1 /* 2 * Copyright (c) 2017, 2025, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "classfile/classLoaderDataGraph.hpp" 26 #include "gc/g1/g1CollectedHeap.hpp" 27 #include "gc/g1/g1FullCollector.inline.hpp" 28 #include "gc/g1/g1FullGCAdjustTask.hpp" 29 #include "gc/g1/g1FullGCCompactTask.hpp" 30 #include "gc/g1/g1FullGCMarker.inline.hpp" 31 #include "gc/g1/g1FullGCMarkTask.hpp" 32 #include "gc/g1/g1FullGCPrepareTask.inline.hpp" 33 #include "gc/g1/g1FullGCResetMetadataTask.hpp" 34 #include "gc/g1/g1FullGCScope.hpp" 35 #include "gc/g1/g1OopClosures.hpp" 36 #include "gc/g1/g1Policy.hpp" 37 #include "gc/g1/g1RegionMarkStatsCache.inline.hpp" 38 #include "gc/shared/gcTraceTime.inline.hpp" 39 #include "gc/shared/preservedMarks.inline.hpp" 40 #include "gc/shared/classUnloadingContext.hpp" 41 #include "gc/shared/referenceProcessor.hpp" 42 #include "gc/shared/verifyOption.hpp" 43 #include "gc/shared/weakProcessor.inline.hpp" 44 #include "gc/shared/workerPolicy.hpp" 45 #include "logging/log.hpp" 46 #include "runtime/handles.inline.hpp" 47 #include "utilities/debug.hpp" 48 49 static void clear_and_activate_derived_pointers() { 50 #if COMPILER2_OR_JVMCI 51 DerivedPointerTable::clear(); 52 #endif 53 } 54 55 static void deactivate_derived_pointers() { 56 #if COMPILER2_OR_JVMCI 57 DerivedPointerTable::set_active(false); 58 #endif 59 } 60 61 static void update_derived_pointers() { 62 #if COMPILER2_OR_JVMCI 63 DerivedPointerTable::update_pointers(); 64 #endif 65 } 66 67 G1CMBitMap* G1FullCollector::mark_bitmap() { 68 return _heap->concurrent_mark()->mark_bitmap(); 69 } 70 71 ReferenceProcessor* G1FullCollector::reference_processor() { 72 return _heap->ref_processor_stw(); 73 } 74 75 uint G1FullCollector::calc_active_workers() { 76 G1CollectedHeap* heap = G1CollectedHeap::heap(); 77 uint max_worker_count = heap->workers()->max_workers(); 78 // Only calculate number of workers if UseDynamicNumberOfGCThreads 79 // is enabled, otherwise use max. 80 if (!UseDynamicNumberOfGCThreads) { 81 return max_worker_count; 82 } 83 84 // Consider G1HeapWastePercent to decide max number of workers. Each worker 85 // will in average cause half a region waste. 86 uint max_wasted_regions_allowed = ((heap->num_regions() * G1HeapWastePercent) / 100); 87 uint waste_worker_count = MAX2((max_wasted_regions_allowed * 2) , 1u); 88 uint heap_waste_worker_limit = MIN2(waste_worker_count, max_worker_count); 89 90 // Also consider HeapSizePerGCThread by calling WorkerPolicy to calculate 91 // the number of workers. 92 uint current_active_workers = heap->workers()->active_workers(); 93 uint active_worker_limit = WorkerPolicy::calc_active_workers(max_worker_count, current_active_workers, 0); 94 95 // Finally consider the amount of used regions. 96 uint used_worker_limit = heap->num_used_regions(); 97 assert(used_worker_limit > 0, "Should never have zero used regions."); 98 99 // Update active workers to the lower of the limits. 100 uint worker_count = MIN3(heap_waste_worker_limit, active_worker_limit, used_worker_limit); 101 log_debug(gc, task)("Requesting %u active workers for full compaction (waste limited workers: %u, " 102 "adaptive workers: %u, used limited workers: %u)", 103 worker_count, heap_waste_worker_limit, active_worker_limit, used_worker_limit); 104 worker_count = heap->workers()->set_active_workers(worker_count); 105 log_info(gc, task)("Using %u workers of %u for full compaction", worker_count, max_worker_count); 106 107 return worker_count; 108 } 109 110 G1FullCollector::G1FullCollector(G1CollectedHeap* heap, 111 bool clear_soft_refs, 112 bool do_maximal_compaction, 113 G1FullGCTracer* tracer) : 114 _heap(heap), 115 _scope(heap->monitoring_support(), clear_soft_refs, do_maximal_compaction, tracer), 116 _num_workers(calc_active_workers()), 117 _has_compaction_targets(false), 118 _has_humongous(false), 119 _oop_queue_set(_num_workers), 120 _array_queue_set(_num_workers), 121 _preserved_marks_set(true), 122 _serial_compaction_point(this, nullptr), 123 _humongous_compaction_point(this, nullptr), 124 _is_alive(this, heap->concurrent_mark()->mark_bitmap()), 125 _is_alive_mutator(heap->ref_processor_stw(), &_is_alive), 126 _humongous_compaction_regions(8), 127 _always_subject_to_discovery(), 128 _is_subject_mutator(heap->ref_processor_stw(), &_always_subject_to_discovery), 129 _region_attr_table() { 130 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint"); 131 132 _preserved_marks_set.init(_num_workers); 133 _markers = NEW_C_HEAP_ARRAY(G1FullGCMarker*, _num_workers, mtGC); 134 _compaction_points = NEW_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _num_workers, mtGC); 135 136 _live_stats = NEW_C_HEAP_ARRAY(G1RegionMarkStats, _heap->max_regions(), mtGC); 137 _compaction_tops = NEW_C_HEAP_ARRAY(HeapWord*, _heap->max_regions(), mtGC); 138 for (uint j = 0; j < heap->max_regions(); j++) { 139 _live_stats[j].clear(); 140 _compaction_tops[j] = nullptr; 141 } 142 143 for (uint i = 0; i < _num_workers; i++) { 144 _markers[i] = new G1FullGCMarker(this, i, _live_stats); 145 _compaction_points[i] = new G1FullGCCompactionPoint(this, _preserved_marks_set.get(i)); 146 _oop_queue_set.register_queue(i, marker(i)->oop_stack()); 147 _array_queue_set.register_queue(i, marker(i)->objarray_stack()); 148 } 149 _serial_compaction_point.set_preserved_stack(_preserved_marks_set.get(0)); 150 _humongous_compaction_point.set_preserved_stack(_preserved_marks_set.get(0)); 151 _region_attr_table.initialize(heap->reserved(), G1HeapRegion::GrainBytes); 152 } 153 154 G1FullCollector::~G1FullCollector() { 155 for (uint i = 0; i < _num_workers; i++) { 156 delete _markers[i]; 157 delete _compaction_points[i]; 158 } 159 160 FREE_C_HEAP_ARRAY(G1FullGCMarker*, _markers); 161 FREE_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _compaction_points); 162 FREE_C_HEAP_ARRAY(HeapWord*, _compaction_tops); 163 FREE_C_HEAP_ARRAY(G1RegionMarkStats, _live_stats); 164 } 165 166 class PrepareRegionsClosure : public G1HeapRegionClosure { 167 G1FullCollector* _collector; 168 169 public: 170 PrepareRegionsClosure(G1FullCollector* collector) : _collector(collector) { } 171 172 bool do_heap_region(G1HeapRegion* hr) { 173 hr->prepare_for_full_gc(); 174 G1CollectedHeap::heap()->prepare_region_for_full_compaction(hr); 175 _collector->before_marking_update_attribute_table(hr); 176 return false; 177 } 178 }; 179 180 void G1FullCollector::prepare_collection() { 181 _heap->policy()->record_full_collection_start(); 182 183 // Verification needs the bitmap, so we should clear the bitmap only later. 184 bool in_concurrent_cycle = _heap->abort_concurrent_cycle(); 185 _heap->verify_before_full_collection(); 186 if (in_concurrent_cycle) { 187 GCTraceTime(Debug, gc) debug("Clear Bitmap"); 188 _heap->concurrent_mark()->clear_bitmap(_heap->workers()); 189 } 190 191 _heap->gc_prologue(true); 192 _heap->retire_tlabs(); 193 _heap->flush_region_pin_cache(); 194 _heap->prepare_heap_for_full_collection(); 195 196 PrepareRegionsClosure cl(this); 197 _heap->heap_region_iterate(&cl); 198 199 reference_processor()->start_discovery(scope()->should_clear_soft_refs()); 200 201 // Clear and activate derived pointer collection. 202 clear_and_activate_derived_pointers(); 203 } 204 205 void G1FullCollector::collect() { 206 G1CollectedHeap::start_codecache_marking_cycle_if_inactive(false /* concurrent_mark_start */); 207 208 phase1_mark_live_objects(); 209 verify_after_marking(); 210 211 // Don't add any more derived pointers during later phases 212 deactivate_derived_pointers(); 213 214 phase2_prepare_compaction(); 215 216 if (has_compaction_targets()) { 217 phase3_adjust_pointers(); 218 219 phase4_do_compaction(); 220 } else { 221 // All regions have a high live ratio thus will not be compacted. 222 // The live ratio is only considered if do_maximal_compaction is false. 223 log_info(gc, phases) ("No Regions selected for compaction. Skipping Phase 3: Adjust pointers and Phase 4: Compact heap"); 224 } 225 226 phase5_reset_metadata(); 227 228 G1CollectedHeap::finish_codecache_marking_cycle(); 229 } 230 231 void G1FullCollector::complete_collection() { 232 // Restore all marks. 233 restore_marks(); 234 235 // When the pointers have been adjusted and moved, we can 236 // update the derived pointer table. 237 update_derived_pointers(); 238 239 // Need completely cleared claim bits for the next concurrent marking or full gc. 240 ClassLoaderDataGraph::clear_claimed_marks(); 241 242 // Prepare the bitmap for the next (potentially concurrent) marking. 243 _heap->concurrent_mark()->clear_bitmap(_heap->workers()); 244 245 _heap->prepare_for_mutator_after_full_collection(); 246 247 _heap->resize_all_tlabs(); 248 249 _heap->young_regions_cardset()->clear(); 250 251 _heap->policy()->record_full_collection_end(); 252 _heap->gc_epilogue(true); 253 254 _heap->verify_after_full_collection(); 255 256 _heap->print_heap_after_full_collection(); 257 } 258 259 void G1FullCollector::before_marking_update_attribute_table(G1HeapRegion* hr) { 260 if (hr->is_free()) { 261 _region_attr_table.set_free(hr->hrm_index()); 262 } else if (hr->is_humongous() || hr->has_pinned_objects()) { 263 // Humongous objects or pinned regions will never be moved in the "main" 264 // compaction phase, but non-pinned regions might afterwards in a special phase. 265 _region_attr_table.set_skip_compacting(hr->hrm_index()); 266 } else { 267 // Everything else should be compacted. 268 _region_attr_table.set_compacting(hr->hrm_index()); 269 } 270 } 271 272 class G1FullGCRefProcProxyTask : public RefProcProxyTask { 273 G1FullCollector& _collector; 274 275 public: 276 G1FullGCRefProcProxyTask(G1FullCollector &collector, uint max_workers) 277 : RefProcProxyTask("G1FullGCRefProcProxyTask", max_workers), 278 _collector(collector) {} 279 280 void work(uint worker_id) override { 281 assert(worker_id < _max_workers, "sanity"); 282 G1IsAliveClosure is_alive(&_collector); 283 uint index = (_tm == RefProcThreadModel::Single) ? 0 : worker_id; 284 G1FullKeepAliveClosure keep_alive(_collector.marker(index)); 285 BarrierEnqueueDiscoveredFieldClosure enqueue; 286 G1FollowStackClosure* complete_gc = _collector.marker(index)->stack_closure(); 287 _rp_task->rp_work(worker_id, &is_alive, &keep_alive, &enqueue, complete_gc); 288 } 289 }; 290 291 void G1FullCollector::phase1_mark_live_objects() { 292 // Recursively traverse all live objects and mark them. 293 GCTraceTime(Info, gc, phases) info("Phase 1: Mark live objects", scope()->timer()); 294 295 { 296 // Do the actual marking. 297 G1FullGCMarkTask marking_task(this); 298 run_task(&marking_task); 299 } 300 301 { 302 uint old_active_mt_degree = reference_processor()->num_queues(); 303 reference_processor()->set_active_mt_degree(workers()); 304 GCTraceTime(Debug, gc, phases) debug("Phase 1: Reference Processing", scope()->timer()); 305 // Process reference objects found during marking. 306 ReferenceProcessorPhaseTimes pt(scope()->timer(), reference_processor()->max_num_queues()); 307 G1FullGCRefProcProxyTask task(*this, reference_processor()->max_num_queues()); 308 const ReferenceProcessorStats& stats = reference_processor()->process_discovered_references(task, pt); 309 scope()->tracer()->report_gc_reference_stats(stats); 310 pt.print_all_references(); 311 assert(marker(0)->oop_stack()->is_empty(), "Should be no oops on the stack"); 312 313 reference_processor()->set_active_mt_degree(old_active_mt_degree); 314 } 315 316 { 317 GCTraceTime(Debug, gc, phases) debug("Phase 1: Flush Mark Stats Cache", scope()->timer()); 318 for (uint i = 0; i < workers(); i++) { 319 marker(i)->flush_mark_stats_cache(); 320 } 321 } 322 323 // Weak oops cleanup. 324 { 325 GCTraceTime(Debug, gc, phases) debug("Phase 1: Weak Processing", scope()->timer()); 326 WeakProcessor::weak_oops_do(_heap->workers(), &_is_alive, &do_nothing_cl, 1); 327 } 328 329 // Class unloading and cleanup. 330 if (ClassUnloading) { 331 _heap->unload_classes_and_code("Phase 1: Class Unloading and Cleanup", &_is_alive, scope()->timer()); 332 } 333 334 { 335 GCTraceTime(Debug, gc, phases) debug("Report Object Count", scope()->timer()); 336 scope()->tracer()->report_object_count_after_gc(&_is_alive, _heap->workers()); 337 } 338 #if TASKQUEUE_STATS 339 oop_queue_set()->print_and_reset_taskqueue_stats("Oop Queue"); 340 array_queue_set()->print_and_reset_taskqueue_stats("ObjArrayOop Queue"); 341 #endif 342 } 343 344 void G1FullCollector::phase2_prepare_compaction() { 345 GCTraceTime(Info, gc, phases) info("Phase 2: Prepare compaction", scope()->timer()); 346 347 phase2a_determine_worklists(); 348 349 if (!has_compaction_targets()) { 350 return; 351 } 352 353 bool has_free_compaction_targets = phase2b_forward_oops(); 354 355 // Try to avoid OOM immediately after Full GC in case there are no free regions 356 // left after determining the result locations (i.e. this phase). Prepare to 357 // maximally compact the tail regions of the compaction queues serially. 358 if (scope()->do_maximal_compaction() || !has_free_compaction_targets) { 359 phase2c_prepare_serial_compaction(); 360 361 if (scope()->do_maximal_compaction() && 362 has_humongous() && 363 serial_compaction_point()->has_regions()) { 364 phase2d_prepare_humongous_compaction(); 365 } 366 } 367 } 368 369 void G1FullCollector::phase2a_determine_worklists() { 370 GCTraceTime(Debug, gc, phases) debug("Phase 2: Determine work lists", scope()->timer()); 371 372 G1DetermineCompactionQueueClosure cl(this); 373 _heap->heap_region_iterate(&cl); 374 } 375 376 bool G1FullCollector::phase2b_forward_oops() { 377 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare parallel compaction", scope()->timer()); 378 379 G1FullGCPrepareTask task(this); 380 run_task(&task); 381 382 return task.has_free_compaction_targets(); 383 } 384 385 uint G1FullCollector::truncate_parallel_cps() { 386 uint lowest_current = UINT_MAX; 387 for (uint i = 0; i < workers(); i++) { 388 G1FullGCCompactionPoint* cp = compaction_point(i); 389 if (cp->has_regions()) { 390 lowest_current = MIN2(lowest_current, cp->current_region()->hrm_index()); 391 } 392 } 393 394 for (uint i = 0; i < workers(); i++) { 395 G1FullGCCompactionPoint* cp = compaction_point(i); 396 if (cp->has_regions()) { 397 cp->remove_at_or_above(lowest_current); 398 } 399 } 400 return lowest_current; 401 } 402 403 void G1FullCollector::phase2c_prepare_serial_compaction() { 404 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare serial compaction", scope()->timer()); 405 // At this point, we know that after parallel compaction there will be regions that 406 // are partially compacted into. Thus, the last compaction region of all 407 // compaction queues still have space in them. We try to re-compact these regions 408 // in serial to avoid a premature OOM when the mutator wants to allocate the first 409 // eden region after gc. 410 411 // For maximum compaction, we need to re-prepare all objects above the lowest 412 // region among the current regions for all thread compaction points. It may 413 // happen that due to the uneven distribution of objects to parallel threads, holes 414 // have been created as threads compact to different target regions between the 415 // lowest and the highest region in the tails of the compaction points. 416 417 uint start_serial = truncate_parallel_cps(); 418 assert(start_serial < _heap->max_reserved_regions(), "Called on empty parallel compaction queues"); 419 420 G1FullGCCompactionPoint* serial_cp = serial_compaction_point(); 421 assert(!serial_cp->is_initialized(), "sanity!"); 422 423 G1HeapRegion* start_hr = _heap->region_at(start_serial); 424 serial_cp->add(start_hr); 425 serial_cp->initialize(start_hr); 426 427 HeapWord* dense_prefix_top = compaction_top(start_hr); 428 G1SerialRePrepareClosure re_prepare(serial_cp, dense_prefix_top); 429 430 for (uint i = start_serial + 1; i < _heap->max_reserved_regions(); i++) { 431 if (is_compaction_target(i)) { 432 G1HeapRegion* current = _heap->region_at(i); 433 set_compaction_top(current, current->bottom()); 434 serial_cp->add(current); 435 current->apply_to_marked_objects(mark_bitmap(), &re_prepare); 436 } 437 } 438 serial_cp->update(); 439 } 440 441 void G1FullCollector::phase2d_prepare_humongous_compaction() { 442 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare humongous compaction", scope()->timer()); 443 G1FullGCCompactionPoint* serial_cp = serial_compaction_point(); 444 assert(serial_cp->has_regions(), "Sanity!" ); 445 446 uint last_serial_target = serial_cp->current_region()->hrm_index(); 447 uint region_index = last_serial_target + 1; 448 uint max_reserved_regions = _heap->max_reserved_regions(); 449 450 G1FullGCCompactionPoint* humongous_cp = humongous_compaction_point(); 451 452 while (region_index < max_reserved_regions) { 453 G1HeapRegion* hr = _heap->region_at_or_null(region_index); 454 455 if (hr == nullptr) { 456 region_index++; 457 continue; 458 } else if (hr->is_starts_humongous()) { 459 size_t obj_size = cast_to_oop(hr->bottom())->size(); 460 uint num_regions = (uint)G1CollectedHeap::humongous_obj_size_in_regions(obj_size); 461 // Even during last-ditch compaction we should not move pinned humongous objects. 462 if (!hr->has_pinned_objects()) { 463 humongous_cp->forward_humongous(hr); 464 } 465 region_index += num_regions; // Advance over all humongous regions. 466 continue; 467 } else if (is_compaction_target(region_index)) { 468 assert(!hr->has_pinned_objects(), "pinned regions should not be compaction targets"); 469 // Add the region to the humongous compaction point. 470 humongous_cp->add(hr); 471 } 472 region_index++; 473 } 474 } 475 476 void G1FullCollector::phase3_adjust_pointers() { 477 // Adjust the pointers to reflect the new locations 478 GCTraceTime(Info, gc, phases) info("Phase 3: Adjust pointers", scope()->timer()); 479 480 G1FullGCAdjustTask task(this); 481 run_task(&task); 482 } 483 484 void G1FullCollector::phase4_do_compaction() { 485 // Compact the heap using the compaction queues created in phase 2. 486 GCTraceTime(Info, gc, phases) info("Phase 4: Compact heap", scope()->timer()); 487 G1FullGCCompactTask task(this); 488 run_task(&task); 489 490 // Serial compact to avoid OOM when very few free regions. 491 if (serial_compaction_point()->has_regions()) { 492 task.serial_compaction(); 493 } 494 495 if (!_humongous_compaction_regions.is_empty()) { 496 assert(scope()->do_maximal_compaction(), "Only compact humongous during maximal compaction"); 497 task.humongous_compaction(); 498 } 499 } 500 501 void G1FullCollector::phase5_reset_metadata() { 502 // Clear region metadata that is invalid after GC for all regions. 503 GCTraceTime(Info, gc, phases) info("Phase 5: Reset Metadata", scope()->timer()); 504 G1FullGCResetMetadataTask task(this); 505 run_task(&task); 506 } 507 508 void G1FullCollector::restore_marks() { 509 _preserved_marks_set.restore(_heap->workers()); 510 _preserved_marks_set.reclaim(); 511 } 512 513 void G1FullCollector::run_task(WorkerTask* task) { 514 _heap->workers()->run_task(task, _num_workers); 515 } 516 517 void G1FullCollector::verify_after_marking() { 518 if (!VerifyDuringGC || !_heap->verifier()->should_verify(G1HeapVerifier::G1VerifyFull)) { 519 // Only do verification if VerifyDuringGC and G1VerifyFull is set. 520 return; 521 } 522 523 #if COMPILER2_OR_JVMCI 524 DerivedPointerTableDeactivate dpt_deact; 525 #endif 526 _heap->prepare_for_verify(); 527 // Note: we can verify only the heap here. When an object is 528 // marked, the previous value of the mark word (including 529 // identity hash values, ages, etc) is preserved, and the mark 530 // word is set to markWord::marked_value - effectively removing 531 // any hash values from the mark word. These hash values are 532 // used when verifying the dictionaries and so removing them 533 // from the mark word can make verification of the dictionaries 534 // fail. At the end of the GC, the original mark word values 535 // (including hash values) are restored to the appropriate 536 // objects. 537 GCTraceTime(Info, gc, verify) tm("Verifying During GC (full)"); 538 _heap->verify(VerifyOption::G1UseFullMarking); 539 }