1 /*
2 * Copyright (c) 2017, 2023, 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 "precompiled.hpp"
26 #include "classfile/classLoaderDataGraph.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "code/codeCache.hpp"
29 #include "compiler/oopMap.hpp"
30 #include "gc/g1/g1CollectedHeap.hpp"
31 #include "gc/g1/g1FullCollector.inline.hpp"
32 #include "gc/g1/g1FullGCAdjustTask.hpp"
33 #include "gc/g1/g1FullGCCompactTask.hpp"
34 #include "gc/g1/g1FullGCMarker.inline.hpp"
35 #include "gc/g1/g1FullGCMarkTask.hpp"
36 #include "gc/g1/g1FullGCPrepareTask.inline.hpp"
37 #include "gc/g1/g1FullGCResetMetadataTask.hpp"
38 #include "gc/g1/g1FullGCScope.hpp"
39 #include "gc/g1/g1OopClosures.hpp"
40 #include "gc/g1/g1Policy.hpp"
41 #include "gc/g1/g1RegionMarkStatsCache.inline.hpp"
42 #include "gc/shared/gcTraceTime.inline.hpp"
43 #include "gc/shared/preservedMarks.inline.hpp"
44 #include "gc/shared/referenceProcessor.hpp"
45 #include "gc/shared/slidingForwarding.hpp"
46 #include "gc/shared/verifyOption.hpp"
47 #include "gc/shared/weakProcessor.inline.hpp"
48 #include "gc/shared/workerPolicy.hpp"
49 #include "logging/log.hpp"
50 #include "runtime/handles.inline.hpp"
51 #include "utilities/debug.hpp"
52
53 static void clear_and_activate_derived_pointers() {
54 #if COMPILER2_OR_JVMCI
55 DerivedPointerTable::clear();
56 #endif
57 }
58
59 static void deactivate_derived_pointers() {
60 #if COMPILER2_OR_JVMCI
61 DerivedPointerTable::set_active(false);
62 #endif
63 }
64
65 static void update_derived_pointers() {
66 #if COMPILER2_OR_JVMCI
67 DerivedPointerTable::update_pointers();
68 #endif
69 }
70
71 G1CMBitMap* G1FullCollector::mark_bitmap() {
72 return _heap->concurrent_mark()->mark_bitmap();
73 }
74
75 ReferenceProcessor* G1FullCollector::reference_processor() {
76 return _heap->ref_processor_stw();
77 }
78
79 uint G1FullCollector::calc_active_workers() {
80 G1CollectedHeap* heap = G1CollectedHeap::heap();
81 uint max_worker_count = heap->workers()->max_workers();
82 // Only calculate number of workers if UseDynamicNumberOfGCThreads
83 // is enabled, otherwise use max.
84 if (!UseDynamicNumberOfGCThreads) {
85 return max_worker_count;
86 }
87
88 // Consider G1HeapWastePercent to decide max number of workers. Each worker
89 // will in average cause half a region waste.
90 uint max_wasted_regions_allowed = ((heap->num_regions() * G1HeapWastePercent) / 100);
91 uint waste_worker_count = MAX2((max_wasted_regions_allowed * 2) , 1u);
92 uint heap_waste_worker_limit = MIN2(waste_worker_count, max_worker_count);
93
94 // Also consider HeapSizePerGCThread by calling WorkerPolicy to calculate
95 // the number of workers.
96 uint current_active_workers = heap->workers()->active_workers();
97 uint active_worker_limit = WorkerPolicy::calc_active_workers(max_worker_count, current_active_workers, 0);
98
99 // Finally consider the amount of used regions.
100 uint used_worker_limit = heap->num_used_regions();
101 assert(used_worker_limit > 0, "Should never have zero used regions.");
102
103 // Update active workers to the lower of the limits.
104 uint worker_count = MIN3(heap_waste_worker_limit, active_worker_limit, used_worker_limit);
105 log_debug(gc, task)("Requesting %u active workers for full compaction (waste limited workers: %u, "
106 "adaptive workers: %u, used limited workers: %u)",
107 worker_count, heap_waste_worker_limit, active_worker_limit, used_worker_limit);
108 worker_count = heap->workers()->set_active_workers(worker_count);
109 log_info(gc, task)("Using %u workers of %u for full compaction", worker_count, max_worker_count);
110
111 return worker_count;
112 }
113
114 G1FullCollector::G1FullCollector(G1CollectedHeap* heap,
115 bool clear_soft_refs,
116 bool do_maximal_compaction,
117 G1FullGCTracer* tracer) :
118 _heap(heap),
119 _scope(heap->monitoring_support(), clear_soft_refs, do_maximal_compaction, tracer),
120 _num_workers(calc_active_workers()),
121 _has_compaction_targets(false),
122 _has_humongous(false),
123 _oop_queue_set(_num_workers),
124 _array_queue_set(_num_workers),
125 _preserved_marks_set(true),
126 _serial_compaction_point(this),
127 _humongous_compaction_point(this),
128 _is_alive(this, heap->concurrent_mark()->mark_bitmap()),
129 _is_alive_mutator(heap->ref_processor_stw(), &_is_alive),
130 _humongous_compaction_regions(8),
131 _always_subject_to_discovery(),
132 _is_subject_mutator(heap->ref_processor_stw(), &_always_subject_to_discovery),
133 _region_attr_table() {
134 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
135
136 _preserved_marks_set.init(_num_workers);
137 _markers = NEW_C_HEAP_ARRAY(G1FullGCMarker*, _num_workers, mtGC);
138 _compaction_points = NEW_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _num_workers, mtGC);
139
140 _live_stats = NEW_C_HEAP_ARRAY(G1RegionMarkStats, _heap->max_regions(), mtGC);
141 _compaction_tops = NEW_C_HEAP_ARRAY(HeapWord*, _heap->max_regions(), mtGC);
142 for (uint j = 0; j < heap->max_regions(); j++) {
143 _live_stats[j].clear();
144 _compaction_tops[j] = nullptr;
145 }
146
147 for (uint i = 0; i < _num_workers; i++) {
148 _markers[i] = new G1FullGCMarker(this, i, _preserved_marks_set.get(i), _live_stats);
149 _compaction_points[i] = new G1FullGCCompactionPoint(this);
150 _oop_queue_set.register_queue(i, marker(i)->oop_stack());
151 _array_queue_set.register_queue(i, marker(i)->objarray_stack());
152 }
153 _region_attr_table.initialize(heap->reserved(), HeapRegion::GrainBytes);
154 }
155
156 G1FullCollector::~G1FullCollector() {
157 for (uint i = 0; i < _num_workers; i++) {
158 delete _markers[i];
159 delete _compaction_points[i];
160 }
161
162 FREE_C_HEAP_ARRAY(G1FullGCMarker*, _markers);
163 FREE_C_HEAP_ARRAY(G1FullGCCompactionPoint*, _compaction_points);
164 FREE_C_HEAP_ARRAY(HeapWord*, _compaction_tops);
165 FREE_C_HEAP_ARRAY(G1RegionMarkStats, _live_stats);
166 }
167
168 class PrepareRegionsClosure : public HeapRegionClosure {
169 G1FullCollector* _collector;
170
171 public:
172 PrepareRegionsClosure(G1FullCollector* collector) : _collector(collector) { }
173
174 bool do_heap_region(HeapRegion* hr) {
175 G1CollectedHeap::heap()->prepare_region_for_full_compaction(hr);
176 _collector->before_marking_update_attribute_table(hr);
177 return false;
178 }
179 };
180
181 void G1FullCollector::prepare_collection() {
182 _heap->policy()->record_full_collection_start();
183
184 // Verification needs the bitmap, so we should clear the bitmap only later.
185 bool in_concurrent_cycle = _heap->abort_concurrent_cycle();
186 _heap->verify_before_full_collection();
187 if (in_concurrent_cycle) {
188 GCTraceTime(Debug, gc) debug("Clear Bitmap");
189 _heap->concurrent_mark()->clear_bitmap(_heap->workers());
190 }
191
192 _heap->gc_prologue(true);
193 _heap->retire_tlabs();
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 SlidingForwarding::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 SlidingForwarding::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->policy()->record_full_collection_end();
254 _heap->gc_epilogue(true);
255
256 _heap->verify_after_full_collection();
257
258 _heap->print_heap_after_full_collection();
259 }
260
261 void G1FullCollector::before_marking_update_attribute_table(HeapRegion* hr) {
262 if (hr->is_free()) {
263 _region_attr_table.set_free(hr->hrm_index());
264 } else if (hr->is_humongous()) {
265 // Humongous objects will never be moved in the "main" compaction phase, but
266 // afterwards in a special phase if needed.
267 _region_attr_table.set_skip_compacting(hr->hrm_index());
268 } else {
269 // Everything else should be compacted.
270 _region_attr_table.set_compacting(hr->hrm_index());
271 }
272 }
273
274 class G1FullGCRefProcProxyTask : public RefProcProxyTask {
275 G1FullCollector& _collector;
276
277 public:
278 G1FullGCRefProcProxyTask(G1FullCollector &collector, uint max_workers)
279 : RefProcProxyTask("G1FullGCRefProcProxyTask", max_workers),
280 _collector(collector) {}
281
282 void work(uint worker_id) override {
283 assert(worker_id < _max_workers, "sanity");
284 G1IsAliveClosure is_alive(&_collector);
285 uint index = (_tm == RefProcThreadModel::Single) ? 0 : worker_id;
286 G1FullKeepAliveClosure keep_alive(_collector.marker(index));
287 BarrierEnqueueDiscoveredFieldClosure enqueue;
288 G1FollowStackClosure* complete_gc = _collector.marker(index)->stack_closure();
289 _rp_task->rp_work(worker_id, &is_alive, &keep_alive, &enqueue, complete_gc);
290 }
291 };
292
293 void G1FullCollector::phase1_mark_live_objects() {
294 // Recursively traverse all live objects and mark them.
295 GCTraceTime(Info, gc, phases) info("Phase 1: Mark live objects", scope()->timer());
296
297 {
298 // Do the actual marking.
299 G1FullGCMarkTask marking_task(this);
300 run_task(&marking_task);
301 }
302
303 {
304 uint old_active_mt_degree = reference_processor()->num_queues();
305 reference_processor()->set_active_mt_degree(workers());
306 GCTraceTime(Debug, gc, phases) debug("Phase 1: Reference Processing", scope()->timer());
307 // Process reference objects found during marking.
308 ReferenceProcessorPhaseTimes pt(scope()->timer(), reference_processor()->max_num_queues());
309 G1FullGCRefProcProxyTask task(*this, reference_processor()->max_num_queues());
310 const ReferenceProcessorStats& stats = reference_processor()->process_discovered_references(task, pt);
311 scope()->tracer()->report_gc_reference_stats(stats);
312 pt.print_all_references();
313 assert(marker(0)->oop_stack()->is_empty(), "Should be no oops on the stack");
314
315 reference_processor()->set_active_mt_degree(old_active_mt_degree);
316 }
317
318 // Weak oops cleanup.
319 {
320 GCTraceTime(Debug, gc, phases) debug("Phase 1: Weak Processing", scope()->timer());
321 WeakProcessor::weak_oops_do(_heap->workers(), &_is_alive, &do_nothing_cl, 1);
322 }
323
324 // Class unloading and cleanup.
325 if (ClassUnloading) {
326 GCTraceTime(Debug, gc, phases) debug("Phase 1: Class Unloading and Cleanup", scope()->timer());
327 {
328 CodeCache::UnlinkingScope unloading_scope(&_is_alive);
329 // Unload classes and purge the SystemDictionary.
330 bool unloading_occurred = SystemDictionary::do_unloading(scope()->timer());
331 _heap->complete_cleaning(unloading_occurred);
332 }
333 CodeCache::flush_unlinked_nmethods();
334 }
335
336 {
337 GCTraceTime(Debug, gc, phases) debug("Report Object Count", scope()->timer());
338 scope()->tracer()->report_object_count_after_gc(&_is_alive, _heap->workers());
339 }
340 #if TASKQUEUE_STATS
341 oop_queue_set()->print_and_reset_taskqueue_stats("Oop Queue");
342 array_queue_set()->print_and_reset_taskqueue_stats("ObjArrayOop Queue");
343 #endif
344 }
345
346 void G1FullCollector::phase2_prepare_compaction() {
347 GCTraceTime(Info, gc, phases) info("Phase 2: Prepare compaction", scope()->timer());
348
349 phase2a_determine_worklists();
350
351 if (!has_compaction_targets()) {
352 return;
353 }
354
355 bool has_free_compaction_targets = phase2b_forward_oops();
356
357 // Try to avoid OOM immediately after Full GC in case there are no free regions
358 // left after determining the result locations (i.e. this phase). Prepare to
359 // maximally compact the tail regions of the compaction queues serially.
360 if (scope()->do_maximal_compaction() || !has_free_compaction_targets) {
361 phase2c_prepare_serial_compaction();
362
363 if (scope()->do_maximal_compaction() &&
364 has_humongous() &&
365 serial_compaction_point()->has_regions()) {
366 phase2d_prepare_humongous_compaction();
367 }
368 }
369 }
370
371 void G1FullCollector::phase2a_determine_worklists() {
372 GCTraceTime(Debug, gc, phases) debug("Phase 2: Determine work lists", scope()->timer());
373
374 G1DetermineCompactionQueueClosure cl(this);
375 _heap->heap_region_iterate(&cl);
376 }
377
378 bool G1FullCollector::phase2b_forward_oops() {
379 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare parallel compaction", scope()->timer());
380
381 G1FullGCPrepareTask task(this);
382 run_task(&task);
383
384 return task.has_free_compaction_targets();
385 }
386
387 uint G1FullCollector::truncate_parallel_cps() {
388 uint lowest_current = UINT_MAX;
389 for (uint i = 0; i < workers(); i++) {
390 G1FullGCCompactionPoint* cp = compaction_point(i);
391 if (cp->has_regions()) {
392 lowest_current = MIN2(lowest_current, cp->current_region()->hrm_index());
393 }
394 }
395
396 for (uint i = 0; i < workers(); i++) {
397 G1FullGCCompactionPoint* cp = compaction_point(i);
398 if (cp->has_regions()) {
399 cp->remove_at_or_above(lowest_current);
400 }
401 }
402 return lowest_current;
403 }
404
405 template <bool ALT_FWD>
406 void G1FullCollector::phase2c_prepare_serial_compaction_impl() {
407 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare serial compaction", scope()->timer());
408 // At this point, we know that after parallel compaction there will be regions that
409 // are partially compacted into. Thus, the last compaction region of all
410 // compaction queues still have space in them. We try to re-compact these regions
411 // in serial to avoid a premature OOM when the mutator wants to allocate the first
412 // eden region after gc.
413
414 // For maximum compaction, we need to re-prepare all objects above the lowest
415 // region among the current regions for all thread compaction points. It may
416 // happen that due to the uneven distribution of objects to parallel threads, holes
417 // have been created as threads compact to different target regions between the
418 // lowest and the highest region in the tails of the compaction points.
419
420 uint start_serial = truncate_parallel_cps();
421 assert(start_serial < _heap->max_reserved_regions(), "Called on empty parallel compaction queues");
422
423 G1FullGCCompactionPoint* serial_cp = serial_compaction_point();
424 assert(!serial_cp->is_initialized(), "sanity!");
425
426 HeapRegion* start_hr = _heap->region_at(start_serial);
427 serial_cp->add(start_hr);
428 serial_cp->initialize(start_hr);
429
430 HeapWord* dense_prefix_top = compaction_top(start_hr);
431 G1SerialRePrepareClosure<ALT_FWD> re_prepare(serial_cp, dense_prefix_top);
432
433 for (uint i = start_serial + 1; i < _heap->max_reserved_regions(); i++) {
434 if (is_compaction_target(i)) {
435 HeapRegion* current = _heap->region_at(i);
436 set_compaction_top(current, current->bottom());
437 serial_cp->add(current);
438 current->apply_to_marked_objects(mark_bitmap(), &re_prepare);
439 }
440 }
441 serial_cp->update();
442 }
443
444 void G1FullCollector::phase2c_prepare_serial_compaction() {
445 if (UseAltGCForwarding) {
446 phase2c_prepare_serial_compaction_impl<true>();
447 } else {
448 phase2c_prepare_serial_compaction_impl<false>();
449 }
450 }
451
452 template <bool ALT_FWD>
453 void G1FullCollector::phase2d_prepare_humongous_compaction_impl() {
454 GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare humongous compaction", scope()->timer());
455 G1FullGCCompactionPoint* serial_cp = serial_compaction_point();
456 assert(serial_cp->has_regions(), "Sanity!" );
457
458 uint last_serial_target = serial_cp->current_region()->hrm_index();
459 uint region_index = last_serial_target + 1;
460 uint max_reserved_regions = _heap->max_reserved_regions();
461
462 G1FullGCCompactionPoint* humongous_cp = humongous_compaction_point();
463
464 while (region_index < max_reserved_regions) {
465 HeapRegion* hr = _heap->region_at_or_null(region_index);
466
467 if (hr == nullptr) {
468 region_index++;
469 continue;
470 } else if (hr->is_starts_humongous()) {
471 uint num_regions = humongous_cp->forward_humongous<ALT_FWD>(hr);
472 region_index += num_regions; // Skip over the continues humongous regions.
473 continue;
474 } else if (is_compaction_target(region_index)) {
475 // Add the region to the humongous compaction point.
476 humongous_cp->add(hr);
477 }
478 region_index++;
479 }
480 }
481
482 void G1FullCollector::phase2d_prepare_humongous_compaction() {
483 if (UseAltGCForwarding) {
484 phase2d_prepare_humongous_compaction_impl<true>();
485 } else {
486 phase2d_prepare_humongous_compaction_impl<false>();
487 }
488 }
489
490 void G1FullCollector::phase3_adjust_pointers() {
491 // Adjust the pointers to reflect the new locations
492 GCTraceTime(Info, gc, phases) info("Phase 3: Adjust pointers", scope()->timer());
493
494 G1FullGCAdjustTask task(this);
495 run_task(&task);
496 }
497
498 void G1FullCollector::phase4_do_compaction() {
499 // Compact the heap using the compaction queues created in phase 2.
500 GCTraceTime(Info, gc, phases) info("Phase 4: Compact heap", scope()->timer());
501 G1FullGCCompactTask task(this);
502 run_task(&task);
503
504 // Serial compact to avoid OOM when very few free regions.
505 if (serial_compaction_point()->has_regions()) {
506 task.serial_compaction();
507 }
508
509 if (!_humongous_compaction_regions.is_empty()) {
510 assert(scope()->do_maximal_compaction(), "Only compact humongous during maximal compaction");
511 task.humongous_compaction();
512 }
513 }
514
515 void G1FullCollector::phase5_reset_metadata() {
516 // Clear region metadata that is invalid after GC for all regions.
517 GCTraceTime(Info, gc, phases) info("Phase 5: Reset Metadata", scope()->timer());
518 G1FullGCResetMetadataTask task(this);
519 run_task(&task);
520 }
521
522 void G1FullCollector::restore_marks() {
523 _preserved_marks_set.restore(_heap->workers());
524 _preserved_marks_set.reclaim();
525 }
526
527 void G1FullCollector::run_task(WorkerTask* task) {
528 _heap->workers()->run_task(task, _num_workers);
529 }
530
531 void G1FullCollector::verify_after_marking() {
532 if (!VerifyDuringGC || !_heap->verifier()->should_verify(G1HeapVerifier::G1VerifyFull)) {
533 // Only do verification if VerifyDuringGC and G1VerifyFull is set.
534 return;
535 }
536
537 #if COMPILER2_OR_JVMCI
538 DerivedPointerTableDeactivate dpt_deact;
539 #endif
540 _heap->prepare_for_verify();
541 // Note: we can verify only the heap here. When an object is
542 // marked, the previous value of the mark word (including
543 // identity hash values, ages, etc) is preserved, and the mark
544 // word is set to markWord::marked_value - effectively removing
545 // any hash values from the mark word. These hash values are
546 // used when verifying the dictionaries and so removing them
547 // from the mark word can make verification of the dictionaries
548 // fail. At the end of the GC, the original mark word values
549 // (including hash values) are restored to the appropriate
550 // objects.
551 GCTraceTime(Info, gc, verify) tm("Verifying During GC (full)");
552 _heap->verify(VerifyOption::G1UseFullMarking);
553 }