1 /*
2 * Copyright (c) 2014, 2021, Red Hat, Inc. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26
27 #include "compiler/oopMap.hpp"
28 #include "gc/shared/continuationGCSupport.hpp"
29 #include "gc/shared/fullGCForwarding.inline.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/shenandoahClosures.inline.hpp"
36 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
37 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
38 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
39 #include "gc/shenandoah/shenandoahFreeSet.hpp"
40 #include "gc/shenandoah/shenandoahFullGC.hpp"
41 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
42 #include "gc/shenandoah/shenandoahMark.inline.hpp"
43 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
44 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
45 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
46 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
47 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
48 #include "gc/shenandoah/shenandoahMetrics.hpp"
49 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
50 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
51 #include "gc/shenandoah/shenandoahSTWMark.hpp"
52 #include "gc/shenandoah/shenandoahUtils.hpp"
53 #include "gc/shenandoah/shenandoahVerifier.hpp"
54 #include "gc/shenandoah/shenandoahVMOperations.hpp"
55 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
56 #include "memory/metaspaceUtils.hpp"
57 #include "memory/universe.hpp"
58 #include "oops/compressedOops.inline.hpp"
59 #include "oops/oop.inline.hpp"
60 #include "runtime/javaThread.hpp"
61 #include "runtime/orderAccess.hpp"
62 #include "runtime/vmThread.hpp"
63 #include "utilities/copy.hpp"
64 #include "utilities/events.hpp"
65 #include "utilities/growableArray.hpp"
66
67 ShenandoahFullGC::ShenandoahFullGC() :
68 _gc_timer(ShenandoahHeap::heap()->gc_timer()),
69 _preserved_marks(new PreservedMarksSet(true)) {}
70
71 ShenandoahFullGC::~ShenandoahFullGC() {
72 delete _preserved_marks;
73 }
74
75 bool ShenandoahFullGC::collect(GCCause::Cause cause) {
76 vmop_entry_full(cause);
77 // Always success
78 return true;
79 }
80
92 static const char* msg = "Pause Full";
93 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */);
94 EventMark em("%s", msg);
95
96 ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(),
97 ShenandoahWorkerPolicy::calc_workers_for_fullgc(),
98 "full gc");
99
100 op_full(cause);
101 }
102
103 void ShenandoahFullGC::op_full(GCCause::Cause cause) {
104 ShenandoahMetricsSnapshot metrics;
105 metrics.snap_before();
106
107 // Perform full GC
108 do_it(cause);
109
110 ShenandoahHeap* const heap = ShenandoahHeap::heap();
111
112 metrics.snap_after();
113
114 if (metrics.is_good_progress()) {
115 heap->notify_gc_progress();
116 } else {
117 // Nothing to do. Tell the allocation path that we have failed to make
118 // progress, and it can finally fail.
119 heap->notify_gc_no_progress();
120 }
121
122 // Regardless if progress was made, we record that we completed a "successful" full GC.
123 heap->heuristics()->record_success_full();
124 heap->shenandoah_policy()->record_success_full();
125 }
126
127 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
128 ShenandoahHeap* heap = ShenandoahHeap::heap();
129
130 if (ShenandoahVerify) {
131 heap->verifier()->verify_before_fullgc();
132 }
133
134 if (VerifyBeforeGC) {
135 Universe::verify();
136 }
137
138 // Degenerated GC may carry concurrent root flags when upgrading to
139 // full GC. We need to reset it before mutators resume.
140 heap->set_concurrent_strong_root_in_progress(false);
141 heap->set_concurrent_weak_root_in_progress(false);
142
143 heap->set_full_gc_in_progress(true);
144
145 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
146 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
147
148 {
149 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);
152
153 {
154 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
155 // Full GC is supposed to recover from any GC state:
156
157 // a0. Remember if we have forwarded objects
158 bool has_forwarded_objects = heap->has_forwarded_objects();
159
160 // a1. Cancel evacuation, if in progress
161 if (heap->is_evacuation_in_progress()) {
162 heap->set_evacuation_in_progress(false);
163 }
164 assert(!heap->is_evacuation_in_progress(), "sanity");
165
166 // a2. Cancel update-refs, if in progress
167 if (heap->is_update_refs_in_progress()) {
168 heap->set_update_refs_in_progress(false);
169 }
170 assert(!heap->is_update_refs_in_progress(), "sanity");
171
172 // b. Cancel concurrent mark, if in progress
173 if (heap->is_concurrent_mark_in_progress()) {
174 ShenandoahConcurrentGC::cancel();
175 heap->set_concurrent_mark_in_progress(false);
176 }
177 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
178
179 // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
180 if (has_forwarded_objects) {
181 update_roots(true /*full_gc*/);
182 }
183
184 // d. Reset the bitmaps for new marking
185 heap->reset_mark_bitmap();
186 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
187 assert(!heap->marking_context()->is_complete(), "sanity");
188
189 // e. Abandon reference discovery and clear all discovered references.
190 ShenandoahReferenceProcessor* rp = heap->ref_processor();
191 rp->abandon_partial_discovery();
192
193 // f. Sync pinned region status from the CP marks
194 heap->sync_pinned_region_status();
195
196 // The rest of prologue:
197 _preserved_marks->init(heap->workers()->active_workers());
198
199 assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
200 }
201
202 if (UseTLAB) {
203 heap->gclabs_retire(ResizeTLAB);
204 heap->tlabs_retire(ResizeTLAB);
205 }
206
207 OrderAccess::fence();
208
209 phase1_mark_heap();
210
211 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
212 // Coming out of Full GC, we would not have any forwarded objects.
213 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
214 heap->set_has_forwarded_objects(false);
215
216 heap->set_full_gc_move_in_progress(true);
217
218 // Setup workers for the rest
219 OrderAccess::fence();
220
221 // Initialize worker slices
222 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
256 heap->verifier()->verify_after_fullgc();
257 }
258
259 if (VerifyAfterGC) {
260 Universe::verify();
261 }
262
263 {
264 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
265 heap->post_full_gc_dump(_gc_timer);
266 }
267 }
268
269 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
270 private:
271 ShenandoahMarkingContext* const _ctx;
272
273 public:
274 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
275
276 void heap_region_do(ShenandoahHeapRegion *r) {
277 _ctx->capture_top_at_mark_start(r);
278 r->clear_live_data();
279 }
280
281 bool is_thread_safe() { return true; }
282 };
283
284 void ShenandoahFullGC::phase1_mark_heap() {
285 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
286 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
287
288 ShenandoahHeap* heap = ShenandoahHeap::heap();
289
290 ShenandoahPrepareForMarkClosure cl;
291 heap->parallel_heap_region_iterate(&cl);
292
293 heap->set_unload_classes(heap->heuristics()->can_unload_classes());
294
295 ShenandoahReferenceProcessor* rp = heap->ref_processor();
296 // enable ("weak") refs discovery
297 rp->set_soft_reference_policy(true); // forcefully purge all soft references
298
299 ShenandoahSTWMark mark(true /*full_gc*/);
300 mark.mark();
301 heap->parallel_cleaning(true /* full_gc */);
302 }
303
304 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
305 private:
306 PreservedMarks* const _preserved_marks;
307 ShenandoahHeap* const _heap;
308 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
309 int _empty_regions_pos;
310 ShenandoahHeapRegion* _to_region;
311 ShenandoahHeapRegion* _from_region;
312 HeapWord* _compact_point;
313
314 public:
315 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
316 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
317 ShenandoahHeapRegion* to_region) :
318 _preserved_marks(preserved_marks),
319 _heap(ShenandoahHeap::heap()),
320 _empty_regions(empty_regions),
321 _empty_regions_pos(0),
409 ShenandoahHeapRegionSetIterator& it,
410 ShenandoahHeapRegion* from_region);
411 };
412
413 void ShenandoahPrepareForCompactionTask::work(uint worker_id) {
414 ShenandoahParallelWorkerSession worker_session(worker_id);
415 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
416 ShenandoahHeapRegionSetIterator it(slice);
417 ShenandoahHeapRegion* from_region = it.next();
418 // No work?
419 if (from_region == nullptr) {
420 return;
421 }
422
423 // Sliding compaction. Walk all regions in the slice, and compact them.
424 // Remember empty regions and reuse them as needed.
425 ResourceMark rm;
426
427 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
428
429 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
430 prepare_for_compaction(cl, empty_regions, it, from_region);
431 }
432
433 template<typename ClosureType>
434 void ShenandoahPrepareForCompactionTask::prepare_for_compaction(ClosureType& cl,
435 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
436 ShenandoahHeapRegionSetIterator& it,
437 ShenandoahHeapRegion* from_region) {
438 while (from_region != nullptr) {
439 assert(is_candidate_region(from_region), "Sanity");
440 cl.set_from_region(from_region);
441 if (from_region->has_live()) {
442 _heap->marked_object_iterate(from_region, &cl);
443 }
444
445 // Compacted the region to somewhere else? From-region is empty then.
446 if (!cl.is_compact_same_region()) {
447 empty_regions.append(from_region);
448 }
449 from_region = it.next();
450 }
457 }
458 }
459
460 void ShenandoahFullGC::calculate_target_humongous_objects() {
461 ShenandoahHeap* heap = ShenandoahHeap::heap();
462
463 // Compute the new addresses for humongous objects. We need to do this after addresses
464 // for regular objects are calculated, and we know what regions in heap suffix are
465 // available for humongous moves.
466 //
467 // Scan the heap backwards, because we are compacting humongous regions towards the end.
468 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
469 // humongous start there.
470 //
471 // The complication is potential non-movable regions during the scan. If such region is
472 // detected, then sliding restarts towards that non-movable region.
473
474 size_t to_begin = heap->num_regions();
475 size_t to_end = heap->num_regions();
476
477 for (size_t c = heap->num_regions(); c > 0; c--) {
478 ShenandoahHeapRegion *r = heap->get_region(c - 1);
479 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
480 // To-region candidate: record this, and continue scan
481 to_begin = r->index();
482 continue;
483 }
484
485 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
486 // From-region candidate: movable humongous region
487 oop old_obj = cast_to_oop(r->bottom());
488 size_t words_size = old_obj->size();
489 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
490
491 size_t start = to_end - num_regions;
492
493 if (start >= to_begin && start != r->index()) {
494 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
495 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
496 FullGCForwarding::forward_to(old_obj, cast_to_oop(heap->get_region(start)->bottom()));
499 }
500 }
501
502 // Failed to fit. Scan starting from current region.
503 to_begin = r->index();
504 to_end = r->index();
505 }
506 }
507
508 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
509 private:
510 ShenandoahHeap* const _heap;
511
512 public:
513 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
514 void heap_region_do(ShenandoahHeapRegion* r) {
515 if (r->is_trash()) {
516 r->recycle();
517 }
518 if (r->is_cset()) {
519 r->make_regular_bypass();
520 }
521 if (r->is_empty_uncommitted()) {
522 r->make_committed_bypass();
523 }
524 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
525
526 // Record current region occupancy: this communicates empty regions are free
527 // to the rest of Full GC code.
528 r->set_new_top(r->top());
529 }
530 };
531
532 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
533 private:
534 ShenandoahHeap* const _heap;
535 ShenandoahMarkingContext* const _ctx;
536
537 public:
538 ShenandoahTrashImmediateGarbageClosure() :
539 _heap(ShenandoahHeap::heap()),
540 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
541
542 void heap_region_do(ShenandoahHeapRegion* r) {
543 if (r->is_humongous_start()) {
544 oop humongous_obj = cast_to_oop(r->bottom());
545 if (!_ctx->is_marked(humongous_obj)) {
546 assert(!r->has_live(),
547 "Region " SIZE_FORMAT " is not marked, should not have live", r->index());
548 _heap->trash_humongous_region_at(r);
549 } else {
550 assert(r->has_live(),
551 "Region " SIZE_FORMAT " should have live", r->index());
552 }
553 } else if (r->is_humongous_continuation()) {
554 // If we hit continuation, the non-live humongous starts should have been trashed already
555 assert(r->humongous_start_region()->has_live(),
556 "Region " SIZE_FORMAT " should have live", r->index());
557 } else if (r->is_regular()) {
558 if (!r->has_live()) {
559 r->make_trash_immediate();
560 }
561 }
562 }
563 };
564
565 void ShenandoahFullGC::distribute_slices(ShenandoahHeapRegionSet** worker_slices) {
566 ShenandoahHeap* heap = ShenandoahHeap::heap();
567
568 uint n_workers = heap->workers()->active_workers();
569 size_t n_regions = heap->num_regions();
570
571 // What we want to accomplish: have the dense prefix of data, while still balancing
572 // out the parallel work.
573 //
574 // Assuming the amount of work is driven by the live data that needs moving, we can slice
575 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each
576 // thread takes all regions in its prefix subset, and then it takes some regions from
699 for (size_t rid = 0; rid < n_regions; rid++) {
700 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
701 bool is_distributed = map.at(rid);
702 assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
703 }
704 #endif
705 }
706
707 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
708 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
709 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
710
711 ShenandoahHeap* heap = ShenandoahHeap::heap();
712
713 // About to figure out which regions can be compacted, make sure pinning status
714 // had been updated in GC prologue.
715 heap->assert_pinned_region_status();
716
717 {
718 // Trash the immediately collectible regions before computing addresses
719 ShenandoahTrashImmediateGarbageClosure tigcl;
720 heap->heap_region_iterate(&tigcl);
721
722 // Make sure regions are in good state: committed, active, clean.
723 // This is needed because we are potentially sliding the data through them.
724 ShenandoahEnsureHeapActiveClosure ecl;
725 heap->heap_region_iterate(&ecl);
726 }
727
728 // Compute the new addresses for regular objects
729 {
730 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
731
732 distribute_slices(worker_slices);
733
734 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
735 heap->workers()->run_task(&task);
736 }
737
738 // Compute the new addresses for humongous objects
739 {
740 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
788
789 class ShenandoahAdjustPointersTask : public WorkerTask {
790 private:
791 ShenandoahHeap* const _heap;
792 ShenandoahRegionIterator _regions;
793
794 public:
795 ShenandoahAdjustPointersTask() :
796 WorkerTask("Shenandoah Adjust Pointers"),
797 _heap(ShenandoahHeap::heap()) {
798 }
799
800 void work(uint worker_id) {
801 ShenandoahParallelWorkerSession worker_session(worker_id);
802 ShenandoahAdjustPointersObjectClosure obj_cl;
803 ShenandoahHeapRegion* r = _regions.next();
804 while (r != nullptr) {
805 if (!r->is_humongous_continuation() && r->has_live()) {
806 _heap->marked_object_iterate(r, &obj_cl);
807 }
808 r = _regions.next();
809 }
810 }
811 };
812
813 class ShenandoahAdjustRootPointersTask : public WorkerTask {
814 private:
815 ShenandoahRootAdjuster* _rp;
816 PreservedMarksSet* _preserved_marks;
817 public:
818 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
819 WorkerTask("Shenandoah Adjust Root Pointers"),
820 _rp(rp),
821 _preserved_marks(preserved_marks) {}
822
823 void work(uint worker_id) {
824 ShenandoahParallelWorkerSession worker_session(worker_id);
825 ShenandoahAdjustPointersClosure cl;
826 _rp->roots_do(worker_id, &cl);
827 _preserved_marks->get(worker_id)->adjust_during_full_gc();
892 void work(uint worker_id) {
893 ShenandoahParallelWorkerSession worker_session(worker_id);
894 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
895
896 ShenandoahCompactObjectsClosure cl(worker_id);
897 ShenandoahHeapRegion* r = slice.next();
898 while (r != nullptr) {
899 assert(!r->is_humongous(), "must not get humongous regions here");
900 if (r->has_live()) {
901 _heap->marked_object_iterate(r, &cl);
902 }
903 r->set_top(r->new_top());
904 r = slice.next();
905 }
906 }
907 };
908
909 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
910 private:
911 ShenandoahHeap* const _heap;
912 size_t _live;
913
914 public:
915 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
916 }
917
918 void heap_region_do(ShenandoahHeapRegion* r) {
919 assert (!r->is_cset(), "cset regions should have been demoted already");
920
921 // Need to reset the complete-top-at-mark-start pointer here because
922 // the complete marking bitmap is no longer valid. This ensures
923 // size-based iteration in marked_object_iterate().
924 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
925 // pinned regions.
926 if (!r->is_pinned()) {
927 _heap->complete_marking_context()->reset_top_at_mark_start(r);
928 }
929
930 size_t live = r->used();
931
932 // Make empty regions that have been allocated into regular
933 if (r->is_empty() && live > 0) {
934 r->make_regular_bypass();
935 if (ZapUnusedHeapArea) {
936 SpaceMangler::mangle_region(MemRegion(r->top(), r->end()));
937 }
938 }
939
940 // Reclaim regular regions that became empty
941 if (r->is_regular() && live == 0) {
942 r->make_trash();
943 }
944
945 // Recycle all trash regions
946 if (r->is_trash()) {
947 live = 0;
948 r->recycle();
949 }
950
951 r->set_live_data(live);
952 r->reset_alloc_metadata();
953 _live += live;
954 }
955
956 size_t get_live() {
957 return _live;
958 }
959 };
960
961 void ShenandoahFullGC::compact_humongous_objects() {
962 // Compact humongous regions, based on their fwdptr objects.
963 //
964 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
965 // humongous regions are already compacted, and do not require further moves, which alleviates
966 // sliding costs. We may consider doing this in parallel in the future.
967
968 ShenandoahHeap* heap = ShenandoahHeap::heap();
969
970 for (size_t c = heap->num_regions(); c > 0; c--) {
971 ShenandoahHeapRegion* r = heap->get_region(c - 1);
972 if (r->is_humongous_start()) {
973 oop old_obj = cast_to_oop(r->bottom());
974 if (!FullGCForwarding::is_forwarded(old_obj)) {
975 // No need to move the object, it stays at the same slot
976 continue;
977 }
978 size_t words_size = old_obj->size();
979 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
980
981 size_t old_start = r->index();
982 size_t old_end = old_start + num_regions - 1;
983 size_t new_start = heap->heap_region_index_containing(FullGCForwarding::forwardee(old_obj));
984 size_t new_end = new_start + num_regions - 1;
985 assert(old_start != new_start, "must be real move");
986 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
987
988 Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
989 ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
990
991 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
992 new_obj->init_mark();
993
994 {
995 for (size_t c = old_start; c <= old_end; c++) {
996 ShenandoahHeapRegion* r = heap->get_region(c);
997 r->make_regular_bypass();
998 r->set_top(r->bottom());
999 }
1000
1001 for (size_t c = new_start; c <= new_end; c++) {
1002 ShenandoahHeapRegion* r = heap->get_region(c);
1003 if (c == new_start) {
1004 r->make_humongous_start_bypass();
1005 } else {
1006 r->make_humongous_cont_bypass();
1007 }
1008
1009 // Trailing region may be non-full, record the remainder there
1010 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1011 if ((c == new_end) && (remainder != 0)) {
1012 r->set_top(r->bottom() + remainder);
1013 } else {
1014 r->set_top(r->end());
1015 }
1016
1017 r->reset_alloc_metadata();
1018 }
1019 }
1020 }
1021 }
1022 }
1023
1024 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1025 // we need to remain able to walk pinned regions.
1026 // Since pinned region do not move and don't get compacted, we will get holes with
1071 }
1072 }
1073
1074 void ShenandoahFullGC::phase5_epilog() {
1075 GCTraceTime(Info, gc, phases) time("Phase 5: Full GC epilog", _gc_timer);
1076 ShenandoahHeap* heap = ShenandoahHeap::heap();
1077
1078 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1079 // and must ensure the bitmap is in sync.
1080 {
1081 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1082 ShenandoahMCResetCompleteBitmapTask task;
1083 heap->workers()->run_task(&task);
1084 }
1085
1086 // Bring regions in proper states after the collection, and set heap properties.
1087 {
1088 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1089 ShenandoahPostCompactClosure post_compact;
1090 heap->heap_region_iterate(&post_compact);
1091 heap->set_used(post_compact.get_live());
1092
1093 heap->collection_set()->clear();
1094 heap->free_set()->rebuild();
1095 heap->clear_cancelled_gc();
1096 }
1097
1098 _preserved_marks->restore(heap->workers());
1099 _preserved_marks->reclaim();
1100 }
|
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/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/shenandoahCollectorPolicy.hpp"
38 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
39 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
40 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
41 #include "gc/shenandoah/shenandoahFreeSet.hpp"
42 #include "gc/shenandoah/shenandoahFullGC.hpp"
43 #include "gc/shenandoah/shenandoahGenerationalFullGC.hpp"
44 #include "gc/shenandoah/shenandoahGlobalGeneration.hpp"
45 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
46 #include "gc/shenandoah/shenandoahMark.inline.hpp"
47 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
48 #include "gc/shenandoah/shenandoahHeapRegionClosures.hpp"
49 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
50 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
51 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
52 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
53 #include "gc/shenandoah/shenandoahMetrics.hpp"
54 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
55 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
56 #include "gc/shenandoah/shenandoahSTWMark.hpp"
57 #include "gc/shenandoah/shenandoahUtils.hpp"
58 #include "gc/shenandoah/shenandoahVerifier.hpp"
59 #include "gc/shenandoah/shenandoahVMOperations.hpp"
60 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
61 #include "memory/metaspaceUtils.hpp"
62 #include "memory/universe.hpp"
63 #include "oops/compressedOops.inline.hpp"
64 #include "oops/oop.inline.hpp"
65 #include "runtime/orderAccess.hpp"
66 #include "runtime/vmThread.hpp"
67 #include "utilities/copy.hpp"
68 #include "utilities/events.hpp"
69 #include "utilities/growableArray.hpp"
70
71 ShenandoahFullGC::ShenandoahFullGC() :
72 _gc_timer(ShenandoahHeap::heap()->gc_timer()),
73 _preserved_marks(new PreservedMarksSet(true)) {}
74
75 ShenandoahFullGC::~ShenandoahFullGC() {
76 delete _preserved_marks;
77 }
78
79 bool ShenandoahFullGC::collect(GCCause::Cause cause) {
80 vmop_entry_full(cause);
81 // Always success
82 return true;
83 }
84
96 static const char* msg = "Pause Full";
97 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */);
98 EventMark em("%s", msg);
99
100 ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(),
101 ShenandoahWorkerPolicy::calc_workers_for_fullgc(),
102 "full gc");
103
104 op_full(cause);
105 }
106
107 void ShenandoahFullGC::op_full(GCCause::Cause cause) {
108 ShenandoahMetricsSnapshot metrics;
109 metrics.snap_before();
110
111 // Perform full GC
112 do_it(cause);
113
114 ShenandoahHeap* const heap = ShenandoahHeap::heap();
115
116 if (heap->mode()->is_generational()) {
117 ShenandoahGenerationalFullGC::handle_completion(heap);
118 }
119
120 metrics.snap_after();
121
122 if (metrics.is_good_progress()) {
123 heap->notify_gc_progress();
124 } else {
125 // Nothing to do. Tell the allocation path that we have failed to make
126 // progress, and it can finally fail.
127 heap->notify_gc_no_progress();
128 }
129
130 // Regardless if progress was made, we record that we completed a "successful" full GC.
131 heap->global_generation()->heuristics()->record_success_full();
132 heap->shenandoah_policy()->record_success_full();
133 }
134
135 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
136 ShenandoahHeap* heap = ShenandoahHeap::heap();
137
138 if (heap->mode()->is_generational()) {
139 ShenandoahGenerationalFullGC::prepare();
140 }
141
142 if (ShenandoahVerify) {
143 heap->verifier()->verify_before_fullgc();
144 }
145
146 if (VerifyBeforeGC) {
147 Universe::verify();
148 }
149
150 // Degenerated GC may carry concurrent root flags when upgrading to
151 // full GC. We need to reset it before mutators resume.
152 heap->set_concurrent_strong_root_in_progress(false);
153 heap->set_concurrent_weak_root_in_progress(false);
154
155 heap->set_full_gc_in_progress(true);
156
157 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
158 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
159
160 {
161 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);
164
165 {
166 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
167 // Full GC is supposed to recover from any GC state:
168
169 // a0. Remember if we have forwarded objects
170 bool has_forwarded_objects = heap->has_forwarded_objects();
171
172 // a1. Cancel evacuation, if in progress
173 if (heap->is_evacuation_in_progress()) {
174 heap->set_evacuation_in_progress(false);
175 }
176 assert(!heap->is_evacuation_in_progress(), "sanity");
177
178 // a2. Cancel update-refs, if in progress
179 if (heap->is_update_refs_in_progress()) {
180 heap->set_update_refs_in_progress(false);
181 }
182 assert(!heap->is_update_refs_in_progress(), "sanity");
183
184 // b. Cancel all concurrent marks, if in progress
185 if (heap->is_concurrent_mark_in_progress()) {
186 heap->cancel_concurrent_mark();
187 }
188 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
189
190 // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
191 if (has_forwarded_objects) {
192 update_roots(true /*full_gc*/);
193 }
194
195 // d. Reset the bitmaps for new marking
196 heap->global_generation()->reset_mark_bitmap();
197 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
198 assert(!heap->global_generation()->is_mark_complete(), "sanity");
199
200 // e. Abandon reference discovery and clear all discovered references.
201 ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
202 rp->abandon_partial_discovery();
203
204 // f. Sync pinned region status from the CP marks
205 heap->sync_pinned_region_status();
206
207 if (heap->mode()->is_generational()) {
208 ShenandoahGenerationalFullGC::restore_top_before_promote(heap);
209 }
210
211 // The rest of prologue:
212 _preserved_marks->init(heap->workers()->active_workers());
213
214 assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
215 }
216
217 if (UseTLAB) {
218 // Note: PLABs are also retired with GCLABs in generational mode.
219 heap->gclabs_retire(ResizeTLAB);
220 heap->tlabs_retire(ResizeTLAB);
221 }
222
223 OrderAccess::fence();
224
225 phase1_mark_heap();
226
227 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
228 // Coming out of Full GC, we would not have any forwarded objects.
229 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
230 heap->set_has_forwarded_objects(false);
231
232 heap->set_full_gc_move_in_progress(true);
233
234 // Setup workers for the rest
235 OrderAccess::fence();
236
237 // Initialize worker slices
238 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
272 heap->verifier()->verify_after_fullgc();
273 }
274
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) override {
293 _ctx->capture_top_at_mark_start(r);
294 r->clear_live_data();
295 }
296
297 bool is_thread_safe() override { return true; }
298 };
299
300 void ShenandoahFullGC::phase1_mark_heap() {
301 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
302 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
303
304 ShenandoahHeap* heap = ShenandoahHeap::heap();
305
306 ShenandoahPrepareForMarkClosure prepare_for_mark;
307 ShenandoahExcludeRegionClosure<FREE> cl(&prepare_for_mark);
308 heap->parallel_heap_region_iterate(&cl);
309
310 heap->set_unload_classes(heap->global_generation()->heuristics()->can_unload_classes());
311
312 ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
313 // enable ("weak") refs discovery
314 rp->set_soft_reference_policy(true); // forcefully purge all soft references
315
316 ShenandoahSTWMark mark(heap->global_generation(), true /*full_gc*/);
317 mark.mark();
318 heap->parallel_cleaning(true /* full_gc */);
319
320 if (ShenandoahHeap::heap()->mode()->is_generational()) {
321 ShenandoahGenerationalFullGC::log_live_in_old(heap);
322 }
323 }
324
325 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
326 private:
327 PreservedMarks* const _preserved_marks;
328 ShenandoahHeap* const _heap;
329 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
330 int _empty_regions_pos;
331 ShenandoahHeapRegion* _to_region;
332 ShenandoahHeapRegion* _from_region;
333 HeapWord* _compact_point;
334
335 public:
336 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
337 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
338 ShenandoahHeapRegion* to_region) :
339 _preserved_marks(preserved_marks),
340 _heap(ShenandoahHeap::heap()),
341 _empty_regions(empty_regions),
342 _empty_regions_pos(0),
430 ShenandoahHeapRegionSetIterator& it,
431 ShenandoahHeapRegion* from_region);
432 };
433
434 void ShenandoahPrepareForCompactionTask::work(uint worker_id) {
435 ShenandoahParallelWorkerSession worker_session(worker_id);
436 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
437 ShenandoahHeapRegionSetIterator it(slice);
438 ShenandoahHeapRegion* from_region = it.next();
439 // No work?
440 if (from_region == nullptr) {
441 return;
442 }
443
444 // Sliding compaction. Walk all regions in the slice, and compact them.
445 // Remember empty regions and reuse them as needed.
446 ResourceMark rm;
447
448 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
449
450 if (_heap->mode()->is_generational()) {
451 ShenandoahPrepareForGenerationalCompactionObjectClosure cl(_preserved_marks->get(worker_id),
452 empty_regions, from_region, worker_id);
453 prepare_for_compaction(cl, empty_regions, it, from_region);
454 } else {
455 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
456 prepare_for_compaction(cl, empty_regions, it, from_region);
457 }
458 }
459
460 template<typename ClosureType>
461 void ShenandoahPrepareForCompactionTask::prepare_for_compaction(ClosureType& cl,
462 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
463 ShenandoahHeapRegionSetIterator& it,
464 ShenandoahHeapRegion* from_region) {
465 while (from_region != nullptr) {
466 assert(is_candidate_region(from_region), "Sanity");
467 cl.set_from_region(from_region);
468 if (from_region->has_live()) {
469 _heap->marked_object_iterate(from_region, &cl);
470 }
471
472 // Compacted the region to somewhere else? From-region is empty then.
473 if (!cl.is_compact_same_region()) {
474 empty_regions.append(from_region);
475 }
476 from_region = it.next();
477 }
484 }
485 }
486
487 void ShenandoahFullGC::calculate_target_humongous_objects() {
488 ShenandoahHeap* heap = ShenandoahHeap::heap();
489
490 // Compute the new addresses for humongous objects. We need to do this after addresses
491 // for regular objects are calculated, and we know what regions in heap suffix are
492 // available for humongous moves.
493 //
494 // Scan the heap backwards, because we are compacting humongous regions towards the end.
495 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
496 // humongous start there.
497 //
498 // The complication is potential non-movable regions during the scan. If such region is
499 // detected, then sliding restarts towards that non-movable region.
500
501 size_t to_begin = heap->num_regions();
502 size_t to_end = heap->num_regions();
503
504 log_debug(gc)("Full GC calculating target humongous objects from end " SIZE_FORMAT, to_end);
505 for (size_t c = heap->num_regions(); c > 0; c--) {
506 ShenandoahHeapRegion *r = heap->get_region(c - 1);
507 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
508 // To-region candidate: record this, and continue scan
509 to_begin = r->index();
510 continue;
511 }
512
513 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
514 // From-region candidate: movable humongous region
515 oop old_obj = cast_to_oop(r->bottom());
516 size_t words_size = old_obj->size();
517 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
518
519 size_t start = to_end - num_regions;
520
521 if (start >= to_begin && start != r->index()) {
522 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
523 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
524 FullGCForwarding::forward_to(old_obj, cast_to_oop(heap->get_region(start)->bottom()));
527 }
528 }
529
530 // Failed to fit. Scan starting from current region.
531 to_begin = r->index();
532 to_end = r->index();
533 }
534 }
535
536 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
537 private:
538 ShenandoahHeap* const _heap;
539
540 public:
541 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
542 void heap_region_do(ShenandoahHeapRegion* r) {
543 if (r->is_trash()) {
544 r->recycle();
545 }
546 if (r->is_cset()) {
547 // Leave affiliation unchanged
548 r->make_regular_bypass();
549 }
550 if (r->is_empty_uncommitted()) {
551 r->make_committed_bypass();
552 }
553 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
554
555 // Record current region occupancy: this communicates empty regions are free
556 // to the rest of Full GC code.
557 r->set_new_top(r->top());
558 }
559 };
560
561 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
562 private:
563 ShenandoahHeap* const _heap;
564 ShenandoahMarkingContext* const _ctx;
565
566 public:
567 ShenandoahTrashImmediateGarbageClosure() :
568 _heap(ShenandoahHeap::heap()),
569 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
570
571 void heap_region_do(ShenandoahHeapRegion* r) override {
572 if (r->is_humongous_start()) {
573 oop humongous_obj = cast_to_oop(r->bottom());
574 if (!_ctx->is_marked(humongous_obj)) {
575 assert(!r->has_live(), "Region " SIZE_FORMAT " is not marked, should not have live", r->index());
576 _heap->trash_humongous_region_at(r);
577 } else {
578 assert(r->has_live(), "Region " SIZE_FORMAT " should have live", r->index());
579 }
580 } else if (r->is_humongous_continuation()) {
581 // If we hit continuation, the non-live humongous starts should have been trashed already
582 assert(r->humongous_start_region()->has_live(), "Region " SIZE_FORMAT " should have live", r->index());
583 } else if (r->is_regular()) {
584 if (!r->has_live()) {
585 r->make_trash_immediate();
586 }
587 }
588 }
589 };
590
591 void ShenandoahFullGC::distribute_slices(ShenandoahHeapRegionSet** worker_slices) {
592 ShenandoahHeap* heap = ShenandoahHeap::heap();
593
594 uint n_workers = heap->workers()->active_workers();
595 size_t n_regions = heap->num_regions();
596
597 // What we want to accomplish: have the dense prefix of data, while still balancing
598 // out the parallel work.
599 //
600 // Assuming the amount of work is driven by the live data that needs moving, we can slice
601 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each
602 // thread takes all regions in its prefix subset, and then it takes some regions from
725 for (size_t rid = 0; rid < n_regions; rid++) {
726 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
727 bool is_distributed = map.at(rid);
728 assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
729 }
730 #endif
731 }
732
733 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
734 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
735 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
736
737 ShenandoahHeap* heap = ShenandoahHeap::heap();
738
739 // About to figure out which regions can be compacted, make sure pinning status
740 // had been updated in GC prologue.
741 heap->assert_pinned_region_status();
742
743 {
744 // Trash the immediately collectible regions before computing addresses
745 ShenandoahTrashImmediateGarbageClosure trash_immediate_garbage;
746 ShenandoahExcludeRegionClosure<FREE> cl(&trash_immediate_garbage);
747 heap->heap_region_iterate(&cl);
748
749 // Make sure regions are in good state: committed, active, clean.
750 // This is needed because we are potentially sliding the data through them.
751 ShenandoahEnsureHeapActiveClosure ecl;
752 heap->heap_region_iterate(&ecl);
753 }
754
755 // Compute the new addresses for regular objects
756 {
757 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
758
759 distribute_slices(worker_slices);
760
761 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
762 heap->workers()->run_task(&task);
763 }
764
765 // Compute the new addresses for humongous objects
766 {
767 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
815
816 class ShenandoahAdjustPointersTask : public WorkerTask {
817 private:
818 ShenandoahHeap* const _heap;
819 ShenandoahRegionIterator _regions;
820
821 public:
822 ShenandoahAdjustPointersTask() :
823 WorkerTask("Shenandoah Adjust Pointers"),
824 _heap(ShenandoahHeap::heap()) {
825 }
826
827 void work(uint worker_id) {
828 ShenandoahParallelWorkerSession worker_session(worker_id);
829 ShenandoahAdjustPointersObjectClosure obj_cl;
830 ShenandoahHeapRegion* r = _regions.next();
831 while (r != nullptr) {
832 if (!r->is_humongous_continuation() && r->has_live()) {
833 _heap->marked_object_iterate(r, &obj_cl);
834 }
835 if (_heap->mode()->is_generational()) {
836 ShenandoahGenerationalFullGC::maybe_coalesce_and_fill_region(r);
837 }
838 r = _regions.next();
839 }
840 }
841 };
842
843 class ShenandoahAdjustRootPointersTask : public WorkerTask {
844 private:
845 ShenandoahRootAdjuster* _rp;
846 PreservedMarksSet* _preserved_marks;
847 public:
848 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
849 WorkerTask("Shenandoah Adjust Root Pointers"),
850 _rp(rp),
851 _preserved_marks(preserved_marks) {}
852
853 void work(uint worker_id) {
854 ShenandoahParallelWorkerSession worker_session(worker_id);
855 ShenandoahAdjustPointersClosure cl;
856 _rp->roots_do(worker_id, &cl);
857 _preserved_marks->get(worker_id)->adjust_during_full_gc();
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->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->recycle();
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 " SIZE_FORMAT " should be movable", r->index());
1049
1050 log_debug(gc)("Full GC compaction moves humongous object from region " SIZE_FORMAT " to region " SIZE_FORMAT, 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
1136 }
1137 }
1138
1139 void ShenandoahFullGC::phase5_epilog() {
1140 GCTraceTime(Info, gc, phases) time("Phase 5: Full GC epilog", _gc_timer);
1141 ShenandoahHeap* heap = ShenandoahHeap::heap();
1142
1143 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1144 // and must ensure the bitmap is in sync.
1145 {
1146 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1147 ShenandoahMCResetCompleteBitmapTask task;
1148 heap->workers()->run_task(&task);
1149 }
1150
1151 // Bring regions in proper states after the collection, and set heap properties.
1152 {
1153 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1154 ShenandoahPostCompactClosure post_compact;
1155 heap->heap_region_iterate(&post_compact);
1156 post_compact.update_generation_usage();
1157
1158 if (heap->mode()->is_generational()) {
1159 ShenandoahGenerationalFullGC::balance_generations_after_gc(heap);
1160 }
1161
1162 heap->collection_set()->clear();
1163 size_t young_cset_regions, old_cset_regions;
1164 size_t first_old, last_old, num_old;
1165 heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
1166
1167 // We also do not expand old generation size following Full GC because we have scrambled age populations and
1168 // no longer have objects separated by age into distinct regions.
1169 if (heap->mode()->is_generational()) {
1170 ShenandoahGenerationalFullGC::compute_balances();
1171 }
1172
1173 heap->free_set()->finish_rebuild(young_cset_regions, old_cset_regions, num_old);
1174
1175 heap->clear_cancelled_gc(true /* clear oom handler */);
1176 }
1177
1178 _preserved_marks->restore(heap->workers());
1179 _preserved_marks->reclaim();
1180
1181 // We defer generation resizing actions until after cset regions have been recycled. We do this even following an
1182 // abbreviated cycle.
1183 if (heap->mode()->is_generational()) {
1184 ShenandoahGenerationalFullGC::balance_generations_after_rebuilding_free_set();
1185 ShenandoahGenerationalFullGC::rebuild_remembered_set(heap);
1186 }
1187 }
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