1 /*
2 * Copyright (c) 2018, 2026, Oracle and/or its affiliates. All rights reserved.
3 * Copyright (c) 2017, Red Hat, Inc. and/or its affiliates.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "cds/cdsConfig.hpp"
27 #include "gc/g1/g1Arguments.hpp"
28 #include "gc/g1/g1CardSet.hpp"
29 #include "gc/g1/g1CardSetContainers.inline.hpp"
30 #include "gc/g1/g1CollectedHeap.inline.hpp"
31 #include "gc/g1/g1HeapRegion.hpp"
32 #include "gc/g1/g1HeapRegionBounds.inline.hpp"
33 #include "gc/g1/g1HeapRegionRemSet.hpp"
34 #include "gc/g1/g1HeapVerifier.hpp"
35 #include "gc/shared/cardTable.hpp"
36 #include "gc/shared/fullGCForwarding.hpp"
37 #include "gc/shared/gcArguments.hpp"
38 #include "gc/shared/workerPolicy.hpp"
39 #include "runtime/flags/jvmFlagLimit.hpp"
40 #include "runtime/globals.hpp"
41 #include "runtime/globals_extension.hpp"
42 #include "runtime/java.hpp"
43
44 static size_t calculate_heap_alignment(size_t space_alignment) {
45 size_t card_table_alignment = CardTable::ct_max_alignment_constraint();
46 size_t page_size = UseLargePages ? os::large_page_size() : os::vm_page_size();
47 return MAX3(card_table_alignment, space_alignment, page_size);
48 }
49
50 void G1Arguments::initialize_alignments() {
51 // Initialize card size before initializing alignments
52 CardTable::initialize_card_size();
53
54 // Set up the region size and associated fields.
55 //
56 // There is a circular dependency here. We base the region size on the heap
57 // size, but the heap size should be aligned with the region size. To get
58 // around this we use the unaligned values for the heap.
59 G1HeapRegion::setup_heap_region_size(MaxHeapSize);
60
61 SpaceAlignment = G1HeapRegion::GrainBytes;
62 HeapAlignment = calculate_heap_alignment(SpaceAlignment);
63
64 // We need to initialize card set configuration as soon as heap region size is
65 // known as it depends on it and is used really early.
66 initialize_card_set_configuration();
67 // Needs remembered set initialization as the ergonomics are based
68 // on it.
69 if (FLAG_IS_DEFAULT(G1EagerReclaimRemSetThreshold)) {
70 FLAG_SET_ERGO(G1EagerReclaimRemSetThreshold, G1RemSetArrayOfCardsEntries);
71 }
72 // G1 prefers to use conditional card marking to avoid overwriting cards that
73 // have already been found to contain a to-collection set reference. This reduces
74 // refinement effort.
75 if (FLAG_IS_DEFAULT(UseCondCardMark)) {
76 FLAG_SET_ERGO(UseCondCardMark, true);
77 }
78 }
79
80 size_t G1Arguments::conservative_max_heap_alignment() {
81 const size_t region_size = FLAG_IS_DEFAULT(G1HeapRegionSize)
82 ? G1HeapRegion::max_ergonomics_size()
83 : G1HeapRegion::max_region_size();
84
85 return calculate_heap_alignment(region_size);
86 }
87
88 void G1Arguments::initialize_verification_types() {
89 if (strlen(VerifyGCType) > 0) {
90 const char delimiter[] = " ,\n";
91 size_t length = strlen(VerifyGCType);
92 char* type_list = NEW_C_HEAP_ARRAY(char, length + 1, mtInternal);
93 strncpy(type_list, VerifyGCType, length + 1);
94 char* save_ptr;
95
96 char* token = strtok_r(type_list, delimiter, &save_ptr);
97 while (token != nullptr) {
98 parse_verification_type(token);
99 token = strtok_r(nullptr, delimiter, &save_ptr);
100 }
101 FREE_C_HEAP_ARRAY(char, type_list);
102 }
103 }
104
105 void G1Arguments::parse_verification_type(const char* type) {
106 if (strcmp(type, "young-normal") == 0) {
107 G1HeapVerifier::enable_verification_type(G1HeapVerifier::G1VerifyYoungNormal);
108 } else if (strcmp(type, "concurrent-start") == 0) {
109 G1HeapVerifier::enable_verification_type(G1HeapVerifier::G1VerifyConcurrentStart);
110 } else if (strcmp(type, "mixed") == 0) {
111 G1HeapVerifier::enable_verification_type(G1HeapVerifier::G1VerifyMixed);
112 } else if (strcmp(type, "young-evac-fail") == 0) {
113 G1HeapVerifier::enable_verification_type(G1HeapVerifier::G1VerifyYoungEvacFail);
114 } else if (strcmp(type, "remark") == 0) {
115 G1HeapVerifier::enable_verification_type(G1HeapVerifier::G1VerifyRemark);
116 } else if (strcmp(type, "cleanup") == 0) {
117 G1HeapVerifier::enable_verification_type(G1HeapVerifier::G1VerifyCleanup);
118 } else if (strcmp(type, "full") == 0) {
119 G1HeapVerifier::enable_verification_type(G1HeapVerifier::G1VerifyFull);
120 } else {
121 log_warning(gc, verify)("VerifyGCType: '%s' is unknown. Available types are: "
122 "young-normal, young-evac-fail, concurrent-start, mixed, remark, cleanup and full", type);
123 }
124 }
125
126 // Returns the maximum number of workers to be used in a concurrent
127 // phase based on the number of GC workers being used in a STW
128 // phase.
129 static uint scale_concurrent_worker_threads(uint num_gc_workers) {
130 return MAX2((num_gc_workers + 2) / 4, 1U);
131 }
132
133 void G1Arguments::initialize_mark_stack_size() {
134 if (FLAG_IS_DEFAULT(MarkStackSize)) {
135 size_t mark_stack_size = MIN2(MarkStackSizeMax,
136 MAX2(MarkStackSize, (size_t)ConcGCThreads * TASKQUEUE_SIZE));
137 FLAG_SET_ERGO(MarkStackSize, mark_stack_size);
138 }
139 }
140
141 void G1Arguments::initialize_card_set_configuration() {
142 assert(G1HeapRegion::LogOfHRGrainBytes != 0, "not initialized");
143 // Array of Cards card set container globals.
144 const uint LOG_M = 20;
145 assert(log2i_exact(G1HeapRegionBounds::min_size()) == LOG_M, "inv");
146 assert(G1HeapRegion::LogOfHRGrainBytes >= LOG_M, "from the above");
147 uint region_size_log_mb = G1HeapRegion::LogOfHRGrainBytes - LOG_M;
148
149 if (FLAG_IS_DEFAULT(G1RemSetArrayOfCardsEntries)) {
150 uint max_cards_in_inline_ptr = G1CardSetConfiguration::max_cards_in_inline_ptr(G1HeapRegion::LogCardsPerRegion);
151 FLAG_SET_ERGO(G1RemSetArrayOfCardsEntries, MAX2(max_cards_in_inline_ptr * 2,
152 G1RemSetArrayOfCardsEntriesBase << region_size_log_mb));
153 }
154
155 // Howl card set container globals.
156 if (FLAG_IS_DEFAULT(G1RemSetHowlNumBuckets)) {
157 FLAG_SET_ERGO(G1RemSetHowlNumBuckets, G1CardSetHowl::num_buckets(G1HeapRegion::CardsPerRegion,
158 G1RemSetArrayOfCardsEntries,
159 G1RemSetHowlMaxNumBuckets));
160 }
161
162 if (FLAG_IS_DEFAULT(G1RemSetHowlMaxNumBuckets)) {
163 FLAG_SET_ERGO(G1RemSetHowlMaxNumBuckets, MAX2(G1RemSetHowlMaxNumBuckets, G1RemSetHowlNumBuckets));
164 } else if (G1RemSetHowlMaxNumBuckets < G1RemSetHowlNumBuckets) {
165 FormatBuffer<> buf("Maximum Howl card set container bucket size %u smaller than requested bucket size %u",
166 G1RemSetHowlMaxNumBuckets, G1RemSetHowlNumBuckets);
167 vm_exit_during_initialization(buf);
168 }
169 }
170
171 void G1Arguments::initialize() {
172 GCArguments::initialize();
173 assert(UseG1GC, "Error");
174 FLAG_SET_DEFAULT(ParallelGCThreads, WorkerPolicy::parallel_worker_threads());
175 if (ParallelGCThreads == 0) {
176 assert(!FLAG_IS_DEFAULT(ParallelGCThreads), "The default value for ParallelGCThreads should not be 0.");
177 vm_exit_during_initialization("The flag -XX:+UseG1GC can not be combined with -XX:ParallelGCThreads=0", nullptr);
178 }
179
180 // When dumping the CDS heap we want to reduce fragmentation by
181 // triggering a full collection. To get as low fragmentation as
182 // possible we only use one worker thread.
183 if (CDSConfig::is_dumping_heap()) {
184 FLAG_SET_ERGO(ParallelGCThreads, 1);
185 }
186
187 if (!G1UseConcRefinement) {
188 if (!FLAG_IS_DEFAULT(G1ConcRefinementThreads)) {
189 log_warning(gc, ergo)("Ignoring -XX:G1ConcRefinementThreads "
190 "because of -XX:-G1UseConcRefinement");
191 }
192 FLAG_SET_DEFAULT(G1ConcRefinementThreads, 0);
193 } else if (FLAG_IS_DEFAULT(G1ConcRefinementThreads)) {
194 const JVMTypedFlagLimit<uint>* conc_refinement_threads_limits = JVMFlagLimit::get_range_at(FLAG_MEMBER_ENUM(G1ConcRefinementThreads))->cast<uint>();
195 FLAG_SET_ERGO(G1ConcRefinementThreads, MIN2(ParallelGCThreads, conc_refinement_threads_limits->max()));
196 }
197
198 if (FLAG_IS_DEFAULT(ConcGCThreads) || ConcGCThreads == 0) {
199 // Calculate the number of concurrent worker threads by scaling
200 // the number of parallel GC threads.
201 uint marking_thread_num = scale_concurrent_worker_threads(ParallelGCThreads);
202 FLAG_SET_ERGO(ConcGCThreads, marking_thread_num);
203 }
204
205 if (FLAG_IS_DEFAULT(GCTimeRatio) || GCTimeRatio == 0) {
206 // In G1, we want the default GC overhead goal to be higher than
207 // it is for PS, or the heap might be expanded too aggressively.
208 // We set it here to 4%.
209 FLAG_SET_DEFAULT(GCTimeRatio, 24);
210 }
211
212 // Do not interfere with GC-Pressure driven heap resizing unless the user
213 // explicitly sets otherwise. G1 heap sizing should be free to grow or shrink
214 // the heap based on GC pressure, rather than being forced to satisfy
215 // MinHeapFreeRatio or MaxHeapFreeRatio defaults that the user did not set.
216 if (FLAG_IS_DEFAULT(MinHeapFreeRatio)) {
217 FLAG_SET_DEFAULT(MinHeapFreeRatio, 0);
218 }
219 if (FLAG_IS_DEFAULT(MaxHeapFreeRatio)) {
220 FLAG_SET_DEFAULT(MaxHeapFreeRatio, 100);
221 }
222
223 // Below, we might need to calculate the pause time interval based on
224 // the pause target. When we do so we are going to give G1 maximum
225 // flexibility and allow it to do pauses when it needs to. So, we'll
226 // arrange that the pause interval to be pause time target + 1 to
227 // ensure that a) the pause time target is maximized with respect to
228 // the pause interval and b) we maintain the invariant that pause
229 // time target < pause interval. If the user does not want this
230 // maximum flexibility, they will have to set the pause interval
231 // explicitly.
232
233 if (FLAG_IS_DEFAULT(MaxGCPauseMillis)) {
234 // The default pause time target in G1 is 200ms
235 FLAG_SET_DEFAULT(MaxGCPauseMillis, 200);
236 }
237
238 // Then, if the interval parameter was not set, set it according to
239 // the pause time target (this will also deal with the case when the
240 // pause time target is the default value).
241 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
242 FLAG_SET_DEFAULT(GCPauseIntervalMillis, MaxGCPauseMillis + 1);
243 }
244
245 #ifdef COMPILER2
246 // Enable loop strip mining to offer better pause time guarantees
247 if (FLAG_IS_DEFAULT(UseCountedLoopSafepoints)) {
248 FLAG_SET_DEFAULT(UseCountedLoopSafepoints, true);
249 if (FLAG_IS_DEFAULT(LoopStripMiningIter)) {
250 FLAG_SET_DEFAULT(LoopStripMiningIter, 1000);
251 }
252 }
253 #endif
254
255 initialize_mark_stack_size();
256 initialize_verification_types();
257
258 // Verify that the maximum parallelism isn't too high to eventually overflow
259 // the refcount in G1CardSetContainer.
260 uint const divisor = 3; // Safe divisor; we increment by 2 for each claim, but there is a small initial value.
261 if (G1ConcRefinementThreads > UINT_MAX / divisor) {
262 vm_exit_during_initialization("Too large parallelism for remembered sets.");
263 }
264
265 FullGCForwarding::initialize_flags(heap_reserved_size_bytes());
266 }
267
268 CollectedHeap* G1Arguments::create_heap() {
269 return new G1CollectedHeap();
270 }
271
272 size_t G1Arguments::heap_reserved_size_bytes() {
273 return MaxHeapSize;
274 }