1 /*
  2  * Copyright (c) 2002, 2019, Oracle and/or its affiliates. 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 #include "aot/aotLoader.hpp"
 27 #include "classfile/classLoaderDataGraph.hpp"
 28 #include "classfile/stringTable.hpp"
 29 #include "code/codeCache.hpp"
 30 #include "gc/parallel/gcTaskManager.hpp"
 31 #include "gc/parallel/parallelScavengeHeap.hpp"
 32 #include "gc/parallel/psAdaptiveSizePolicy.hpp"
 33 #include "gc/parallel/psClosure.inline.hpp"
 34 #include "gc/parallel/psMarkSweepProxy.hpp"
 35 #include "gc/parallel/psParallelCompact.inline.hpp"
 36 #include "gc/parallel/psPromotionManager.inline.hpp"
 37 #include "gc/parallel/psRootType.inline.hpp"
 38 #include "gc/parallel/psScavenge.inline.hpp"
 39 #include "gc/parallel/psTasks.hpp"
 40 #include "gc/shared/gcCause.hpp"
 41 #include "gc/shared/gcHeapSummary.hpp"
 42 #include "gc/shared/gcId.hpp"
 43 #include "gc/shared/gcLocker.hpp"
 44 #include "gc/shared/gcTimer.hpp"
 45 #include "gc/shared/gcTrace.hpp"
 46 #include "gc/shared/gcTraceTime.inline.hpp"
 47 #include "gc/shared/isGCActiveMark.hpp"
 48 #include "gc/shared/referencePolicy.hpp"
 49 #include "gc/shared/referenceProcessor.hpp"
 50 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
 51 #include "gc/shared/scavengableNMethods.hpp"
 52 #include "gc/shared/spaceDecorator.hpp"
 53 #include "gc/shared/weakProcessor.hpp"
 54 #include "gc/shared/workerPolicy.hpp"
 55 #include "gc/shared/workgroup.hpp"
 56 #if INCLUDE_JVMCI
 57 #include "jvmci/jvmci.hpp"
 58 #endif
 59 #include "memory/resourceArea.hpp"
 60 #include "memory/universe.hpp"
 61 #include "logging/log.hpp"
 62 #include "oops/access.inline.hpp"
 63 #include "oops/compressedOops.inline.hpp"
 64 #include "oops/oop.inline.hpp"
 65 #include "runtime/biasedLocking.hpp"
 66 #include "runtime/handles.inline.hpp"
 67 #include "runtime/threadCritical.hpp"
 68 #include "runtime/vmThread.hpp"
 69 #include "runtime/vmOperations.hpp"
 70 #include "services/management.hpp"
 71 #include "services/memoryService.hpp"
 72 #include "utilities/stack.inline.hpp"
 73 
 74 
 75 HeapWord*                     PSScavenge::_to_space_top_before_gc = NULL;
 76 int                           PSScavenge::_consecutive_skipped_scavenges = 0;
 77 SpanSubjectToDiscoveryClosure PSScavenge::_span_based_discoverer;
 78 ReferenceProcessor*           PSScavenge::_ref_processor = NULL;
 79 PSCardTable*                  PSScavenge::_card_table = NULL;
 80 bool                          PSScavenge::_survivor_overflow = false;
 81 uint                          PSScavenge::_tenuring_threshold = 0;
 82 HeapWord*                     PSScavenge::_young_generation_boundary = NULL;
 83 uintptr_t                     PSScavenge::_young_generation_boundary_compressed = 0;
 84 elapsedTimer                  PSScavenge::_accumulated_time;
 85 STWGCTimer                    PSScavenge::_gc_timer;
 86 ParallelScavengeTracer        PSScavenge::_gc_tracer;
 87 CollectorCounters*            PSScavenge::_counters = NULL;
 88 
 89 void scavenge_roots_task(Parallel::RootType::Value root_type, uint which) {
 90   assert(ParallelScavengeHeap::heap()->is_gc_active(), "called outside gc");
 91 
 92   PSPromotionManager* pm = PSPromotionManager::gc_thread_promotion_manager(which);
 93   PSScavengeRootsClosure roots_closure(pm);
 94   PSPromoteRootsClosure  roots_to_old_closure(pm);
 95 
 96   switch (root_type) {
 97     case Parallel::RootType::universe:
 98       Universe::oops_do(&roots_closure);
 99       break;
100 
101     case Parallel::RootType::jni_handles:
102       JNIHandles::oops_do(&roots_closure);
103       break;
104 
105     case Parallel::RootType::object_synchronizer:
106       ObjectSynchronizer::oops_do(&roots_closure);
107       break;
108 
109     case Parallel::RootType::system_dictionary:
110       SystemDictionary::oops_do(&roots_closure);
111       break;
112 
113     case Parallel::RootType::class_loader_data:
114       {
115         PSScavengeCLDClosure cld_closure(pm);
116         ClassLoaderDataGraph::cld_do(&cld_closure);
117       }
118       break;
119 
120     case Parallel::RootType::management:
121       Management::oops_do(&roots_closure);
122       break;
123 
124     case Parallel::RootType::jvmti:
125       JvmtiExport::oops_do(&roots_closure);
126       break;
127 
128     case Parallel::RootType::code_cache:
129       {
130         MarkingCodeBlobClosure code_closure(&roots_to_old_closure, CodeBlobToOopClosure::FixRelocations);
131         ScavengableNMethods::nmethods_do(&code_closure);
132         AOTLoader::oops_do(&roots_closure);
133       }
134       break;
135 
136 #if INCLUDE_JVMCI
137     case Parallel::RootType::jvmci:
138       JVMCI::oops_do(&roots_closure);
139       break;
140 #endif
141 
142     case Parallel::RootType::sentinel:
143     DEBUG_ONLY(default:) // DEBUG_ONLY hack will create compile error on release builds (-Wswitch) and runtime check on debug builds
144       fatal("Bad enumeration value: %u", root_type);
145       break;
146   }
147 
148   // Do the real work
149   pm->drain_stacks(false);
150 }
151 
152 void steal_task(ParallelTaskTerminator& terminator, uint worker_id) {
153   assert(ParallelScavengeHeap::heap()->is_gc_active(), "called outside gc");
154 
155   PSPromotionManager* pm =
156     PSPromotionManager::gc_thread_promotion_manager(worker_id);
157   pm->drain_stacks(true);
158   guarantee(pm->stacks_empty(),
159             "stacks should be empty at this point");
160 
161   while (true) {
162     StarTask p;
163     if (PSPromotionManager::steal_depth(worker_id, p)) {
164       TASKQUEUE_STATS_ONLY(pm->record_steal(p));
165       pm->process_popped_location_depth(p);
166       pm->drain_stacks_depth(true);
167     } else {
168       if (terminator.offer_termination()) {
169         break;
170       }
171     }
172   }
173   guarantee(pm->stacks_empty(), "stacks should be empty at this point");
174 }
175 
176 // Define before use
177 class PSIsAliveClosure: public BoolObjectClosure {
178 public:
179   bool do_object_b(oop p) {
180     return (!PSScavenge::is_obj_in_young(p)) || p->is_forwarded();
181   }
182 };
183 
184 PSIsAliveClosure PSScavenge::_is_alive_closure;
185 
186 class PSKeepAliveClosure: public OopClosure {
187 protected:
188   MutableSpace* _to_space;
189   PSPromotionManager* _promotion_manager;
190 
191 public:
192   PSKeepAliveClosure(PSPromotionManager* pm) : _promotion_manager(pm) {
193     ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
194     _to_space = heap->young_gen()->to_space();
195 
196     assert(_promotion_manager != NULL, "Sanity");
197   }
198 
199   template <class T> void do_oop_work(T* p) {
200     assert (oopDesc::is_oop(RawAccess<IS_NOT_NULL>::oop_load(p)),
201             "expected an oop while scanning weak refs");
202 
203     // Weak refs may be visited more than once.
204     if (PSScavenge::should_scavenge(p, _to_space)) {
205       _promotion_manager->copy_and_push_safe_barrier<T, /*promote_immediately=*/false>(p);
206     }
207   }
208   virtual void do_oop(oop* p)       { PSKeepAliveClosure::do_oop_work(p); }
209   virtual void do_oop(narrowOop* p) { PSKeepAliveClosure::do_oop_work(p); }
210 };
211 
212 class PSEvacuateFollowersClosure: public VoidClosure {
213  private:
214   PSPromotionManager* _promotion_manager;
215  public:
216   PSEvacuateFollowersClosure(PSPromotionManager* pm) : _promotion_manager(pm) {}
217 
218   virtual void do_void() {
219     assert(_promotion_manager != NULL, "Sanity");
220     _promotion_manager->drain_stacks(true);
221     guarantee(_promotion_manager->stacks_empty(),
222               "stacks should be empty at this point");
223   }
224 };
225 
226 class PSRefProcTaskProxy: public GCTask {
227   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
228   ProcessTask & _rp_task;
229   uint          _work_id;
230 public:
231   PSRefProcTaskProxy(ProcessTask & rp_task, uint work_id)
232     : _rp_task(rp_task),
233       _work_id(work_id)
234   { }
235 
236 private:
237   virtual char* name() { return (char *)"Process referents by policy in parallel"; }
238   virtual void do_it(GCTaskManager* manager, uint which);
239 };
240 
241 void PSRefProcTaskProxy::do_it(GCTaskManager* manager, uint which)
242 {
243   PSPromotionManager* promotion_manager =
244     PSPromotionManager::gc_thread_promotion_manager(which);
245   assert(promotion_manager != NULL, "sanity check");
246   PSKeepAliveClosure keep_alive(promotion_manager);
247   PSEvacuateFollowersClosure evac_followers(promotion_manager);
248   PSIsAliveClosure is_alive;
249   _rp_task.work(_work_id, is_alive, keep_alive, evac_followers);
250 }
251 
252 class PSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
253   virtual void execute(ProcessTask& task, uint ergo_workers);
254 };
255 
256 void PSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers)
257 {
258   GCTaskQueue* q = GCTaskQueue::create();
259   GCTaskManager* manager = ParallelScavengeHeap::gc_task_manager();
260   uint active_workers = manager->active_workers();
261 
262   assert(active_workers == ergo_workers,
263          "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
264          ergo_workers, active_workers);
265 
266   for(uint i=0; i < active_workers; i++) {
267     q->enqueue(new PSRefProcTaskProxy(task, i));
268   }
269   TaskTerminator terminator(active_workers,
270                             (TaskQueueSetSuper*) PSPromotionManager::stack_array_depth());
271   if (task.marks_oops_alive() && active_workers > 1) {
272     for (uint j = 0; j < active_workers; j++) {
273       q->enqueue(new StealTask(terminator.terminator()));
274     }
275   }
276   manager->execute_and_wait(q);
277 }
278 
279 // This method contains all heap specific policy for invoking scavenge.
280 // PSScavenge::invoke_no_policy() will do nothing but attempt to
281 // scavenge. It will not clean up after failed promotions, bail out if
282 // we've exceeded policy time limits, or any other special behavior.
283 // All such policy should be placed here.
284 //
285 // Note that this method should only be called from the vm_thread while
286 // at a safepoint!
287 bool PSScavenge::invoke() {
288   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
289   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
290   assert(!ParallelScavengeHeap::heap()->is_gc_active(), "not reentrant");
291 
292   ParallelScavengeHeap* const heap = ParallelScavengeHeap::heap();
293   PSAdaptiveSizePolicy* policy = heap->size_policy();
294   IsGCActiveMark mark;
295 
296   const bool scavenge_done = PSScavenge::invoke_no_policy();
297   const bool need_full_gc = !scavenge_done ||
298     policy->should_full_GC(heap->old_gen()->free_in_bytes());
299   bool full_gc_done = false;
300 
301   if (UsePerfData) {
302     PSGCAdaptivePolicyCounters* const counters = heap->gc_policy_counters();
303     const int ffs_val = need_full_gc ? full_follows_scavenge : not_skipped;
304     counters->update_full_follows_scavenge(ffs_val);
305   }
306 
307   if (need_full_gc) {
308     GCCauseSetter gccs(heap, GCCause::_adaptive_size_policy);
309     SoftRefPolicy* srp = heap->soft_ref_policy();
310     const bool clear_all_softrefs = srp->should_clear_all_soft_refs();
311 
312     if (UseParallelOldGC) {
313       full_gc_done = PSParallelCompact::invoke_no_policy(clear_all_softrefs);
314     } else {
315       full_gc_done = PSMarkSweepProxy::invoke_no_policy(clear_all_softrefs);
316     }
317   }
318 
319   return full_gc_done;
320 }
321 
322 class PSThreadRootsTaskClosure : public ThreadClosure {
323   uint _worker_id;
324 public:
325   PSThreadRootsTaskClosure(uint worker_id) : _worker_id(worker_id) { }
326   virtual void do_thread(Thread* thread) {
327     assert(ParallelScavengeHeap::heap()->is_gc_active(), "called outside gc");
328 
329     PSPromotionManager* pm = PSPromotionManager::gc_thread_promotion_manager(_worker_id);
330     PSScavengeRootsClosure roots_closure(pm);
331     MarkingCodeBlobClosure roots_in_blobs(&roots_closure, CodeBlobToOopClosure::FixRelocations);
332 
333     thread->oops_do(&roots_closure, &roots_in_blobs);
334 
335     // Do the real work
336     pm->drain_stacks(false);
337   }
338 };
339 //
340 // OldToYoungRootsTask
341 //
342 // This task is used to scan old to young roots in parallel
343 //
344 // A GC thread executing this tasks divides the generation (old gen)
345 // into slices and takes a stripe in the slice as its part of the
346 // work.
347 //
348 //      +===============+        slice 0
349 //      |  stripe 0     |
350 //      +---------------+
351 //      |  stripe 1     |
352 //      +---------------+
353 //      |  stripe 2     |
354 //      +---------------+
355 //      |  stripe 3     |
356 //      +===============+        slice 1
357 //      |  stripe 0     |
358 //      +---------------+
359 //      |  stripe 1     |
360 //      +---------------+
361 //      |  stripe 2     |
362 //      +---------------+
363 //      |  stripe 3     |
364 //      +===============+        slice 2
365 //      ...
366 //
367 // A task is created for each stripe.  In this case there are 4 tasks
368 // created.  A GC thread first works on its stripe within slice 0
369 // and then moves to its stripe in the next slice until all stripes
370 // exceed the top of the generation.  Note that having fewer GC threads
371 // than stripes works because all the tasks are executed so all stripes
372 // will be covered.  In this example if 4 tasks have been created to cover
373 // all the stripes and there are only 3 threads, one of the threads will
374 // get the tasks with the 4th stripe.  However, there is a dependence in
375 // PSCardTable::scavenge_contents_parallel() on the number
376 // of tasks created.  In scavenge_contents_parallel the distance
377 // to the next stripe is calculated based on the number of tasks.
378 // If the stripe width is ssize, a task's next stripe is at
379 // ssize * number_of_tasks (= slice_stride).  In this case after
380 // finishing stripe 0 in slice 0, the thread finds the stripe 0 in slice1
381 // by adding slice_stride to the start of stripe 0 in slice 0 to get
382 // to the start of stride 0 in slice 1.
383 
384 class ScavengeRootsTask : public AbstractGangTask {
385   StrongRootsScope _strong_roots_scope; // needed for Threads::possibly_parallel_threads_do
386   EnumClaimer<Parallel::RootType::Value> _enum_claimer;
387   PSOldGen* _old_gen;
388   HeapWord* _gen_top;
389   uint _active_workers;
390   bool _is_empty;
391   TaskTerminator _terminator;
392 
393 public:
394   ScavengeRootsTask(
395     PSOldGen* old_gen,
396     HeapWord* gen_top,
397     uint active_workers,
398     bool is_empty)
399     : AbstractGangTask("ScavengeRootsTask"),
400       _strong_roots_scope(active_workers),
401       _enum_claimer(Parallel::RootType::sentinel),
402       _old_gen(old_gen),
403       _gen_top(gen_top),
404       _active_workers(active_workers),
405       _is_empty(is_empty),
406       _terminator(active_workers, PSPromotionManager::vm_thread_promotion_manager()->stack_array_depth()) {
407   }
408 
409   virtual void work(uint worker_id) {
410     ResourceMark rm;
411 
412     if (!_is_empty) {
413       // There are only old-to-young pointers if there are objects
414       // in the old gen.
415 
416       // There are not old-to-young pointers if the old gen is empty.
417       assert(!_old_gen->object_space()->is_empty(),
418         "Should not be called is there is no work");
419       assert(_old_gen != NULL, "Sanity");
420       assert(_old_gen->object_space()->contains(_gen_top) || _gen_top == _old_gen->object_space()->top(), "Sanity");
421       assert(worker_id < ParallelGCThreads, "Sanity");
422 
423       {
424         PSPromotionManager* pm = PSPromotionManager::gc_thread_promotion_manager(worker_id);
425         PSCardTable* card_table = ParallelScavengeHeap::heap()->card_table();
426 
427         card_table->scavenge_contents_parallel(_old_gen->start_array(),
428                                                _old_gen->object_space(),
429                                                _gen_top,
430                                                pm,
431                                                worker_id,
432                                                _active_workers);
433 
434         // Do the real work
435         pm->drain_stacks(false);
436       }
437     }
438 
439     for (Parallel::RootType::Value root_type; _enum_claimer.try_claim(root_type); /* empty */) {
440       scavenge_roots_task(root_type, worker_id);
441     }
442 
443     PSThreadRootsTaskClosure closure(worker_id);
444     Threads::possibly_parallel_threads_do(true /*parallel */, &closure);
445 
446 
447     // If active_workers can exceed 1, add a StrealTask.
448     // PSPromotionManager::drain_stacks_depth() does not fully drain its
449     // stacks and expects a StealTask to complete the draining if
450     // ParallelGCThreads is > 1.
451 
452     if (_active_workers > 1) {
453       steal_task(*_terminator.terminator() , worker_id);
454     }
455   }
456 };
457 
458 // This method contains no policy. You should probably
459 // be calling invoke() instead.
460 bool PSScavenge::invoke_no_policy() {
461   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
462   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
463 
464   _gc_timer.register_gc_start();
465 
466   TimeStamp scavenge_entry;
467   TimeStamp scavenge_midpoint;
468   TimeStamp scavenge_exit;
469 
470   scavenge_entry.update();
471 
472   if (GCLocker::check_active_before_gc()) {
473     return false;
474   }
475 
476   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
477   GCCause::Cause gc_cause = heap->gc_cause();
478 
479   // Check for potential problems.
480   if (!should_attempt_scavenge()) {
481     return false;
482   }
483 
484   GCIdMark gc_id_mark;
485   _gc_tracer.report_gc_start(heap->gc_cause(), _gc_timer.gc_start());
486 
487   bool promotion_failure_occurred = false;
488 
489   PSYoungGen* young_gen = heap->young_gen();
490   PSOldGen* old_gen = heap->old_gen();
491   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
492 
493   heap->increment_total_collections();
494 
495   if (AdaptiveSizePolicy::should_update_eden_stats(gc_cause)) {
496     // Gather the feedback data for eden occupancy.
497     young_gen->eden_space()->accumulate_statistics();
498   }
499 
500   heap->print_heap_before_gc();
501   heap->trace_heap_before_gc(&_gc_tracer);
502 
503   assert(!NeverTenure || _tenuring_threshold == markOopDesc::max_age + 1, "Sanity");
504   assert(!AlwaysTenure || _tenuring_threshold == 0, "Sanity");
505 
506   // Fill in TLABs
507   heap->ensure_parsability(true);  // retire TLABs
508 
509   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
510     HandleMark hm;  // Discard invalid handles created during verification
511     Universe::verify("Before GC");
512   }
513 
514   {
515     ResourceMark rm;
516     HandleMark hm;
517 
518     GCTraceCPUTime tcpu;
519     GCTraceTime(Info, gc) tm("Pause Young", NULL, gc_cause, true);
520     TraceCollectorStats tcs(counters());
521     TraceMemoryManagerStats tms(heap->young_gc_manager(), gc_cause);
522 
523     if (log_is_enabled(Debug, gc, heap, exit)) {
524       accumulated_time()->start();
525     }
526 
527     // Let the size policy know we're starting
528     size_policy->minor_collection_begin();
529 
530     // Verify the object start arrays.
531     if (VerifyObjectStartArray &&
532         VerifyBeforeGC) {
533       old_gen->verify_object_start_array();
534     }
535 
536     // Verify no unmarked old->young roots
537     if (VerifyRememberedSets) {
538       heap->card_table()->verify_all_young_refs_imprecise();
539     }
540 
541     assert(young_gen->to_space()->is_empty(),
542            "Attempt to scavenge with live objects in to_space");
543     young_gen->to_space()->clear(SpaceDecorator::Mangle);
544 
545     save_to_space_top_before_gc();
546 
547 #if COMPILER2_OR_JVMCI
548     DerivedPointerTable::clear();
549 #endif
550 
551     reference_processor()->enable_discovery();
552     reference_processor()->setup_policy(false);
553 
554     PreGCValues pre_gc_values(heap);
555 
556     // Reset our survivor overflow.
557     set_survivor_overflow(false);
558 
559     // We need to save the old top values before
560     // creating the promotion_manager. We pass the top
561     // values to the card_table, to prevent it from
562     // straying into the promotion labs.
563     HeapWord* old_top = old_gen->object_space()->top();
564 
565     uint active_workers = ParallelScavengeHeap::heap()->workers().update_active_workers(WorkerPolicy::calc_active_workers(
566       ParallelScavengeHeap::heap()->workers().total_workers(),
567       ParallelScavengeHeap::heap()->workers().active_workers(),
568       Threads::number_of_non_daemon_threads()));
569 
570     // Release all previously held resources
571     gc_task_manager()->release_all_resources();
572 
573     // Set the number of GC threads to be used in this collection
574     gc_task_manager()->set_active_gang();
575     gc_task_manager()->task_idle_workers();
576 
577     assert(active_workers == gc_task_manager()->active_workers(), "sanity, taskmanager and workgang ought to agree");
578 
579     PSPromotionManager::pre_scavenge();
580 
581     // We'll use the promotion manager again later.
582     PSPromotionManager* promotion_manager = PSPromotionManager::vm_thread_promotion_manager();
583     {
584       GCTraceTime(Debug, gc, phases) tm("Scavenge", &_gc_timer);
585 
586       ScavengeRootsTask task(old_gen, old_top, active_workers, old_gen->object_space()->is_empty());
587       ParallelScavengeHeap::heap()->workers().run_task(&task);
588     }
589 
590     scavenge_midpoint.update();
591 
592     // Process reference objects discovered during scavenge
593     {
594       GCTraceTime(Debug, gc, phases) tm("Reference Processing", &_gc_timer);
595 
596       reference_processor()->setup_policy(false); // not always_clear
597       reference_processor()->set_active_mt_degree(active_workers);
598       PSKeepAliveClosure keep_alive(promotion_manager);
599       PSEvacuateFollowersClosure evac_followers(promotion_manager);
600       ReferenceProcessorStats stats;
601       ReferenceProcessorPhaseTimes pt(&_gc_timer, reference_processor()->max_num_queues());
602       if (reference_processor()->processing_is_mt()) {
603         PSRefProcTaskExecutor task_executor;
604         stats = reference_processor()->process_discovered_references(
605           &_is_alive_closure, &keep_alive, &evac_followers, &task_executor,
606           &pt);
607       } else {
608         stats = reference_processor()->process_discovered_references(
609           &_is_alive_closure, &keep_alive, &evac_followers, NULL, &pt);
610       }
611 
612       _gc_tracer.report_gc_reference_stats(stats);
613       pt.print_all_references();
614     }
615 
616     assert(promotion_manager->stacks_empty(),"stacks should be empty at this point");
617 
618     PSScavengeRootsClosure root_closure(promotion_manager);
619 
620     {
621       GCTraceTime(Debug, gc, phases) tm("Weak Processing", &_gc_timer);
622       WeakProcessor::weak_oops_do(&_is_alive_closure, &root_closure);
623     }
624 
625     // Verify that usage of root_closure didn't copy any objects.
626     assert(promotion_manager->stacks_empty(),"stacks should be empty at this point");
627 
628     // Finally, flush the promotion_manager's labs, and deallocate its stacks.
629     promotion_failure_occurred = PSPromotionManager::post_scavenge(_gc_tracer);
630     if (promotion_failure_occurred) {
631       clean_up_failed_promotion();
632       log_info(gc, promotion)("Promotion failed");
633     }
634 
635     _gc_tracer.report_tenuring_threshold(tenuring_threshold());
636 
637     // Let the size policy know we're done.  Note that we count promotion
638     // failure cleanup time as part of the collection (otherwise, we're
639     // implicitly saying it's mutator time).
640     size_policy->minor_collection_end(gc_cause);
641 
642     if (!promotion_failure_occurred) {
643       // Swap the survivor spaces.
644       young_gen->eden_space()->clear(SpaceDecorator::Mangle);
645       young_gen->from_space()->clear(SpaceDecorator::Mangle);
646       young_gen->swap_spaces();
647 
648       size_t survived = young_gen->from_space()->used_in_bytes();
649       size_t promoted = old_gen->used_in_bytes() - pre_gc_values.old_gen_used();
650       size_policy->update_averages(_survivor_overflow, survived, promoted);
651 
652       // A successful scavenge should restart the GC time limit count which is
653       // for full GC's.
654       size_policy->reset_gc_overhead_limit_count();
655       if (UseAdaptiveSizePolicy) {
656         // Calculate the new survivor size and tenuring threshold
657 
658         log_debug(gc, ergo)("AdaptiveSizeStart:  collection: %d ", heap->total_collections());
659         log_trace(gc, ergo)("old_gen_capacity: " SIZE_FORMAT " young_gen_capacity: " SIZE_FORMAT,
660                             old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes());
661 
662         if (UsePerfData) {
663           PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
664           counters->update_old_eden_size(
665             size_policy->calculated_eden_size_in_bytes());
666           counters->update_old_promo_size(
667             size_policy->calculated_promo_size_in_bytes());
668           counters->update_old_capacity(old_gen->capacity_in_bytes());
669           counters->update_young_capacity(young_gen->capacity_in_bytes());
670           counters->update_survived(survived);
671           counters->update_promoted(promoted);
672           counters->update_survivor_overflowed(_survivor_overflow);
673         }
674 
675         size_t max_young_size = young_gen->max_size();
676 
677         // Deciding a free ratio in the young generation is tricky, so if
678         // MinHeapFreeRatio or MaxHeapFreeRatio are in use (implicating
679         // that the old generation size may have been limited because of them) we
680         // should then limit our young generation size using NewRatio to have it
681         // follow the old generation size.
682         if (MinHeapFreeRatio != 0 || MaxHeapFreeRatio != 100) {
683           max_young_size = MIN2(old_gen->capacity_in_bytes() / NewRatio, young_gen->max_size());
684         }
685 
686         size_t survivor_limit =
687           size_policy->max_survivor_size(max_young_size);
688         _tenuring_threshold =
689           size_policy->compute_survivor_space_size_and_threshold(
690                                                            _survivor_overflow,
691                                                            _tenuring_threshold,
692                                                            survivor_limit);
693 
694        log_debug(gc, age)("Desired survivor size " SIZE_FORMAT " bytes, new threshold %u (max threshold " UINTX_FORMAT ")",
695                           size_policy->calculated_survivor_size_in_bytes(),
696                           _tenuring_threshold, MaxTenuringThreshold);
697 
698         if (UsePerfData) {
699           PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
700           counters->update_tenuring_threshold(_tenuring_threshold);
701           counters->update_survivor_size_counters();
702         }
703 
704         // Do call at minor collections?
705         // Don't check if the size_policy is ready at this
706         // level.  Let the size_policy check that internally.
707         if (UseAdaptiveGenerationSizePolicyAtMinorCollection &&
708             (AdaptiveSizePolicy::should_update_eden_stats(gc_cause))) {
709           // Calculate optimal free space amounts
710           assert(young_gen->max_size() >
711             young_gen->from_space()->capacity_in_bytes() +
712             young_gen->to_space()->capacity_in_bytes(),
713             "Sizes of space in young gen are out-of-bounds");
714 
715           size_t young_live = young_gen->used_in_bytes();
716           size_t eden_live = young_gen->eden_space()->used_in_bytes();
717           size_t cur_eden = young_gen->eden_space()->capacity_in_bytes();
718           size_t max_old_gen_size = old_gen->max_gen_size();
719           size_t max_eden_size = max_young_size -
720             young_gen->from_space()->capacity_in_bytes() -
721             young_gen->to_space()->capacity_in_bytes();
722 
723           // Used for diagnostics
724           size_policy->clear_generation_free_space_flags();
725 
726           size_policy->compute_eden_space_size(young_live,
727                                                eden_live,
728                                                cur_eden,
729                                                max_eden_size,
730                                                false /* not full gc*/);
731 
732           size_policy->check_gc_overhead_limit(eden_live,
733                                                max_old_gen_size,
734                                                max_eden_size,
735                                                false /* not full gc*/,
736                                                gc_cause,
737                                                heap->soft_ref_policy());
738 
739           size_policy->decay_supplemental_growth(false /* not full gc*/);
740         }
741         // Resize the young generation at every collection
742         // even if new sizes have not been calculated.  This is
743         // to allow resizes that may have been inhibited by the
744         // relative location of the "to" and "from" spaces.
745 
746         // Resizing the old gen at young collections can cause increases
747         // that don't feed back to the generation sizing policy until
748         // a full collection.  Don't resize the old gen here.
749 
750         heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
751                         size_policy->calculated_survivor_size_in_bytes());
752 
753         log_debug(gc, ergo)("AdaptiveSizeStop: collection: %d ", heap->total_collections());
754       }
755 
756       // Update the structure of the eden. With NUMA-eden CPU hotplugging or offlining can
757       // cause the change of the heap layout. Make sure eden is reshaped if that's the case.
758       // Also update() will case adaptive NUMA chunk resizing.
759       assert(young_gen->eden_space()->is_empty(), "eden space should be empty now");
760       young_gen->eden_space()->update();
761 
762       heap->gc_policy_counters()->update_counters();
763 
764       heap->resize_all_tlabs();
765 
766       assert(young_gen->to_space()->is_empty(), "to space should be empty now");
767     }
768 
769 #if COMPILER2_OR_JVMCI
770     DerivedPointerTable::update_pointers();
771 #endif
772 
773     NOT_PRODUCT(reference_processor()->verify_no_references_recorded());
774 
775     // Re-verify object start arrays
776     if (VerifyObjectStartArray &&
777         VerifyAfterGC) {
778       old_gen->verify_object_start_array();
779     }
780 
781     // Verify all old -> young cards are now precise
782     if (VerifyRememberedSets) {
783       // Precise verification will give false positives. Until this is fixed,
784       // use imprecise verification.
785       // heap->card_table()->verify_all_young_refs_precise();
786       heap->card_table()->verify_all_young_refs_imprecise();
787     }
788 
789     if (log_is_enabled(Debug, gc, heap, exit)) {
790       accumulated_time()->stop();
791     }
792 
793     young_gen->print_used_change(pre_gc_values.young_gen_used());
794     old_gen->print_used_change(pre_gc_values.old_gen_used());
795     MetaspaceUtils::print_metaspace_change(pre_gc_values.metadata_used());
796 
797     // Track memory usage and detect low memory
798     MemoryService::track_memory_usage();
799     heap->update_counters();
800 
801     gc_task_manager()->release_idle_workers();
802   }
803 
804   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
805     HandleMark hm;  // Discard invalid handles created during verification
806     Universe::verify("After GC");
807   }
808 
809   heap->print_heap_after_gc();
810   heap->trace_heap_after_gc(&_gc_tracer);
811 
812   scavenge_exit.update();
813 
814   log_debug(gc, task, time)("VM-Thread " JLONG_FORMAT " " JLONG_FORMAT " " JLONG_FORMAT,
815                             scavenge_entry.ticks(), scavenge_midpoint.ticks(),
816                             scavenge_exit.ticks());
817   gc_task_manager()->print_task_time_stamps();
818 
819 #ifdef TRACESPINNING
820   ParallelTaskTerminator::print_termination_counts();
821 #endif
822 
823   AdaptiveSizePolicyOutput::print(size_policy, heap->total_collections());
824 
825   _gc_timer.register_gc_end();
826 
827   _gc_tracer.report_gc_end(_gc_timer.gc_end(), _gc_timer.time_partitions());
828 
829   return !promotion_failure_occurred;
830 }
831 
832 // This method iterates over all objects in the young generation,
833 // removing all forwarding references. It then restores any preserved marks.
834 void PSScavenge::clean_up_failed_promotion() {
835   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
836   PSYoungGen* young_gen = heap->young_gen();
837 
838   RemoveForwardedPointerClosure remove_fwd_ptr_closure;
839   young_gen->object_iterate(&remove_fwd_ptr_closure);
840 
841   PSPromotionManager::restore_preserved_marks();
842 
843   // Reset the PromotionFailureALot counters.
844   NOT_PRODUCT(heap->reset_promotion_should_fail();)
845 }
846 
847 bool PSScavenge::should_attempt_scavenge() {
848   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
849   PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
850 
851   if (UsePerfData) {
852     counters->update_scavenge_skipped(not_skipped);
853   }
854 
855   PSYoungGen* young_gen = heap->young_gen();
856   PSOldGen* old_gen = heap->old_gen();
857 
858   // Do not attempt to promote unless to_space is empty
859   if (!young_gen->to_space()->is_empty()) {
860     _consecutive_skipped_scavenges++;
861     if (UsePerfData) {
862       counters->update_scavenge_skipped(to_space_not_empty);
863     }
864     return false;
865   }
866 
867   // Test to see if the scavenge will likely fail.
868   PSAdaptiveSizePolicy* policy = heap->size_policy();
869 
870   // A similar test is done in the policy's should_full_GC().  If this is
871   // changed, decide if that test should also be changed.
872   size_t avg_promoted = (size_t) policy->padded_average_promoted_in_bytes();
873   size_t promotion_estimate = MIN2(avg_promoted, young_gen->used_in_bytes());
874   bool result = promotion_estimate < old_gen->free_in_bytes();
875 
876   log_trace(ergo)("%s scavenge: average_promoted " SIZE_FORMAT " padded_average_promoted " SIZE_FORMAT " free in old gen " SIZE_FORMAT,
877                 result ? "Do" : "Skip", (size_t) policy->average_promoted_in_bytes(),
878                 (size_t) policy->padded_average_promoted_in_bytes(),
879                 old_gen->free_in_bytes());
880   if (young_gen->used_in_bytes() < (size_t) policy->padded_average_promoted_in_bytes()) {
881     log_trace(ergo)(" padded_promoted_average is greater than maximum promotion = " SIZE_FORMAT, young_gen->used_in_bytes());
882   }
883 
884   if (result) {
885     _consecutive_skipped_scavenges = 0;
886   } else {
887     _consecutive_skipped_scavenges++;
888     if (UsePerfData) {
889       counters->update_scavenge_skipped(promoted_too_large);
890     }
891   }
892   return result;
893 }
894 
895   // Used to add tasks
896 GCTaskManager* const PSScavenge::gc_task_manager() {
897   assert(ParallelScavengeHeap::gc_task_manager() != NULL,
898    "shouldn't return NULL");
899   return ParallelScavengeHeap::gc_task_manager();
900 }
901 
902 // Adaptive size policy support.  When the young generation/old generation
903 // boundary moves, _young_generation_boundary must be reset
904 void PSScavenge::set_young_generation_boundary(HeapWord* v) {
905   _young_generation_boundary = v;
906   if (UseCompressedOops) {
907     _young_generation_boundary_compressed = (uintptr_t)CompressedOops::encode((oop)v);
908   }
909 }
910 
911 void PSScavenge::initialize() {
912   // Arguments must have been parsed
913 
914   if (AlwaysTenure || NeverTenure) {
915     assert(MaxTenuringThreshold == 0 || MaxTenuringThreshold == markOopDesc::max_age + 1,
916            "MaxTenuringThreshold should be 0 or markOopDesc::max_age + 1, but is %d", (int) MaxTenuringThreshold);
917     _tenuring_threshold = MaxTenuringThreshold;
918   } else {
919     // We want to smooth out our startup times for the AdaptiveSizePolicy
920     _tenuring_threshold = (UseAdaptiveSizePolicy) ? InitialTenuringThreshold :
921                                                     MaxTenuringThreshold;
922   }
923 
924   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
925   PSYoungGen* young_gen = heap->young_gen();
926   PSOldGen* old_gen = heap->old_gen();
927 
928   // Set boundary between young_gen and old_gen
929   assert(old_gen->reserved().end() <= young_gen->eden_space()->bottom(),
930          "old above young");
931   set_young_generation_boundary(young_gen->eden_space()->bottom());
932 
933   // Initialize ref handling object for scavenging.
934   _span_based_discoverer.set_span(young_gen->reserved());
935   _ref_processor =
936     new ReferenceProcessor(&_span_based_discoverer,
937                            ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
938                            ParallelGCThreads,          // mt processing degree
939                            true,                       // mt discovery
940                            ParallelGCThreads,          // mt discovery degree
941                            true,                       // atomic_discovery
942                            NULL,                       // header provides liveness info
943                            false);
944 
945   // Cache the cardtable
946   _card_table = heap->card_table();
947 
948   _counters = new CollectorCounters("Parallel young collection pauses", 0);
949 }