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/gcTraceTime.inline.hpp"
30 #include "gc/shared/preservedMarks.inline.hpp"
31 #include "gc/shared/tlab_globals.hpp"
32 #include "gc/shared/workerThread.hpp"
33 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
34 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
35 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
36 #include "gc/shenandoah/shenandoahFreeSet.hpp"
37 #include "gc/shenandoah/shenandoahFullGC.hpp"
38 #include "gc/shenandoah/shenandoahGeneration.hpp"
39 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
40 #include "gc/shenandoah/shenandoahMark.inline.hpp"
41 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
42 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
43 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
44 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
45 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
46 #include "gc/shenandoah/shenandoahMetrics.hpp"
47 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
48 #include "gc/shenandoah/shenandoahOopClosures.inline.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 "gc/shenandoah/shenandoahYoungGeneration.hpp"
57 #include "memory/metaspaceUtils.hpp"
58 #include "memory/universe.hpp"
59 #include "oops/compressedOops.inline.hpp"
60 #include "oops/oop.inline.hpp"
61 #include "runtime/javaThread.hpp"
62 #include "runtime/orderAccess.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "utilities/copy.hpp"
65 #include "utilities/events.hpp"
66 #include "utilities/growableArray.hpp"
67
68 // After Full GC is done, reconstruct the remembered set by iterating over OLD regions,
69 // registering all objects between bottom() and top(), and setting remembered set cards to
70 // DIRTY if they hold interesting pointers.
71 class ShenandoahReconstructRememberedSetTask : public WorkerTask {
72 private:
73 ShenandoahRegionIterator _regions;
74
75 public:
76 ShenandoahReconstructRememberedSetTask() :
77 WorkerTask("Shenandoah Reset Bitmap") { }
78
79 void work(uint worker_id) {
80 ShenandoahParallelWorkerSession worker_session(worker_id);
81 ShenandoahHeapRegion* r = _regions.next();
82 ShenandoahHeap* heap = ShenandoahHeap::heap();
83 RememberedScanner* scanner = heap->card_scan();
84 ShenandoahSetRememberedCardsToDirtyClosure dirty_cards_for_interesting_pointers;
85
86 while (r != nullptr) {
87 if (r->is_old() && r->is_active()) {
88 HeapWord* obj_addr = r->bottom();
89 if (r->is_humongous_start()) {
90 // First, clear the remembered set
91 oop obj = cast_to_oop(obj_addr);
92 size_t size = obj->size();
93 HeapWord* end_object = r->bottom() + size;
94
95 // First, clear the remembered set for all spanned humongous regions
96 size_t num_regions = (size + ShenandoahHeapRegion::region_size_words() - 1) / ShenandoahHeapRegion::region_size_words();
97 size_t region_span = num_regions * ShenandoahHeapRegion::region_size_words();
98 scanner->reset_remset(r->bottom(), region_span);
99 size_t region_index = r->index();
100 ShenandoahHeapRegion* humongous_region = heap->get_region(region_index);
101 while (num_regions-- != 0) {
102 scanner->reset_object_range(humongous_region->bottom(), humongous_region->end());
103 region_index++;
104 humongous_region = heap->get_region(region_index);
105 }
106
107 // Then register the humongous object and DIRTY relevant remembered set cards
108 scanner->register_object_wo_lock(obj_addr);
109 obj->oop_iterate(&dirty_cards_for_interesting_pointers);
110 } else if (!r->is_humongous()) {
111 // First, clear the remembered set
112 scanner->reset_remset(r->bottom(), ShenandoahHeapRegion::region_size_words());
113 scanner->reset_object_range(r->bottom(), r->end());
114
115 // Then iterate over all objects, registering object and DIRTYing relevant remembered set cards
116 HeapWord* t = r->top();
117 while (obj_addr < t) {
118 oop obj = cast_to_oop(obj_addr);
119 size_t size = obj->size();
120 scanner->register_object_wo_lock(obj_addr);
121 obj_addr += obj->oop_iterate_size(&dirty_cards_for_interesting_pointers);
122 }
123 } // else, ignore humongous continuation region
124 }
125 // else, this region is FREE or YOUNG or inactive and we can ignore it.
126 r = _regions.next();
127 }
128 }
129 };
130
131 ShenandoahFullGC::ShenandoahFullGC() :
132 _gc_timer(ShenandoahHeap::heap()->gc_timer()),
133 _preserved_marks(new PreservedMarksSet(true)) {}
134
135 ShenandoahFullGC::~ShenandoahFullGC() {
136 delete _preserved_marks;
137 }
138
139 bool ShenandoahFullGC::collect(GCCause::Cause cause) {
140 vmop_entry_full(cause);
141 // Always success
142 return true;
143 }
144
145 void ShenandoahFullGC::vmop_entry_full(GCCause::Cause cause) {
146 ShenandoahHeap* const heap = ShenandoahHeap::heap();
147 TraceCollectorStats tcs(heap->monitoring_support()->full_stw_collection_counters());
148 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::full_gc_gross);
149
150 heap->try_inject_alloc_failure();
151 VM_ShenandoahFullGC op(cause, this);
152 VMThread::execute(&op);
153 }
154
155 void ShenandoahFullGC::entry_full(GCCause::Cause cause) {
156 static const char* msg = "Pause Full";
157 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */);
158 EventMark em("%s", msg);
159
160 ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(),
161 ShenandoahWorkerPolicy::calc_workers_for_fullgc(),
162 "full gc");
163
164 op_full(cause);
165 }
166
167 void ShenandoahFullGC::op_full(GCCause::Cause cause) {
168 ShenandoahHeap* const heap = ShenandoahHeap::heap();
169 ShenandoahMetricsSnapshot metrics;
170 metrics.snap_before();
171
172 // Perform full GC
173 do_it(cause);
174
175 metrics.snap_after();
176 if (heap->mode()->is_generational()) {
177 heap->log_heap_status("At end of Full GC");
178
179 // Since we allow temporary violation of these constraints during Full GC, we want to enforce that the assertions are
180 // made valid by the time Full GC completes.
181 assert(heap->old_generation()->used_regions_size() <= heap->old_generation()->adjusted_capacity(),
182 "Old generation affiliated regions must be less than capacity");
183 assert(heap->young_generation()->used_regions_size() <= heap->young_generation()->adjusted_capacity(),
184 "Young generation affiliated regions must be less than capacity");
185 }
186 if (metrics.is_good_progress()) {
187 ShenandoahHeap::heap()->notify_gc_progress();
188 } else {
189 // Nothing to do. Tell the allocation path that we have failed to make
190 // progress, and it can finally fail.
191 ShenandoahHeap::heap()->notify_gc_no_progress();
192 }
193 }
194
195 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
196 ShenandoahHeap* heap = ShenandoahHeap::heap();
197 // Since we may arrive here from degenerated GC failure of either young or old, establish generation as GLOBAL.
198 heap->set_gc_generation(heap->global_generation());
199
200 if (heap->mode()->is_generational()) {
201 // Defer unadjust_available() invocations until after Full GC finishes its efforts because Full GC makes use
202 // of young-gen memory that may have been loaned from old-gen.
203
204 // No need to old_gen->increase_used(). That was done when plabs were allocated, accounting for both old evacs and promotions.
205
206 heap->set_alloc_supplement_reserve(0);
207 heap->set_young_evac_reserve(0);
208 heap->set_old_evac_reserve(0);
209 heap->reset_old_evac_expended();
210 heap->set_promoted_reserve(0);
211
212 // Full GC supersedes any marking or coalescing in old generation.
213 heap->cancel_old_gc();
214 }
215
216 if (ShenandoahVerify) {
217 heap->verifier()->verify_before_fullgc();
218 }
219
220 if (VerifyBeforeGC) {
221 Universe::verify();
222 }
223
224 // Degenerated GC may carry concurrent root flags when upgrading to
225 // full GC. We need to reset it before mutators resume.
226 heap->set_concurrent_strong_root_in_progress(false);
227 heap->set_concurrent_weak_root_in_progress(false);
228
229 heap->set_full_gc_in_progress(true);
230
231 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
232 assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
233
234 {
235 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);
236 heap->pre_full_gc_dump(_gc_timer);
237 }
238
239 {
240 ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
241 // Full GC is supposed to recover from any GC state:
242
243 // a0. Remember if we have forwarded objects
244 bool has_forwarded_objects = heap->has_forwarded_objects();
245
246 // a1. Cancel evacuation, if in progress
247 if (heap->is_evacuation_in_progress()) {
248 heap->set_evacuation_in_progress(false);
249 }
250 assert(!heap->is_evacuation_in_progress(), "sanity");
251
252 // a2. Cancel update-refs, if in progress
253 if (heap->is_update_refs_in_progress()) {
254 heap->set_update_refs_in_progress(false);
255 }
256 assert(!heap->is_update_refs_in_progress(), "sanity");
257
258 // b. Cancel all concurrent marks, if in progress
259 if (heap->is_concurrent_mark_in_progress()) {
260 heap->cancel_concurrent_mark();
261 }
262 assert(!heap->is_concurrent_mark_in_progress(), "sanity");
263
264 // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
265 if (has_forwarded_objects) {
266 update_roots(true /*full_gc*/);
267 }
268
269 // d. Reset the bitmaps for new marking
270 heap->global_generation()->reset_mark_bitmap();
271 assert(heap->marking_context()->is_bitmap_clear(), "sanity");
272 assert(!heap->global_generation()->is_mark_complete(), "sanity");
273
274 // e. Abandon reference discovery and clear all discovered references.
275 ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
276 rp->abandon_partial_discovery();
277
278 // f. Sync pinned region status from the CP marks
279 heap->sync_pinned_region_status();
280
281 // The rest of prologue:
282 _preserved_marks->init(heap->workers()->active_workers());
283
284 assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
285 }
286
287 if (UseTLAB) {
288 // TODO: Do we need to explicitly retire PLABs?
289 heap->gclabs_retire(ResizeTLAB);
290 heap->tlabs_retire(ResizeTLAB);
291 }
292
293 OrderAccess::fence();
294
295 phase1_mark_heap();
296
297 // Once marking is done, which may have fixed up forwarded objects, we can drop it.
298 // Coming out of Full GC, we would not have any forwarded objects.
299 // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
300 heap->set_has_forwarded_objects(false);
301
302 heap->set_full_gc_move_in_progress(true);
303
304 // Setup workers for the rest
305 OrderAccess::fence();
306
307 // Initialize worker slices
308 ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);
309 for (uint i = 0; i < heap->max_workers(); i++) {
310 worker_slices[i] = new ShenandoahHeapRegionSet();
311 }
312
313 {
314 // The rest of code performs region moves, where region status is undefined
315 // until all phases run together.
316 ShenandoahHeapLocker lock(heap->lock());
317
318 phase2_calculate_target_addresses(worker_slices);
319
320 OrderAccess::fence();
321
322 phase3_update_references();
323
324 phase4_compact_objects(worker_slices);
325 }
326
327 {
328 // Epilogue
329 _preserved_marks->restore(heap->workers());
330 _preserved_marks->reclaim();
331
332 if (heap->mode()->is_generational()) {
333 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_reconstruct_remembered_set);
334 ShenandoahReconstructRememberedSetTask task;
335 heap->workers()->run_task(&task);
336 }
337 }
338
339 // Resize metaspace
340 MetaspaceGC::compute_new_size();
341
342 heap->adjust_generation_sizes();
343
344 // Free worker slices
345 for (uint i = 0; i < heap->max_workers(); i++) {
346 delete worker_slices[i];
347 }
348 FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
349
350 heap->set_full_gc_move_in_progress(false);
351 heap->set_full_gc_in_progress(false);
352
353 if (ShenandoahVerify) {
354 if (heap->mode()->is_generational()) {
355 heap->verifier()->verify_after_generational_fullgc();
356 } else {
357 heap->verifier()->verify_after_fullgc();
358 }
359 }
360
361 // Having reclaimed all dead memory, it is now safe to restore capacities to original values.
362 heap->young_generation()->unadjust_available();
363 heap->old_generation()->unadjust_available();
364
365 if (VerifyAfterGC) {
366 Universe::verify();
367 }
368
369 {
370 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
371 heap->post_full_gc_dump(_gc_timer);
372 }
373 }
374
375 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
376 private:
377 ShenandoahMarkingContext* const _ctx;
378
379 public:
380 ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
381
382 void heap_region_do(ShenandoahHeapRegion *r) {
383 if (r->affiliation() != FREE) {
384 _ctx->capture_top_at_mark_start(r);
385 r->clear_live_data();
386 }
387 }
388
389 bool is_thread_safe() { return true; }
390 };
391
392 void ShenandoahFullGC::phase1_mark_heap() {
393 GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
394 ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
395
396 ShenandoahHeap* heap = ShenandoahHeap::heap();
397
398 ShenandoahPrepareForMarkClosure cl;
399 heap->parallel_heap_region_iterate(&cl);
400
401 heap->set_unload_classes(heap->global_generation()->heuristics()->can_unload_classes());
402
403 ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
404 // enable ("weak") refs discovery
405 rp->set_soft_reference_policy(true); // forcefully purge all soft references
406
407 ShenandoahSTWMark mark(heap->global_generation(), true /*full_gc*/);
408 mark.mark();
409 heap->parallel_cleaning(true /* full_gc */);
410 }
411
412 class ShenandoahPrepareForCompactionTask : public WorkerTask {
413 private:
414 PreservedMarksSet* const _preserved_marks;
415 ShenandoahHeap* const _heap;
416 ShenandoahHeapRegionSet** const _worker_slices;
417 size_t const _num_workers;
418
419 public:
420 ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks, ShenandoahHeapRegionSet **worker_slices,
421 size_t num_workers);
422
423 static bool is_candidate_region(ShenandoahHeapRegion* r) {
424 // Empty region: get it into the slice to defragment the slice itself.
425 // We could have skipped this without violating correctness, but we really
426 // want to compact all live regions to the start of the heap, which sometimes
427 // means moving them into the fully empty regions.
428 if (r->is_empty()) return true;
429
430 // Can move the region, and this is not the humongous region. Humongous
431 // moves are special cased here, because their moves are handled separately.
432 return r->is_stw_move_allowed() && !r->is_humongous();
433 }
434
435 void work(uint worker_id);
436 };
437
438 class ShenandoahPrepareForGenerationalCompactionObjectClosure : public ObjectClosure {
439 private:
440 ShenandoahPrepareForCompactionTask* _compactor;
441 PreservedMarks* const _preserved_marks;
442 ShenandoahHeap* const _heap;
443
444 // _empty_regions is a thread-local list of heap regions that have been completely emptied by this worker thread's
445 // compaction efforts. The worker thread that drives these efforts adds compacted regions to this list if the
446 // region has not been compacted onto itself.
447 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
448 int _empty_regions_pos;
449 ShenandoahHeapRegion* _old_to_region;
450 ShenandoahHeapRegion* _young_to_region;
451 ShenandoahHeapRegion* _from_region;
452 ShenandoahRegionAffiliation _from_affiliation;
453 HeapWord* _old_compact_point;
454 HeapWord* _young_compact_point;
455 uint _worker_id;
456
457 public:
458 ShenandoahPrepareForGenerationalCompactionObjectClosure(ShenandoahPrepareForCompactionTask* compactor,
459 PreservedMarks* preserved_marks,
460 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
461 ShenandoahHeapRegion* old_to_region,
462 ShenandoahHeapRegion* young_to_region, uint worker_id) :
463 _compactor(compactor),
464 _preserved_marks(preserved_marks),
465 _heap(ShenandoahHeap::heap()),
466 _empty_regions(empty_regions),
467 _empty_regions_pos(0),
468 _old_to_region(old_to_region),
469 _young_to_region(young_to_region),
470 _from_region(nullptr),
471 _old_compact_point((old_to_region != nullptr)? old_to_region->bottom(): nullptr),
472 _young_compact_point((young_to_region != nullptr)? young_to_region->bottom(): nullptr),
473 _worker_id(worker_id) {}
474
475 void set_from_region(ShenandoahHeapRegion* from_region) {
476 _from_region = from_region;
477 _from_affiliation = from_region->affiliation();
478 if (_from_region->has_live()) {
479 if (_from_affiliation == ShenandoahRegionAffiliation::OLD_GENERATION) {
480 if (_old_to_region == nullptr) {
481 _old_to_region = from_region;
482 _old_compact_point = from_region->bottom();
483 }
484 } else {
485 assert(_from_affiliation == ShenandoahRegionAffiliation::YOUNG_GENERATION, "from_region must be OLD or YOUNG");
486 if (_young_to_region == nullptr) {
487 _young_to_region = from_region;
488 _young_compact_point = from_region->bottom();
489 }
490 }
491 } // else, we won't iterate over this _from_region so we don't need to set up to region to hold copies
492 }
493
494 void finish() {
495 finish_old_region();
496 finish_young_region();
497 }
498
499 void finish_old_region() {
500 if (_old_to_region != nullptr) {
501 log_debug(gc)("Planned compaction into Old Region " SIZE_FORMAT ", used: " SIZE_FORMAT " tabulated by worker %u",
502 _old_to_region->index(), _old_compact_point - _old_to_region->bottom(), _worker_id);
503 _old_to_region->set_new_top(_old_compact_point);
504 _old_to_region = nullptr;
505 }
506 }
507
508 void finish_young_region() {
509 if (_young_to_region != nullptr) {
510 log_debug(gc)("Worker %u planned compaction into Young Region " SIZE_FORMAT ", used: " SIZE_FORMAT,
511 _worker_id, _young_to_region->index(), _young_compact_point - _young_to_region->bottom());
512 _young_to_region->set_new_top(_young_compact_point);
513 _young_to_region = nullptr;
514 }
515 }
516
517 bool is_compact_same_region() {
518 return (_from_region == _old_to_region) || (_from_region == _young_to_region);
519 }
520
521 int empty_regions_pos() {
522 return _empty_regions_pos;
523 }
524
525 void do_object(oop p) {
526 assert(_from_region != nullptr, "must set before work");
527 assert((_from_region->bottom() <= cast_from_oop<HeapWord*>(p)) && (cast_from_oop<HeapWord*>(p) < _from_region->top()),
528 "Object must reside in _from_region");
529 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
530 assert(!_heap->complete_marking_context()->allocated_after_mark_start(p), "must be truly marked");
531
532 size_t obj_size = p->size();
533 uint from_region_age = _from_region->age();
534 uint object_age = p->age();
535
536 bool promote_object = false;
537 if ((_from_affiliation == ShenandoahRegionAffiliation::YOUNG_GENERATION) &&
538 (from_region_age + object_age >= InitialTenuringThreshold)) {
539 if ((_old_to_region != nullptr) && (_old_compact_point + obj_size > _old_to_region->end())) {
540 finish_old_region();
541 _old_to_region = nullptr;
542 }
543 if (_old_to_region == nullptr) {
544 if (_empty_regions_pos < _empty_regions.length()) {
545 ShenandoahHeapRegion* new_to_region = _empty_regions.at(_empty_regions_pos);
546 _empty_regions_pos++;
547 new_to_region->set_affiliation(OLD_GENERATION);
548 _old_to_region = new_to_region;
549 _old_compact_point = _old_to_region->bottom();
550 promote_object = true;
551 }
552 // Else this worker thread does not yet have any empty regions into which this aged object can be promoted so
553 // we leave promote_object as false, deferring the promotion.
554 } else {
555 promote_object = true;
556 }
557 }
558
559 if (promote_object || (_from_affiliation == ShenandoahRegionAffiliation::OLD_GENERATION)) {
560 assert(_old_to_region != nullptr, "_old_to_region should not be nullptr when evacuating to OLD region");
561 if (_old_compact_point + obj_size > _old_to_region->end()) {
562 ShenandoahHeapRegion* new_to_region;
563
564 log_debug(gc)("Worker %u finishing old region " SIZE_FORMAT ", compact_point: " PTR_FORMAT ", obj_size: " SIZE_FORMAT
565 ", &compact_point[obj_size]: " PTR_FORMAT ", region end: " PTR_FORMAT, _worker_id, _old_to_region->index(),
566 p2i(_old_compact_point), obj_size, p2i(_old_compact_point + obj_size), p2i(_old_to_region->end()));
567
568 // Object does not fit. Get a new _old_to_region.
569 finish_old_region();
570 if (_empty_regions_pos < _empty_regions.length()) {
571 new_to_region = _empty_regions.at(_empty_regions_pos);
572 _empty_regions_pos++;
573 new_to_region->set_affiliation(OLD_GENERATION);
574 } else {
575 // If we've exhausted the previously selected _old_to_region, we know that the _old_to_region is distinct
576 // from _from_region. That's because there is always room for _from_region to be compacted into itself.
577 // Since we're out of empty regions, let's use _from_region to hold the results of its own compaction.
578 new_to_region = _from_region;
579 }
580
581 assert(new_to_region != _old_to_region, "must not reuse same OLD to-region");
582 assert(new_to_region != nullptr, "must not be nullptr");
583 _old_to_region = new_to_region;
584 _old_compact_point = _old_to_region->bottom();
585 }
586
587 // Object fits into current region, record new location:
588 assert(_old_compact_point + obj_size <= _old_to_region->end(), "must fit");
589 shenandoah_assert_not_forwarded(nullptr, p);
590 _preserved_marks->push_if_necessary(p, p->mark());
591 p->forward_to(cast_to_oop(_old_compact_point));
592 _old_compact_point += obj_size;
593 } else {
594 assert(_from_affiliation == ShenandoahRegionAffiliation::YOUNG_GENERATION,
595 "_from_region must be OLD_GENERATION or YOUNG_GENERATION");
596 assert(_young_to_region != nullptr, "_young_to_region should not be nullptr when compacting YOUNG _from_region");
597
598 // After full gc compaction, all regions have age 0. Embed the region's age into the object's age in order to preserve
599 // tenuring progress.
600 if (_heap->is_aging_cycle()) {
601 _heap->increase_object_age(p, from_region_age + 1);
602 } else {
603 _heap->increase_object_age(p, from_region_age);
604 }
605
606 if (_young_compact_point + obj_size > _young_to_region->end()) {
607 ShenandoahHeapRegion* new_to_region;
608
609 log_debug(gc)("Worker %u finishing young region " SIZE_FORMAT ", compact_point: " PTR_FORMAT ", obj_size: " SIZE_FORMAT
610 ", &compact_point[obj_size]: " PTR_FORMAT ", region end: " PTR_FORMAT, _worker_id, _young_to_region->index(),
611 p2i(_young_compact_point), obj_size, p2i(_young_compact_point + obj_size), p2i(_young_to_region->end()));
612
613 // Object does not fit. Get a new _young_to_region.
614 finish_young_region();
615 if (_empty_regions_pos < _empty_regions.length()) {
616 new_to_region = _empty_regions.at(_empty_regions_pos);
617 _empty_regions_pos++;
618 new_to_region->set_affiliation(YOUNG_GENERATION);
619 } else {
620 // If we've exhausted the previously selected _young_to_region, we know that the _young_to_region is distinct
621 // from _from_region. That's because there is always room for _from_region to be compacted into itself.
622 // Since we're out of empty regions, let's use _from_region to hold the results of its own compaction.
623 new_to_region = _from_region;
624 }
625
626 assert(new_to_region != _young_to_region, "must not reuse same OLD to-region");
627 assert(new_to_region != nullptr, "must not be nullptr");
628 _young_to_region = new_to_region;
629 _young_compact_point = _young_to_region->bottom();
630 }
631
632 // Object fits into current region, record new location:
633 assert(_young_compact_point + obj_size <= _young_to_region->end(), "must fit");
634 shenandoah_assert_not_forwarded(nullptr, p);
635 _preserved_marks->push_if_necessary(p, p->mark());
636 p->forward_to(cast_to_oop(_young_compact_point));
637 _young_compact_point += obj_size;
638 }
639 }
640 };
641
642
643 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
644 private:
645 PreservedMarks* const _preserved_marks;
646 ShenandoahHeap* const _heap;
647 GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
648 int _empty_regions_pos;
649 ShenandoahHeapRegion* _to_region;
650 ShenandoahHeapRegion* _from_region;
651 HeapWord* _compact_point;
652
653 public:
654 ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
655 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
656 ShenandoahHeapRegion* to_region) :
657 _preserved_marks(preserved_marks),
658 _heap(ShenandoahHeap::heap()),
659 _empty_regions(empty_regions),
660 _empty_regions_pos(0),
661 _to_region(to_region),
662 _from_region(nullptr),
663 _compact_point(to_region->bottom()) {}
664
665 void set_from_region(ShenandoahHeapRegion* from_region) {
666 _from_region = from_region;
667 }
668
669 void finish_region() {
670 assert(_to_region != nullptr, "should not happen");
671 assert(!_heap->mode()->is_generational(), "Generational GC should use different Closure");
672 _to_region->set_new_top(_compact_point);
673 }
674
675 bool is_compact_same_region() {
676 return _from_region == _to_region;
677 }
678
679 int empty_regions_pos() {
680 return _empty_regions_pos;
681 }
682
683 void do_object(oop p) {
684 assert(_from_region != nullptr, "must set before work");
685 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
686 assert(!_heap->complete_marking_context()->allocated_after_mark_start(p), "must be truly marked");
687
688 size_t obj_size = p->size();
689 if (_compact_point + obj_size > _to_region->end()) {
690 finish_region();
691
692 // Object doesn't fit. Pick next empty region and start compacting there.
693 ShenandoahHeapRegion* new_to_region;
694 if (_empty_regions_pos < _empty_regions.length()) {
695 new_to_region = _empty_regions.at(_empty_regions_pos);
696 _empty_regions_pos++;
697 } else {
698 // Out of empty region? Compact within the same region.
699 new_to_region = _from_region;
700 }
701
702 assert(new_to_region != _to_region, "must not reuse same to-region");
703 assert(new_to_region != nullptr, "must not be null");
704 _to_region = new_to_region;
705 _compact_point = _to_region->bottom();
706 }
707
708 // Object fits into current region, record new location:
709 assert(_compact_point + obj_size <= _to_region->end(), "must fit");
710 shenandoah_assert_not_forwarded(nullptr, p);
711 _preserved_marks->push_if_necessary(p, p->mark());
712 p->forward_to(cast_to_oop(_compact_point));
713 _compact_point += obj_size;
714 }
715 };
716
717
718 ShenandoahPrepareForCompactionTask::ShenandoahPrepareForCompactionTask(PreservedMarksSet *preserved_marks,
719 ShenandoahHeapRegionSet **worker_slices,
720 size_t num_workers) :
721 WorkerTask("Shenandoah Prepare For Compaction"),
722 _preserved_marks(preserved_marks), _heap(ShenandoahHeap::heap()),
723 _worker_slices(worker_slices), _num_workers(num_workers) { }
724
725
726 void ShenandoahPrepareForCompactionTask::work(uint worker_id) {
727 ShenandoahParallelWorkerSession worker_session(worker_id);
728 ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
729 ShenandoahHeapRegionSetIterator it(slice);
730 ShenandoahHeapRegion* from_region = it.next();
731 // No work?
732 if (from_region == nullptr) {
733 return;
734 }
735
736 // Sliding compaction. Walk all regions in the slice, and compact them.
737 // Remember empty regions and reuse them as needed.
738 ResourceMark rm;
739
740 GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
741
742 if (_heap->mode()->is_generational()) {
743 ShenandoahHeapRegion* old_to_region = (from_region->is_old())? from_region: nullptr;
744 ShenandoahHeapRegion* young_to_region = (from_region->is_young())? from_region: nullptr;
745 ShenandoahPrepareForGenerationalCompactionObjectClosure cl(this, _preserved_marks->get(worker_id), empty_regions,
746 old_to_region, young_to_region, worker_id);
747 while (from_region != nullptr) {
748 assert(is_candidate_region(from_region), "Sanity");
749 log_debug(gc)("Worker %u compacting %s Region " SIZE_FORMAT " which had used " SIZE_FORMAT " and %s live",
750 worker_id, affiliation_name(from_region->affiliation()),
751 from_region->index(), from_region->used(), from_region->has_live()? "has": "does not have");
752 cl.set_from_region(from_region);
753 if (from_region->has_live()) {
754 _heap->marked_object_iterate(from_region, &cl);
755 }
756 // Compacted the region to somewhere else? From-region is empty then.
757 if (!cl.is_compact_same_region()) {
758 empty_regions.append(from_region);
759 }
760 from_region = it.next();
761 }
762 cl.finish();
763
764 // Mark all remaining regions as empty
765 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
766 ShenandoahHeapRegion* r = empty_regions.at(pos);
767 r->set_new_top(r->bottom());
768 }
769 } else {
770 ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
771 while (from_region != nullptr) {
772 assert(is_candidate_region(from_region), "Sanity");
773 cl.set_from_region(from_region);
774 if (from_region->has_live()) {
775 _heap->marked_object_iterate(from_region, &cl);
776 }
777
778 // Compacted the region to somewhere else? From-region is empty then.
779 if (!cl.is_compact_same_region()) {
780 empty_regions.append(from_region);
781 }
782 from_region = it.next();
783 }
784 cl.finish_region();
785
786 // Mark all remaining regions as empty
787 for (int pos = cl.empty_regions_pos(); pos < empty_regions.length(); ++pos) {
788 ShenandoahHeapRegion* r = empty_regions.at(pos);
789 r->set_new_top(r->bottom());
790 }
791 }
792 }
793
794 void ShenandoahFullGC::calculate_target_humongous_objects() {
795 ShenandoahHeap* heap = ShenandoahHeap::heap();
796
797 // Compute the new addresses for humongous objects. We need to do this after addresses
798 // for regular objects are calculated, and we know what regions in heap suffix are
799 // available for humongous moves.
800 //
801 // Scan the heap backwards, because we are compacting humongous regions towards the end.
802 // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
803 // humongous start there.
804 //
805 // The complication is potential non-movable regions during the scan. If such region is
806 // detected, then sliding restarts towards that non-movable region.
807
808 size_t to_begin = heap->num_regions();
809 size_t to_end = heap->num_regions();
810
811 log_debug(gc)("Full GC calculating target humongous objects from end " SIZE_FORMAT, to_end);
812 for (size_t c = heap->num_regions(); c > 0; c--) {
813 ShenandoahHeapRegion *r = heap->get_region(c - 1);
814 if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
815 // To-region candidate: record this, and continue scan
816 to_begin = r->index();
817 continue;
818 }
819
820 if (r->is_humongous_start() && r->is_stw_move_allowed()) {
821 // From-region candidate: movable humongous region
822 oop old_obj = cast_to_oop(r->bottom());
823 size_t words_size = old_obj->size();
824 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
825
826 size_t start = to_end - num_regions;
827
828 if (start >= to_begin && start != r->index()) {
829 // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
830 _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
831 old_obj->forward_to(cast_to_oop(heap->get_region(start)->bottom()));
832 to_end = start;
833 continue;
834 }
835 }
836
837 // Failed to fit. Scan starting from current region.
838 to_begin = r->index();
839 to_end = r->index();
840 }
841 }
842
843 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
844 private:
845 ShenandoahHeap* const _heap;
846
847 public:
848 ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
849 void heap_region_do(ShenandoahHeapRegion* r) {
850 bool is_generational = _heap->mode()->is_generational();
851 if (r->is_trash()) {
852 r->recycle();
853 }
854 if (r->is_cset()) {
855 // Leave afffiliation unchanged.
856 r->make_regular_bypass();
857 }
858 if (r->is_empty_uncommitted()) {
859 r->make_committed_bypass();
860 }
861 assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
862
863 // Record current region occupancy: this communicates empty regions are free
864 // to the rest of Full GC code.
865 r->set_new_top(r->top());
866 }
867 };
868
869 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
870 private:
871 ShenandoahHeap* const _heap;
872 ShenandoahMarkingContext* const _ctx;
873
874 public:
875 ShenandoahTrashImmediateGarbageClosure() :
876 _heap(ShenandoahHeap::heap()),
877 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
878
879 void heap_region_do(ShenandoahHeapRegion* r) {
880 if (r->affiliation() != FREE) {
881 if (r->is_humongous_start()) {
882 oop humongous_obj = cast_to_oop(r->bottom());
883 if (!_ctx->is_marked(humongous_obj)) {
884 assert(!r->has_live(),
885 "Humongous Start %s Region " SIZE_FORMAT " is not marked, should not have live",
886 affiliation_name(r->affiliation()), r->index());
887 log_debug(gc)("Trashing immediate humongous region " SIZE_FORMAT " because not marked", r->index());
888 _heap->trash_humongous_region_at(r);
889 } else {
890 assert(r->has_live(),
891 "Humongous Start %s Region " SIZE_FORMAT " should have live", affiliation_name(r->affiliation()), r->index());
892 }
893 } else if (r->is_humongous_continuation()) {
894 // If we hit continuation, the non-live humongous starts should have been trashed already
895 assert(r->humongous_start_region()->has_live(),
896 "Humongous Continuation %s Region " SIZE_FORMAT " should have live", affiliation_name(r->affiliation()), r->index());
897 } else if (r->is_regular()) {
898 if (!r->has_live()) {
899 log_debug(gc)("Trashing immediate regular region " SIZE_FORMAT " because has no live", r->index());
900 r->make_trash_immediate();
901 }
902 }
903 }
904 // else, ignore this FREE region.
905 // TODO: change iterators so they do not process FREE regions.
906 }
907 };
908
909 void ShenandoahFullGC::distribute_slices(ShenandoahHeapRegionSet** worker_slices) {
910 ShenandoahHeap* heap = ShenandoahHeap::heap();
911
912 uint n_workers = heap->workers()->active_workers();
913 size_t n_regions = heap->num_regions();
914
915 // What we want to accomplish: have the dense prefix of data, while still balancing
916 // out the parallel work.
917 //
918 // Assuming the amount of work is driven by the live data that needs moving, we can slice
919 // the entire heap into equal-live-sized prefix slices, and compact into them. So, each
920 // thread takes all regions in its prefix subset, and then it takes some regions from
921 // the tail.
922 //
923 // Tail region selection becomes interesting.
924 //
925 // First, we want to distribute the regions fairly between the workers, and those regions
926 // might have different amount of live data. So, until we sure no workers need live data,
927 // we need to only take what the worker needs.
928 //
929 // Second, since we slide everything to the left in each slice, the most busy regions
930 // would be the ones on the left. Which means we want to have all workers have their after-tail
931 // regions as close to the left as possible.
932 //
933 // The easiest way to do this is to distribute after-tail regions in round-robin between
934 // workers that still need live data.
935 //
936 // Consider parallel workers A, B, C, then the target slice layout would be:
937 //
938 // AAAAAAAABBBBBBBBCCCCCCCC|ABCABCABCABCABCABCABCABABABABABABABABABABAAAAA
939 //
940 // (.....dense-prefix.....) (.....................tail...................)
941 // [all regions fully live] [left-most regions are fuller that right-most]
942 //
943
944 // Compute how much live data is there. This would approximate the size of dense prefix
945 // we target to create.
946 size_t total_live = 0;
947 for (size_t idx = 0; idx < n_regions; idx++) {
948 ShenandoahHeapRegion *r = heap->get_region(idx);
949 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
950 total_live += r->get_live_data_words();
951 }
952 }
953
954 // Estimate the size for the dense prefix. Note that we specifically count only the
955 // "full" regions, so there would be some non-full regions in the slice tail.
956 size_t live_per_worker = total_live / n_workers;
957 size_t prefix_regions_per_worker = live_per_worker / ShenandoahHeapRegion::region_size_words();
958 size_t prefix_regions_total = prefix_regions_per_worker * n_workers;
959 prefix_regions_total = MIN2(prefix_regions_total, n_regions);
960 assert(prefix_regions_total <= n_regions, "Sanity");
961
962 // There might be non-candidate regions in the prefix. To compute where the tail actually
963 // ends up being, we need to account those as well.
964 size_t prefix_end = prefix_regions_total;
965 for (size_t idx = 0; idx < prefix_regions_total; idx++) {
966 ShenandoahHeapRegion *r = heap->get_region(idx);
967 if (!ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
968 prefix_end++;
969 }
970 }
971 prefix_end = MIN2(prefix_end, n_regions);
972 assert(prefix_end <= n_regions, "Sanity");
973
974 // Distribute prefix regions per worker: each thread definitely gets its own same-sized
975 // subset of dense prefix.
976 size_t prefix_idx = 0;
977
978 size_t* live = NEW_C_HEAP_ARRAY(size_t, n_workers, mtGC);
979
980 for (size_t wid = 0; wid < n_workers; wid++) {
981 ShenandoahHeapRegionSet* slice = worker_slices[wid];
982
983 live[wid] = 0;
984 size_t regs = 0;
985
986 // Add all prefix regions for this worker
987 while (prefix_idx < prefix_end && regs < prefix_regions_per_worker) {
988 ShenandoahHeapRegion *r = heap->get_region(prefix_idx);
989 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
990 slice->add_region(r);
991 live[wid] += r->get_live_data_words();
992 regs++;
993 }
994 prefix_idx++;
995 }
996 }
997
998 // Distribute the tail among workers in round-robin fashion.
999 size_t wid = n_workers - 1;
1000
1001 for (size_t tail_idx = prefix_end; tail_idx < n_regions; tail_idx++) {
1002 ShenandoahHeapRegion *r = heap->get_region(tail_idx);
1003 if (ShenandoahPrepareForCompactionTask::is_candidate_region(r)) {
1004 assert(wid < n_workers, "Sanity");
1005
1006 size_t live_region = r->get_live_data_words();
1007
1008 // Select next worker that still needs live data.
1009 size_t old_wid = wid;
1010 do {
1011 wid++;
1012 if (wid == n_workers) wid = 0;
1013 } while (live[wid] + live_region >= live_per_worker && old_wid != wid);
1014
1015 if (old_wid == wid) {
1016 // Circled back to the same worker? This means liveness data was
1017 // miscalculated. Bump the live_per_worker limit so that
1018 // everyone gets a piece of the leftover work.
1019 live_per_worker += ShenandoahHeapRegion::region_size_words();
1020 }
1021
1022 worker_slices[wid]->add_region(r);
1023 live[wid] += live_region;
1024 }
1025 }
1026
1027 FREE_C_HEAP_ARRAY(size_t, live);
1028
1029 #ifdef ASSERT
1030 ResourceBitMap map(n_regions);
1031 for (size_t wid = 0; wid < n_workers; wid++) {
1032 ShenandoahHeapRegionSetIterator it(worker_slices[wid]);
1033 ShenandoahHeapRegion* r = it.next();
1034 while (r != nullptr) {
1035 size_t idx = r->index();
1036 assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: " SIZE_FORMAT, idx);
1037 assert(!map.at(idx), "No region distributed twice: " SIZE_FORMAT, idx);
1038 map.at_put(idx, true);
1039 r = it.next();
1040 }
1041 }
1042
1043 for (size_t rid = 0; rid < n_regions; rid++) {
1044 bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
1045 bool is_distributed = map.at(rid);
1046 assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
1047 }
1048 #endif
1049 }
1050
1051 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
1052 GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
1053 ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
1054
1055 ShenandoahHeap* heap = ShenandoahHeap::heap();
1056
1057 // About to figure out which regions can be compacted, make sure pinning status
1058 // had been updated in GC prologue.
1059 heap->assert_pinned_region_status();
1060
1061 {
1062 // Trash the immediately collectible regions before computing addresses
1063 ShenandoahTrashImmediateGarbageClosure tigcl;
1064 heap->heap_region_iterate(&tigcl);
1065
1066 // Make sure regions are in good state: committed, active, clean.
1067 // This is needed because we are potentially sliding the data through them.
1068 ShenandoahEnsureHeapActiveClosure ecl;
1069 heap->heap_region_iterate(&ecl);
1070 }
1071
1072 if (heap->mode()->is_generational()) {
1073 heap->young_generation()->clear_used();
1074 heap->old_generation()->clear_used();
1075 }
1076
1077 // Compute the new addresses for regular objects
1078 {
1079 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
1080
1081 distribute_slices(worker_slices);
1082
1083 size_t num_workers = heap->max_workers();
1084
1085 ResourceMark rm;
1086 ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices, num_workers);
1087 heap->workers()->run_task(&task);
1088 }
1089
1090 // Compute the new addresses for humongous objects
1091 {
1092 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
1093 calculate_target_humongous_objects();
1094 }
1095 }
1096
1097 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
1098 private:
1099 ShenandoahHeap* const _heap;
1100 ShenandoahMarkingContext* const _ctx;
1101
1102 template <class T>
1103 inline void do_oop_work(T* p) {
1104 T o = RawAccess<>::oop_load(p);
1105 if (!CompressedOops::is_null(o)) {
1106 oop obj = CompressedOops::decode_not_null(o);
1107 assert(_ctx->is_marked(obj), "must be marked");
1108 if (obj->is_forwarded()) {
1109 oop forw = obj->forwardee();
1110 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
1111 }
1112 }
1113 }
1114
1115 public:
1116 ShenandoahAdjustPointersClosure() :
1117 _heap(ShenandoahHeap::heap()),
1118 _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
1119
1120 void do_oop(oop* p) { do_oop_work(p); }
1121 void do_oop(narrowOop* p) { do_oop_work(p); }
1122 void do_method(Method* m) {}
1123 void do_nmethod(nmethod* nm) {}
1124 };
1125
1126 class ShenandoahAdjustPointersObjectClosure : public ObjectClosure {
1127 private:
1128 ShenandoahHeap* const _heap;
1129 ShenandoahAdjustPointersClosure _cl;
1130
1131 public:
1132 ShenandoahAdjustPointersObjectClosure() :
1133 _heap(ShenandoahHeap::heap()) {
1134 }
1135 void do_object(oop p) {
1136 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
1137 p->oop_iterate(&_cl);
1138 }
1139 };
1140
1141 class ShenandoahAdjustPointersTask : public WorkerTask {
1142 private:
1143 ShenandoahHeap* const _heap;
1144 ShenandoahRegionIterator _regions;
1145
1146 public:
1147 ShenandoahAdjustPointersTask() :
1148 WorkerTask("Shenandoah Adjust Pointers"),
1149 _heap(ShenandoahHeap::heap()) {
1150 }
1151
1152 void work(uint worker_id) {
1153 ShenandoahParallelWorkerSession worker_session(worker_id);
1154 ShenandoahAdjustPointersObjectClosure obj_cl;
1155 ShenandoahHeapRegion* r = _regions.next();
1156 while (r != nullptr) {
1157 if (!r->is_humongous_continuation() && r->has_live()) {
1158 _heap->marked_object_iterate(r, &obj_cl);
1159 }
1160 if (r->is_pinned() && r->is_old() && r->is_active() && !r->is_humongous()) {
1161 // Pinned regions are not compacted so they may still hold unmarked objects with
1162 // reference to reclaimed memory. Remembered set scanning will crash if it attempts
1163 // to iterate the oops in these objects.
1164 r->begin_preemptible_coalesce_and_fill();
1165 r->oop_fill_and_coalesce_wo_cancel();
1166 }
1167 r = _regions.next();
1168 }
1169 }
1170 };
1171
1172 class ShenandoahAdjustRootPointersTask : public WorkerTask {
1173 private:
1174 ShenandoahRootAdjuster* _rp;
1175 PreservedMarksSet* _preserved_marks;
1176 public:
1177 ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
1178 WorkerTask("Shenandoah Adjust Root Pointers"),
1179 _rp(rp),
1180 _preserved_marks(preserved_marks) {}
1181
1182 void work(uint worker_id) {
1183 ShenandoahParallelWorkerSession worker_session(worker_id);
1184 ShenandoahAdjustPointersClosure cl;
1185 _rp->roots_do(worker_id, &cl);
1186 _preserved_marks->get(worker_id)->adjust_during_full_gc();
1187 }
1188 };
1189
1190 void ShenandoahFullGC::phase3_update_references() {
1191 GCTraceTime(Info, gc, phases) time("Phase 3: Adjust pointers", _gc_timer);
1192 ShenandoahGCPhase adjust_pointer_phase(ShenandoahPhaseTimings::full_gc_adjust_pointers);
1193
1194 ShenandoahHeap* heap = ShenandoahHeap::heap();
1195
1196 WorkerThreads* workers = heap->workers();
1197 uint nworkers = workers->active_workers();
1198 {
1199 #if COMPILER2_OR_JVMCI
1200 DerivedPointerTable::clear();
1201 #endif
1202 ShenandoahRootAdjuster rp(nworkers, ShenandoahPhaseTimings::full_gc_adjust_roots);
1203 ShenandoahAdjustRootPointersTask task(&rp, _preserved_marks);
1204 workers->run_task(&task);
1205 #if COMPILER2_OR_JVMCI
1206 DerivedPointerTable::update_pointers();
1207 #endif
1208 }
1209
1210 ShenandoahAdjustPointersTask adjust_pointers_task;
1211 workers->run_task(&adjust_pointers_task);
1212 }
1213
1214 class ShenandoahCompactObjectsClosure : public ObjectClosure {
1215 private:
1216 ShenandoahHeap* const _heap;
1217 uint const _worker_id;
1218
1219 public:
1220 ShenandoahCompactObjectsClosure(uint worker_id) :
1221 _heap(ShenandoahHeap::heap()), _worker_id(worker_id) {}
1222
1223 void do_object(oop p) {
1224 assert(_heap->complete_marking_context()->is_marked(p), "must be marked");
1225 size_t size = p->size();
1226 if (p->is_forwarded()) {
1227 HeapWord* compact_from = cast_from_oop<HeapWord*>(p);
1228 HeapWord* compact_to = cast_from_oop<HeapWord*>(p->forwardee());
1229 Copy::aligned_conjoint_words(compact_from, compact_to, size);
1230 oop new_obj = cast_to_oop(compact_to);
1231
1232 ContinuationGCSupport::relativize_stack_chunk(new_obj);
1233 new_obj->init_mark();
1234 }
1235 }
1236 };
1237
1238 class ShenandoahCompactObjectsTask : public WorkerTask {
1239 private:
1240 ShenandoahHeap* const _heap;
1241 ShenandoahHeapRegionSet** const _worker_slices;
1242
1243 public:
1244 ShenandoahCompactObjectsTask(ShenandoahHeapRegionSet** worker_slices) :
1245 WorkerTask("Shenandoah Compact Objects"),
1246 _heap(ShenandoahHeap::heap()),
1247 _worker_slices(worker_slices) {
1248 }
1249
1250 void work(uint worker_id) {
1251 ShenandoahParallelWorkerSession worker_session(worker_id);
1252 ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
1253
1254 ShenandoahCompactObjectsClosure cl(worker_id);
1255 ShenandoahHeapRegion* r = slice.next();
1256 while (r != nullptr) {
1257 assert(!r->is_humongous(), "must not get humongous regions here");
1258 if (r->has_live()) {
1259 _heap->marked_object_iterate(r, &cl);
1260 }
1261 r->set_top(r->new_top());
1262 r = slice.next();
1263 }
1264 }
1265 };
1266
1267 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
1268 private:
1269 ShenandoahHeap* const _heap;
1270 size_t _live;
1271
1272 public:
1273 ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {
1274 _heap->free_set()->clear();
1275 }
1276
1277 void heap_region_do(ShenandoahHeapRegion* r) {
1278 assert (!r->is_cset(), "cset regions should have been demoted already");
1279 bool is_generational = _heap->mode()->is_generational();
1280
1281 // Need to reset the complete-top-at-mark-start pointer here because
1282 // the complete marking bitmap is no longer valid. This ensures
1283 // size-based iteration in marked_object_iterate().
1284 // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
1285 // pinned regions.
1286 if (!r->is_pinned()) {
1287 _heap->complete_marking_context()->reset_top_at_mark_start(r);
1288 }
1289
1290 size_t live = r->used();
1291
1292 // Make empty regions that have been allocated into regular
1293 if (r->is_empty() && live > 0) {
1294 if (!is_generational) {
1295 r->make_young_maybe();
1296 }
1297 // else, generational mode compaction has already established affiliation.
1298 r->make_regular_bypass();
1299 }
1300
1301 // Reclaim regular regions that became empty
1302 if (r->is_regular() && live == 0) {
1303 r->make_trash();
1304 }
1305
1306 // Recycle all trash regions
1307 if (r->is_trash()) {
1308 live = 0;
1309 r->recycle();
1310 }
1311
1312 // Update final usage for generations
1313 if (is_generational && live != 0) {
1314 if (r->is_young()) {
1315 _heap->young_generation()->increase_used(live);
1316 } else if (r->is_old()) {
1317 _heap->old_generation()->increase_used(live);
1318 }
1319 }
1320
1321 r->set_live_data(live);
1322 r->reset_alloc_metadata();
1323 _live += live;
1324 }
1325
1326 size_t get_live() {
1327 return _live;
1328 }
1329 };
1330
1331 void ShenandoahFullGC::compact_humongous_objects() {
1332 // Compact humongous regions, based on their fwdptr objects.
1333 //
1334 // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
1335 // humongous regions are already compacted, and do not require further moves, which alleviates
1336 // sliding costs. We may consider doing this in parallel in future.
1337
1338 ShenandoahHeap* heap = ShenandoahHeap::heap();
1339
1340 for (size_t c = heap->num_regions(); c > 0; c--) {
1341 ShenandoahHeapRegion* r = heap->get_region(c - 1);
1342 if (r->is_humongous_start()) {
1343 oop old_obj = cast_to_oop(r->bottom());
1344 if (!old_obj->is_forwarded()) {
1345 // No need to move the object, it stays at the same slot
1346 continue;
1347 }
1348 size_t words_size = old_obj->size();
1349 size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
1350
1351 size_t old_start = r->index();
1352 size_t old_end = old_start + num_regions - 1;
1353 size_t new_start = heap->heap_region_index_containing(old_obj->forwardee());
1354 size_t new_end = new_start + num_regions - 1;
1355 assert(old_start != new_start, "must be real move");
1356 assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
1357
1358 ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(heap->get_region(old_start)->bottom()));
1359 log_debug(gc)("Full GC compaction moves humongous object from region " SIZE_FORMAT " to region " SIZE_FORMAT,
1360 old_start, new_start);
1361
1362 Copy::aligned_conjoint_words(heap->get_region(old_start)->bottom(),
1363 heap->get_region(new_start)->bottom(),
1364 words_size);
1365
1366 oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
1367 new_obj->init_mark();
1368
1369 {
1370 ShenandoahRegionAffiliation original_affiliation = r->affiliation();
1371 for (size_t c = old_start; c <= old_end; c++) {
1372 ShenandoahHeapRegion* r = heap->get_region(c);
1373 // Leave humongous region affiliation unchanged.
1374 r->make_regular_bypass();
1375 r->set_top(r->bottom());
1376 }
1377
1378 for (size_t c = new_start; c <= new_end; c++) {
1379 ShenandoahHeapRegion* r = heap->get_region(c);
1380 if (c == new_start) {
1381 r->make_humongous_start_bypass(original_affiliation);
1382 } else {
1383 r->make_humongous_cont_bypass(original_affiliation);
1384 }
1385
1386 // Trailing region may be non-full, record the remainder there
1387 size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1388 if ((c == new_end) && (remainder != 0)) {
1389 r->set_top(r->bottom() + remainder);
1390 } else {
1391 r->set_top(r->end());
1392 }
1393
1394 r->reset_alloc_metadata();
1395 }
1396 }
1397 }
1398 }
1399 }
1400
1401 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1402 // we need to remain able to walk pinned regions.
1403 // Since pinned region do not move and don't get compacted, we will get holes with
1404 // unreachable objects in them (which may have pointers to unloaded Klasses and thus
1405 // cannot be iterated over using oop->size(). The only way to safely iterate over those is using
1406 // a valid marking bitmap and valid TAMS pointer. This class only resets marking
1407 // bitmaps for un-pinned regions, and later we only reset TAMS for unpinned regions.
1408 class ShenandoahMCResetCompleteBitmapTask : public WorkerTask {
1409 private:
1410 ShenandoahRegionIterator _regions;
1411
1412 public:
1413 ShenandoahMCResetCompleteBitmapTask() :
1414 WorkerTask("Shenandoah Reset Bitmap") {
1415 }
1416
1417 void work(uint worker_id) {
1418 ShenandoahParallelWorkerSession worker_session(worker_id);
1419 ShenandoahHeapRegion* region = _regions.next();
1420 ShenandoahHeap* heap = ShenandoahHeap::heap();
1421 ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
1422 while (region != nullptr) {
1423 if (heap->is_bitmap_slice_committed(region) && !region->is_pinned() && region->has_live()) {
1424 ctx->clear_bitmap(region);
1425 }
1426 region = _regions.next();
1427 }
1428 }
1429 };
1430
1431 void ShenandoahFullGC::phase4_compact_objects(ShenandoahHeapRegionSet** worker_slices) {
1432 GCTraceTime(Info, gc, phases) time("Phase 4: Move objects", _gc_timer);
1433 ShenandoahGCPhase compaction_phase(ShenandoahPhaseTimings::full_gc_copy_objects);
1434
1435 ShenandoahHeap* heap = ShenandoahHeap::heap();
1436
1437 // Compact regular objects first
1438 {
1439 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_regular);
1440 ShenandoahCompactObjectsTask compact_task(worker_slices);
1441 heap->workers()->run_task(&compact_task);
1442 }
1443
1444 // Compact humongous objects after regular object moves
1445 {
1446 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_humong);
1447 compact_humongous_objects();
1448 }
1449
1450 // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1451 // and must ensure the bitmap is in sync.
1452 {
1453 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1454 ShenandoahMCResetCompleteBitmapTask task;
1455 heap->workers()->run_task(&task);
1456 }
1457
1458 // Bring regions in proper states after the collection, and set heap properties.
1459 {
1460 ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1461
1462 if (heap->mode()->is_generational()) {
1463 heap->young_generation()->clear_used();
1464 heap->old_generation()->clear_used();
1465 }
1466
1467 ShenandoahPostCompactClosure post_compact;
1468 heap->heap_region_iterate(&post_compact);
1469 heap->set_used(post_compact.get_live());
1470 if (heap->mode()->is_generational()) {
1471 log_info(gc)("FullGC done: GLOBAL usage: " SIZE_FORMAT ", young usage: " SIZE_FORMAT ", old usage: " SIZE_FORMAT,
1472 post_compact.get_live(), heap->young_generation()->used(), heap->old_generation()->used());
1473 }
1474
1475 heap->collection_set()->clear();
1476 heap->free_set()->rebuild();
1477 }
1478
1479 heap->clear_cancelled_gc(true /* clear oom handler */);
1480 }