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