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