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src/hotspot/share/gc/shenandoah/shenandoahFullGC.cpp

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   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/shenandoahCollectorPolicy.hpp"
  35 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
  36 #include "gc/shenandoah/shenandoahCollectionSet.hpp"

  37 #include "gc/shenandoah/shenandoahFreeSet.hpp"
  38 #include "gc/shenandoah/shenandoahFullGC.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/shenandoahOopClosures.inline.hpp"
  48 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
  49 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
  50 #include "gc/shenandoah/shenandoahSTWMark.hpp"
  51 #include "gc/shenandoah/shenandoahUtils.hpp"
  52 #include "gc/shenandoah/shenandoahVerifier.hpp"
  53 #include "gc/shenandoah/shenandoahVMOperations.hpp"
  54 #include "gc/shenandoah/shenandoahWorkerPolicy.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/javaThread.hpp"
  60 #include "runtime/orderAccess.hpp"
  61 #include "runtime/vmThread.hpp"
  62 #include "utilities/copy.hpp"
  63 #include "utilities/events.hpp"
  64 #include "utilities/growableArray.hpp"
  65 
  66 ShenandoahFullGC::ShenandoahFullGC() :
  67   _gc_timer(ShenandoahHeap::heap()->gc_timer()),
  68   _preserved_marks(new PreservedMarksSet(true)) {}
  69 
  70 ShenandoahFullGC::~ShenandoahFullGC() {
  71   delete _preserved_marks;
  72 }
  73 
  74 bool ShenandoahFullGC::collect(GCCause::Cause cause) {
  75   vmop_entry_full(cause);
  76   // Always success
  77   return true;
  78 }
  79 

  91   static const char* msg = "Pause Full";
  92   ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */);
  93   EventMark em("%s", msg);
  94 
  95   ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(),
  96                               ShenandoahWorkerPolicy::calc_workers_for_fullgc(),
  97                               "full gc");
  98 
  99   op_full(cause);
 100 }
 101 
 102 void ShenandoahFullGC::op_full(GCCause::Cause cause) {
 103   ShenandoahMetricsSnapshot metrics;
 104   metrics.snap_before();
 105 
 106   // Perform full GC
 107   do_it(cause);
 108 
 109   ShenandoahHeap* const heap = ShenandoahHeap::heap();
 110 




 111   metrics.snap_after();
 112 
 113   if (metrics.is_good_progress()) {
 114     heap->notify_gc_progress();
 115   } else {
 116     // Nothing to do. Tell the allocation path that we have failed to make
 117     // progress, and it can finally fail.
 118     heap->notify_gc_no_progress();
 119   }
 120 
 121   // Regardless if progress was made, we record that we completed a "successful" full GC.
 122   heap->heuristics()->record_success_full();
 123   heap->shenandoah_policy()->record_success_full();
 124 }
 125 
 126 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
 127   ShenandoahHeap* heap = ShenandoahHeap::heap();
 128 




 129   if (ShenandoahVerify) {
 130     heap->verifier()->verify_before_fullgc();
 131   }
 132 
 133   if (VerifyBeforeGC) {
 134     Universe::verify();
 135   }
 136 
 137   // Degenerated GC may carry concurrent root flags when upgrading to
 138   // full GC. We need to reset it before mutators resume.
 139   heap->set_concurrent_strong_root_in_progress(false);
 140   heap->set_concurrent_weak_root_in_progress(false);
 141 
 142   heap->set_full_gc_in_progress(true);
 143 
 144   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
 145   assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
 146 
 147   {
 148     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);

 151 
 152   {
 153     ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
 154     // Full GC is supposed to recover from any GC state:
 155 
 156     // a0. Remember if we have forwarded objects
 157     bool has_forwarded_objects = heap->has_forwarded_objects();
 158 
 159     // a1. Cancel evacuation, if in progress
 160     if (heap->is_evacuation_in_progress()) {
 161       heap->set_evacuation_in_progress(false);
 162     }
 163     assert(!heap->is_evacuation_in_progress(), "sanity");
 164 
 165     // a2. Cancel update-refs, if in progress
 166     if (heap->is_update_refs_in_progress()) {
 167       heap->set_update_refs_in_progress(false);
 168     }
 169     assert(!heap->is_update_refs_in_progress(), "sanity");
 170 
 171     // b. Cancel concurrent mark, if in progress
 172     if (heap->is_concurrent_mark_in_progress()) {
 173       ShenandoahConcurrentGC::cancel();
 174       heap->set_concurrent_mark_in_progress(false);
 175     }
 176     assert(!heap->is_concurrent_mark_in_progress(), "sanity");
 177 
 178     // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
 179     if (has_forwarded_objects) {
 180       update_roots(true /*full_gc*/);
 181     }
 182 
 183     // d. Reset the bitmaps for new marking
 184     heap->reset_mark_bitmap();
 185     assert(heap->marking_context()->is_bitmap_clear(), "sanity");
 186     assert(!heap->marking_context()->is_complete(), "sanity");
 187 
 188     // e. Abandon reference discovery and clear all discovered references.
 189     ShenandoahReferenceProcessor* rp = heap->ref_processor();
 190     rp->abandon_partial_discovery();
 191 
 192     // f. Sync pinned region status from the CP marks
 193     heap->sync_pinned_region_status();
 194 




 195     // The rest of prologue:
 196     _preserved_marks->init(heap->workers()->active_workers());
 197 
 198     assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
 199   }
 200 
 201   if (UseTLAB) {

 202     heap->gclabs_retire(ResizeTLAB);
 203     heap->tlabs_retire(ResizeTLAB);
 204   }
 205 
 206   OrderAccess::fence();
 207 
 208   phase1_mark_heap();
 209 
 210   // Once marking is done, which may have fixed up forwarded objects, we can drop it.
 211   // Coming out of Full GC, we would not have any forwarded objects.
 212   // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
 213   heap->set_has_forwarded_objects(false);
 214 
 215   heap->set_full_gc_move_in_progress(true);
 216 
 217   // Setup workers for the rest
 218   OrderAccess::fence();
 219 
 220   // Initialize worker slices
 221   ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);

 238 
 239     phase5_epilog();
 240   }
 241 
 242   // Resize metaspace
 243   MetaspaceGC::compute_new_size();
 244 
 245   // Free worker slices
 246   for (uint i = 0; i < heap->max_workers(); i++) {
 247     delete worker_slices[i];
 248   }
 249   FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
 250 
 251   heap->set_full_gc_move_in_progress(false);
 252   heap->set_full_gc_in_progress(false);
 253 
 254   if (ShenandoahVerify) {
 255     heap->verifier()->verify_after_fullgc();
 256   }
 257 

 258   if (VerifyAfterGC) {
 259     Universe::verify();
 260   }
 261 
 262   {
 263     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
 264     heap->post_full_gc_dump(_gc_timer);
 265   }
 266 }
 267 
 268 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
 269 private:
 270   ShenandoahMarkingContext* const _ctx;
 271 
 272 public:
 273   ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
 274 
 275   void heap_region_do(ShenandoahHeapRegion *r) {
 276     _ctx->capture_top_at_mark_start(r);
 277     r->clear_live_data();



 278   }
 279 
 280   bool is_thread_safe() { return true; }
 281 };
 282 
 283 void ShenandoahFullGC::phase1_mark_heap() {
 284   GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
 285   ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
 286 
 287   ShenandoahHeap* heap = ShenandoahHeap::heap();
 288 
 289   ShenandoahPrepareForMarkClosure cl;
 290   heap->parallel_heap_region_iterate(&cl);
 291 
 292   heap->set_unload_classes(heap->heuristics()->can_unload_classes());
 293 
 294   ShenandoahReferenceProcessor* rp = heap->ref_processor();
 295   // enable ("weak") refs discovery
 296   rp->set_soft_reference_policy(true); // forcefully purge all soft references
 297 
 298   ShenandoahSTWMark mark(true /*full_gc*/);
 299   mark.mark();
 300   heap->parallel_cleaning(true /* full_gc */);




 301 }
 302 
 303 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
 304 private:
 305   PreservedMarks*          const _preserved_marks;
 306   ShenandoahHeap*          const _heap;
 307   GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
 308   int _empty_regions_pos;
 309   ShenandoahHeapRegion*          _to_region;
 310   ShenandoahHeapRegion*          _from_region;
 311   HeapWord* _compact_point;
 312 
 313 public:
 314   ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
 315                                               GrowableArray<ShenandoahHeapRegion*>& empty_regions,
 316                                               ShenandoahHeapRegion* to_region) :
 317     _preserved_marks(preserved_marks),
 318     _heap(ShenandoahHeap::heap()),
 319     _empty_regions(empty_regions),
 320     _empty_regions_pos(0),

 408                               ShenandoahHeapRegionSetIterator& it,
 409                               ShenandoahHeapRegion* from_region);
 410 };
 411 
 412 void ShenandoahPrepareForCompactionTask::work(uint worker_id) {
 413   ShenandoahParallelWorkerSession worker_session(worker_id);
 414   ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
 415   ShenandoahHeapRegionSetIterator it(slice);
 416   ShenandoahHeapRegion* from_region = it.next();
 417   // No work?
 418   if (from_region == nullptr) {
 419     return;
 420   }
 421 
 422   // Sliding compaction. Walk all regions in the slice, and compact them.
 423   // Remember empty regions and reuse them as needed.
 424   ResourceMark rm;
 425 
 426   GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
 427 
 428   ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
 429   prepare_for_compaction(cl, empty_regions, it, from_region);






 430 }
 431 
 432 template<typename ClosureType>
 433 void ShenandoahPrepareForCompactionTask::prepare_for_compaction(ClosureType& cl,
 434                                                                 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
 435                                                                 ShenandoahHeapRegionSetIterator& it,
 436                                                                 ShenandoahHeapRegion* from_region) {
 437   while (from_region != nullptr) {
 438     assert(is_candidate_region(from_region), "Sanity");
 439     cl.set_from_region(from_region);
 440     if (from_region->has_live()) {
 441       _heap->marked_object_iterate(from_region, &cl);
 442     }
 443 
 444     // Compacted the region to somewhere else? From-region is empty then.
 445     if (!cl.is_compact_same_region()) {
 446       empty_regions.append(from_region);
 447     }
 448     from_region = it.next();
 449   }

 456   }
 457 }
 458 
 459 void ShenandoahFullGC::calculate_target_humongous_objects() {
 460   ShenandoahHeap* heap = ShenandoahHeap::heap();
 461 
 462   // Compute the new addresses for humongous objects. We need to do this after addresses
 463   // for regular objects are calculated, and we know what regions in heap suffix are
 464   // available for humongous moves.
 465   //
 466   // Scan the heap backwards, because we are compacting humongous regions towards the end.
 467   // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
 468   // humongous start there.
 469   //
 470   // The complication is potential non-movable regions during the scan. If such region is
 471   // detected, then sliding restarts towards that non-movable region.
 472 
 473   size_t to_begin = heap->num_regions();
 474   size_t to_end = heap->num_regions();
 475 

 476   for (size_t c = heap->num_regions(); c > 0; c--) {
 477     ShenandoahHeapRegion *r = heap->get_region(c - 1);
 478     if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
 479       // To-region candidate: record this, and continue scan
 480       to_begin = r->index();
 481       continue;
 482     }
 483 
 484     if (r->is_humongous_start() && r->is_stw_move_allowed()) {
 485       // From-region candidate: movable humongous region
 486       oop old_obj = cast_to_oop(r->bottom());
 487       size_t words_size = old_obj->size();
 488       size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
 489 
 490       size_t start = to_end - num_regions;
 491 
 492       if (start >= to_begin && start != r->index()) {
 493         // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
 494         _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
 495         old_obj->forward_to(cast_to_oop(heap->get_region(start)->bottom()));

 498       }
 499     }
 500 
 501     // Failed to fit. Scan starting from current region.
 502     to_begin = r->index();
 503     to_end = r->index();
 504   }
 505 }
 506 
 507 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
 508 private:
 509   ShenandoahHeap* const _heap;
 510 
 511 public:
 512   ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
 513   void heap_region_do(ShenandoahHeapRegion* r) {
 514     if (r->is_trash()) {
 515       r->recycle();
 516     }
 517     if (r->is_cset()) {

 518       r->make_regular_bypass();
 519     }
 520     if (r->is_empty_uncommitted()) {
 521       r->make_committed_bypass();
 522     }
 523     assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
 524 
 525     // Record current region occupancy: this communicates empty regions are free
 526     // to the rest of Full GC code.
 527     r->set_new_top(r->top());
 528   }
 529 };
 530 
 531 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
 532 private:
 533   ShenandoahHeap* const _heap;
 534   ShenandoahMarkingContext* const _ctx;
 535 
 536 public:
 537   ShenandoahTrashImmediateGarbageClosure() :
 538     _heap(ShenandoahHeap::heap()),
 539     _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
 540 
 541   void heap_region_do(ShenandoahHeapRegion* r) {






 542     if (r->is_humongous_start()) {
 543       oop humongous_obj = cast_to_oop(r->bottom());
 544       if (!_ctx->is_marked(humongous_obj)) {
 545         assert(!r->has_live(),
 546                "Region " SIZE_FORMAT " is not marked, should not have live", r->index());
 547         _heap->trash_humongous_region_at(r);
 548       } else {
 549         assert(r->has_live(),
 550                "Region " SIZE_FORMAT " should have live", r->index());
 551       }
 552     } else if (r->is_humongous_continuation()) {
 553       // If we hit continuation, the non-live humongous starts should have been trashed already
 554       assert(r->humongous_start_region()->has_live(),
 555              "Region " SIZE_FORMAT " should have live", r->index());
 556     } else if (r->is_regular()) {
 557       if (!r->has_live()) {
 558         r->make_trash_immediate();
 559       }
 560     }
 561   }

 686   for (size_t wid = 0; wid < n_workers; wid++) {
 687     ShenandoahHeapRegionSetIterator it(worker_slices[wid]);
 688     ShenandoahHeapRegion* r = it.next();
 689     while (r != nullptr) {
 690       size_t idx = r->index();
 691       assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: " SIZE_FORMAT, idx);
 692       assert(!map.at(idx), "No region distributed twice: " SIZE_FORMAT, idx);
 693       map.at_put(idx, true);
 694       r = it.next();
 695     }
 696   }
 697 
 698   for (size_t rid = 0; rid < n_regions; rid++) {
 699     bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
 700     bool is_distributed = map.at(rid);
 701     assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
 702   }
 703 #endif
 704 }
 705 





 706 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
 707   GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
 708   ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
 709 
 710   ShenandoahHeap* heap = ShenandoahHeap::heap();
 711 
 712   // About to figure out which regions can be compacted, make sure pinning status
 713   // had been updated in GC prologue.
 714   heap->assert_pinned_region_status();
 715 
 716   {
 717     // Trash the immediately collectible regions before computing addresses
 718     ShenandoahTrashImmediateGarbageClosure tigcl;
 719     heap->heap_region_iterate(&tigcl);
 720 
 721     // Make sure regions are in good state: committed, active, clean.
 722     // This is needed because we are potentially sliding the data through them.
 723     ShenandoahEnsureHeapActiveClosure ecl;
 724     heap->heap_region_iterate(&ecl);
 725   }
 726 
 727   // Compute the new addresses for regular objects
 728   {
 729     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
 730 
 731     distribute_slices(worker_slices);
 732 


 733     ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
 734     heap->workers()->run_task(&task);
 735   }
 736 
 737   // Compute the new addresses for humongous objects
 738   {
 739     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
 740     calculate_target_humongous_objects();
 741   }
 742 }
 743 
 744 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
 745 private:
 746   ShenandoahHeap* const _heap;
 747   ShenandoahMarkingContext* const _ctx;
 748 
 749   template <class T>
 750   inline void do_oop_work(T* p) {
 751     T o = RawAccess<>::oop_load(p);
 752     if (!CompressedOops::is_null(o)) {

 787 
 788 class ShenandoahAdjustPointersTask : public WorkerTask {
 789 private:
 790   ShenandoahHeap*          const _heap;
 791   ShenandoahRegionIterator       _regions;
 792 
 793 public:
 794   ShenandoahAdjustPointersTask() :
 795     WorkerTask("Shenandoah Adjust Pointers"),
 796     _heap(ShenandoahHeap::heap()) {
 797   }
 798 
 799   void work(uint worker_id) {
 800     ShenandoahParallelWorkerSession worker_session(worker_id);
 801     ShenandoahAdjustPointersObjectClosure obj_cl;
 802     ShenandoahHeapRegion* r = _regions.next();
 803     while (r != nullptr) {
 804       if (!r->is_humongous_continuation() && r->has_live()) {
 805         _heap->marked_object_iterate(r, &obj_cl);
 806       }



 807       r = _regions.next();
 808     }
 809   }
 810 };
 811 
 812 class ShenandoahAdjustRootPointersTask : public WorkerTask {
 813 private:
 814   ShenandoahRootAdjuster* _rp;
 815   PreservedMarksSet* _preserved_marks;
 816 public:
 817   ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
 818     WorkerTask("Shenandoah Adjust Root Pointers"),
 819     _rp(rp),
 820     _preserved_marks(preserved_marks) {}
 821 
 822   void work(uint worker_id) {
 823     ShenandoahParallelWorkerSession worker_session(worker_id);
 824     ShenandoahAdjustPointersClosure cl;
 825     _rp->roots_do(worker_id, &cl);
 826     _preserved_marks->get(worker_id)->adjust_during_full_gc();

 891   void work(uint worker_id) {
 892     ShenandoahParallelWorkerSession worker_session(worker_id);
 893     ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
 894 
 895     ShenandoahCompactObjectsClosure cl(worker_id);
 896     ShenandoahHeapRegion* r = slice.next();
 897     while (r != nullptr) {
 898       assert(!r->is_humongous(), "must not get humongous regions here");
 899       if (r->has_live()) {
 900         _heap->marked_object_iterate(r, &cl);
 901       }
 902       r->set_top(r->new_top());
 903       r = slice.next();
 904     }
 905   }
 906 };
 907 
 908 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
 909 private:
 910   ShenandoahHeap* const _heap;
 911   size_t _live;


 912 
 913 public:
 914   ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()), _live(0) {









 915   }
 916 
 917   void heap_region_do(ShenandoahHeapRegion* r) {
 918     assert (!r->is_cset(), "cset regions should have been demoted already");
 919 
 920     // Need to reset the complete-top-at-mark-start pointer here because
 921     // the complete marking bitmap is no longer valid. This ensures
 922     // size-based iteration in marked_object_iterate().
 923     // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
 924     // pinned regions.
 925     if (!r->is_pinned()) {
 926       _heap->complete_marking_context()->reset_top_at_mark_start(r);
 927     }
 928 
 929     size_t live = r->used();
 930 
 931     // Make empty regions that have been allocated into regular
 932     if (r->is_empty() && live > 0) {




 933       r->make_regular_bypass();
 934       if (ZapUnusedHeapArea) {
 935         SpaceMangler::mangle_region(MemRegion(r->top(), r->end()));
 936       }
 937     }
 938 
 939     // Reclaim regular regions that became empty
 940     if (r->is_regular() && live == 0) {
 941       r->make_trash();
 942     }
 943 
 944     // Recycle all trash regions
 945     if (r->is_trash()) {
 946       live = 0;
 947       r->recycle();






 948     }
 949 
 950     r->set_live_data(live);
 951     r->reset_alloc_metadata();
 952     _live += live;
 953   }
 954 
 955   size_t get_live() {
 956     return _live;













 957   }
 958 };
 959 
 960 void ShenandoahFullGC::compact_humongous_objects() {
 961   // Compact humongous regions, based on their fwdptr objects.
 962   //
 963   // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
 964   // humongous regions are already compacted, and do not require further moves, which alleviates
 965   // sliding costs. We may consider doing this in parallel in the future.
 966 
 967   ShenandoahHeap* heap = ShenandoahHeap::heap();
 968 
 969   for (size_t c = heap->num_regions(); c > 0; c--) {
 970     ShenandoahHeapRegion* r = heap->get_region(c - 1);
 971     if (r->is_humongous_start()) {
 972       oop old_obj = cast_to_oop(r->bottom());
 973       if (!old_obj->is_forwarded()) {
 974         // No need to move the object, it stays at the same slot
 975         continue;
 976       }
 977       size_t words_size = old_obj->size();
 978       size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
 979 
 980       size_t old_start = r->index();
 981       size_t old_end   = old_start + num_regions - 1;
 982       size_t new_start = heap->heap_region_index_containing(old_obj->forwardee());
 983       size_t new_end   = new_start + num_regions - 1;
 984       assert(old_start != new_start, "must be real move");
 985       assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
 986 

 987       Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
 988       ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
 989 
 990       oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
 991       new_obj->init_mark();
 992 
 993       {

 994         for (size_t c = old_start; c <= old_end; c++) {
 995           ShenandoahHeapRegion* r = heap->get_region(c);

 996           r->make_regular_bypass();
 997           r->set_top(r->bottom());
 998         }
 999 
1000         for (size_t c = new_start; c <= new_end; c++) {
1001           ShenandoahHeapRegion* r = heap->get_region(c);
1002           if (c == new_start) {
1003             r->make_humongous_start_bypass();
1004           } else {
1005             r->make_humongous_cont_bypass();
1006           }
1007 
1008           // Trailing region may be non-full, record the remainder there
1009           size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1010           if ((c == new_end) && (remainder != 0)) {
1011             r->set_top(r->bottom() + remainder);
1012           } else {
1013             r->set_top(r->end());
1014           }
1015 
1016           r->reset_alloc_metadata();
1017         }
1018       }
1019     }
1020   }
1021 }
1022 
1023 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1024 // we need to remain able to walk pinned regions.
1025 // Since pinned region do not move and don't get compacted, we will get holes with

1070   }
1071 }
1072 
1073 void ShenandoahFullGC::phase5_epilog() {
1074   GCTraceTime(Info, gc, phases) time("Phase 5: Full GC epilog", _gc_timer);
1075   ShenandoahHeap* heap = ShenandoahHeap::heap();
1076 
1077   // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1078   // and must ensure the bitmap is in sync.
1079   {
1080     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1081     ShenandoahMCResetCompleteBitmapTask task;
1082     heap->workers()->run_task(&task);
1083   }
1084 
1085   // Bring regions in proper states after the collection, and set heap properties.
1086   {
1087     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1088     ShenandoahPostCompactClosure post_compact;
1089     heap->heap_region_iterate(&post_compact);
1090     heap->set_used(post_compact.get_live());




1091 
1092     heap->collection_set()->clear();
1093     heap->free_set()->rebuild();
1094     heap->clear_cancelled_gc();


















1095   }
1096 
1097   _preserved_marks->restore(heap->workers());
1098   _preserved_marks->reclaim();







1099 }

   1 /*
   2  * Copyright (c) 2014, 2021, Red Hat, Inc. All rights reserved.
   3  * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
   4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   5  *
   6  * This code is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License version 2 only, as
   8  * published by the Free Software Foundation.
   9  *
  10  * This code is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13  * version 2 for more details (a copy is included in the LICENSE file that
  14  * accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License version
  17  * 2 along with this work; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  19  *
  20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  21  * or visit www.oracle.com if you need additional information or have any
  22  * questions.
  23  *
  24  */
  25 
  26 #include "precompiled.hpp"
  27 
  28 #include "compiler/oopMap.hpp"
  29 #include "gc/shared/continuationGCSupport.hpp"
  30 #include "gc/shared/gcTraceTime.inline.hpp"
  31 #include "gc/shared/preservedMarks.inline.hpp"
  32 #include "gc/shared/tlab_globals.hpp"
  33 #include "gc/shared/workerThread.hpp"
  34 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
  35 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
  36 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
  37 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
  38 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
  39 #include "gc/shenandoah/shenandoahFreeSet.hpp"
  40 #include "gc/shenandoah/shenandoahFullGC.hpp"
  41 #include "gc/shenandoah/shenandoahGenerationalFullGC.hpp"
  42 #include "gc/shenandoah/shenandoahGlobalGeneration.hpp"
  43 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
  44 #include "gc/shenandoah/shenandoahMark.inline.hpp"
  45 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
  46 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
  47 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  48 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
  49 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
  50 #include "gc/shenandoah/shenandoahMetrics.hpp"
  51 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
  52 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
  53 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
  54 #include "gc/shenandoah/shenandoahSTWMark.hpp"
  55 #include "gc/shenandoah/shenandoahUtils.hpp"
  56 #include "gc/shenandoah/shenandoahVerifier.hpp"
  57 #include "gc/shenandoah/shenandoahVMOperations.hpp"
  58 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
  59 #include "memory/metaspaceUtils.hpp"
  60 #include "memory/universe.hpp"
  61 #include "oops/compressedOops.inline.hpp"
  62 #include "oops/oop.inline.hpp"

  63 #include "runtime/orderAccess.hpp"
  64 #include "runtime/vmThread.hpp"
  65 #include "utilities/copy.hpp"
  66 #include "utilities/events.hpp"
  67 #include "utilities/growableArray.hpp"
  68 
  69 ShenandoahFullGC::ShenandoahFullGC() :
  70   _gc_timer(ShenandoahHeap::heap()->gc_timer()),
  71   _preserved_marks(new PreservedMarksSet(true)) {}
  72 
  73 ShenandoahFullGC::~ShenandoahFullGC() {
  74   delete _preserved_marks;
  75 }
  76 
  77 bool ShenandoahFullGC::collect(GCCause::Cause cause) {
  78   vmop_entry_full(cause);
  79   // Always success
  80   return true;
  81 }
  82 

  94   static const char* msg = "Pause Full";
  95   ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::full_gc, true /* log_heap_usage */);
  96   EventMark em("%s", msg);
  97 
  98   ShenandoahWorkerScope scope(ShenandoahHeap::heap()->workers(),
  99                               ShenandoahWorkerPolicy::calc_workers_for_fullgc(),
 100                               "full gc");
 101 
 102   op_full(cause);
 103 }
 104 
 105 void ShenandoahFullGC::op_full(GCCause::Cause cause) {
 106   ShenandoahMetricsSnapshot metrics;
 107   metrics.snap_before();
 108 
 109   // Perform full GC
 110   do_it(cause);
 111 
 112   ShenandoahHeap* const heap = ShenandoahHeap::heap();
 113 
 114   if (heap->mode()->is_generational()) {
 115     ShenandoahGenerationalFullGC::handle_completion(heap);
 116   }
 117 
 118   metrics.snap_after();
 119 
 120   if (metrics.is_good_progress()) {
 121     heap->notify_gc_progress();
 122   } else {
 123     // Nothing to do. Tell the allocation path that we have failed to make
 124     // progress, and it can finally fail.
 125     heap->notify_gc_no_progress();
 126   }
 127 
 128   // Regardless if progress was made, we record that we completed a "successful" full GC.
 129   heap->global_generation()->heuristics()->record_success_full();
 130   heap->shenandoah_policy()->record_success_full();
 131 }
 132 
 133 void ShenandoahFullGC::do_it(GCCause::Cause gc_cause) {
 134   ShenandoahHeap* heap = ShenandoahHeap::heap();
 135 
 136   if (heap->mode()->is_generational()) {
 137     ShenandoahGenerationalFullGC::prepare();
 138   }
 139 
 140   if (ShenandoahVerify) {
 141     heap->verifier()->verify_before_fullgc();
 142   }
 143 
 144   if (VerifyBeforeGC) {
 145     Universe::verify();
 146   }
 147 
 148   // Degenerated GC may carry concurrent root flags when upgrading to
 149   // full GC. We need to reset it before mutators resume.
 150   heap->set_concurrent_strong_root_in_progress(false);
 151   heap->set_concurrent_weak_root_in_progress(false);
 152 
 153   heap->set_full_gc_in_progress(true);
 154 
 155   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
 156   assert(Thread::current()->is_VM_thread(), "Do full GC only while world is stopped");
 157 
 158   {
 159     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_pre);

 162 
 163   {
 164     ShenandoahGCPhase prepare_phase(ShenandoahPhaseTimings::full_gc_prepare);
 165     // Full GC is supposed to recover from any GC state:
 166 
 167     // a0. Remember if we have forwarded objects
 168     bool has_forwarded_objects = heap->has_forwarded_objects();
 169 
 170     // a1. Cancel evacuation, if in progress
 171     if (heap->is_evacuation_in_progress()) {
 172       heap->set_evacuation_in_progress(false);
 173     }
 174     assert(!heap->is_evacuation_in_progress(), "sanity");
 175 
 176     // a2. Cancel update-refs, if in progress
 177     if (heap->is_update_refs_in_progress()) {
 178       heap->set_update_refs_in_progress(false);
 179     }
 180     assert(!heap->is_update_refs_in_progress(), "sanity");
 181 
 182     // b. Cancel all concurrent marks, if in progress
 183     if (heap->is_concurrent_mark_in_progress()) {
 184       // TODO: Send cancel_concurrent_mark upstream? Does it really not have it already?
 185       heap->cancel_concurrent_mark();
 186     }
 187     assert(!heap->is_concurrent_mark_in_progress(), "sanity");
 188 
 189     // c. Update roots if this full GC is due to evac-oom, which may carry from-space pointers in roots.
 190     if (has_forwarded_objects) {
 191       update_roots(true /*full_gc*/);
 192     }
 193 
 194     // d. Reset the bitmaps for new marking
 195     heap->global_generation()->reset_mark_bitmap();
 196     assert(heap->marking_context()->is_bitmap_clear(), "sanity");
 197     assert(!heap->global_generation()->is_mark_complete(), "sanity");
 198 
 199     // e. Abandon reference discovery and clear all discovered references.
 200     ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
 201     rp->abandon_partial_discovery();
 202 
 203     // f. Sync pinned region status from the CP marks
 204     heap->sync_pinned_region_status();
 205 
 206     if (heap->mode()->is_generational()) {
 207       ShenandoahGenerationalFullGC::restore_top_before_promote(heap);
 208     }
 209 
 210     // The rest of prologue:
 211     _preserved_marks->init(heap->workers()->active_workers());
 212 
 213     assert(heap->has_forwarded_objects() == has_forwarded_objects, "This should not change");
 214   }
 215 
 216   if (UseTLAB) {
 217     // TODO: Do we need to explicitly retire PLABs?
 218     heap->gclabs_retire(ResizeTLAB);
 219     heap->tlabs_retire(ResizeTLAB);
 220   }
 221 
 222   OrderAccess::fence();
 223 
 224   phase1_mark_heap();
 225 
 226   // Once marking is done, which may have fixed up forwarded objects, we can drop it.
 227   // Coming out of Full GC, we would not have any forwarded objects.
 228   // This also prevents resolves with fwdptr from kicking in while adjusting pointers in phase3.
 229   heap->set_has_forwarded_objects(false);
 230 
 231   heap->set_full_gc_move_in_progress(true);
 232 
 233   // Setup workers for the rest
 234   OrderAccess::fence();
 235 
 236   // Initialize worker slices
 237   ShenandoahHeapRegionSet** worker_slices = NEW_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, heap->max_workers(), mtGC);

 254 
 255     phase5_epilog();
 256   }
 257 
 258   // Resize metaspace
 259   MetaspaceGC::compute_new_size();
 260 
 261   // Free worker slices
 262   for (uint i = 0; i < heap->max_workers(); i++) {
 263     delete worker_slices[i];
 264   }
 265   FREE_C_HEAP_ARRAY(ShenandoahHeapRegionSet*, worker_slices);
 266 
 267   heap->set_full_gc_move_in_progress(false);
 268   heap->set_full_gc_in_progress(false);
 269 
 270   if (ShenandoahVerify) {
 271     heap->verifier()->verify_after_fullgc();
 272   }
 273 
 274   // Humongous regions are promoted on demand and are accounted for by normal Full GC mechanisms.
 275   if (VerifyAfterGC) {
 276     Universe::verify();
 277   }
 278 
 279   {
 280     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_heapdump_post);
 281     heap->post_full_gc_dump(_gc_timer);
 282   }
 283 }
 284 
 285 class ShenandoahPrepareForMarkClosure: public ShenandoahHeapRegionClosure {
 286 private:
 287   ShenandoahMarkingContext* const _ctx;
 288 
 289 public:
 290   ShenandoahPrepareForMarkClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
 291 
 292   void heap_region_do(ShenandoahHeapRegion *r) {
 293     // TODO: Add API to heap to skip free regions
 294     if (r->is_affiliated()) {
 295       _ctx->capture_top_at_mark_start(r);
 296       r->clear_live_data();
 297     }
 298   }
 299 
 300   bool is_thread_safe() { return true; }
 301 };
 302 
 303 void ShenandoahFullGC::phase1_mark_heap() {
 304   GCTraceTime(Info, gc, phases) time("Phase 1: Mark live objects", _gc_timer);
 305   ShenandoahGCPhase mark_phase(ShenandoahPhaseTimings::full_gc_mark);
 306 
 307   ShenandoahHeap* heap = ShenandoahHeap::heap();
 308 
 309   ShenandoahPrepareForMarkClosure cl;
 310   heap->parallel_heap_region_iterate(&cl);
 311 
 312   heap->set_unload_classes(heap->global_generation()->heuristics()->can_unload_classes());
 313 
 314   ShenandoahReferenceProcessor* rp = heap->global_generation()->ref_processor();
 315   // enable ("weak") refs discovery
 316   rp->set_soft_reference_policy(true); // forcefully purge all soft references
 317 
 318   ShenandoahSTWMark mark(heap->global_generation(), true /*full_gc*/);
 319   mark.mark();
 320   heap->parallel_cleaning(true /* full_gc */);
 321 
 322   if (ShenandoahHeap::heap()->mode()->is_generational()) {
 323     ShenandoahGenerationalFullGC::log_live_in_old(heap);
 324   }
 325 }
 326 
 327 class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
 328 private:
 329   PreservedMarks*          const _preserved_marks;
 330   ShenandoahHeap*          const _heap;
 331   GrowableArray<ShenandoahHeapRegion*>& _empty_regions;
 332   int _empty_regions_pos;
 333   ShenandoahHeapRegion*          _to_region;
 334   ShenandoahHeapRegion*          _from_region;
 335   HeapWord* _compact_point;
 336 
 337 public:
 338   ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
 339                                               GrowableArray<ShenandoahHeapRegion*>& empty_regions,
 340                                               ShenandoahHeapRegion* to_region) :
 341     _preserved_marks(preserved_marks),
 342     _heap(ShenandoahHeap::heap()),
 343     _empty_regions(empty_regions),
 344     _empty_regions_pos(0),

 432                               ShenandoahHeapRegionSetIterator& it,
 433                               ShenandoahHeapRegion* from_region);
 434 };
 435 
 436 void ShenandoahPrepareForCompactionTask::work(uint worker_id) {
 437   ShenandoahParallelWorkerSession worker_session(worker_id);
 438   ShenandoahHeapRegionSet* slice = _worker_slices[worker_id];
 439   ShenandoahHeapRegionSetIterator it(slice);
 440   ShenandoahHeapRegion* from_region = it.next();
 441   // No work?
 442   if (from_region == nullptr) {
 443     return;
 444   }
 445 
 446   // Sliding compaction. Walk all regions in the slice, and compact them.
 447   // Remember empty regions and reuse them as needed.
 448   ResourceMark rm;
 449 
 450   GrowableArray<ShenandoahHeapRegion*> empty_regions((int)_heap->num_regions());
 451 
 452   if (_heap->mode()->is_generational()) {
 453     ShenandoahPrepareForGenerationalCompactionObjectClosure cl(_preserved_marks->get(worker_id),
 454                                                                empty_regions, from_region, worker_id);
 455     prepare_for_compaction(cl, empty_regions, it, from_region);
 456   } else {
 457     ShenandoahPrepareForCompactionObjectClosure cl(_preserved_marks->get(worker_id), empty_regions, from_region);
 458     prepare_for_compaction(cl, empty_regions, it, from_region);
 459   }
 460 }
 461 
 462 template<typename ClosureType>
 463 void ShenandoahPrepareForCompactionTask::prepare_for_compaction(ClosureType& cl,
 464                                                                 GrowableArray<ShenandoahHeapRegion*>& empty_regions,
 465                                                                 ShenandoahHeapRegionSetIterator& it,
 466                                                                 ShenandoahHeapRegion* from_region) {
 467   while (from_region != nullptr) {
 468     assert(is_candidate_region(from_region), "Sanity");
 469     cl.set_from_region(from_region);
 470     if (from_region->has_live()) {
 471       _heap->marked_object_iterate(from_region, &cl);
 472     }
 473 
 474     // Compacted the region to somewhere else? From-region is empty then.
 475     if (!cl.is_compact_same_region()) {
 476       empty_regions.append(from_region);
 477     }
 478     from_region = it.next();
 479   }

 486   }
 487 }
 488 
 489 void ShenandoahFullGC::calculate_target_humongous_objects() {
 490   ShenandoahHeap* heap = ShenandoahHeap::heap();
 491 
 492   // Compute the new addresses for humongous objects. We need to do this after addresses
 493   // for regular objects are calculated, and we know what regions in heap suffix are
 494   // available for humongous moves.
 495   //
 496   // Scan the heap backwards, because we are compacting humongous regions towards the end.
 497   // Maintain the contiguous compaction window in [to_begin; to_end), so that we can slide
 498   // humongous start there.
 499   //
 500   // The complication is potential non-movable regions during the scan. If such region is
 501   // detected, then sliding restarts towards that non-movable region.
 502 
 503   size_t to_begin = heap->num_regions();
 504   size_t to_end = heap->num_regions();
 505 
 506   log_debug(gc)("Full GC calculating target humongous objects from end " SIZE_FORMAT, to_end);
 507   for (size_t c = heap->num_regions(); c > 0; c--) {
 508     ShenandoahHeapRegion *r = heap->get_region(c - 1);
 509     if (r->is_humongous_continuation() || (r->new_top() == r->bottom())) {
 510       // To-region candidate: record this, and continue scan
 511       to_begin = r->index();
 512       continue;
 513     }
 514 
 515     if (r->is_humongous_start() && r->is_stw_move_allowed()) {
 516       // From-region candidate: movable humongous region
 517       oop old_obj = cast_to_oop(r->bottom());
 518       size_t words_size = old_obj->size();
 519       size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
 520 
 521       size_t start = to_end - num_regions;
 522 
 523       if (start >= to_begin && start != r->index()) {
 524         // Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
 525         _preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
 526         old_obj->forward_to(cast_to_oop(heap->get_region(start)->bottom()));

 529       }
 530     }
 531 
 532     // Failed to fit. Scan starting from current region.
 533     to_begin = r->index();
 534     to_end = r->index();
 535   }
 536 }
 537 
 538 class ShenandoahEnsureHeapActiveClosure: public ShenandoahHeapRegionClosure {
 539 private:
 540   ShenandoahHeap* const _heap;
 541 
 542 public:
 543   ShenandoahEnsureHeapActiveClosure() : _heap(ShenandoahHeap::heap()) {}
 544   void heap_region_do(ShenandoahHeapRegion* r) {
 545     if (r->is_trash()) {
 546       r->recycle();
 547     }
 548     if (r->is_cset()) {
 549       // Leave affiliation unchanged
 550       r->make_regular_bypass();
 551     }
 552     if (r->is_empty_uncommitted()) {
 553       r->make_committed_bypass();
 554     }
 555     assert (r->is_committed(), "only committed regions in heap now, see region " SIZE_FORMAT, r->index());
 556 
 557     // Record current region occupancy: this communicates empty regions are free
 558     // to the rest of Full GC code.
 559     r->set_new_top(r->top());
 560   }
 561 };
 562 
 563 class ShenandoahTrashImmediateGarbageClosure: public ShenandoahHeapRegionClosure {
 564 private:
 565   ShenandoahHeap* const _heap;
 566   ShenandoahMarkingContext* const _ctx;
 567 
 568 public:
 569   ShenandoahTrashImmediateGarbageClosure() :
 570     _heap(ShenandoahHeap::heap()),
 571     _ctx(ShenandoahHeap::heap()->complete_marking_context()) {}
 572 
 573   void heap_region_do(ShenandoahHeapRegion* r) {
 574     if (!r->is_affiliated()) {
 575       // Ignore free regions
 576       // TODO: change iterators so they do not process FREE regions.
 577       return;
 578     }
 579 
 580     if (r->is_humongous_start()) {
 581       oop humongous_obj = cast_to_oop(r->bottom());
 582       if (!_ctx->is_marked(humongous_obj)) {
 583         assert(!r->has_live(),
 584                "Region " SIZE_FORMAT " is not marked, should not have live", r->index());
 585         _heap->trash_humongous_region_at(r);
 586       } else {
 587         assert(r->has_live(),
 588                "Region " SIZE_FORMAT " should have live", r->index());
 589       }
 590     } else if (r->is_humongous_continuation()) {
 591       // If we hit continuation, the non-live humongous starts should have been trashed already
 592       assert(r->humongous_start_region()->has_live(),
 593              "Region " SIZE_FORMAT " should have live", r->index());
 594     } else if (r->is_regular()) {
 595       if (!r->has_live()) {
 596         r->make_trash_immediate();
 597       }
 598     }
 599   }

 724   for (size_t wid = 0; wid < n_workers; wid++) {
 725     ShenandoahHeapRegionSetIterator it(worker_slices[wid]);
 726     ShenandoahHeapRegion* r = it.next();
 727     while (r != nullptr) {
 728       size_t idx = r->index();
 729       assert(ShenandoahPrepareForCompactionTask::is_candidate_region(r), "Sanity: " SIZE_FORMAT, idx);
 730       assert(!map.at(idx), "No region distributed twice: " SIZE_FORMAT, idx);
 731       map.at_put(idx, true);
 732       r = it.next();
 733     }
 734   }
 735 
 736   for (size_t rid = 0; rid < n_regions; rid++) {
 737     bool is_candidate = ShenandoahPrepareForCompactionTask::is_candidate_region(heap->get_region(rid));
 738     bool is_distributed = map.at(rid);
 739     assert(is_distributed || !is_candidate, "All candidates are distributed: " SIZE_FORMAT, rid);
 740   }
 741 #endif
 742 }
 743 
 744 // TODO:
 745 //  Consider compacting old-gen objects toward the high end of memory and young-gen objects towards the low-end
 746 //  of memory.  As currently implemented, all regions are compacted toward the low-end of memory.  This creates more
 747 //  fragmentation of the heap, because old-gen regions get scattered among low-address regions such that it becomes
 748 //  more difficult to find contiguous regions for humongous objects.
 749 void ShenandoahFullGC::phase2_calculate_target_addresses(ShenandoahHeapRegionSet** worker_slices) {
 750   GCTraceTime(Info, gc, phases) time("Phase 2: Compute new object addresses", _gc_timer);
 751   ShenandoahGCPhase calculate_address_phase(ShenandoahPhaseTimings::full_gc_calculate_addresses);
 752 
 753   ShenandoahHeap* heap = ShenandoahHeap::heap();
 754 
 755   // About to figure out which regions can be compacted, make sure pinning status
 756   // had been updated in GC prologue.
 757   heap->assert_pinned_region_status();
 758 
 759   {
 760     // Trash the immediately collectible regions before computing addresses
 761     ShenandoahTrashImmediateGarbageClosure tigcl;
 762     heap->heap_region_iterate(&tigcl);
 763 
 764     // Make sure regions are in good state: committed, active, clean.
 765     // This is needed because we are potentially sliding the data through them.
 766     ShenandoahEnsureHeapActiveClosure ecl;
 767     heap->heap_region_iterate(&ecl);
 768   }
 769 
 770   // Compute the new addresses for regular objects
 771   {
 772     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_regular);
 773 
 774     distribute_slices(worker_slices);
 775 
 776     // TODO: This is ResourceMark is missing upstream.
 777     ResourceMark rm;
 778     ShenandoahPrepareForCompactionTask task(_preserved_marks, worker_slices);
 779     heap->workers()->run_task(&task);
 780   }
 781 
 782   // Compute the new addresses for humongous objects
 783   {
 784     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_calculate_addresses_humong);
 785     calculate_target_humongous_objects();
 786   }
 787 }
 788 
 789 class ShenandoahAdjustPointersClosure : public MetadataVisitingOopIterateClosure {
 790 private:
 791   ShenandoahHeap* const _heap;
 792   ShenandoahMarkingContext* const _ctx;
 793 
 794   template <class T>
 795   inline void do_oop_work(T* p) {
 796     T o = RawAccess<>::oop_load(p);
 797     if (!CompressedOops::is_null(o)) {

 832 
 833 class ShenandoahAdjustPointersTask : public WorkerTask {
 834 private:
 835   ShenandoahHeap*          const _heap;
 836   ShenandoahRegionIterator       _regions;
 837 
 838 public:
 839   ShenandoahAdjustPointersTask() :
 840     WorkerTask("Shenandoah Adjust Pointers"),
 841     _heap(ShenandoahHeap::heap()) {
 842   }
 843 
 844   void work(uint worker_id) {
 845     ShenandoahParallelWorkerSession worker_session(worker_id);
 846     ShenandoahAdjustPointersObjectClosure obj_cl;
 847     ShenandoahHeapRegion* r = _regions.next();
 848     while (r != nullptr) {
 849       if (!r->is_humongous_continuation() && r->has_live()) {
 850         _heap->marked_object_iterate(r, &obj_cl);
 851       }
 852       if (_heap->mode()->is_generational()) {
 853         ShenandoahGenerationalFullGC::maybe_coalesce_and_fill_region(r);
 854       }
 855       r = _regions.next();
 856     }
 857   }
 858 };
 859 
 860 class ShenandoahAdjustRootPointersTask : public WorkerTask {
 861 private:
 862   ShenandoahRootAdjuster* _rp;
 863   PreservedMarksSet* _preserved_marks;
 864 public:
 865   ShenandoahAdjustRootPointersTask(ShenandoahRootAdjuster* rp, PreservedMarksSet* preserved_marks) :
 866     WorkerTask("Shenandoah Adjust Root Pointers"),
 867     _rp(rp),
 868     _preserved_marks(preserved_marks) {}
 869 
 870   void work(uint worker_id) {
 871     ShenandoahParallelWorkerSession worker_session(worker_id);
 872     ShenandoahAdjustPointersClosure cl;
 873     _rp->roots_do(worker_id, &cl);
 874     _preserved_marks->get(worker_id)->adjust_during_full_gc();

 939   void work(uint worker_id) {
 940     ShenandoahParallelWorkerSession worker_session(worker_id);
 941     ShenandoahHeapRegionSetIterator slice(_worker_slices[worker_id]);
 942 
 943     ShenandoahCompactObjectsClosure cl(worker_id);
 944     ShenandoahHeapRegion* r = slice.next();
 945     while (r != nullptr) {
 946       assert(!r->is_humongous(), "must not get humongous regions here");
 947       if (r->has_live()) {
 948         _heap->marked_object_iterate(r, &cl);
 949       }
 950       r->set_top(r->new_top());
 951       r = slice.next();
 952     }
 953   }
 954 };
 955 
 956 class ShenandoahPostCompactClosure : public ShenandoahHeapRegionClosure {
 957 private:
 958   ShenandoahHeap* const _heap;
 959   bool _is_generational;
 960   size_t _young_regions, _young_usage, _young_humongous_waste;
 961   size_t _old_regions, _old_usage, _old_humongous_waste;
 962 
 963 public:
 964   ShenandoahPostCompactClosure() : _heap(ShenandoahHeap::heap()),
 965                                    _is_generational(_heap->mode()->is_generational()),
 966                                    _young_regions(0),
 967                                    _young_usage(0),
 968                                    _young_humongous_waste(0),
 969                                    _old_regions(0),
 970                                    _old_usage(0),
 971                                    _old_humongous_waste(0)
 972   {
 973     _heap->free_set()->clear();
 974   }
 975 
 976   void heap_region_do(ShenandoahHeapRegion* r) {
 977     assert (!r->is_cset(), "cset regions should have been demoted already");
 978 
 979     // Need to reset the complete-top-at-mark-start pointer here because
 980     // the complete marking bitmap is no longer valid. This ensures
 981     // size-based iteration in marked_object_iterate().
 982     // NOTE: See blurb at ShenandoahMCResetCompleteBitmapTask on why we need to skip
 983     // pinned regions.
 984     if (!r->is_pinned()) {
 985       _heap->complete_marking_context()->reset_top_at_mark_start(r);
 986     }
 987 
 988     size_t live = r->used();
 989 
 990     // Make empty regions that have been allocated into regular
 991     if (r->is_empty() && live > 0) {
 992       if (!_is_generational) {
 993         r->make_young_maybe();
 994       }
 995       // else, generational mode compaction has already established affiliation.
 996       r->make_regular_bypass();
 997       if (ZapUnusedHeapArea) {
 998         SpaceMangler::mangle_region(MemRegion(r->top(), r->end()));
 999       }
1000     }
1001 
1002     // Reclaim regular regions that became empty
1003     if (r->is_regular() && live == 0) {
1004       r->make_trash();
1005     }
1006 
1007     // Recycle all trash regions
1008     if (r->is_trash()) {
1009       live = 0;
1010       r->recycle();
1011     } else {
1012       if (r->is_old()) {
1013         ShenandoahGenerationalFullGC::account_for_region(r, _old_regions, _old_usage, _old_humongous_waste);
1014       } else if (r->is_young()) {
1015         ShenandoahGenerationalFullGC::account_for_region(r, _young_regions, _young_usage, _young_humongous_waste);
1016       }
1017     }

1018     r->set_live_data(live);
1019     r->reset_alloc_metadata();

1020   }
1021 
1022   void update_generation_usage() {
1023     if (_is_generational) {
1024       _heap->old_generation()->establish_usage(_old_regions, _old_usage, _old_humongous_waste);
1025       _heap->young_generation()->establish_usage(_young_regions, _young_usage, _young_humongous_waste);
1026     } else {
1027       assert(_old_regions == 0, "Old regions only expected in generational mode");
1028       assert(_old_usage == 0, "Old usage only expected in generational mode");
1029       assert(_old_humongous_waste == 0, "Old humongous waste only expected in generational mode");
1030     }
1031 
1032     // In generational mode, global usage should be the sum of young and old. This is also true
1033     // for non-generational modes except that there are no old regions.
1034     _heap->global_generation()->establish_usage(_old_regions + _young_regions,
1035                                                 _old_usage + _young_usage,
1036                                                 _old_humongous_waste + _young_humongous_waste);
1037   }
1038 };
1039 
1040 void ShenandoahFullGC::compact_humongous_objects() {
1041   // Compact humongous regions, based on their fwdptr objects.
1042   //
1043   // This code is serial, because doing the in-slice parallel sliding is tricky. In most cases,
1044   // humongous regions are already compacted, and do not require further moves, which alleviates
1045   // sliding costs. We may consider doing this in parallel in the future.
1046 
1047   ShenandoahHeap* heap = ShenandoahHeap::heap();
1048 
1049   for (size_t c = heap->num_regions(); c > 0; c--) {
1050     ShenandoahHeapRegion* r = heap->get_region(c - 1);
1051     if (r->is_humongous_start()) {
1052       oop old_obj = cast_to_oop(r->bottom());
1053       if (!old_obj->is_forwarded()) {
1054         // No need to move the object, it stays at the same slot
1055         continue;
1056       }
1057       size_t words_size = old_obj->size();
1058       size_t num_regions = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);
1059 
1060       size_t old_start = r->index();
1061       size_t old_end   = old_start + num_regions - 1;
1062       size_t new_start = heap->heap_region_index_containing(old_obj->forwardee());
1063       size_t new_end   = new_start + num_regions - 1;
1064       assert(old_start != new_start, "must be real move");
1065       assert(r->is_stw_move_allowed(), "Region " SIZE_FORMAT " should be movable", r->index());
1066 
1067       log_debug(gc)("Full GC compaction moves humongous object from region " SIZE_FORMAT " to region " SIZE_FORMAT, old_start, new_start);
1068       Copy::aligned_conjoint_words(r->bottom(), heap->get_region(new_start)->bottom(), words_size);
1069       ContinuationGCSupport::relativize_stack_chunk(cast_to_oop<HeapWord*>(r->bottom()));
1070 
1071       oop new_obj = cast_to_oop(heap->get_region(new_start)->bottom());
1072       new_obj->init_mark();
1073 
1074       {
1075         ShenandoahAffiliation original_affiliation = r->affiliation();
1076         for (size_t c = old_start; c <= old_end; c++) {
1077           ShenandoahHeapRegion* r = heap->get_region(c);
1078           // Leave humongous region affiliation unchanged.
1079           r->make_regular_bypass();
1080           r->set_top(r->bottom());
1081         }
1082 
1083         for (size_t c = new_start; c <= new_end; c++) {
1084           ShenandoahHeapRegion* r = heap->get_region(c);
1085           if (c == new_start) {
1086             r->make_humongous_start_bypass(original_affiliation);
1087           } else {
1088             r->make_humongous_cont_bypass(original_affiliation);
1089           }
1090 
1091           // Trailing region may be non-full, record the remainder there
1092           size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();
1093           if ((c == new_end) && (remainder != 0)) {
1094             r->set_top(r->bottom() + remainder);
1095           } else {
1096             r->set_top(r->end());
1097           }
1098 
1099           r->reset_alloc_metadata();
1100         }
1101       }
1102     }
1103   }
1104 }
1105 
1106 // This is slightly different to ShHeap::reset_next_mark_bitmap:
1107 // we need to remain able to walk pinned regions.
1108 // Since pinned region do not move and don't get compacted, we will get holes with

1153   }
1154 }
1155 
1156 void ShenandoahFullGC::phase5_epilog() {
1157   GCTraceTime(Info, gc, phases) time("Phase 5: Full GC epilog", _gc_timer);
1158   ShenandoahHeap* heap = ShenandoahHeap::heap();
1159 
1160   // Reset complete bitmap. We're about to reset the complete-top-at-mark-start pointer
1161   // and must ensure the bitmap is in sync.
1162   {
1163     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_reset_complete);
1164     ShenandoahMCResetCompleteBitmapTask task;
1165     heap->workers()->run_task(&task);
1166   }
1167 
1168   // Bring regions in proper states after the collection, and set heap properties.
1169   {
1170     ShenandoahGCPhase phase(ShenandoahPhaseTimings::full_gc_copy_objects_rebuild);
1171     ShenandoahPostCompactClosure post_compact;
1172     heap->heap_region_iterate(&post_compact);
1173     post_compact.update_generation_usage();
1174 
1175     if (heap->mode()->is_generational()) {
1176       ShenandoahGenerationalFullGC::balance_generations_after_gc(heap);
1177     }
1178 
1179     heap->collection_set()->clear();
1180     size_t young_cset_regions, old_cset_regions;
1181     size_t first_old, last_old, num_old;
1182     heap->free_set()->prepare_to_rebuild(young_cset_regions, old_cset_regions, first_old, last_old, num_old);
1183 
1184     // We also do not expand old generation size following Full GC because we have scrambled age populations and
1185     // no longer have objects separated by age into distinct regions.
1186 
1187     // TODO: Do we need to fix FullGC so that it maintains aged segregation of objects into distinct regions?
1188     //       A partial solution would be to remember how many objects are of tenure age following Full GC, but
1189     //       this is probably suboptimal, because most of these objects will not reside in a region that will be
1190     //       selected for the next evacuation phase.
1191 
1192 
1193     if (heap->mode()->is_generational()) {
1194       ShenandoahGenerationalFullGC::compute_balances();
1195     }
1196 
1197     heap->free_set()->rebuild(young_cset_regions, old_cset_regions);
1198 
1199     heap->clear_cancelled_gc(true /* clear oom handler */);
1200   }
1201 
1202   _preserved_marks->restore(heap->workers());
1203   _preserved_marks->reclaim();
1204 
1205   // We defer generation resizing actions until after cset regions have been recycled.  We do this even following an
1206   // abbreviated cycle.
1207   if (heap->mode()->is_generational()) {
1208     ShenandoahGenerationalFullGC::balance_generations_after_rebuilding_free_set();
1209     ShenandoahGenerationalFullGC::rebuild_remembered_set(heap);
1210   }
1211 }
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