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