1 /*
2 * Copyright (c) 2014, 2021, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "precompiled.hpp"
27
28 #include "compiler/oopMap.hpp"
29 #include "gc/shared/continuationGCSupport.hpp"
30 #include "gc/shared/gcTraceTime.inline.hpp"
31 #include "gc/shared/preservedMarks.inline.hpp"
32 #include "gc/shared/tlab_globals.hpp"
33 #include "gc/shared/workerThread.hpp"
34 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
35 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
36 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
37 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
38 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
39 #include "gc/shenandoah/shenandoahFreeSet.hpp"
40 #include "gc/shenandoah/shenandoahFullGC.hpp"
41 #include "gc/shenandoah/shenandoahGenerationalFullGC.hpp"
42 #include "gc/shenandoah/shenandoahGlobalGeneration.hpp"
43 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
44 #include "gc/shenandoah/shenandoahMark.inline.hpp"
45 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
46 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
47 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
48 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
49 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
50 #include "gc/shenandoah/shenandoahMetrics.hpp"
51 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
52 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
53 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
54 #include "gc/shenandoah/shenandoahSTWMark.hpp"
55 #include "gc/shenandoah/shenandoahUtils.hpp"
56 #include "gc/shenandoah/shenandoahVerifier.hpp"
57 #include "gc/shenandoah/shenandoahVMOperations.hpp"
58 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
59 #include "memory/metaspaceUtils.hpp"
60 #include "memory/universe.hpp"
61 #include "oops/compressedOops.inline.hpp"
62 #include "oops/oop.inline.hpp"
63 #include "runtime/orderAccess.hpp"
64 #include "runtime/vmThread.hpp"
65 #include "utilities/copy.hpp"
66 #include "utilities/events.hpp"
67 #include "utilities/growableArray.hpp"
68
69 ShenandoahFullGC::ShenandoahFullGC() :
70 _gc_timer(ShenandoahHeap::heap()->gc_timer()),
71 _preserved_marks(new PreservedMarksSet(true)) {}
72
73 ShenandoahFullGC::~ShenandoahFullGC() {
74 delete _preserved_marks;
75 }
76
77 bool ShenandoahFullGC::collect(GCCause::Cause cause) {
78 vmop_entry_full(cause);
79 // Always success
80 return true;
81 }
82
83 void ShenandoahFullGC::vmop_entry_full(GCCause::Cause cause) {
84 ShenandoahHeap* const heap = ShenandoahHeap::heap();
85 TraceCollectorStats tcs(heap->monitoring_support()->full_stw_collection_counters());
86 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::full_gc_gross);
87
88 heap->try_inject_alloc_failure();
89 VM_ShenandoahFullGC op(cause, this);
90 VMThread::execute(&op);
91 }
92
93 void ShenandoahFullGC::entry_full(GCCause::Cause cause) {
94 static const char* msg = "Pause Full";
95 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */);
96 EventMark em("%s", msg);
97
98 ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(),
99 ShenandoahWorkerPolicy::calc_workers_for_fullgc(),
100 "full gc");
101
102 op_full(cause);
103 }
104
105 void ShenandoahFullGC::op_full(GCCause::Cause cause) {
106 ShenandoahMetricsSnapshot metrics;
107 metrics.snap_before();
108
109 // Perform full GC
110 do_it(cause);
111
112 ShenandoahHeap* const heap = ShenandoahHeap::heap();
113
114 if (heap->mode()->is_generational()) {
115 ShenandoahGenerationalFullGC::handle_completion(heap);
116 }
117
118 metrics.snap_after();
119
120 if (metrics.is_good_progress()) {
121 heap->notify_gc_progress();
122 } else {
123 // Nothing to do. Tell the allocation path that we have failed to make
124 // progress, and it can finally fail.
125 heap->notify_gc_no_progress();
126 }
127
128 // Regardless if progress was made, we record that we completed a "successful" full GC.
129 heap->global_generation()->heuristics()->record_success_full();
130 heap->shenandoah_policy()->record_success_full();
131 }
132
133 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
134 ShenandoahHeap* heap = ShenandoahHeap::heap();
135
136 if (heap->mode()->is_generational()) {
137 ShenandoahGenerationalFullGC::prepare();
138 }
139
140 if (ShenandoahVerify) {
141 heap->verifier()->verify_before_fullgc();
142 }
143
144 if (VerifyBeforeGC) {
145 Universe::verify();
146 }
147
148 // Degenerated GC may carry concurrent root flags when upgrading to
149 // full GC. We need to reset it before mutators resume.
150 heap->set_concurrent_strong_root_in_progress(false);
151 heap->set_concurrent_weak_root_in_progress(false);
152
153 heap->set_full_gc_in_progress(true);
154
155 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
156 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
157
158 {
159 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);
160 heap->pre_full_gc_dump(_gc_timer);
161 }
162
163 {
164 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
165 // Full GC is supposed to recover from any GC state:
166
167 // a0. Remember if we have forwarded objects
168 bool has_forwarded_objects = heap->has_forwarded_objects();
169
170 // a1. Cancel evacuation, if in progress
171 if (heap->is_evacuation_in_progress()) {
172 heap->set_evacuation_in_progress(false);
173 }
174 assert(!heap->is_evacuation_in_progress(), "sanity");
175
176 // a2. Cancel update-refs, if in progress
177 if (heap->is_update_refs_in_progress()) {
178 heap->set_update_refs_in_progress(false);
179 }
180 assert(!heap->is_update_refs_in_progress(), "sanity");
181
182 // b. Cancel all concurrent marks, if in progress
183 if (heap->is_concurrent_mark_in_progress()) {
184 // TODO: Send cancel_concurrent_mark upstream? Does it really not have it already?
185 heap->cancel_concurrent_mark();
186 }
187 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
188
189 // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
190 if (has_forwarded_objects) {
191 update_roots(true /*full_gc*/);
192 }
193
194 // d. Reset the bitmaps for new marking
195 heap->global_generation()->reset_mark_bitmap();
196 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
197 assert(!heap->global_generation()->is_mark_complete(), "sanity");
198
199 // e. Abandon reference discovery and clear all discovered references.
200 ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
201 rp->abandon_partial_discovery();
202
203 // f. 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 // TODO: Do we need to explicitly retire PLABs?
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 {
243 // The rest of code performs region moves, where region status is undefined
244 // until all phases run together.
245 ShenandoahHeapLocker lock(heap->lock());
246
247 phase2_calculate_target_addresses(worker_slices);
248
249 OrderAccess::fence();
250
251 phase3_update_references();
252
253 phase4_compact_objects(worker_slices);
254
255 phase5_epilog();
256 }
257
258 // Resize metaspace
259 MetaspaceGC::compute_new_size();
260
261 // Free worker slices
262 for (uint i = 0; i < heap->max_workers(); i++) {
263 delete worker_slices[i];
264 }
265 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
266
267 heap->set_full_gc_move_in_progress(false);
268 heap->set_full_gc_in_progress(false);
269
270 if (ShenandoahVerify) {
271 heap->verifier()->verify_after_fullgc();
272 }
273
274 // Humongous regions are promoted on demand and are accounted for by normal Full GC mechanisms.
275 if (VerifyAfterGC) {
276 Universe::verify();
277 }
278
279 {
280 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
281 heap->post_full_gc_dump(_gc_timer);
282 }
283 }
284
285 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
286 private:
287 ShenandoahMarkingContext* const _ctx;
288
289 public:
290 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
291
292 void heap_region_do(ShenandoahHeapRegion *r) {
293 // TODO: Add API to heap to skip free regions
294 if (r->is_affiliated()) {
295 _ctx->capture_top_at_mark_start(r);
296 r->clear_live_data();
297 }
298 }
299
300 bool is_thread_safe() { return true; }
301 };
302
303 void ShenandoahFullGC::phase1_mark_heap() {
304 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
305 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
306
307 ShenandoahHeap* heap = ShenandoahHeap::heap();
308
309 ShenandoahPrepareForMarkClosure cl;
310 heap->parallel_heap_region_iterate(&cl);
311
312 heap->set_unload_classes(heap->global_generation()->heuristics()->can_unload_classes());
313
314 ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
315 // enable ("weak") refs discovery
316 rp->set_soft_reference_policy(true); // forcefully purge all soft references
317
318 ShenandoahSTWMark mark(heap->global_generation(), true /*full_gc*/);
319 mark.mark();
320 heap->parallel_cleaning(true /* full_gc */);
321
322 if (ShenandoahHeap::heap()->mode()->is_generational()) {
323 ShenandoahGenerationalFullGC::log_live_in_old(heap);
324 }
325 }
326
327 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
328 private:
329 PreservedMarks* const _preserved_marks;
330 ShenandoahHeap* const _heap;
331 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
332 int _empty_regions_pos;
333 ShenandoahHeapRegion* _to_region;
334 ShenandoahHeapRegion* _from_region;
335 HeapWord* _compact_point;
336
337 public:
338 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
339 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
340 ShenandoahHeapRegion* to_region) :
341 _preserved_marks(preserved_marks),
342 _heap(ShenandoahHeap::heap()),
343 _empty_regions(empty_regions),
344 _empty_regions_pos(0),
345 _to_region(to_region),
346 _from_region(nullptr),
347 _compact_point(to_region->bottom()) {}
348
349 void set_from_region(ShenandoahHeapRegion* from_region) {
350 _from_region = from_region;
351 }
352
353 void finish() {
354 assert(_to_region != nullptr, "should not happen");
355 _to_region->set_new_top(_compact_point);
356 }
357
358 bool is_compact_same_region() {
359 return _from_region == _to_region;
360 }
361
362 int empty_regions_pos() {
363 return _empty_regions_pos;
364 }
365
366 void do_object(oop p) {
367 assert(_from_region != nullptr, "must set before work");
368 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
369 assert(!_heap->complete_marking_context()->allocated_after_mark_start(p), "must be truly marked");
370
371 size_t obj_size = p->size();
372 if (_compact_point + obj_size > _to_region->end()) {
373 finish();
374
375 // Object doesn't fit. Pick next empty region and start compacting there.
376 ShenandoahHeapRegion* new_to_region;
377 if (_empty_regions_pos < _empty_regions.length()) {
378 new_to_region = _empty_regions.at(_empty_regions_pos);
379 _empty_regions_pos++;
380 } else {
381 // Out of empty region? Compact within the same region.
382 new_to_region = _from_region;
383 }
384
385 assert(new_to_region != _to_region, "must not reuse same to-region");
386 assert(new_to_region != nullptr, "must not be null");
387 _to_region = new_to_region;
388 _compact_point = _to_region->bottom();
389 }
390
391 // Object fits into current region, record new location, if object does not move:
392 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
393 shenandoah_assert_not_forwarded(nullptr, p);
394 if (_compact_point != cast_from_oop<HeapWord*>(p)) {
395 _preserved_marks->push_if_necessary(p, p->mark());
396 p->forward_to(cast_to_oop(_compact_point));
397 }
398 _compact_point += obj_size;
399 }
400 };
401
402 class ShenandoahPrepareForCompactionTask : public WorkerTask {
403 private:
404 PreservedMarksSet* const _preserved_marks;
405 ShenandoahHeap* const _heap;
406 ShenandoahHeapRegionSet** const _worker_slices;
407
408 public:
409 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices) :
410 WorkerTask("Shenandoah Prepare For Compaction"),
411 _preserved_marks(preserved_marks),
412 _heap(ShenandoahHeap::heap()), _worker_slices(worker_slices) {
413 }
414
415 static bool is_candidate_region(ShenandoahHeapRegion* r) {
416 // Empty region: get it into the slice to defragment the slice itself.
417 // We could have skipped this without violating correctness, but we really
418 // want to compact all live regions to the start of the heap, which sometimes
419 // means moving them into the fully empty regions.
420 if (r->is_empty()) return true;
421
422 // Can move the region, and this is not the humongous region. Humongous
423 // moves are special cased here, because their moves are handled separately.
424 return r->is_stw_move_allowed() && !r->is_humongous();
425 }
426
427 void work(uint worker_id) override;
428 private:
429 template<typename ClosureType>
430 void prepare_for_compaction(ClosureType& cl,
431 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
432 ShenandoahHeapRegionSetIterator& it,
433 ShenandoahHeapRegion* from_region);
434 };
435
436 void ShenandoahPrepareForCompactionTask::work(uint worker_id) {
437 ShenandoahParallelWorkerSession worker_session(worker_id);
438 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
439 ShenandoahHeapRegionSetIterator it(slice);
440 ShenandoahHeapRegion* from_region = it.next();
441 // No work?
442 if (from_region == nullptr) {
443 return;
444 }
445
446 // Sliding compaction. Walk all regions in the slice, and compact them.
447 // Remember empty regions and reuse them as needed.
448 ResourceMark rm;
449
450 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
451
452 if (_heap->mode()->is_generational()) {
453 ShenandoahPrepareForGenerationalCompactionObjectClosure cl(_preserved_marks->get(worker_id),
454 empty_regions, from_region, worker_id);
455 prepare_for_compaction(cl, empty_regions, it, from_region);
456 } else {
457 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
458 prepare_for_compaction(cl, empty_regions, it, from_region);
459 }
460 }
461
462 template<typename ClosureType>
463 void ShenandoahPrepareForCompactionTask::prepare_for_compaction(ClosureType& cl,
464 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
465 ShenandoahHeapRegionSetIterator& it,
466 ShenandoahHeapRegion* from_region) {
467 while (from_region != nullptr) {
468 assert(is_candidate_region(from_region), "Sanity");
469 cl.set_from_region(from_region);
470 if (from_region->has_live()) {
471 _heap->marked_object_iterate(from_region, &cl);
472 }
473
474 // Compacted the region to somewhere else? From-region is empty then.
475 if (!cl.is_compact_same_region()) {
476 empty_regions.append(from_region);
477 }
478 from_region = it.next();
479 }
480 cl.finish();
481
482 // Mark all remaining regions as empty
483 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
484 ShenandoahHeapRegion* r = empty_regions.at(pos);
485 r->set_new_top(r->bottom());
486 }
487 }
488
489 void ShenandoahFullGC::calculate_target_humongous_objects() {
490 ShenandoahHeap* heap = ShenandoahHeap::heap();
491
492 // Compute the new addresses for humongous objects. We need to do this after addresses
493 // for regular objects are calculated, and we know what regions in heap suffix are
494 // available for humongous moves.
495 //
496 // Scan the heap backwards, because we are compacting humongous regions towards the end.
497 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
498 // humongous start there.
499 //
500 // The complication is potential non-movable regions during the scan. If such region is
501 // detected, then sliding restarts towards that non-movable region.
502
503 size_t to_begin = heap->num_regions();
504 size_t to_end = heap->num_regions();
505
506 log_debug(gc)("Full GC calculating target humongous objects from end " SIZE_FORMAT, to_end);
507 for (size_t c = heap->num_regions(); c > 0; c--) {
508 ShenandoahHeapRegion *r = heap->get_region(c - 1);
509 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
510 // To-region candidate: record this, and continue scan
511 to_begin = r->index();
512 continue;
513 }
514
515 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
516 // From-region candidate: movable humongous region
517 oop old_obj = cast_to_oop(r->bottom());
518 size_t words_size = old_obj->size();
519 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
520
521 size_t start = to_end - num_regions;
522
523 if (start >= to_begin && start != r->index()) {
524 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
525 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
526 old_obj->forward_to(cast_to_oop(heap->get_region(start)->bottom()));
527 to_end = start;
528 continue;
529 }
530 }
531
532 // Failed to fit. Scan starting from current region.
533 to_begin = r->index();
534 to_end = r->index();
535 }
536 }
537
538 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
539 private:
540 ShenandoahHeap* const _heap;
541
542 public:
543 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
544 void heap_region_do(ShenandoahHeapRegion* r) {
545 if (r->is_trash()) {
546 r->recycle();
547 }
548 if (r->is_cset()) {
549 // Leave affiliation unchanged
550 r->make_regular_bypass();
551 }
552 if (r->is_empty_uncommitted()) {
553 r->make_committed_bypass();
554 }
555 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
556
557 // Record current region occupancy: this communicates empty regions are free
558 // to the rest of Full GC code.
559 r->set_new_top(r->top());
560 }
561 };
562
563 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
564 private:
565 ShenandoahHeap* const _heap;
566 ShenandoahMarkingContext* const _ctx;
567
568 public:
569 ShenandoahTrashImmediateGarbageClosure() :
570 _heap(ShenandoahHeap::heap()),
571 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
572
573 void heap_region_do(ShenandoahHeapRegion* r) {
574 if (!r->is_affiliated()) {
575 // Ignore free regions
576 // TODO: change iterators so they do not process FREE regions.
577 return;
578 }
579
580 if (r->is_humongous_start()) {
581 oop humongous_obj = cast_to_oop(r->bottom());
582 if (!_ctx->is_marked(humongous_obj)) {
583 assert(!r->has_live(),
584 "Region " SIZE_FORMAT " is not marked, should not have live", r->index());
585 _heap->trash_humongous_region_at(r);
586 } else {
587 assert(r->has_live(),
588 "Region " SIZE_FORMAT " should have live", r->index());
589 }
590 } else if (r->is_humongous_continuation()) {
591 // If we hit continuation, the non-live humongous starts should have been trashed already
592 assert(r->humongous_start_region()->has_live(),
593 "Region " SIZE_FORMAT " should have live", r->index());
594 } else if (r->is_regular()) {
595 if (!r->has_live()) {
596 r->make_trash_immediate();
597 }
598 }
599 }
600 };
601
602 void ShenandoahFullGC::distribute_slices(ShenandoahHeapRegionSet** worker_slices) {
603 ShenandoahHeap* heap = ShenandoahHeap::heap();
604
605 uint n_workers = heap->workers()->active_workers();
606 size_t n_regions = heap->num_regions();
607
608 // What we want to accomplish: have the dense prefix of data, while still balancing
609 // out the parallel work.
610 //
611 // Assuming the amount of work is driven by the live data that needs moving, we can slice
612 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each
613 // thread takes all regions in its prefix subset, and then it takes some regions from
614 // the tail.
615 //
616 // Tail region selection becomes interesting.
617 //
618 // First, we want to distribute the regions fairly between the workers, and those regions
619 // might have different amount of live data. So, until we sure no workers need live data,
620 // we need to only take what the worker needs.
621 //
622 // Second, since we slide everything to the left in each slice, the most busy regions
623 // would be the ones on the left. Which means we want to have all workers have their after-tail
624 // regions as close to the left as possible.
625 //
626 // The easiest way to do this is to distribute after-tail regions in round-robin between
627 // workers that still need live data.
628 //
629 // Consider parallel workers A, B, C, then the target slice layout would be:
630 //
631 // AAAAAAAABBBBBBBBCCCCCCCC|ABCABCABCABCABCABCABCABABABABABABABABABABAAAAA
632 //
633 // (.....dense-prefix.....) (.....................tail...................)
634 // [all regions fully live] [left-most regions are fuller that right-most]
635 //
636
637 // Compute how much live data is there. This would approximate the size of dense prefix
638 // we target to create.
639 size_t total_live = 0;
640 for (size_t idx = 0; idx < n_regions; idx++) {
641 ShenandoahHeapRegion *r = heap->get_region(idx);
642 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
643 total_live += r->get_live_data_words();
644 }
645 }
646
647 // Estimate the size for the dense prefix. Note that we specifically count only the
648 // "full" regions, so there would be some non-full regions in the slice tail.
649 size_t live_per_worker = total_live / n_workers;
650 size_t prefix_regions_per_worker = live_per_worker / ShenandoahHeapRegion::region_size_words();
651 size_t prefix_regions_total = prefix_regions_per_worker * n_workers;
652 prefix_regions_total = MIN2(prefix_regions_total, n_regions);
653 assert(prefix_regions_total <= n_regions, "Sanity");
654
655 // There might be non-candidate regions in the prefix. To compute where the tail actually
656 // ends up being, we need to account those as well.
657 size_t prefix_end = prefix_regions_total;
658 for (size_t idx = 0; idx < prefix_regions_total; idx++) {
659 ShenandoahHeapRegion *r = heap->get_region(idx);
660 if (!ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
661 prefix_end++;
662 }
663 }
664 prefix_end = MIN2(prefix_end, n_regions);
665 assert(prefix_end <= n_regions, "Sanity");
666
667 // Distribute prefix regions per worker: each thread definitely gets its own same-sized
668 // subset of dense prefix.
669 size_t prefix_idx = 0;
670
671 size_t* live = NEW_C_HEAP_ARRAY(size_t, n_workers, mtGC);
672
673 for (size_t wid = 0; wid < n_workers; wid++) {
674 ShenandoahHeapRegionSet* slice = worker_slices[wid];
675
676 live[wid] = 0;
677 size_t regs = 0;
678
679 // Add all prefix regions for this worker
680 while (prefix_idx < prefix_end && regs < prefix_regions_per_worker) {
681 ShenandoahHeapRegion *r = heap->get_region(prefix_idx);
682 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
683 slice->add_region(r);
684 live[wid] += r->get_live_data_words();
685 regs++;
686 }
687 prefix_idx++;
688 }
689 }
690
691 // Distribute the tail among workers in round-robin fashion.
692 size_t wid = n_workers - 1;
693
694 for (size_t tail_idx = prefix_end; tail_idx < n_regions; tail_idx++) {
695 ShenandoahHeapRegion *r = heap->get_region(tail_idx);
696 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
697 assert(wid < n_workers, "Sanity");
698
699 size_t live_region = r->get_live_data_words();
700
701 // Select next worker that still needs live data.
702 size_t old_wid = wid;
703 do {
704 wid++;
705 if (wid == n_workers) wid = 0;
706 } while (live[wid] + live_region >= live_per_worker && old_wid != wid);
707
708 if (old_wid == wid) {
709 // Circled back to the same worker? This means liveness data was
710 // miscalculated. Bump the live_per_worker limit so that
711 // everyone gets a piece of the leftover work.
712 live_per_worker += ShenandoahHeapRegion::region_size_words();
713 }
714
715 worker_slices[wid]->add_region(r);
716 live[wid] += live_region;
717 }
718 }
719
720 FREE_C_HEAP_ARRAY(size_t, live);
721
722 #ifdef ASSERT
723 ResourceBitMap map(n_regions);
724 for (size_t wid = 0; wid < n_workers; wid++) {
725 ShenandoahHeapRegionSetIterator it(worker_slices[wid]);
726 ShenandoahHeapRegion* r = it.next();
727 while (r != nullptr) {
728 size_t idx = r->index();
729 assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: " SIZE_FORMAT, idx);
730 assert(!map.at(idx), "No region distributed twice: " SIZE_FORMAT, idx);
731 map.at_put(idx, true);
732 r = it.next();
733 }
734 }
735
736 for (size_t rid = 0; rid < n_regions; rid++) {
737 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
738 bool is_distributed = map.at(rid);
739 assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
740 }
741 #endif
742 }
743
744 // TODO:
745 // Consider compacting old-gen objects toward the high end of memory and young-gen objects towards the low-end
746 // of memory. As currently implemented, all regions are compacted toward the low-end of memory. This creates more
747 // fragmentation of the heap, because old-gen regions get scattered among low-address regions such that it becomes
748 // more difficult to find contiguous regions for humongous objects.
749 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
750 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
751 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
752
753 ShenandoahHeap* heap = ShenandoahHeap::heap();
754
755 // About to figure out which regions can be compacted, make sure pinning status
756 // had been updated in GC prologue.
757 heap->assert_pinned_region_status();
758
759 {
760 // Trash the immediately collectible regions before computing addresses
761 ShenandoahTrashImmediateGarbageClosure tigcl;
762 heap->heap_region_iterate(&tigcl);
763
764 // Make sure regions are in good state: committed, active, clean.
765 // This is needed because we are potentially sliding the data through them.
766 ShenandoahEnsureHeapActiveClosure ecl;
767 heap->heap_region_iterate(&ecl);
768 }
769
770 // Compute the new addresses for regular objects
771 {
772 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
773
774 distribute_slices(worker_slices);
775
776 // TODO: This is ResourceMark is missing upstream.
777 ResourceMark rm;
778 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
779 heap->workers()->run_task(&task);
780 }
781
782 // Compute the new addresses for humongous objects
783 {
784 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
785 calculate_target_humongous_objects();
786 }
787 }
788
789 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
790 private:
791 ShenandoahHeap* const _heap;
792 ShenandoahMarkingContext* const _ctx;
793
794 template <class T>
795 inline void do_oop_work(T* p) {
796 T o = RawAccess<>::oop_load(p);
797 if (!CompressedOops::is_null(o)) {
798 oop obj = CompressedOops::decode_not_null(o);
799 assert(_ctx->is_marked(obj), "must be marked");
800 if (obj->is_forwarded()) {
801 oop forw = obj->forwardee();
802 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
803 }
804 }
805 }
806
807 public:
808 ShenandoahAdjustPointersClosure() :
809 _heap(ShenandoahHeap::heap()),
810 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
811
812 void do_oop(oop* p) { do_oop_work(p); }
813 void do_oop(narrowOop* p) { do_oop_work(p); }
814 void do_method(Method* m) {}
815 void do_nmethod(nmethod* nm) {}
816 };
817
818 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
819 private:
820 ShenandoahHeap* const _heap;
821 ShenandoahAdjustPointersClosure _cl;
822
823 public:
824 ShenandoahAdjustPointersObjectClosure() :
825 _heap(ShenandoahHeap::heap()) {
826 }
827 void do_object(oop p) {
828 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
829 p->oop_iterate(&_cl);
830 }
831 };
832
833 class ShenandoahAdjustPointersTask : public WorkerTask {
834 private:
835 ShenandoahHeap* const _heap;
836 ShenandoahRegionIterator _regions;
837
838 public:
839 ShenandoahAdjustPointersTask() :
840 WorkerTask("Shenandoah Adjust Pointers"),
841 _heap(ShenandoahHeap::heap()) {
842 }
843
844 void work(uint worker_id) {
845 ShenandoahParallelWorkerSession worker_session(worker_id);
846 ShenandoahAdjustPointersObjectClosure obj_cl;
847 ShenandoahHeapRegion* r = _regions.next();
848 while (r != nullptr) {
849 if (!r->is_humongous_continuation() && r->has_live()) {
850 _heap->marked_object_iterate(r, &obj_cl);
851 }
852 if (_heap->mode()->is_generational()) {
853 ShenandoahGenerationalFullGC::maybe_coalesce_and_fill_region(r);
854 }
855 r = _regions.next();
856 }
857 }
858 };
859
860 class ShenandoahAdjustRootPointersTask : public WorkerTask {
861 private:
862 ShenandoahRootAdjuster* _rp;
863 PreservedMarksSet* _preserved_marks;
864 public:
865 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
866 WorkerTask("Shenandoah Adjust Root Pointers"),
867 _rp(rp),
868 _preserved_marks(preserved_marks) {}
869
870 void work(uint worker_id) {
871 ShenandoahParallelWorkerSession worker_session(worker_id);
872 ShenandoahAdjustPointersClosure cl;
873 _rp->roots_do(worker_id, &cl);
874 _preserved_marks->get(worker_id)->adjust_during_full_gc();
875 }
876 };
877
878 void ShenandoahFullGC::phase3_update_references() {
879 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
880 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
881
882 ShenandoahHeap* heap = ShenandoahHeap::heap();
883
884 WorkerThreads* workers = heap->workers();
885 uint nworkers = workers->active_workers();
886 {
887 #if COMPILER2_OR_JVMCI
888 DerivedPointerTable::clear();
889 #endif
890 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
891 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
892 workers->run_task(&task);
893 #if COMPILER2_OR_JVMCI
894 DerivedPointerTable::update_pointers();
895 #endif
896 }
897
898 ShenandoahAdjustPointersTask adjust_pointers_task;
899 workers->run_task(&adjust_pointers_task);
900 }
901
902 class ShenandoahCompactObjectsClosure : public ObjectClosure {
903 private:
904 ShenandoahHeap* const _heap;
905 uint const _worker_id;
906
907 public:
908 ShenandoahCompactObjectsClosure(uint worker_id) :
909 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
910
911 void do_object(oop p) {
912 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
913 size_t size = p->size();
914 if (p->is_forwarded()) {
915 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
916 HeapWord* compact_to = cast_from_oop<HeapWord*>(p->forwardee());
917 assert(compact_from != compact_to, "Forwarded object should move");
918 Copy::aligned_conjoint_words(compact_from, compact_to, size);
919 oop new_obj = cast_to_oop(compact_to);
920
921 ContinuationGCSupport::relativize_stack_chunk(new_obj);
922 new_obj->init_mark();
923 }
924 }
925 };
926
927 class ShenandoahCompactObjectsTask : public WorkerTask {
928 private:
929 ShenandoahHeap* const _heap;
930 ShenandoahHeapRegionSet** const _worker_slices;
931
932 public:
933 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
934 WorkerTask("Shenandoah Compact Objects"),
935 _heap(ShenandoahHeap::heap()),
936 _worker_slices(worker_slices) {
937 }
938
939 void work(uint worker_id) {
940 ShenandoahParallelWorkerSession worker_session(worker_id);
941 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
942
943 ShenandoahCompactObjectsClosure cl(worker_id);
944 ShenandoahHeapRegion* r = slice.next();
945 while (r != nullptr) {
946 assert(!r->is_humongous(), "must not get humongous regions here");
947 if (r->has_live()) {
948 _heap->marked_object_iterate(r, &cl);
949 }
950 r->set_top(r->new_top());
951 r = slice.next();
952 }
953 }
954 };
955
956 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
957 private:
958 ShenandoahHeap* const _heap;
959 bool _is_generational;
960 size_t _young_regions, _young_usage, _young_humongous_waste;
961 size_t _old_regions, _old_usage, _old_humongous_waste;
962
963 public:
964 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()),
965 _is_generational(_heap->mode()->is_generational()),
966 _young_regions(0),
967 _young_usage(0),
968 _young_humongous_waste(0),
969 _old_regions(0),
970 _old_usage(0),
971 _old_humongous_waste(0)
972 {
973 _heap->free_set()->clear();
974 }
975
976 void heap_region_do(ShenandoahHeapRegion* r) {
977 assert (!r->is_cset(), "cset regions should have been demoted already");
978
979 // Need to reset the complete-top-at-mark-start pointer here because
980 // the complete marking bitmap is no longer valid. This ensures
981 // size-based iteration in marked_object_iterate().
982 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
983 // pinned regions.
984 if (!r->is_pinned()) {
985 _heap->complete_marking_context()->reset_top_at_mark_start(r);
986 }
987
988 size_t live = r->used();
989
990 // Make empty regions that have been allocated into regular
991 if (r->is_empty() && live > 0) {
992 if (!_is_generational) {
993 r->make_young_maybe();
994 }
995 // else, generational mode compaction has already established affiliation.
996 r->make_regular_bypass();
997 if (ZapUnusedHeapArea) {
998 SpaceMangler::mangle_region(MemRegion(r->top(), r->end()));
999 }
1000 }
1001
1002 // Reclaim regular regions that became empty
1003 if (r->is_regular() && live == 0) {
1004 r->make_trash();
1005 }
1006
1007 // Recycle all trash regions
1008 if (r->is_trash()) {
1009 live = 0;
1010 r->recycle();
1011 } else {
1012 if (r->is_old()) {
1013 ShenandoahGenerationalFullGC::account_for_region(r, _old_regions, _old_usage, _old_humongous_waste);
1014 } else if (r->is_young()) {
1015 ShenandoahGenerationalFullGC::account_for_region(r, _young_regions, _young_usage, _young_humongous_waste);
1016 }
1017 }
1018 r->set_live_data(live);
1019 r->reset_alloc_metadata();
1020 }
1021
1022 void update_generation_usage() {
1023 if (_is_generational) {
1024 _heap->old_generation()->establish_usage(_old_regions, _old_usage, _old_humongous_waste);
1025 _heap->young_generation()->establish_usage(_young_regions, _young_usage, _young_humongous_waste);
1026 } else {
1027 assert(_old_regions == 0, "Old regions only expected in generational mode");
1028 assert(_old_usage == 0, "Old usage only expected in generational mode");
1029 assert(_old_humongous_waste == 0, "Old humongous waste only expected in generational mode");
1030 }
1031
1032 // In generational mode, global usage should be the sum of young and old. This is also true
1033 // for non-generational modes except that there are no old regions.
1034 _heap->global_generation()->establish_usage(_old_regions + _young_regions,
1035 _old_usage + _young_usage,
1036 _old_humongous_waste + _young_humongous_waste);
1037 }
1038 };
1039
1040 void ShenandoahFullGC::compact_humongous_objects() {
1041 // Compact humongous regions, based on their fwdptr objects.
1042 //
1043 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
1044 // humongous regions are already compacted, and do not require further moves, which alleviates
1045 // sliding costs. We may consider doing this in parallel in the future.
1046
1047 ShenandoahHeap* heap = ShenandoahHeap::heap();
1048
1049 for (size_t c = heap->num_regions(); c > 0; c--) {
1050 ShenandoahHeapRegion* r = heap->get_region(c - 1);
1051 if (r->is_humongous_start()) {
1052 oop old_obj = cast_to_oop(r->bottom());
1053 if (!old_obj->is_forwarded()) {
1054 // No need to move the object, it stays at the same slot
1055 continue;
1056 }
1057 size_t words_size = old_obj->size();
1058 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
1059
1060 size_t old_start = r->index();
1061 size_t old_end = old_start + num_regions - 1;
1062 size_t new_start = heap->heap_region_index_containing(old_obj->forwardee());
1063 size_t new_end = new_start + num_regions - 1;
1064 assert(old_start != new_start, "must be real move");
1065 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
1066
1067 log_debug(gc)("Full GC compaction moves humongous object from region " SIZE_FORMAT " to region " SIZE_FORMAT, old_start, new_start);
1068 Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
1069 ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
1070
1071 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
1072 new_obj->init_mark();
1073
1074 {
1075 ShenandoahAffiliation original_affiliation = r->affiliation();
1076 for (size_t c = old_start; c <= old_end; c++) {
1077 ShenandoahHeapRegion* r = heap->get_region(c);
1078 // Leave humongous region affiliation unchanged.
1079 r->make_regular_bypass();
1080 r->set_top(r->bottom());
1081 }
1082
1083 for (size_t c = new_start; c <= new_end; c++) {
1084 ShenandoahHeapRegion* r = heap->get_region(c);
1085 if (c == new_start) {
1086 r->make_humongous_start_bypass(original_affiliation);
1087 } else {
1088 r->make_humongous_cont_bypass(original_affiliation);
1089 }
1090
1091 // Trailing region may be non-full, record the remainder there
1092 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1093 if ((c == new_end) && (remainder != 0)) {
1094 r->set_top(r->bottom() + remainder);
1095 } else {
1096 r->set_top(r->end());
1097 }
1098
1099 r->reset_alloc_metadata();
1100 }
1101 }
1102 }
1103 }
1104 }
1105
1106 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1107 // we need to remain able to walk pinned regions.
1108 // Since pinned region do not move and don't get compacted, we will get holes with
1109 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
1110 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
1111 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
1112 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
1113 class ShenandoahMCResetCompleteBitmapTask : public WorkerTask {
1114 private:
1115 ShenandoahRegionIterator _regions;
1116
1117 public:
1118 ShenandoahMCResetCompleteBitmapTask() :
1119 WorkerTask("Shenandoah Reset Bitmap") {
1120 }
1121
1122 void work(uint worker_id) {
1123 ShenandoahParallelWorkerSession worker_session(worker_id);
1124 ShenandoahHeapRegion* region = _regions.next();
1125 ShenandoahHeap* heap = ShenandoahHeap::heap();
1126 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
1127 while (region != nullptr) {
1128 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
1129 ctx->clear_bitmap(region);
1130 }
1131 region = _regions.next();
1132 }
1133 }
1134 };
1135
1136 void ShenandoahFullGC::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
1137 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
1138 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
1139
1140 ShenandoahHeap* heap = ShenandoahHeap::heap();
1141
1142 // Compact regular objects first
1143 {
1144 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
1145 ShenandoahCompactObjectsTask compact_task(worker_slices);
1146 heap->workers()->run_task(&compact_task);
1147 }
1148
1149 // Compact humongous objects after regular object moves
1150 {
1151 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
1152 compact_humongous_objects();
1153 }
1154 }
1155
1156 void ShenandoahFullGC::phase5_epilog() {
1157 GCTraceTime(Info, gc, phases) time("Phase 5: Full GC epilog", _gc_timer);
1158 ShenandoahHeap* heap = ShenandoahHeap::heap();
1159
1160 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1161 // and must ensure the bitmap is in sync.
1162 {
1163 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1164 ShenandoahMCResetCompleteBitmapTask task;
1165 heap->workers()->run_task(&task);
1166 }
1167
1168 // Bring regions in proper states after the collection, and set heap properties.
1169 {
1170 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1171 ShenandoahPostCompactClosure post_compact;
1172 heap->heap_region_iterate(&post_compact);
1173 post_compact.update_generation_usage();
1174
1175 if (heap->mode()->is_generational()) {
1176 ShenandoahGenerationalFullGC::balance_generations_after_gc(heap);
1177 }
1178
1179 heap->collection_set()->clear();
1180 size_t young_cset_regions, old_cset_regions;
1181 size_t first_old, last_old, num_old;
1182 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
1183
1184 // We also do not expand old generation size following Full GC because we have scrambled age populations and
1185 // no longer have objects separated by age into distinct regions.
1186
1187 // TODO: Do we need to fix FullGC so that it maintains aged segregation of objects into distinct regions?
1188 // A partial solution would be to remember how many objects are of tenure age following Full GC, but
1189 // this is probably suboptimal, because most of these objects will not reside in a region that will be
1190 // selected for the next evacuation phase.
1191
1192
1193 if (heap->mode()->is_generational()) {
1194 ShenandoahGenerationalFullGC::compute_balances();
1195 }
1196
1197 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old);
1198
1199 heap->clear_cancelled_gc(true /* clear oom handler */);
1200 }
1201
1202 _preserved_marks->restore(heap->workers());
1203 _preserved_marks->reclaim();
1204
1205 // We defer generation resizing actions until after cset regions have been recycled. We do this even following an
1206 // abbreviated cycle.
1207 if (heap->mode()->is_generational()) {
1208 ShenandoahGenerationalFullGC::balance_generations_after_rebuilding_free_set();
1209 ShenandoahGenerationalFullGC::rebuild_remembered_set(heap);
1210 }
1211 }