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/classUnloadingContext.hpp"
39 #include "gc/shared/gcTraceTime.inline.hpp"
40 #include "gc/shared/preservedMarks.inline.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 FullGCForwarding::begin();
215
216 phase2_prepare_compaction();
217
218 if (has_compaction_targets()) {
219 phase3_adjust_pointers();
220
221 phase4_do_compaction();
222 } else {
223 // All regions have a high live ratio thus will not be compacted.
224 // The live ratio is only considered if do_maximal_compaction is false.
225 log_info(gc, phases) ("No Regions selected for compaction. Skipping Phase 3: Adjust pointers and Phase 4: Compact heap");
226 }
227
228 FullGCForwarding::end();
229
230 phase5_reset_metadata();
231
232 G1CollectedHeap::finish_codecache_marking_cycle();
233 }
234
235 void G1FullCollector::complete_collection() {
236 // Restore all marks.
237 restore_marks();
238
239 // When the pointers have been adjusted and moved, we can
240 // update the derived pointer table.
241 update_derived_pointers();
242
243 // Need completely cleared claim bits for the next concurrent marking or full gc.
244 ClassLoaderDataGraph::clear_claimed_marks();
245
246 // Prepare the bitmap for the next (potentially concurrent) marking.
247 _heap->concurrent_mark()->clear_bitmap(_heap->workers());
248
249 _heap->prepare_for_mutator_after_full_collection();
250
251 _heap->resize_all_tlabs();
252
253 _heap->young_regions_cset_group()->clear();
254
255 _heap->policy()->record_full_collection_end();
256 _heap->gc_epilogue(true);
257
258 _heap->verify_after_full_collection();
259
260 _heap->print_heap_after_full_collection();
261 }
262
263 void G1FullCollector::before_marking_update_attribute_table(G1HeapRegion* hr) {
264 if (hr->is_free()) {
265 _region_attr_table.set_free(hr->hrm_index());
266 } else if (hr->is_humongous() || hr->has_pinned_objects()) {
267 // Humongous objects or pinned regions will never be moved in the "main"
268 // compaction phase, but non-pinned regions might afterwards in a special phase.
269 _region_attr_table.set_skip_compacting(hr->hrm_index());
270 } else {
271 // Everything else should be compacted.
272 _region_attr_table.set_compacting(hr->hrm_index());
273 }
274 }
275
276 class G1FullGCRefProcProxyTask : public RefProcProxyTask {
277 G1FullCollector& _collector;
278
279 public:
280 G1FullGCRefProcProxyTask(G1FullCollector &collector, uint max_workers)
281 : RefProcProxyTask("G1FullGCRefProcProxyTask", max_workers),
282 _collector(collector) {}
283
284 void work(uint worker_id) override {
285 assert(worker_id < _max_workers, "sanity");
286 G1IsAliveClosure is_alive(&_collector);
287 uint index = (_tm == RefProcThreadModel::Single) ? 0 : worker_id;
288 G1FullKeepAliveClosure keep_alive(_collector.marker(index));
289 BarrierEnqueueDiscoveredFieldClosure enqueue;
290 G1FollowStackClosure* complete_gc = _collector.marker(index)->stack_closure();
291 _rp_task->rp_work(worker_id, &is_alive, &keep_alive, &enqueue, complete_gc);
292 }
293 };
294
295 void G1FullCollector::phase1_mark_live_objects() {
296 // Recursively traverse all live objects and mark them.
297 GCTraceTime(Info, gc, phases) info("Phase 1: Mark live objects", scope()->timer());
298
299 {
300 // Do the actual marking.
301 G1FullGCMarkTask marking_task(this);
302 run_task(&marking_task);
303 }
304
305 {
306 uint old_active_mt_degree = reference_processor()->num_queues();
307 reference_processor()->set_active_mt_degree(workers());
308 GCTraceTime(Debug, gc, phases) debug("Phase 1: Reference Processing", scope()->timer());
309 // Process reference objects found during marking.
310 ReferenceProcessorPhaseTimes pt(scope()->timer(), reference_processor()->max_num_queues());
311 G1FullGCRefProcProxyTask task(*this, reference_processor()->max_num_queues());
312 const ReferenceProcessorStats& stats = reference_processor()->process_discovered_references(task, pt);
313 scope()->tracer()->report_gc_reference_stats(stats);
314 pt.print_all_references();
315 assert(marker(0)->oop_stack()->is_empty(), "Should be no oops on the stack");
316
317 reference_processor()->set_active_mt_degree(old_active_mt_degree);
318 }
319
320 {
321 GCTraceTime(Debug, gc, phases) debug("Phase 1: Flush Mark Stats Cache", scope()->timer());
322 for (uint i = 0; i < workers(); i++) {
323 marker(i)->flush_mark_stats_cache();
324 }
325 }
326
327 // Weak oops cleanup.
328 {
329 GCTraceTime(Debug, gc, phases) debug("Phase 1: Weak Processing", scope()->timer());
330 WeakProcessor::weak_oops_do(_heap->workers(), &_is_alive, &do_nothing_cl, 1);
331 }
332
333 // Class unloading and cleanup.
334 if (ClassUnloading) {
335 _heap->unload_classes_and_code("Phase 1: Class Unloading and Cleanup", &_is_alive, scope()->timer());
336 }
337
338 {
339 GCTraceTime(Debug, gc, phases) debug("Report Object Count", scope()->timer());
340 scope()->tracer()->report_object_count_after_gc(&_is_alive, _heap->workers());
341 }
342 #if TASKQUEUE_STATS
343 oop_queue_set()->print_and_reset_taskqueue_stats("Oop Queue");
344 array_queue_set()->print_and_reset_taskqueue_stats("ObjArrayOop Queue");
345 #endif
346 }
347
348 void G1FullCollector::phase2_prepare_compaction() {
349 GCTraceTime(Info, gc, phases) info("Phase 2: Prepare compaction", scope()->timer());
350
351 phase2a_determine_worklists();
352
353 if (!has_compaction_targets()) {
354 return;
355 }
356
357 bool has_free_compaction_targets = phase2b_forward_oops();
358
359 // Try to avoid OOM immediately after Full GC in case there are no free regions
360 // left after determining the result locations (i.e. this phase). Prepare to
361 // maximally compact the tail regions of the compaction queues serially.
362 if (scope()->do_maximal_compaction() || !has_free_compaction_targets) {
363 phase2c_prepare_serial_compaction();
364
365 if (scope()->do_maximal_compaction() &&
366 has_humongous() &&
367 serial_compaction_point()->has_regions()) {
368 phase2d_prepare_humongous_compaction();
369 }
370 }
371 }
372
373 void G1FullCollector::phase2a_determine_worklists() {
374 GCTraceTime(Debug, gc, phases) debug("Phase 2: Determine work lists", scope()->timer());
375
376 G1DetermineCompactionQueueClosure cl(this);
377 _heap->heap_region_iterate(&cl);
378 }
379
380 bool G1FullCollector::phase2b_forward_oops() {
381 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare parallel compaction", scope()->timer());
382
383 G1FullGCPrepareTask task(this);
384 run_task(&task);
385
386 return task.has_free_compaction_targets();
387 }
388
389 uint G1FullCollector::truncate_parallel_cps() {
390 uint lowest_current = UINT_MAX;
391 for (uint i = 0; i < workers(); i++) {
392 G1FullGCCompactionPoint* cp = compaction_point(i);
393 if (cp->has_regions()) {
394 lowest_current = MIN2(lowest_current, cp->current_region()->hrm_index());
395 }
396 }
397
398 for (uint i = 0; i < workers(); i++) {
399 G1FullGCCompactionPoint* cp = compaction_point(i);
400 if (cp->has_regions()) {
401 cp->remove_at_or_above(lowest_current);
402 }
403 }
404 return lowest_current;
405 }
406
407 void G1FullCollector::phase2c_prepare_serial_compaction() {
408 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare serial compaction", scope()->timer());
409 // At this point, we know that after parallel compaction there will be regions that
410 // are partially compacted into. Thus, the last compaction region of all
411 // compaction queues still have space in them. We try to re-compact these regions
412 // in serial to avoid a premature OOM when the mutator wants to allocate the first
413 // eden region after gc.
414
415 // For maximum compaction, we need to re-prepare all objects above the lowest
416 // region among the current regions for all thread compaction points. It may
417 // happen that due to the uneven distribution of objects to parallel threads, holes
418 // have been created as threads compact to different target regions between the
419 // lowest and the highest region in the tails of the compaction points.
420
421 uint start_serial = truncate_parallel_cps();
422 assert(start_serial < _heap->max_reserved_regions(), "Called on empty parallel compaction queues");
423
424 G1FullGCCompactionPoint* serial_cp = serial_compaction_point();
425 assert(!serial_cp->is_initialized(), "sanity!");
426
427 G1HeapRegion* start_hr = _heap->region_at(start_serial);
428 serial_cp->add(start_hr);
429 serial_cp->initialize(start_hr);
430
431 HeapWord* dense_prefix_top = compaction_top(start_hr);
432 G1SerialRePrepareClosure re_prepare(serial_cp, dense_prefix_top);
433
434 for (uint i = start_serial + 1; i < _heap->max_reserved_regions(); i++) {
435 if (is_compaction_target(i)) {
436 G1HeapRegion* current = _heap->region_at(i);
437 set_compaction_top(current, current->bottom());
438 serial_cp->add(current);
439 current->apply_to_marked_objects(mark_bitmap(), &re_prepare);
440 }
441 }
442 serial_cp->update();
443 }
444
445 void G1FullCollector::phase2d_prepare_humongous_compaction() {
446 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare humongous compaction", scope()->timer());
447 G1FullGCCompactionPoint* serial_cp = serial_compaction_point();
448 assert(serial_cp->has_regions(), "Sanity!" );
449
450 uint last_serial_target = serial_cp->current_region()->hrm_index();
451 uint region_index = last_serial_target + 1;
452 uint max_reserved_regions = _heap->max_reserved_regions();
453
454 G1FullGCCompactionPoint* humongous_cp = humongous_compaction_point();
455
456 while (region_index < max_reserved_regions) {
457 G1HeapRegion* hr = _heap->region_at_or_null(region_index);
458
459 if (hr == nullptr) {
460 region_index++;
461 continue;
462 } else if (hr->is_starts_humongous()) {
463 size_t obj_size = cast_to_oop(hr->bottom())->size();
464 uint num_regions = (uint)G1CollectedHeap::humongous_obj_size_in_regions(obj_size);
465 // Even during last-ditch compaction we should not move pinned humongous objects.
466 if (!hr->has_pinned_objects()) {
467 humongous_cp->forward_humongous(hr);
468 }
469 region_index += num_regions; // Advance over all humongous regions.
470 continue;
471 } else if (is_compaction_target(region_index)) {
472 assert(!hr->has_pinned_objects(), "pinned regions should not be compaction targets");
473 // Add the region to the humongous compaction point.
474 humongous_cp->add(hr);
475 }
476 region_index++;
477 }
478 }
479
480 void G1FullCollector::phase3_adjust_pointers() {
481 // Adjust the pointers to reflect the new locations
482 GCTraceTime(Info, gc, phases) info("Phase 3: Adjust pointers", scope()->timer());
483
484 G1FullGCAdjustTask task(this);
485 run_task(&task);
486 }
487
488 void G1FullCollector::phase4_do_compaction() {
489 // Compact the heap using the compaction queues created in phase 2.
490 GCTraceTime(Info, gc, phases) info("Phase 4: Compact heap", scope()->timer());
491 G1FullGCCompactTask task(this);
492 run_task(&task);
493
494 // Serial compact to avoid OOM when very few free regions.
495 if (serial_compaction_point()->has_regions()) {
496 task.serial_compaction();
497 }
498
499 if (!_humongous_compaction_regions.is_empty()) {
500 assert(scope()->do_maximal_compaction(), "Only compact humongous during maximal compaction");
501 task.humongous_compaction();
502 }
503 }
504
505 void G1FullCollector::phase5_reset_metadata() {
506 // Clear region metadata that is invalid after GC for all regions.
507 GCTraceTime(Info, gc, phases) info("Phase 5: Reset Metadata", scope()->timer());
508 G1FullGCResetMetadataTask task(this);
509 run_task(&task);
510 }
511
512 void G1FullCollector::restore_marks() {
513 _preserved_marks_set.restore(_heap->workers());
514 _preserved_marks_set.reclaim();
515 }
516
517 void G1FullCollector::run_task(WorkerTask* task) {
518 _heap->workers()->run_task(task, _num_workers);
519 }
520
521 void G1FullCollector::verify_after_marking() {
522 if (!VerifyDuringGC || !_heap->verifier()->should_verify(G1HeapVerifier::G1VerifyFull)) {
523 // Only do verification if VerifyDuringGC and G1VerifyFull is set.
524 return;
525 }
526
527 #if COMPILER2_OR_JVMCI
528 DerivedPointerTableDeactivate dpt_deact;
529 #endif
530 _heap->prepare_for_verify();
531 // Note: we can verify only the heap here. When an object is
532 // marked, the previous value of the mark word (including
533 // identity hash values, ages, etc) is preserved, and the mark
534 // word is set to markWord::marked_value - effectively removing
535 // any hash values from the mark word. These hash values are
536 // used when verifying the dictionaries and so removing them
537 // from the mark word can make verification of the dictionaries
538 // fail. At the end of the GC, the original mark word values
539 // (including hash values) are restored to the appropriate
540 // objects.
541 GCTraceTime(Info, gc, verify) tm("Verifying During GC (full)");
542 _heap->verify(VerifyOption::G1UseFullMarking);
543 }