1 /*
   2  * Copyright (c) 2002, 2010, 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 
  26 # include "incls/_precompiled.incl"
  27 # include "incls/_psScavenge.cpp.incl"
  28 
  29 HeapWord*                  PSScavenge::_to_space_top_before_gc = NULL;
  30 int                        PSScavenge::_consecutive_skipped_scavenges = 0;
  31 ReferenceProcessor*        PSScavenge::_ref_processor = NULL;
  32 CardTableExtension*        PSScavenge::_card_table = NULL;
  33 bool                       PSScavenge::_survivor_overflow = false;
  34 int                        PSScavenge::_tenuring_threshold = 0;
  35 HeapWord*                  PSScavenge::_young_generation_boundary = NULL;
  36 elapsedTimer               PSScavenge::_accumulated_time;
  37 Stack<markOop>             PSScavenge::_preserved_mark_stack;
  38 Stack<oop>                 PSScavenge::_preserved_oop_stack;
  39 CollectorCounters*         PSScavenge::_counters = NULL;
  40 bool                       PSScavenge::_promotion_failed = false;
  41 
  42 // Define before use
  43 class PSIsAliveClosure: public BoolObjectClosure {
  44 public:
  45   void do_object(oop p) {
  46     assert(false, "Do not call.");
  47   }
  48   bool do_object_b(oop p) {
  49     return (!PSScavenge::is_obj_in_young((HeapWord*) p)) || p->is_forwarded();
  50   }
  51 };
  52 
  53 PSIsAliveClosure PSScavenge::_is_alive_closure;
  54 
  55 class PSKeepAliveClosure: public OopClosure {
  56 protected:
  57   MutableSpace* _to_space;
  58   PSPromotionManager* _promotion_manager;
  59 
  60 public:
  61   PSKeepAliveClosure(PSPromotionManager* pm) : _promotion_manager(pm) {
  62     ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
  63     assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
  64     _to_space = heap->young_gen()->to_space();
  65 
  66     assert(_promotion_manager != NULL, "Sanity");
  67   }
  68 
  69   template <class T> void do_oop_work(T* p) {
  70     assert (!oopDesc::is_null(*p), "expected non-null ref");
  71     assert ((oopDesc::load_decode_heap_oop_not_null(p))->is_oop(),
  72             "expected an oop while scanning weak refs");
  73 
  74     // Weak refs may be visited more than once.
  75     if (PSScavenge::should_scavenge(p, _to_space)) {
  76       PSScavenge::copy_and_push_safe_barrier(_promotion_manager, p);
  77     }
  78   }
  79   virtual void do_oop(oop* p)       { PSKeepAliveClosure::do_oop_work(p); }
  80   virtual void do_oop(narrowOop* p) { PSKeepAliveClosure::do_oop_work(p); }
  81 };
  82 
  83 class PSEvacuateFollowersClosure: public VoidClosure {
  84  private:
  85   PSPromotionManager* _promotion_manager;
  86  public:
  87   PSEvacuateFollowersClosure(PSPromotionManager* pm) : _promotion_manager(pm) {}
  88 
  89   virtual void do_void() {
  90     assert(_promotion_manager != NULL, "Sanity");
  91     _promotion_manager->drain_stacks(true);
  92     guarantee(_promotion_manager->stacks_empty(),
  93               "stacks should be empty at this point");
  94   }
  95 };
  96 
  97 class PSPromotionFailedClosure : public ObjectClosure {
  98   virtual void do_object(oop obj) {
  99     if (obj->is_forwarded()) {
 100       obj->init_mark();
 101     }
 102   }
 103 };
 104 
 105 class PSRefProcTaskProxy: public GCTask {
 106   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
 107   ProcessTask & _rp_task;
 108   uint          _work_id;
 109 public:
 110   PSRefProcTaskProxy(ProcessTask & rp_task, uint work_id)
 111     : _rp_task(rp_task),
 112       _work_id(work_id)
 113   { }
 114 
 115 private:
 116   virtual char* name() { return (char *)"Process referents by policy in parallel"; }
 117   virtual void do_it(GCTaskManager* manager, uint which);
 118 };
 119 
 120 void PSRefProcTaskProxy::do_it(GCTaskManager* manager, uint which)
 121 {
 122   PSPromotionManager* promotion_manager =
 123     PSPromotionManager::gc_thread_promotion_manager(which);
 124   assert(promotion_manager != NULL, "sanity check");
 125   PSKeepAliveClosure keep_alive(promotion_manager);
 126   PSEvacuateFollowersClosure evac_followers(promotion_manager);
 127   PSIsAliveClosure is_alive;
 128   _rp_task.work(_work_id, is_alive, keep_alive, evac_followers);
 129 }
 130 
 131 class PSRefEnqueueTaskProxy: public GCTask {
 132   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
 133   EnqueueTask& _enq_task;
 134   uint         _work_id;
 135 
 136 public:
 137   PSRefEnqueueTaskProxy(EnqueueTask& enq_task, uint work_id)
 138     : _enq_task(enq_task),
 139       _work_id(work_id)
 140   { }
 141 
 142   virtual char* name() { return (char *)"Enqueue reference objects in parallel"; }
 143   virtual void do_it(GCTaskManager* manager, uint which)
 144   {
 145     _enq_task.work(_work_id);
 146   }
 147 };
 148 
 149 class PSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
 150   virtual void execute(ProcessTask& task);
 151   virtual void execute(EnqueueTask& task);
 152 };
 153 
 154 void PSRefProcTaskExecutor::execute(ProcessTask& task)
 155 {
 156   GCTaskQueue* q = GCTaskQueue::create();
 157   for(uint i=0; i<ParallelGCThreads; i++) {
 158     q->enqueue(new PSRefProcTaskProxy(task, i));
 159   }
 160   ParallelTaskTerminator terminator(
 161                  ParallelScavengeHeap::gc_task_manager()->workers(),
 162                  (TaskQueueSetSuper*) PSPromotionManager::stack_array_depth());
 163   if (task.marks_oops_alive() && ParallelGCThreads > 1) {
 164     for (uint j=0; j<ParallelGCThreads; j++) {
 165       q->enqueue(new StealTask(&terminator));
 166     }
 167   }
 168   ParallelScavengeHeap::gc_task_manager()->execute_and_wait(q);
 169 }
 170 
 171 
 172 void PSRefProcTaskExecutor::execute(EnqueueTask& task)
 173 {
 174   GCTaskQueue* q = GCTaskQueue::create();
 175   for(uint i=0; i<ParallelGCThreads; i++) {
 176     q->enqueue(new PSRefEnqueueTaskProxy(task, i));
 177   }
 178   ParallelScavengeHeap::gc_task_manager()->execute_and_wait(q);
 179 }
 180 
 181 // This method contains all heap specific policy for invoking scavenge.
 182 // PSScavenge::invoke_no_policy() will do nothing but attempt to
 183 // scavenge. It will not clean up after failed promotions, bail out if
 184 // we've exceeded policy time limits, or any other special behavior.
 185 // All such policy should be placed here.
 186 //
 187 // Note that this method should only be called from the vm_thread while
 188 // at a safepoint!
 189 void PSScavenge::invoke() {
 190   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
 191   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
 192   assert(!Universe::heap()->is_gc_active(), "not reentrant");
 193 
 194   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 195   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 196 
 197   PSAdaptiveSizePolicy* policy = heap->size_policy();
 198   IsGCActiveMark mark;
 199 
 200   bool scavenge_was_done = PSScavenge::invoke_no_policy();
 201 
 202   PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
 203   if (UsePerfData)
 204     counters->update_full_follows_scavenge(0);
 205   if (!scavenge_was_done ||
 206       policy->should_full_GC(heap->old_gen()->free_in_bytes())) {
 207     if (UsePerfData)
 208       counters->update_full_follows_scavenge(full_follows_scavenge);
 209     GCCauseSetter gccs(heap, GCCause::_adaptive_size_policy);
 210     CollectorPolicy* cp = heap->collector_policy();
 211     const bool clear_all_softrefs = cp->should_clear_all_soft_refs();
 212 
 213     if (UseParallelOldGC) {
 214       PSParallelCompact::invoke_no_policy(clear_all_softrefs);
 215     } else {
 216       PSMarkSweep::invoke_no_policy(clear_all_softrefs);
 217     }
 218   }
 219 }
 220 
 221 // This method contains no policy. You should probably
 222 // be calling invoke() instead.
 223 bool PSScavenge::invoke_no_policy() {
 224   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
 225   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
 226 
 227   assert(_preserved_mark_stack.is_empty(), "should be empty");
 228   assert(_preserved_oop_stack.is_empty(), "should be empty");
 229 
 230   TimeStamp scavenge_entry;
 231   TimeStamp scavenge_midpoint;
 232   TimeStamp scavenge_exit;
 233 
 234   scavenge_entry.update();
 235 
 236   if (GC_locker::check_active_before_gc()) {
 237     return false;
 238   }
 239 
 240   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 241   GCCause::Cause gc_cause = heap->gc_cause();
 242   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 243 
 244   // Check for potential problems.
 245   if (!should_attempt_scavenge()) {
 246     return false;
 247   }
 248 
 249   bool promotion_failure_occurred = false;
 250 
 251   PSYoungGen* young_gen = heap->young_gen();
 252   PSOldGen* old_gen = heap->old_gen();
 253   PSPermGen* perm_gen = heap->perm_gen();
 254   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 255   heap->increment_total_collections();
 256 
 257   AdaptiveSizePolicyOutput(size_policy, heap->total_collections());
 258 
 259   if ((gc_cause != GCCause::_java_lang_system_gc) ||
 260        UseAdaptiveSizePolicyWithSystemGC) {
 261     // Gather the feedback data for eden occupancy.
 262     young_gen->eden_space()->accumulate_statistics();
 263   }
 264 
 265   if (ZapUnusedHeapArea) {
 266     // Save information needed to minimize mangling
 267     heap->record_gen_tops_before_GC();
 268   }
 269 
 270   if (PrintHeapAtGC) {
 271     Universe::print_heap_before_gc();
 272   }
 273 
 274   assert(!NeverTenure || _tenuring_threshold == markOopDesc::max_age + 1, "Sanity");
 275   assert(!AlwaysTenure || _tenuring_threshold == 0, "Sanity");
 276 
 277   size_t prev_used = heap->used();
 278   assert(promotion_failed() == false, "Sanity");
 279 
 280   // Fill in TLABs
 281   heap->accumulate_statistics_all_tlabs();
 282   heap->ensure_parsability(true);  // retire TLABs
 283 
 284   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {
 285     HandleMark hm;  // Discard invalid handles created during verification
 286     gclog_or_tty->print(" VerifyBeforeGC:");
 287     Universe::verify(true);
 288   }
 289 
 290   {
 291     ResourceMark rm;
 292     HandleMark hm;
 293 
 294     gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
 295     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
 296     TraceTime t1("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
 297     TraceCollectorStats tcs(counters());
 298     TraceMemoryManagerStats tms(false /* not full GC */);
 299 
 300     if (TraceGen0Time) accumulated_time()->start();
 301 
 302     // Let the size policy know we're starting
 303     size_policy->minor_collection_begin();
 304 
 305     // Verify the object start arrays.
 306     if (VerifyObjectStartArray &&
 307         VerifyBeforeGC) {
 308       old_gen->verify_object_start_array();
 309       perm_gen->verify_object_start_array();
 310     }
 311 
 312     // Verify no unmarked old->young roots
 313     if (VerifyRememberedSets) {
 314       CardTableExtension::verify_all_young_refs_imprecise();
 315     }
 316 
 317     if (!ScavengeWithObjectsInToSpace) {
 318       assert(young_gen->to_space()->is_empty(),
 319              "Attempt to scavenge with live objects in to_space");
 320       young_gen->to_space()->clear(SpaceDecorator::Mangle);
 321     } else if (ZapUnusedHeapArea) {
 322       young_gen->to_space()->mangle_unused_area();
 323     }
 324     save_to_space_top_before_gc();
 325 
 326     NOT_PRODUCT(reference_processor()->verify_no_references_recorded());
 327     COMPILER2_PRESENT(DerivedPointerTable::clear());
 328 
 329     reference_processor()->enable_discovery();
 330     reference_processor()->setup_policy(false);
 331 
 332     // We track how much was promoted to the next generation for
 333     // the AdaptiveSizePolicy.
 334     size_t old_gen_used_before = old_gen->used_in_bytes();
 335 
 336     // For PrintGCDetails
 337     size_t young_gen_used_before = young_gen->used_in_bytes();
 338 
 339     // Reset our survivor overflow.
 340     set_survivor_overflow(false);
 341 
 342     // We need to save the old/perm top values before
 343     // creating the promotion_manager. We pass the top
 344     // values to the card_table, to prevent it from
 345     // straying into the promotion labs.
 346     HeapWord* old_top = old_gen->object_space()->top();
 347     HeapWord* perm_top = perm_gen->object_space()->top();
 348 
 349     // Release all previously held resources
 350     gc_task_manager()->release_all_resources();
 351 
 352     PSPromotionManager::pre_scavenge();
 353 
 354     // We'll use the promotion manager again later.
 355     PSPromotionManager* promotion_manager = PSPromotionManager::vm_thread_promotion_manager();
 356     {
 357       // TraceTime("Roots");
 358       ParallelScavengeHeap::ParStrongRootsScope psrs;
 359 
 360       GCTaskQueue* q = GCTaskQueue::create();
 361 
 362       for(uint i=0; i<ParallelGCThreads; i++) {
 363         q->enqueue(new OldToYoungRootsTask(old_gen, old_top, i));
 364       }
 365 
 366       q->enqueue(new SerialOldToYoungRootsTask(perm_gen, perm_top));
 367 
 368       q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::universe));
 369       q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::jni_handles));
 370       // We scan the thread roots in parallel
 371       Threads::create_thread_roots_tasks(q);
 372       q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::object_synchronizer));
 373       q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::flat_profiler));
 374       q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::management));
 375       q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::system_dictionary));
 376       q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::jvmti));
 377       q->enqueue(new ScavengeRootsTask(ScavengeRootsTask::code_cache));
 378 
 379       ParallelTaskTerminator terminator(
 380                   gc_task_manager()->workers(),
 381                   (TaskQueueSetSuper*) promotion_manager->stack_array_depth());
 382       if (ParallelGCThreads>1) {
 383         for (uint j=0; j<ParallelGCThreads; j++) {
 384           q->enqueue(new StealTask(&terminator));
 385         }
 386       }
 387 
 388       gc_task_manager()->execute_and_wait(q);
 389     }
 390 
 391     scavenge_midpoint.update();
 392 
 393     // Process reference objects discovered during scavenge
 394     {
 395       reference_processor()->setup_policy(false); // not always_clear
 396       PSKeepAliveClosure keep_alive(promotion_manager);
 397       PSEvacuateFollowersClosure evac_followers(promotion_manager);
 398       if (reference_processor()->processing_is_mt()) {
 399         PSRefProcTaskExecutor task_executor;
 400         reference_processor()->process_discovered_references(
 401           &_is_alive_closure, &keep_alive, &evac_followers, &task_executor);
 402       } else {
 403         reference_processor()->process_discovered_references(
 404           &_is_alive_closure, &keep_alive, &evac_followers, NULL);
 405       }
 406     }
 407 
 408     // Enqueue reference objects discovered during scavenge.
 409     if (reference_processor()->processing_is_mt()) {
 410       PSRefProcTaskExecutor task_executor;
 411       reference_processor()->enqueue_discovered_references(&task_executor);
 412     } else {
 413       reference_processor()->enqueue_discovered_references(NULL);
 414     }
 415 
 416     // Finally, flush the promotion_manager's labs, and deallocate its stacks.
 417     PSPromotionManager::post_scavenge();
 418 
 419     promotion_failure_occurred = promotion_failed();
 420     if (promotion_failure_occurred) {
 421       clean_up_failed_promotion();
 422       if (PrintGC) {
 423         gclog_or_tty->print("--");
 424       }
 425     }
 426 
 427     // Let the size policy know we're done.  Note that we count promotion
 428     // failure cleanup time as part of the collection (otherwise, we're
 429     // implicitly saying it's mutator time).
 430     size_policy->minor_collection_end(gc_cause);
 431 
 432     if (!promotion_failure_occurred) {
 433       // Swap the survivor spaces.
 434 
 435 
 436       young_gen->eden_space()->clear(SpaceDecorator::Mangle);
 437       young_gen->from_space()->clear(SpaceDecorator::Mangle);
 438       young_gen->swap_spaces();
 439 
 440       size_t survived = young_gen->from_space()->used_in_bytes();
 441       size_t promoted = old_gen->used_in_bytes() - old_gen_used_before;
 442       size_policy->update_averages(_survivor_overflow, survived, promoted);
 443 
 444       // A successful scavenge should restart the GC time limit count which is
 445       // for full GC's.
 446       size_policy->reset_gc_overhead_limit_count();
 447       if (UseAdaptiveSizePolicy) {
 448         // Calculate the new survivor size and tenuring threshold
 449 
 450         if (PrintAdaptiveSizePolicy) {
 451           gclog_or_tty->print("AdaptiveSizeStart: ");
 452           gclog_or_tty->stamp();
 453           gclog_or_tty->print_cr(" collection: %d ",
 454                          heap->total_collections());
 455 
 456           if (Verbose) {
 457             gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d"
 458               " perm_gen_capacity: %d ",
 459               old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes(),
 460               perm_gen->capacity_in_bytes());
 461           }
 462         }
 463 
 464 
 465         if (UsePerfData) {
 466           PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
 467           counters->update_old_eden_size(
 468             size_policy->calculated_eden_size_in_bytes());
 469           counters->update_old_promo_size(
 470             size_policy->calculated_promo_size_in_bytes());
 471           counters->update_old_capacity(old_gen->capacity_in_bytes());
 472           counters->update_young_capacity(young_gen->capacity_in_bytes());
 473           counters->update_survived(survived);
 474           counters->update_promoted(promoted);
 475           counters->update_survivor_overflowed(_survivor_overflow);
 476         }
 477 
 478         size_t survivor_limit =
 479           size_policy->max_survivor_size(young_gen->max_size());
 480         _tenuring_threshold =
 481           size_policy->compute_survivor_space_size_and_threshold(
 482                                                            _survivor_overflow,
 483                                                            _tenuring_threshold,
 484                                                            survivor_limit);
 485 
 486        if (PrintTenuringDistribution) {
 487          gclog_or_tty->cr();
 488          gclog_or_tty->print_cr("Desired survivor size %ld bytes, new threshold %d (max %d)",
 489                                 size_policy->calculated_survivor_size_in_bytes(),
 490                                 _tenuring_threshold, MaxTenuringThreshold);
 491        }
 492 
 493         if (UsePerfData) {
 494           PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
 495           counters->update_tenuring_threshold(_tenuring_threshold);
 496           counters->update_survivor_size_counters();
 497         }
 498 
 499         // Do call at minor collections?
 500         // Don't check if the size_policy is ready at this
 501         // level.  Let the size_policy check that internally.
 502         if (UseAdaptiveSizePolicy &&
 503             UseAdaptiveGenerationSizePolicyAtMinorCollection &&
 504             ((gc_cause != GCCause::_java_lang_system_gc) ||
 505               UseAdaptiveSizePolicyWithSystemGC)) {
 506 
 507           // Calculate optimial free space amounts
 508           assert(young_gen->max_size() >
 509             young_gen->from_space()->capacity_in_bytes() +
 510             young_gen->to_space()->capacity_in_bytes(),
 511             "Sizes of space in young gen are out-of-bounds");
 512           size_t max_eden_size = young_gen->max_size() -
 513             young_gen->from_space()->capacity_in_bytes() -
 514             young_gen->to_space()->capacity_in_bytes();
 515           size_policy->compute_generation_free_space(young_gen->used_in_bytes(),
 516                                    young_gen->eden_space()->used_in_bytes(),
 517                                    old_gen->used_in_bytes(),
 518                                    perm_gen->used_in_bytes(),
 519                                    young_gen->eden_space()->capacity_in_bytes(),
 520                                    old_gen->max_gen_size(),
 521                                    max_eden_size,
 522                                    false  /* full gc*/,
 523                                    gc_cause,
 524                                    heap->collector_policy());
 525 
 526         }
 527         // Resize the young generation at every collection
 528         // even if new sizes have not been calculated.  This is
 529         // to allow resizes that may have been inhibited by the
 530         // relative location of the "to" and "from" spaces.
 531 
 532         // Resizing the old gen at minor collects can cause increases
 533         // that don't feed back to the generation sizing policy until
 534         // a major collection.  Don't resize the old gen here.
 535 
 536         heap->resize_young_gen(size_policy->calculated_eden_size_in_bytes(),
 537                         size_policy->calculated_survivor_size_in_bytes());
 538 
 539         if (PrintAdaptiveSizePolicy) {
 540           gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",
 541                          heap->total_collections());
 542         }
 543       }
 544 
 545       // Update the structure of the eden. With NUMA-eden CPU hotplugging or offlining can
 546       // cause the change of the heap layout. Make sure eden is reshaped if that's the case.
 547       // Also update() will case adaptive NUMA chunk resizing.
 548       assert(young_gen->eden_space()->is_empty(), "eden space should be empty now");
 549       young_gen->eden_space()->update();
 550 
 551       heap->gc_policy_counters()->update_counters();
 552 
 553       heap->resize_all_tlabs();
 554 
 555       assert(young_gen->to_space()->is_empty(), "to space should be empty now");
 556     }
 557 
 558     COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
 559 
 560     NOT_PRODUCT(reference_processor()->verify_no_references_recorded());
 561 
 562     // Re-verify object start arrays
 563     if (VerifyObjectStartArray &&
 564         VerifyAfterGC) {
 565       old_gen->verify_object_start_array();
 566       perm_gen->verify_object_start_array();
 567     }
 568 
 569     // Verify all old -> young cards are now precise
 570     if (VerifyRememberedSets) {
 571       // Precise verification will give false positives. Until this is fixed,
 572       // use imprecise verification.
 573       // CardTableExtension::verify_all_young_refs_precise();
 574       CardTableExtension::verify_all_young_refs_imprecise();
 575     }
 576 
 577     if (TraceGen0Time) accumulated_time()->stop();
 578 
 579     if (PrintGC) {
 580       if (PrintGCDetails) {
 581         // Don't print a GC timestamp here.  This is after the GC so
 582         // would be confusing.
 583         young_gen->print_used_change(young_gen_used_before);
 584       }
 585       heap->print_heap_change(prev_used);
 586     }
 587 
 588     // Track memory usage and detect low memory
 589     MemoryService::track_memory_usage();
 590     heap->update_counters();
 591   }
 592 
 593   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {
 594     HandleMark hm;  // Discard invalid handles created during verification
 595     gclog_or_tty->print(" VerifyAfterGC:");
 596     Universe::verify(false);
 597   }
 598 
 599   if (PrintHeapAtGC) {
 600     Universe::print_heap_after_gc();
 601   }
 602 
 603   if (ZapUnusedHeapArea) {
 604     young_gen->eden_space()->check_mangled_unused_area_complete();
 605     young_gen->from_space()->check_mangled_unused_area_complete();
 606     young_gen->to_space()->check_mangled_unused_area_complete();
 607   }
 608 
 609   scavenge_exit.update();
 610 
 611   if (PrintGCTaskTimeStamps) {
 612     tty->print_cr("VM-Thread " INT64_FORMAT " " INT64_FORMAT " " INT64_FORMAT,
 613                   scavenge_entry.ticks(), scavenge_midpoint.ticks(),
 614                   scavenge_exit.ticks());
 615     gc_task_manager()->print_task_time_stamps();
 616   }
 617 
 618 #ifdef TRACESPINNING
 619   ParallelTaskTerminator::print_termination_counts();
 620 #endif
 621 
 622   return !promotion_failure_occurred;
 623 }
 624 
 625 // This method iterates over all objects in the young generation,
 626 // unforwarding markOops. It then restores any preserved mark oops,
 627 // and clears the _preserved_mark_stack.
 628 void PSScavenge::clean_up_failed_promotion() {
 629   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 630   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 631   assert(promotion_failed(), "Sanity");
 632 
 633   PSYoungGen* young_gen = heap->young_gen();
 634 
 635   {
 636     ResourceMark rm;
 637 
 638     // Unforward all pointers in the young gen.
 639     PSPromotionFailedClosure unforward_closure;
 640     young_gen->object_iterate(&unforward_closure);
 641 
 642     if (PrintGC && Verbose) {
 643       gclog_or_tty->print_cr("Restoring %d marks", _preserved_oop_stack.size());
 644     }
 645 
 646     // Restore any saved marks.
 647     while (!_preserved_oop_stack.is_empty()) {
 648       oop obj      = _preserved_oop_stack.pop();
 649       markOop mark = _preserved_mark_stack.pop();
 650       obj->set_mark(mark);
 651     }
 652 
 653     // Clear the preserved mark and oop stack caches.
 654     _preserved_mark_stack.clear(true);
 655     _preserved_oop_stack.clear(true);
 656     _promotion_failed = false;
 657   }
 658 
 659   // Reset the PromotionFailureALot counters.
 660   NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
 661 }
 662 
 663 // This method is called whenever an attempt to promote an object
 664 // fails. Some markOops will need preservation, some will not. Note
 665 // that the entire eden is traversed after a failed promotion, with
 666 // all forwarded headers replaced by the default markOop. This means
 667 // it is not neccessary to preserve most markOops.
 668 void PSScavenge::oop_promotion_failed(oop obj, markOop obj_mark) {
 669   _promotion_failed = true;
 670   if (obj_mark->must_be_preserved_for_promotion_failure(obj)) {
 671     ThreadCritical tc;
 672     _preserved_oop_stack.push(obj);
 673     _preserved_mark_stack.push(obj_mark);
 674   }
 675 }
 676 
 677 bool PSScavenge::should_attempt_scavenge() {
 678   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 679   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 680   PSGCAdaptivePolicyCounters* counters = heap->gc_policy_counters();
 681 
 682   if (UsePerfData) {
 683     counters->update_scavenge_skipped(not_skipped);
 684   }
 685 
 686   PSYoungGen* young_gen = heap->young_gen();
 687   PSOldGen* old_gen = heap->old_gen();
 688 
 689   if (!ScavengeWithObjectsInToSpace) {
 690     // Do not attempt to promote unless to_space is empty
 691     if (!young_gen->to_space()->is_empty()) {
 692       _consecutive_skipped_scavenges++;
 693       if (UsePerfData) {
 694         counters->update_scavenge_skipped(to_space_not_empty);
 695       }
 696       return false;
 697     }
 698   }
 699 
 700   // Test to see if the scavenge will likely fail.
 701   PSAdaptiveSizePolicy* policy = heap->size_policy();
 702 
 703   // A similar test is done in the policy's should_full_GC().  If this is
 704   // changed, decide if that test should also be changed.
 705   size_t avg_promoted = (size_t) policy->padded_average_promoted_in_bytes();
 706   size_t promotion_estimate = MIN2(avg_promoted, young_gen->used_in_bytes());
 707   bool result = promotion_estimate < old_gen->free_in_bytes();
 708 
 709   if (PrintGCDetails && Verbose) {
 710     gclog_or_tty->print(result ? "  do scavenge: " : "  skip scavenge: ");
 711     gclog_or_tty->print_cr(" average_promoted " SIZE_FORMAT
 712       " padded_average_promoted " SIZE_FORMAT
 713       " free in old gen " SIZE_FORMAT,
 714       (size_t) policy->average_promoted_in_bytes(),
 715       (size_t) policy->padded_average_promoted_in_bytes(),
 716       old_gen->free_in_bytes());
 717     if (young_gen->used_in_bytes() <
 718         (size_t) policy->padded_average_promoted_in_bytes()) {
 719       gclog_or_tty->print_cr(" padded_promoted_average is greater"
 720         " than maximum promotion = " SIZE_FORMAT, young_gen->used_in_bytes());
 721     }
 722   }
 723 
 724   if (result) {
 725     _consecutive_skipped_scavenges = 0;
 726   } else {
 727     _consecutive_skipped_scavenges++;
 728     if (UsePerfData) {
 729       counters->update_scavenge_skipped(promoted_too_large);
 730     }
 731   }
 732   return result;
 733 }
 734 
 735   // Used to add tasks
 736 GCTaskManager* const PSScavenge::gc_task_manager() {
 737   assert(ParallelScavengeHeap::gc_task_manager() != NULL,
 738    "shouldn't return NULL");
 739   return ParallelScavengeHeap::gc_task_manager();
 740 }
 741 
 742 void PSScavenge::initialize() {
 743   // Arguments must have been parsed
 744 
 745   if (AlwaysTenure) {
 746     _tenuring_threshold = 0;
 747   } else if (NeverTenure) {
 748     _tenuring_threshold = markOopDesc::max_age + 1;
 749   } else {
 750     // We want to smooth out our startup times for the AdaptiveSizePolicy
 751     _tenuring_threshold = (UseAdaptiveSizePolicy) ? InitialTenuringThreshold :
 752                                                     MaxTenuringThreshold;
 753   }
 754 
 755   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
 756   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
 757 
 758   PSYoungGen* young_gen = heap->young_gen();
 759   PSOldGen* old_gen = heap->old_gen();
 760   PSPermGen* perm_gen = heap->perm_gen();
 761 
 762   // Set boundary between young_gen and old_gen
 763   assert(perm_gen->reserved().end() <= old_gen->object_space()->bottom(),
 764          "perm above old");
 765   assert(old_gen->reserved().end() <= young_gen->eden_space()->bottom(),
 766          "old above young");
 767   _young_generation_boundary = young_gen->eden_space()->bottom();
 768 
 769   // Initialize ref handling object for scavenging.
 770   MemRegion mr = young_gen->reserved();
 771   _ref_processor = ReferenceProcessor::create_ref_processor(
 772     mr,                         // span
 773     true,                       // atomic_discovery
 774     true,                       // mt_discovery
 775     NULL,                       // is_alive_non_header
 776     ParallelGCThreads,
 777     ParallelRefProcEnabled);
 778 
 779   // Cache the cardtable
 780   BarrierSet* bs = Universe::heap()->barrier_set();
 781   assert(bs->kind() == BarrierSet::CardTableModRef, "Wrong barrier set kind");
 782   _card_table = (CardTableExtension*)bs;
 783 
 784   _counters = new CollectorCounters("PSScavenge", 0);
 785 }