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