ShenandoahGCMode, "generational") && FLAG_IS_DEFAULT(TLABAllocationWeight)) {
183 FLAG_SET_DEFAULT(TLABAllocationWeight, 90);
184 }
185 // In generational mode, let TLABAllocationWeight keeps its default value of 35.
186
187 if (GCCardSizeInBytes < ShenandoahMinCardSizeInBytes) {
188 vm_exit_during_initialization(
189 err_msg("GCCardSizeInBytes ( %u ) must be >= %u\n", GCCardSizeInBytes, ShenandoahMinCardSizeInBytes));
190 }
191
192 // Gen shen does not support any ShenandoahGCHeuristics value except for the default "adaptive"
193 if ((strcmp(ShenandoahGCMode, "generational") == 0)
194 && strcmp(ShenandoahGCHeuristics, "adaptive") != 0) {
195 log_warning(gc)("Ignoring -XX:ShenandoahGCHeuristics input: %s, because generational shenandoah only"
196 " supports adaptive heuristics", ShenandoahGCHeuristics);
197 FLAG_SET_ERGO(ShenandoahGCHeuristics, "adaptive");
198 }
199
200 if (ShenandoahMomentaryAllocRateSampleWindow > ShenandoahRecentAllocRateSampleWindow
201 || ShenandoahRecentAllocRateSampleWindow > ShenandoahAllocRateSampleWindow) {
202 vm_exit_during_initialization(
203 err_msg("Relation must hold: ShenandoahMomentaryAllocRateSampleWindow (%u) "
204 "<= ShenandoahRecentAllocRateSampleWindow (%u) "
205 "<= ShenandoahAllocRateSampleWindow (%u)",
206 ShenandoahMomentaryAllocRateSampleWindow, ShenandoahRecentAllocRateSampleWindow,
207 ShenandoahAllocRateSampleWindow));
208 }
209 }
210
211 size_t ShenandoahArguments::conservative_max_heap_alignment() {
212 static_assert(is_power_of_2(ShenandoahHeapRegion::MAX_REGION_SIZE), "Max region size must be a power of 2.");
213 size_t align = ShenandoahHeapRegion::MAX_REGION_SIZE;
214 if (UseLargePages) {
215 align = MAX2(align, os::large_page_size());
216 }
217 return align;
218 }
219
220 void ShenandoahArguments::initialize_alignments() {
221 CardTable::initialize_card_size();
222
223 // Need to setup sizes early to get correct alignments.
224 MaxHeapSize = ShenandoahHeapRegion::setup_sizes(MaxHeapSize);
225
226 // This is expected by our algorithm for ShenandoahHeap::heap_region_containing().
227 size_t align = ShenandoahHeapRegion::region_size_bytes();
228 if (UseLargePages) {
229 align = MAX2(align, os::large_page_size());
230 }
231 SpaceAlignment = align;
232 HeapAlignment = align;
233
234 if (FLAG_IS_DEFAULT(TLABSize)) {
235 TLABSize = MAX2(ShenandoahHeapRegion::region_size_bytes() / 256, (size_t) 32 * 1024);
236 }
237 }
238
239 CollectedHeap* ShenandoahArguments::create_heap() {
240 if (strcmp(ShenandoahGCMode, "generational") != 0) {
241 // Not generational
242 return new ShenandoahHeap(new ShenandoahCollectorPolicy());
243 } else {
244 return new ShenandoahGenerationalHeap(new ShenandoahCollectorPolicy());
245 }
246 }