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