1 /*
2 * Copyright (c) 2014, 2021, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
4 * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
5 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
6 *
7 * This code is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License version 2 only, as
9 * published by the Free Software Foundation.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 *
25 */
26
27
28 #include "compiler/oopMap.hpp"
29 #include "gc/shared/continuationGCSupport.hpp"
30 #include "gc/shared/fullGCForwarding.inline.hpp"
31 #include "gc/shared/gcTraceTime.inline.hpp"
32 #include "gc/shared/preservedMarks.inline.hpp"
33 #include "gc/shared/tlab_globals.hpp"
34 #include "gc/shared/workerThread.hpp"
35 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
36 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
37 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
38 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
39 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
40 #include "gc/shenandoah/shenandoahFreeSet.hpp"
41 #include "gc/shenandoah/shenandoahFullGC.hpp"
42 #include "gc/shenandoah/shenandoahGenerationalFullGC.hpp"
43 #include "gc/shenandoah/shenandoahGlobalGeneration.hpp"
44 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
45 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
46 #include "gc/shenandoah/shenandoahHeapRegionClosures.hpp"
47 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
48 #include "gc/shenandoah/shenandoahMark.inline.hpp"
49 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
50 #include "gc/shenandoah/shenandoahMetrics.hpp"
51 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
52 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
53 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
54 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
55 #include "gc/shenandoah/shenandoahSTWMark.hpp"
56 #include "gc/shenandoah/shenandoahUtils.hpp"
57 #include "gc/shenandoah/shenandoahVerifier.hpp"
58 #include "gc/shenandoah/shenandoahVMOperations.hpp"
59 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
60 #include "memory/metaspaceUtils.hpp"
61 #include "memory/universe.hpp"
62 #include "oops/compressedOops.inline.hpp"
63 #include "oops/oop.inline.hpp"
64 #include "runtime/orderAccess.hpp"
65 #include "runtime/vmThread.hpp"
66 #include "utilities/copy.hpp"
67 #include "utilities/events.hpp"
68 #include "utilities/growableArray.hpp"
69
70 ShenandoahFullGC::ShenandoahFullGC() :
71 _gc_timer(ShenandoahHeap::heap()->gc_timer()),
72 _preserved_marks(new PreservedMarksSet(true)) {}
73
74 ShenandoahFullGC::~ShenandoahFullGC() {
75 delete _preserved_marks;
76 }
77
78 bool ShenandoahFullGC::collect(GCCause::Cause cause) {
79 vmop_entry_full(cause);
80 // Always success
81 return true;
82 }
83
84 void ShenandoahFullGC::vmop_entry_full(GCCause::Cause cause) {
85 ShenandoahHeap* const heap = ShenandoahHeap::heap();
86 TraceCollectorStats tcs(heap->monitoring_support()->full_stw_collection_counters());
87 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::full_gc_gross);
88
89 heap->try_inject_alloc_failure();
90 VM_ShenandoahFullGC op(cause, this);
91 VMThread::execute(&op);
92 }
93
94 void ShenandoahFullGC::entry_full(GCCause::Cause cause) {
95 static const char* msg = "Pause Full";
96 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */);
97 EventMark em("%s", msg);
98
99 ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(),
100 ShenandoahWorkerPolicy::calc_workers_for_fullgc(),
101 "full gc");
102
103 op_full(cause);
104 }
105
106 void ShenandoahFullGC::op_full(GCCause::Cause cause) {
107 ShenandoahMetricsSnapshot metrics;
108 metrics.snap_before();
109
110 // Perform full GC
111 do_it(cause);
112
113 ShenandoahHeap* const heap = ShenandoahHeap::heap();
114
115 if (heap->mode()->is_generational()) {
116 ShenandoahGenerationalFullGC::handle_completion(heap);
117 }
118
119 metrics.snap_after();
120
121 if (metrics.is_good_progress(heap->global_generation())) {
122 heap->notify_gc_progress();
123 } else {
124 // Nothing to do. Tell the allocation path that we have failed to make
125 // progress, and it can finally fail.
126 heap->notify_gc_no_progress();
127 }
128
129 // Regardless if progress was made, we record that we completed a "successful" full GC.
130 heap->global_generation()->heuristics()->record_success_full();
131 heap->shenandoah_policy()->record_success_full();
132
133 {
134 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::full_gc_propagate_gc_state);
135 heap->propagate_gc_state_to_all_threads();
136 }
137 }
138
139 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
140 ShenandoahHeap* heap = ShenandoahHeap::heap();
141
142 if (heap->mode()->is_generational()) {
143 ShenandoahGenerationalFullGC::prepare();
144 }
145
146 if (ShenandoahVerify) {
147 heap->verifier()->verify_before_fullgc();
148 }
149
150 if (VerifyBeforeGC) {
151 Universe::verify();
152 }
153
154 // Degenerated GC may carry concurrent root flags when upgrading to
155 // full GC. We need to reset it before mutators resume.
156 heap->set_concurrent_strong_root_in_progress(false);
157 heap->set_concurrent_weak_root_in_progress(false);
158
159 heap->set_full_gc_in_progress(true);
160
161 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
162 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
163
164 {
165 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);
166 heap->pre_full_gc_dump(_gc_timer);
167 }
168
169 {
170 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
171 // Full GC is supposed to recover from any GC state:
172
173 // a0. Remember if we have forwarded objects
174 bool has_forwarded_objects = heap->has_forwarded_objects();
175
176 // a1. Cancel evacuation, if in progress
177 if (heap->is_evacuation_in_progress()) {
178 heap->set_evacuation_in_progress(false);
179 }
180 assert(!heap->is_evacuation_in_progress(), "sanity");
181
182 // a2. Cancel update-refs, if in progress
183 if (heap->is_update_refs_in_progress()) {
184 heap->set_update_refs_in_progress(false);
185 }
186 assert(!heap->is_update_refs_in_progress(), "sanity");
187
188 // b. Cancel all concurrent marks, if in progress
189 if (heap->is_concurrent_mark_in_progress()) {
190 heap->cancel_concurrent_mark();
191 }
192 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
193
194 // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
195 if (has_forwarded_objects) {
196 update_roots(true /*full_gc*/);
197 }
198
199 // d. Abandon reference discovery and clear all discovered references.
200 ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
201 rp->abandon_partial_discovery();
202
203 // e. Sync pinned region status from the CP marks
204 heap->sync_pinned_region_status();
205
206 if (heap->mode()->is_generational()) {
207 ShenandoahGenerationalFullGC::restore_top_before_promote(heap);
208 }
209
210 // The rest of prologue:
211 _preserved_marks->init(heap->workers()->active_workers());
212
213 assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
214 }
215
216 if (UseTLAB) {
217 // Note: PLABs are also retired with GCLABs in generational mode.
218 heap->gclabs_retire(ResizeTLAB);
219 heap->tlabs_retire(ResizeTLAB);
220 }
221
222 OrderAccess::fence();
223
224 phase1_mark_heap();
225
226 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
227 // Coming out of Full GC, we would not have any forwarded objects.
228 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
229 heap->set_has_forwarded_objects(false);
230
231 heap->set_full_gc_move_in_progress(true);
232
233 // Setup workers for the rest
234 OrderAccess::fence();
235
236 // Initialize worker slices
237 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
238 for (uint i = 0; i < heap->max_workers(); i++) {
239 worker_slices[i] = new ShenandoahHeapRegionSet();
240 }
241
242 ShenandoahGenerationalHeap::TransferResult result;
243 {
244 // The rest of code performs region moves, where region status is undefined
245 // until all phases run together.
246 ShenandoahHeapLocker lock(heap->lock());
247
248 FullGCForwarding::begin();
249
250 phase2_calculate_target_addresses(worker_slices);
251
252 OrderAccess::fence();
253
254 phase3_update_references();
255
256 phase4_compact_objects(worker_slices);
257
258 result = phase5_epilog();
259
260 FullGCForwarding::end();
261 }
262 if (heap->mode()->is_generational()) {
263 LogTarget(Info, gc, ergo) lt;
264 if (lt.is_enabled()) {
265 LogStream ls(lt);
266 result.print_on("Full GC", &ls);
267 }
268 }
269
270 // Resize metaspace
271 MetaspaceGC::compute_new_size();
272
273 // Free worker slices
274 for (uint i = 0; i < heap->max_workers(); i++) {
275 delete worker_slices[i];
276 }
277 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
278
279 heap->set_full_gc_move_in_progress(false);
280 heap->set_full_gc_in_progress(false);
281
282 if (ShenandoahVerify) {
283 heap->verifier()->verify_after_fullgc();
284 }
285
286 if (VerifyAfterGC) {
287 Universe::verify();
288 }
289
290 {
291 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
292 heap->post_full_gc_dump(_gc_timer);
293 }
294 }
295
296 void ShenandoahFullGC::phase1_mark_heap() {
297 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
298 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
299
300 ShenandoahHeap* heap = ShenandoahHeap::heap();
301
302 heap->global_generation()->reset_mark_bitmap<true, true>();
303 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
304 assert(!heap->global_generation()->is_mark_complete(), "sanity");
305
306 heap->set_unload_classes(heap->global_generation()->heuristics()->can_unload_classes());
307
308 ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
309 // enable ("weak") refs discovery
310 rp->set_soft_reference_policy(true); // forcefully purge all soft references
311
312 ShenandoahSTWMark mark(heap->global_generation(), true /*full_gc*/);
313 mark.mark();
314 heap->parallel_cleaning(true /* full_gc */);
315
316 if (ShenandoahHeap::heap()->mode()->is_generational()) {
317 ShenandoahGenerationalFullGC::log_live_in_old(heap);
318 }
319 }
320
321 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
322 private:
323 PreservedMarks* const _preserved_marks;
324 ShenandoahHeap* const _heap;
325 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
326 int _empty_regions_pos;
327 ShenandoahHeapRegion* _to_region;
328 ShenandoahHeapRegion* _from_region;
329 HeapWord* _compact_point;
330
331 public:
332 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
333 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
334 ShenandoahHeapRegion* to_region) :
335 _preserved_marks(preserved_marks),
336 _heap(ShenandoahHeap::heap()),
337 _empty_regions(empty_regions),
338 _empty_regions_pos(0),
339 _to_region(to_region),
340 _from_region(nullptr),
341 _compact_point(to_region->bottom()) {}
342
343 void set_from_region(ShenandoahHeapRegion* from_region) {
344 _from_region = from_region;
345 }
346
347 void finish() {
348 assert(_to_region != nullptr, "should not happen");
349 _to_region->set_new_top(_compact_point);
350 }
351
352 bool is_compact_same_region() {
353 return _from_region == _to_region;
354 }
355
356 int empty_regions_pos() {
357 return _empty_regions_pos;
358 }
359
360 void do_object(oop p) {
361 assert(_from_region != nullptr, "must set before work");
362 assert(_heap->gc_generation()->complete_marking_context()->is_marked(p), "must be marked");
363 assert(!_heap->gc_generation()->complete_marking_context()->allocated_after_mark_start(p), "must be truly marked");
364
365 size_t old_size = p->size();
366 size_t new_size = p->copy_size(old_size, p->mark());
367 size_t obj_size = _compact_point == cast_from_oop<HeapWord*>(p) ? old_size : new_size;
368 if (_compact_point + obj_size > _to_region->end()) {
369 finish();
370
371 // Object doesn't fit. Pick next empty region and start compacting there.
372 ShenandoahHeapRegion* new_to_region;
373 if (_empty_regions_pos < _empty_regions.length()) {
374 new_to_region = _empty_regions.at(_empty_regions_pos);
375 _empty_regions_pos++;
376 } else {
377 // Out of empty region? Compact within the same region.
378 new_to_region = _from_region;
379 }
380
381 assert(new_to_region != _to_region, "must not reuse same to-region");
382 assert(new_to_region != nullptr, "must not be null");
383 _to_region = new_to_region;
384 _compact_point = _to_region->bottom();
385 obj_size = _compact_point == cast_from_oop<HeapWord*>(p) ? old_size : new_size;
386 }
387
388 // Object fits into current region, record new location, if object does not move:
389 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
390 shenandoah_assert_not_forwarded(nullptr, p);
391 if (_compact_point != cast_from_oop<HeapWord*>(p)) {
392 _preserved_marks->push_if_necessary(p, p->mark());
393 FullGCForwarding::forward_to(p, cast_to_oop(_compact_point));
394 }
395 _compact_point += obj_size;
396 }
397 };
398
399 class ShenandoahPrepareForCompactionTask : public WorkerTask {
400 private:
401 PreservedMarksSet* const _preserved_marks;
402 ShenandoahHeap* const _heap;
403 ShenandoahHeapRegionSet** const _worker_slices;
404
405 public:
406 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
407 WorkerTask("Shenandoah Prepare For Compaction"),
408 _preserved_marks(preserved_marks),
409 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
410 }
411
412 static bool is_candidate_region(ShenandoahHeapRegion* r) {
413 // Empty region: get it into the slice to defragment the slice itself.
414 // We could have skipped this without violating correctness, but we really
415 // want to compact all live regions to the start of the heap, which sometimes
416 // means moving them into the fully empty regions.
417 if (r->is_empty()) return true;
418
419 // Can move the region, and this is not the humongous region. Humongous
420 // moves are special cased here, because their moves are handled separately.
421 return r->is_stw_move_allowed() && !r->is_humongous();
422 }
423
424 void work(uint worker_id) override;
425 private:
426 template<typename ClosureType>
427 void prepare_for_compaction(ClosureType& cl,
428 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
429 ShenandoahHeapRegionSetIterator& it,
430 ShenandoahHeapRegion* from_region);
431 };
432
433 void ShenandoahPrepareForCompactionTask::work(uint worker_id) {
434 ShenandoahParallelWorkerSession worker_session(worker_id);
435 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
436 ShenandoahHeapRegionSetIterator it(slice);
437 ShenandoahHeapRegion* from_region = it.next();
438 // No work?
439 if (from_region == nullptr) {
440 return;
441 }
442
443 // Sliding compaction. Walk all regions in the slice, and compact them.
444 // Remember empty regions and reuse them as needed.
445 ResourceMark rm;
446
447 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
448
449 if (_heap->mode()->is_generational()) {
450 ShenandoahPrepareForGenerationalCompactionObjectClosure cl(_preserved_marks->get(worker_id),
451 empty_regions, from_region, worker_id);
452 prepare_for_compaction(cl, empty_regions, it, from_region);
453 } else {
454 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
455 prepare_for_compaction(cl, empty_regions, it, from_region);
456 }
457 }
458
459 template<typename ClosureType>
460 void ShenandoahPrepareForCompactionTask::prepare_for_compaction(ClosureType& cl,
461 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
462 ShenandoahHeapRegionSetIterator& it,
463 ShenandoahHeapRegion* from_region) {
464 while (from_region != nullptr) {
465 assert(is_candidate_region(from_region), "Sanity");
466 cl.set_from_region(from_region);
467 if (from_region->has_live()) {
468 _heap->marked_object_iterate(from_region, &cl);
469 }
470
471 // Compacted the region to somewhere else? From-region is empty then.
472 if (!cl.is_compact_same_region()) {
473 empty_regions.append(from_region);
474 }
475 from_region = it.next();
476 }
477 cl.finish();
478
479 // Mark all remaining regions as empty
480 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
481 ShenandoahHeapRegion* r = empty_regions.at(pos);
482 r->set_new_top(r->bottom());
483 }
484 }
485
486 void ShenandoahFullGC::calculate_target_humongous_objects() {
487 ShenandoahHeap* heap = ShenandoahHeap::heap();
488
489 // Compute the new addresses for humongous objects. We need to do this after addresses
490 // for regular objects are calculated, and we know what regions in heap suffix are
491 // available for humongous moves.
492 //
493 // Scan the heap backwards, because we are compacting humongous regions towards the end.
494 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
495 // humongous start there.
496 //
497 // The complication is potential non-movable regions during the scan. If such region is
498 // detected, then sliding restarts towards that non-movable region.
499
500 size_t to_begin = heap->num_regions();
501 size_t to_end = heap->num_regions();
502
503 log_debug(gc)("Full GC calculating target humongous objects from end %zu", to_end);
504 for (size_t c = heap->num_regions(); c > 0; c--) {
505 ShenandoahHeapRegion *r = heap->get_region(c - 1);
506 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
507 // To-region candidate: record this, and continue scan
508 to_begin = r->index();
509 continue;
510 }
511
512 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
513 // From-region candidate: movable humongous region
514 oop old_obj = cast_to_oop(r->bottom());
515 size_t words_size = old_obj->size();
516 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
517
518 size_t start = to_end - num_regions;
519
520 if (start >= to_begin && start != r->index()) {
521 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
522 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
523 FullGCForwarding::forward_to(old_obj, cast_to_oop(heap->get_region(start)->bottom()));
524 to_end = start;
525 continue;
526 }
527 }
528
529 // Failed to fit. Scan starting from current region.
530 to_begin = r->index();
531 to_end = r->index();
532 }
533 }
534
535 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
536 private:
537 ShenandoahHeap* const _heap;
538
539 public:
540 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
541 void heap_region_do(ShenandoahHeapRegion* r) {
542 if (r->is_trash()) {
543 r->try_recycle_under_lock();
544 }
545 if (r->is_cset()) {
546 // Leave affiliation unchanged
547 r->make_regular_bypass();
548 }
549 if (r->is_empty_uncommitted()) {
550 r->make_committed_bypass();
551 }
552 assert (r->is_committed(), "only committed regions in heap now, see region %zu", r->index());
553
554 // Record current region occupancy: this communicates empty regions are free
555 // to the rest of Full GC code.
556 r->set_new_top(r->top());
557 }
558 };
559
560 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
561 private:
562 ShenandoahHeap* const _heap;
563 ShenandoahMarkingContext* const _ctx;
564
565 public:
566 ShenandoahTrashImmediateGarbageClosure() :
567 _heap(ShenandoahHeap::heap()),
568 _ctx(ShenandoahHeap::heap()->global_generation()->complete_marking_context()) {}
569
570 void heap_region_do(ShenandoahHeapRegion* r) override {
571 if (r->is_humongous_start()) {
572 oop humongous_obj = cast_to_oop(r->bottom());
573 if (!_ctx->is_marked(humongous_obj)) {
574 assert(!r->has_live(), "Region %zu is not marked, should not have live", r->index());
575 _heap->trash_humongous_region_at(r);
576 } else {
577 assert(r->has_live(), "Region %zu should have live", r->index());
578 }
579 } else if (r->is_humongous_continuation()) {
580 // If we hit continuation, the non-live humongous starts should have been trashed already
581 assert(r->humongous_start_region()->has_live(), "Region %zu should have live", r->index());
582 } else if (r->is_regular()) {
583 if (!r->has_live()) {
584 r->make_trash_immediate();
585 }
586 }
587 }
588 };
589
590 void ShenandoahFullGC::distribute_slices(ShenandoahHeapRegionSet** worker_slices) {
591 ShenandoahHeap* heap = ShenandoahHeap::heap();
592
593 uint n_workers = heap->workers()->active_workers();
594 size_t n_regions = heap->num_regions();
595
596 // What we want to accomplish: have the dense prefix of data, while still balancing
597 // out the parallel work.
598 //
599 // Assuming the amount of work is driven by the live data that needs moving, we can slice
600 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each
601 // thread takes all regions in its prefix subset, and then it takes some regions from
602 // the tail.
603 //
604 // Tail region selection becomes interesting.
605 //
606 // First, we want to distribute the regions fairly between the workers, and those regions
607 // might have different amount of live data. So, until we sure no workers need live data,
608 // we need to only take what the worker needs.
609 //
610 // Second, since we slide everything to the left in each slice, the most busy regions
611 // would be the ones on the left. Which means we want to have all workers have their after-tail
612 // regions as close to the left as possible.
613 //
614 // The easiest way to do this is to distribute after-tail regions in round-robin between
615 // workers that still need live data.
616 //
617 // Consider parallel workers A, B, C, then the target slice layout would be:
618 //
619 // AAAAAAAABBBBBBBBCCCCCCCC|ABCABCABCABCABCABCABCABABABABABABABABABABAAAAA
620 //
621 // (.....dense-prefix.....) (.....................tail...................)
622 // [all regions fully live] [left-most regions are fuller that right-most]
623 //
624
625 // Compute how much live data is there. This would approximate the size of dense prefix
626 // we target to create.
627 size_t total_live = 0;
628 for (size_t idx = 0; idx < n_regions; idx++) {
629 ShenandoahHeapRegion *r = heap->get_region(idx);
630 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
631 total_live += r->get_live_data_words();
632 }
633 }
634
635 // Estimate the size for the dense prefix. Note that we specifically count only the
636 // "full" regions, so there would be some non-full regions in the slice tail.
637 size_t live_per_worker = total_live / n_workers;
638 size_t prefix_regions_per_worker = live_per_worker / ShenandoahHeapRegion::region_size_words();
639 size_t prefix_regions_total = prefix_regions_per_worker * n_workers;
640 prefix_regions_total = MIN2(prefix_regions_total, n_regions);
641 assert(prefix_regions_total <= n_regions, "Sanity");
642
643 // There might be non-candidate regions in the prefix. To compute where the tail actually
644 // ends up being, we need to account those as well.
645 size_t prefix_end = prefix_regions_total;
646 for (size_t idx = 0; idx < prefix_regions_total; idx++) {
647 ShenandoahHeapRegion *r = heap->get_region(idx);
648 if (!ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
649 prefix_end++;
650 }
651 }
652 prefix_end = MIN2(prefix_end, n_regions);
653 assert(prefix_end <= n_regions, "Sanity");
654
655 // Distribute prefix regions per worker: each thread definitely gets its own same-sized
656 // subset of dense prefix.
657 size_t prefix_idx = 0;
658
659 size_t* live = NEW_C_HEAP_ARRAY(size_t, n_workers, mtGC);
660
661 for (size_t wid = 0; wid < n_workers; wid++) {
662 ShenandoahHeapRegionSet* slice = worker_slices[wid];
663
664 live[wid] = 0;
665 size_t regs = 0;
666
667 // Add all prefix regions for this worker
668 while (prefix_idx < prefix_end && regs < prefix_regions_per_worker) {
669 ShenandoahHeapRegion *r = heap->get_region(prefix_idx);
670 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
671 slice->add_region(r);
672 live[wid] += r->get_live_data_words();
673 regs++;
674 }
675 prefix_idx++;
676 }
677 }
678
679 // Distribute the tail among workers in round-robin fashion.
680 size_t wid = n_workers - 1;
681
682 for (size_t tail_idx = prefix_end; tail_idx < n_regions; tail_idx++) {
683 ShenandoahHeapRegion *r = heap->get_region(tail_idx);
684 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
685 assert(wid < n_workers, "Sanity");
686
687 size_t live_region = r->get_live_data_words();
688
689 // Select next worker that still needs live data.
690 size_t old_wid = wid;
691 do {
692 wid++;
693 if (wid == n_workers) wid = 0;
694 } while (live[wid] + live_region >= live_per_worker && old_wid != wid);
695
696 if (old_wid == wid) {
697 // Circled back to the same worker? This means liveness data was
698 // miscalculated. Bump the live_per_worker limit so that
699 // everyone gets a piece of the leftover work.
700 live_per_worker += ShenandoahHeapRegion::region_size_words();
701 }
702
703 worker_slices[wid]->add_region(r);
704 live[wid] += live_region;
705 }
706 }
707
708 FREE_C_HEAP_ARRAY(size_t, live);
709
710 #ifdef ASSERT
711 ResourceBitMap map(n_regions);
712 for (size_t wid = 0; wid < n_workers; wid++) {
713 ShenandoahHeapRegionSetIterator it(worker_slices[wid]);
714 ShenandoahHeapRegion* r = it.next();
715 while (r != nullptr) {
716 size_t idx = r->index();
717 assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: %zu", idx);
718 assert(!map.at(idx), "No region distributed twice: %zu", idx);
719 map.at_put(idx, true);
720 r = it.next();
721 }
722 }
723
724 for (size_t rid = 0; rid < n_regions; rid++) {
725 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
726 bool is_distributed = map.at(rid);
727 assert(is_distributed || !is_candidate, "All candidates are distributed: %zu", rid);
728 }
729 #endif
730 }
731
732 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
733 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
734 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
735
736 ShenandoahHeap* heap = ShenandoahHeap::heap();
737
738 // About to figure out which regions can be compacted, make sure pinning status
739 // had been updated in GC prologue.
740 heap->assert_pinned_region_status();
741
742 {
743 // Trash the immediately collectible regions before computing addresses
744 ShenandoahTrashImmediateGarbageClosure trash_immediate_garbage;
745 ShenandoahExcludeRegionClosure<FREE> cl(&trash_immediate_garbage);
746 heap->heap_region_iterate(&cl);
747
748 // Make sure regions are in good state: committed, active, clean.
749 // This is needed because we are potentially sliding the data through them.
750 ShenandoahEnsureHeapActiveClosure ecl;
751 heap->heap_region_iterate(&ecl);
752 }
753
754 // Compute the new addresses for regular objects
755 {
756 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
757
758 distribute_slices(worker_slices);
759
760 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
761 heap->workers()->run_task(&task);
762 }
763
764 // Compute the new addresses for humongous objects
765 {
766 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
767 calculate_target_humongous_objects();
768 }
769 }
770
771 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
772 private:
773 ShenandoahHeap* const _heap;
774 ShenandoahMarkingContext* const _ctx;
775
776 template <class T>
777 inline void do_oop_work(T* p) {
778 T o = RawAccess<>::oop_load(p);
779 if (!CompressedOops::is_null(o)) {
780 oop obj = CompressedOops::decode_not_null(o);
781 assert(_ctx->is_marked(obj), "must be marked");
782 if (FullGCForwarding::is_forwarded(obj)) {
783 oop forw = FullGCForwarding::forwardee(obj);
784 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
785 }
786 }
787 }
788
789 public:
790 ShenandoahAdjustPointersClosure() :
791 _heap(ShenandoahHeap::heap()),
792 _ctx(ShenandoahHeap::heap()->gc_generation()->complete_marking_context()) {}
793
794 void do_oop(oop* p) { do_oop_work(p); }
795 void do_oop(narrowOop* p) { do_oop_work(p); }
796 void do_method(Method* m) {}
797 void do_nmethod(nmethod* nm) {}
798 };
799
800 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
801 private:
802 ShenandoahHeap* const _heap;
803 ShenandoahAdjustPointersClosure _cl;
804
805 public:
806 ShenandoahAdjustPointersObjectClosure() :
807 _heap(ShenandoahHeap::heap()) {
808 }
809 void do_object(oop p) {
810 assert(_heap->gc_generation()->complete_marking_context()->is_marked(p), "must be marked");
811 p->oop_iterate(&_cl);
812 }
813 };
814
815 class ShenandoahAdjustPointersTask : public WorkerTask {
816 private:
817 ShenandoahHeap* const _heap;
818 ShenandoahRegionIterator _regions;
819
820 public:
821 ShenandoahAdjustPointersTask() :
822 WorkerTask("Shenandoah Adjust Pointers"),
823 _heap(ShenandoahHeap::heap()) {
824 }
825
826 void work(uint worker_id) {
827 ShenandoahParallelWorkerSession worker_session(worker_id);
828 ShenandoahAdjustPointersObjectClosure obj_cl;
829 ShenandoahHeapRegion* r = _regions.next();
830 while (r != nullptr) {
831 if (!r->is_humongous_continuation() && r->has_live()) {
832 _heap->marked_object_iterate(r, &obj_cl);
833 }
834 if (_heap->mode()->is_generational()) {
835 ShenandoahGenerationalFullGC::maybe_coalesce_and_fill_region(r);
836 }
837 r = _regions.next();
838 }
839 }
840 };
841
842 class ShenandoahAdjustRootPointersTask : public WorkerTask {
843 private:
844 ShenandoahRootAdjuster* _rp;
845 PreservedMarksSet* _preserved_marks;
846 public:
847 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
848 WorkerTask("Shenandoah Adjust Root Pointers"),
849 _rp(rp),
850 _preserved_marks(preserved_marks) {}
851
852 void work(uint worker_id) {
853 ShenandoahParallelWorkerSession worker_session(worker_id);
854 ShenandoahAdjustPointersClosure cl;
855 _rp->roots_do(worker_id, &cl);
856 _preserved_marks->get(worker_id)->adjust_during_full_gc();
857 }
858 };
859
860 void ShenandoahFullGC::phase3_update_references() {
861 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
862 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
863
864 ShenandoahHeap* heap = ShenandoahHeap::heap();
865
866 WorkerThreads* workers = heap->workers();
867 uint nworkers = workers->active_workers();
868 {
869 #if COMPILER2_OR_JVMCI
870 DerivedPointerTable::clear();
871 #endif
872 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
873 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
874 workers->run_task(&task);
875 #if COMPILER2_OR_JVMCI
876 DerivedPointerTable::update_pointers();
877 #endif
878 }
879
880 ShenandoahAdjustPointersTask adjust_pointers_task;
881 workers->run_task(&adjust_pointers_task);
882 }
883
884 class ShenandoahCompactObjectsClosure : public ObjectClosure {
885 private:
886 ShenandoahHeap* const _heap;
887 uint const _worker_id;
888
889 public:
890 ShenandoahCompactObjectsClosure(uint worker_id) :
891 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
892
893 void do_object(oop p) {
894 assert(_heap->gc_generation()->complete_marking_context()->is_marked(p), "must be marked");
895 size_t size = p->size();
896 if (FullGCForwarding::is_forwarded(p)) {
897 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
898 HeapWord* compact_to = cast_from_oop<HeapWord*>(FullGCForwarding::forwardee(p));
899 assert(compact_from != compact_to, "Forwarded object should move");
900 Copy::aligned_conjoint_words(compact_from, compact_to, size);
901 oop new_obj = cast_to_oop(compact_to);
902
903 ContinuationGCSupport::relativize_stack_chunk(new_obj);
904 new_obj->init_mark();
905 new_obj->initialize_hash_if_necessary(p);
906 }
907 }
908 };
909
910 class ShenandoahCompactObjectsTask : public WorkerTask {
911 private:
912 ShenandoahHeap* const _heap;
913 ShenandoahHeapRegionSet** const _worker_slices;
914
915 public:
916 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
917 WorkerTask("Shenandoah Compact Objects"),
918 _heap(ShenandoahHeap::heap()),
919 _worker_slices(worker_slices) {
920 }
921
922 void work(uint worker_id) {
923 ShenandoahParallelWorkerSession worker_session(worker_id);
924 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
925
926 ShenandoahCompactObjectsClosure cl(worker_id);
927 ShenandoahHeapRegion* r = slice.next();
928 while (r != nullptr) {
929 assert(!r->is_humongous(), "must not get humongous regions here");
930 if (r->has_live()) {
931 _heap->marked_object_iterate(r, &cl);
932 }
933 r->set_top(r->new_top());
934 r = slice.next();
935 }
936 }
937 };
938
939 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
940 private:
941 ShenandoahHeap* const _heap;
942 bool _is_generational;
943 size_t _young_regions, _young_usage, _young_humongous_waste;
944 size_t _old_regions, _old_usage, _old_humongous_waste;
945
946 public:
947 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()),
948 _is_generational(_heap->mode()->is_generational()),
949 _young_regions(0),
950 _young_usage(0),
951 _young_humongous_waste(0),
952 _old_regions(0),
953 _old_usage(0),
954 _old_humongous_waste(0)
955 {
956 _heap->free_set()->clear();
957 }
958
959 void heap_region_do(ShenandoahHeapRegion* r) {
960 assert (!r->is_cset(), "cset regions should have been demoted already");
961
962 // Need to reset the complete-top-at-mark-start pointer here because
963 // the complete marking bitmap is no longer valid. This ensures
964 // size-based iteration in marked_object_iterate().
965 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
966 // pinned regions.
967 if (!r->is_pinned()) {
968 _heap->gc_generation()->complete_marking_context()->reset_top_at_mark_start(r);
969 }
970
971 size_t live = r->used();
972
973 // Make empty regions that have been allocated into regular
974 if (r->is_empty() && live > 0) {
975 if (!_is_generational) {
976 r->make_affiliated_maybe();
977 }
978 // else, generational mode compaction has already established affiliation.
979 r->make_regular_bypass();
980 if (ZapUnusedHeapArea) {
981 SpaceMangler::mangle_region(MemRegion(r->top(), r->end()));
982 }
983 }
984
985 // Reclaim regular regions that became empty
986 if (r->is_regular() && live == 0) {
987 r->make_trash();
988 }
989
990 // Recycle all trash regions
991 if (r->is_trash()) {
992 live = 0;
993 r->try_recycle_under_lock();
994 } else {
995 if (r->is_old()) {
996 ShenandoahGenerationalFullGC::account_for_region(r, _old_regions, _old_usage, _old_humongous_waste);
997 } else if (r->is_young()) {
998 ShenandoahGenerationalFullGC::account_for_region(r, _young_regions, _young_usage, _young_humongous_waste);
999 }
1000 }
1001 r->set_live_data(live);
1002 r->reset_alloc_metadata();
1003 }
1004
1005 void update_generation_usage() {
1006 if (_is_generational) {
1007 _heap->old_generation()->establish_usage(_old_regions, _old_usage, _old_humongous_waste);
1008 _heap->young_generation()->establish_usage(_young_regions, _young_usage, _young_humongous_waste);
1009 } else {
1010 assert(_old_regions == 0, "Old regions only expected in generational mode");
1011 assert(_old_usage == 0, "Old usage only expected in generational mode");
1012 assert(_old_humongous_waste == 0, "Old humongous waste only expected in generational mode");
1013 }
1014
1015 // In generational mode, global usage should be the sum of young and old. This is also true
1016 // for non-generational modes except that there are no old regions.
1017 _heap->global_generation()->establish_usage(_old_regions + _young_regions,
1018 _old_usage + _young_usage,
1019 _old_humongous_waste + _young_humongous_waste);
1020 }
1021 };
1022
1023 void ShenandoahFullGC::compact_humongous_objects() {
1024 // Compact humongous regions, based on their fwdptr objects.
1025 //
1026 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
1027 // humongous regions are already compacted, and do not require further moves, which alleviates
1028 // sliding costs. We may consider doing this in parallel in the future.
1029
1030 ShenandoahHeap* heap = ShenandoahHeap::heap();
1031
1032 for (size_t c = heap->num_regions(); c > 0; c--) {
1033 ShenandoahHeapRegion* r = heap->get_region(c - 1);
1034 if (r->is_humongous_start()) {
1035 oop old_obj = cast_to_oop(r->bottom());
1036 if (!FullGCForwarding::is_forwarded(old_obj)) {
1037 // No need to move the object, it stays at the same slot
1038 continue;
1039 }
1040 size_t words_size = old_obj->size();
1041 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
1042
1043 size_t old_start = r->index();
1044 size_t old_end = old_start + num_regions - 1;
1045 size_t new_start = heap->heap_region_index_containing(FullGCForwarding::forwardee(old_obj));
1046 size_t new_end = new_start + num_regions - 1;
1047 assert(old_start != new_start, "must be real move");
1048 assert(r->is_stw_move_allowed(), "Region %zu should be movable", r->index());
1049
1050 log_debug(gc)("Full GC compaction moves humongous object from region %zu to region %zu", old_start, new_start);
1051 Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
1052 ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
1053
1054 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
1055 new_obj->init_mark();
1056
1057 {
1058 ShenandoahAffiliation original_affiliation = r->affiliation();
1059 for (size_t c = old_start; c <= old_end; c++) {
1060 ShenandoahHeapRegion* r = heap->get_region(c);
1061 // Leave humongous region affiliation unchanged.
1062 r->make_regular_bypass();
1063 r->set_top(r->bottom());
1064 }
1065
1066 for (size_t c = new_start; c <= new_end; c++) {
1067 ShenandoahHeapRegion* r = heap->get_region(c);
1068 if (c == new_start) {
1069 r->make_humongous_start_bypass(original_affiliation);
1070 } else {
1071 r->make_humongous_cont_bypass(original_affiliation);
1072 }
1073
1074 // Trailing region may be non-full, record the remainder there
1075 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1076 if ((c == new_end) && (remainder != 0)) {
1077 r->set_top(r->bottom() + remainder);
1078 } else {
1079 r->set_top(r->end());
1080 }
1081
1082 r->reset_alloc_metadata();
1083 }
1084 }
1085 }
1086 }
1087 }
1088
1089 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1090 // we need to remain able to walk pinned regions.
1091 // Since pinned region do not move and don't get compacted, we will get holes with
1092 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
1093 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
1094 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
1095 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
1096 class ShenandoahMCResetCompleteBitmapTask : public WorkerTask {
1097 private:
1098 ShenandoahRegionIterator _regions;
1099
1100 public:
1101 ShenandoahMCResetCompleteBitmapTask() :
1102 WorkerTask("Shenandoah Reset Bitmap") {
1103 }
1104
1105 void work(uint worker_id) {
1106 ShenandoahParallelWorkerSession worker_session(worker_id);
1107 ShenandoahHeapRegion* region = _regions.next();
1108 ShenandoahHeap* heap = ShenandoahHeap::heap();
1109 ShenandoahMarkingContext* const ctx = heap->gc_generation()->complete_marking_context();
1110 while (region != nullptr) {
1111 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
1112 ctx->clear_bitmap(region);
1113 }
1114 region = _regions.next();
1115 }
1116 }
1117 };
1118
1119 void ShenandoahFullGC::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
1120 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
1121 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
1122
1123 ShenandoahHeap* heap = ShenandoahHeap::heap();
1124
1125 // Compact regular objects first
1126 {
1127 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
1128 ShenandoahCompactObjectsTask compact_task(worker_slices);
1129 heap->workers()->run_task(&compact_task);
1130 }
1131
1132 // Compact humongous objects after regular object moves
1133 {
1134 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
1135 compact_humongous_objects();
1136 }
1137 }
1138
1139 ShenandoahGenerationalHeap::TransferResult ShenandoahFullGC::phase5_epilog() {
1140 GCTraceTime(Info, gc, phases) time("Phase 5: Full GC epilog", _gc_timer);
1141 ShenandoahHeap* heap = ShenandoahHeap::heap();
1142 ShenandoahGenerationalHeap::TransferResult result;
1143
1144 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1145 // and must ensure the bitmap is in sync.
1146 {
1147 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1148 ShenandoahMCResetCompleteBitmapTask task;
1149 heap->workers()->run_task(&task);
1150 }
1151
1152 // Bring regions in proper states after the collection, and set heap properties.
1153 {
1154 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1155 ShenandoahPostCompactClosure post_compact;
1156 heap->heap_region_iterate(&post_compact);
1157 post_compact.update_generation_usage();
1158
1159 if (heap->mode()->is_generational()) {
1160 ShenandoahGenerationalFullGC::balance_generations_after_gc(heap);
1161 }
1162
1163 heap->collection_set()->clear();
1164 size_t young_cset_regions, old_cset_regions;
1165 size_t first_old, last_old, num_old;
1166 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
1167
1168 // We also do not expand old generation size following Full GC because we have scrambled age populations and
1169 // no longer have objects separated by age into distinct regions.
1170 if (heap->mode()->is_generational()) {
1171 ShenandoahGenerationalFullGC::compute_balances();
1172 }
1173
1174 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old);
1175
1176 // Set mark incomplete because the marking bitmaps have been reset except pinned regions.
1177 heap->global_generation()->set_mark_incomplete();
1178
1179 heap->clear_cancelled_gc(true /* clear oom handler */);
1180 }
1181
1182 _preserved_marks->restore(heap->workers());
1183 _preserved_marks->reclaim();
1184
1185 // We defer generation resizing actions until after cset regions have been recycled. We do this even following an
1186 // abbreviated cycle.
1187 if (heap->mode()->is_generational()) {
1188 result = ShenandoahGenerationalFullGC::balance_generations_after_rebuilding_free_set();
1189 ShenandoahGenerationalFullGC::rebuild_remembered_set(heap);
1190 }
1191 return result;
1192 }