src/hotspot/share/gc/serial/defNewGeneration.cpp - master - githubmirror/jdk11u-dev

src/hotspot/share/gc/serial/defNewGeneration.cpp
997 строк36 KB
Andrew Lu
8292946: GC lock/jni/jnilock001 test failed "assert(gch->gc_cause() == GCCause::_scavenge_alot || !gch->incremental_collection_failed()) failed: Twice in a row"
08 дек 2023, 11:48
08 дек 2023, 11:48325a93f
/*
 * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "precompiled.hpp"
#include "gc/serial/defNewGeneration.inline.hpp"
#include "gc/serial/serialHeap.inline.hpp"
#include "gc/serial/tenuredGeneration.hpp"
#include "gc/shared/adaptiveSizePolicy.hpp"
#include "gc/shared/ageTable.inline.hpp"
#include "gc/shared/cardTableRS.hpp"
#include "gc/shared/collectorCounters.hpp"
#include "gc/shared/gcHeapSummary.hpp"
#include "gc/shared/gcLocker.hpp"
#include "gc/shared/gcPolicyCounters.hpp"
#include "gc/shared/gcTimer.hpp"
#include "gc/shared/gcTrace.hpp"
#include "gc/shared/gcTraceTime.inline.hpp"
#include "gc/shared/genOopClosures.inline.hpp"
#include "gc/shared/generationSpec.hpp"
#include "gc/shared/preservedMarks.inline.hpp"
#include "gc/shared/referencePolicy.hpp"
#include "gc/shared/referenceProcessorPhaseTimes.hpp"
#include "gc/shared/space.inline.hpp"
#include "gc/shared/spaceDecorator.hpp"
#include "gc/shared/strongRootsScope.hpp"
#include "gc/shared/weakProcessor.hpp"
#include "logging/log.hpp"
#include "memory/iterator.inline.hpp"
#include "memory/resourceArea.hpp"
#include "oops/instanceRefKlass.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/java.hpp"
#include "runtime/prefetch.inline.hpp"
#include "runtime/thread.inline.hpp"
#include "utilities/align.hpp"
#include "utilities/copy.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/stack.inline.hpp"

//
// DefNewGeneration functions.

// Methods of protected closure types.

DefNewGeneration::IsAliveClosure::IsAliveClosure(Generation* young_gen) : _young_gen(young_gen) {
  assert(_young_gen->kind() == Generation::ParNew ||
         _young_gen->kind() == Generation::DefNew, "Expected the young generation here");
}

bool DefNewGeneration::IsAliveClosure::do_object_b(oop p) {
  return (HeapWord*)p >= _young_gen->reserved().end() || p->is_forwarded();
}

DefNewGeneration::KeepAliveClosure::
KeepAliveClosure(ScanWeakRefClosure* cl) : _cl(cl) {
  _rs = GenCollectedHeap::heap()->rem_set();
}

void DefNewGeneration::KeepAliveClosure::do_oop(oop* p)       { DefNewGeneration::KeepAliveClosure::do_oop_work(p); }
void DefNewGeneration::KeepAliveClosure::do_oop(narrowOop* p) { DefNewGeneration::KeepAliveClosure::do_oop_work(p); }


DefNewGeneration::FastKeepAliveClosure::
FastKeepAliveClosure(DefNewGeneration* g, ScanWeakRefClosure* cl) :
  DefNewGeneration::KeepAliveClosure(cl) {
  _boundary = g->reserved().end();
}

void DefNewGeneration::FastKeepAliveClosure::do_oop(oop* p)       { DefNewGeneration::FastKeepAliveClosure::do_oop_work(p); }
void DefNewGeneration::FastKeepAliveClosure::do_oop(narrowOop* p) { DefNewGeneration::FastKeepAliveClosure::do_oop_work(p); }

DefNewGeneration::FastEvacuateFollowersClosure::
FastEvacuateFollowersClosure(SerialHeap* heap,
                             FastScanClosure* cur,
                             FastScanClosure* older) :
  _heap(heap), _scan_cur_or_nonheap(cur), _scan_older(older)
{
}

void DefNewGeneration::FastEvacuateFollowersClosure::do_void() {
  do {
    _heap->oop_since_save_marks_iterate(_scan_cur_or_nonheap, _scan_older);
  } while (!_heap->no_allocs_since_save_marks());
  guarantee(_heap->young_gen()->promo_failure_scan_is_complete(), "Failed to finish scan");
}

ScanClosure::ScanClosure(DefNewGeneration* g, bool gc_barrier) :
    OopsInClassLoaderDataOrGenClosure(g), _g(g), _gc_barrier(gc_barrier)
{
  _boundary = _g->reserved().end();
}

FastScanClosure::FastScanClosure(DefNewGeneration* g, bool gc_barrier) :
    OopsInClassLoaderDataOrGenClosure(g), _g(g), _gc_barrier(gc_barrier)
{
  _boundary = _g->reserved().end();
}

void CLDScanClosure::do_cld(ClassLoaderData* cld) {
  NOT_PRODUCT(ResourceMark rm);
  log_develop_trace(gc, scavenge)("CLDScanClosure::do_cld " PTR_FORMAT ", %s, dirty: %s",
                                  p2i(cld),
                                  cld->loader_name_and_id(),
                                  cld->has_modified_oops() ? "true" : "false");

  // If the cld has not been dirtied we know that there's
  // no references into  the young gen and we can skip it.
  if (cld->has_modified_oops()) {
    if (_accumulate_modified_oops) {
      cld->accumulate_modified_oops();
    }

    // Tell the closure which CLD is being scanned so that it can be dirtied
    // if oops are left pointing into the young gen.
    _scavenge_closure->set_scanned_cld(cld);

    // Clean the cld since we're going to scavenge all the metadata.
    cld->oops_do(_scavenge_closure, false, /*clear_modified_oops*/true);

    _scavenge_closure->set_scanned_cld(NULL);
  }
}

ScanWeakRefClosure::ScanWeakRefClosure(DefNewGeneration* g) :
  _g(g)
{
  _boundary = _g->reserved().end();
}

DefNewGeneration::DefNewGeneration(ReservedSpace rs,
                                   size_t initial_size,
                                   const char* policy)
  : Generation(rs, initial_size),
    _preserved_marks_set(false /* in_c_heap */),
    _promo_failure_drain_in_progress(false),
    _should_allocate_from_space(false)
{
  MemRegion cmr((HeapWord*)_virtual_space.low(),
                (HeapWord*)_virtual_space.high());
  GenCollectedHeap* gch = GenCollectedHeap::heap();

  gch->rem_set()->resize_covered_region(cmr);

  _eden_space = new ContiguousSpace();
  _from_space = new ContiguousSpace();
  _to_space   = new ContiguousSpace();

  if (_eden_space == NULL || _from_space == NULL || _to_space == NULL) {
    vm_exit_during_initialization("Could not allocate a new gen space");
  }

  // Compute the maximum eden and survivor space sizes. These sizes
  // are computed assuming the entire reserved space is committed.
  // These values are exported as performance counters.
  uintx alignment = gch->collector_policy()->space_alignment();
  uintx size = _virtual_space.reserved_size();
  _max_survivor_size = compute_survivor_size(size, alignment);
  _max_eden_size = size - (2*_max_survivor_size);

  // allocate the performance counters
  GenCollectorPolicy* gcp = gch->gen_policy();

  // Generation counters -- generation 0, 3 subspaces
  _gen_counters = new GenerationCounters("new", 0, 3,
      gcp->min_young_size(), gcp->max_young_size(), &_virtual_space);
  _gc_counters = new CollectorCounters(policy, 0);

  _eden_counters = new CSpaceCounters("eden", 0, _max_eden_size, _eden_space,
                                      _gen_counters);
  _from_counters = new CSpaceCounters("s0", 1, _max_survivor_size, _from_space,
                                      _gen_counters);
  _to_counters = new CSpaceCounters("s1", 2, _max_survivor_size, _to_space,
                                    _gen_counters);

  compute_space_boundaries(0, SpaceDecorator::Clear, SpaceDecorator::Mangle);
  update_counters();
  _old_gen = NULL;
  _tenuring_threshold = MaxTenuringThreshold;
  _pretenure_size_threshold_words = PretenureSizeThreshold >> LogHeapWordSize;

  _gc_timer = new (ResourceObj::C_HEAP, mtGC) STWGCTimer();
}

void DefNewGeneration::compute_space_boundaries(uintx minimum_eden_size,
                                                bool clear_space,
                                                bool mangle_space) {
  uintx alignment =
    GenCollectedHeap::heap()->collector_policy()->space_alignment();

  // If the spaces are being cleared (only done at heap initialization
  // currently), the survivor spaces need not be empty.
  // Otherwise, no care is taken for used areas in the survivor spaces
  // so check.
  assert(clear_space || (to()->is_empty() && from()->is_empty()),
    "Initialization of the survivor spaces assumes these are empty");

  // Compute sizes
  uintx size = _virtual_space.committed_size();
  uintx survivor_size = compute_survivor_size(size, alignment);
  uintx eden_size = size - (2*survivor_size);
  assert(eden_size > 0 && survivor_size <= eden_size, "just checking");

  if (eden_size < minimum_eden_size) {
    // May happen due to 64Kb rounding, if so adjust eden size back up
    minimum_eden_size = align_up(minimum_eden_size, alignment);
    uintx maximum_survivor_size = (size - minimum_eden_size) / 2;
    uintx unaligned_survivor_size =
      align_down(maximum_survivor_size, alignment);
    survivor_size = MAX2(unaligned_survivor_size, alignment);
    eden_size = size - (2*survivor_size);
    assert(eden_size > 0 && survivor_size <= eden_size, "just checking");
    assert(eden_size >= minimum_eden_size, "just checking");
  }

  char *eden_start = _virtual_space.low();
  char *from_start = eden_start + eden_size;
  char *to_start   = from_start + survivor_size;
  char *to_end     = to_start   + survivor_size;

  assert(to_end == _virtual_space.high(), "just checking");
  assert(Space::is_aligned(eden_start), "checking alignment");
  assert(Space::is_aligned(from_start), "checking alignment");
  assert(Space::is_aligned(to_start),   "checking alignment");

  MemRegion edenMR((HeapWord*)eden_start, (HeapWord*)from_start);
  MemRegion fromMR((HeapWord*)from_start, (HeapWord*)to_start);
  MemRegion toMR  ((HeapWord*)to_start, (HeapWord*)to_end);

  // A minimum eden size implies that there is a part of eden that
  // is being used and that affects the initialization of any
  // newly formed eden.
  bool live_in_eden = minimum_eden_size > 0;

  // If not clearing the spaces, do some checking to verify that
  // the space are already mangled.
  if (!clear_space) {
    // Must check mangling before the spaces are reshaped.  Otherwise,
    // the bottom or end of one space may have moved into another
    // a failure of the check may not correctly indicate which space
    // is not properly mangled.
    if (ZapUnusedHeapArea) {
      HeapWord* limit = (HeapWord*) _virtual_space.high();
      eden()->check_mangled_unused_area(limit);
      from()->check_mangled_unused_area(limit);
        to()->check_mangled_unused_area(limit);
    }
  }

  // Reset the spaces for their new regions.
  eden()->initialize(edenMR,
                     clear_space && !live_in_eden,
                     SpaceDecorator::Mangle);
  // If clear_space and live_in_eden, we will not have cleared any
  // portion of eden above its top. This can cause newly
  // expanded space not to be mangled if using ZapUnusedHeapArea.
  // We explicitly do such mangling here.
  if (ZapUnusedHeapArea && clear_space && live_in_eden && mangle_space) {
    eden()->mangle_unused_area();
  }
  from()->initialize(fromMR, clear_space, mangle_space);
  to()->initialize(toMR, clear_space, mangle_space);

  // Set next compaction spaces.
  eden()->set_next_compaction_space(from());
  // The to-space is normally empty before a compaction so need
  // not be considered.  The exception is during promotion
  // failure handling when to-space can contain live objects.
  from()->set_next_compaction_space(NULL);
}

void DefNewGeneration::swap_spaces() {
  ContiguousSpace* s = from();
  _from_space        = to();
  _to_space          = s;
  eden()->set_next_compaction_space(from());
  // The to-space is normally empty before a compaction so need
  // not be considered.  The exception is during promotion
  // failure handling when to-space can contain live objects.
  from()->set_next_compaction_space(NULL);

  if (UsePerfData) {
    CSpaceCounters* c = _from_counters;
    _from_counters = _to_counters;
    _to_counters = c;
  }
}

bool DefNewGeneration::expand(size_t bytes) {
  MutexLocker x(ExpandHeap_lock);
  HeapWord* prev_high = (HeapWord*) _virtual_space.high();
  bool success = _virtual_space.expand_by(bytes);
  if (success && ZapUnusedHeapArea) {
    // Mangle newly committed space immediately because it
    // can be done here more simply that after the new
    // spaces have been computed.
    HeapWord* new_high = (HeapWord*) _virtual_space.high();
    MemRegion mangle_region(prev_high, new_high);
    SpaceMangler::mangle_region(mangle_region);
  }

  // Do not attempt an expand-to-the reserve size.  The
  // request should properly observe the maximum size of
  // the generation so an expand-to-reserve should be
  // unnecessary.  Also a second call to expand-to-reserve
  // value potentially can cause an undue expansion.
  // For example if the first expand fail for unknown reasons,
  // but the second succeeds and expands the heap to its maximum
  // value.
  if (GCLocker::is_active()) {
    log_debug(gc)("Garbage collection disabled, expanded heap instead");
  }

  return success;
}

size_t DefNewGeneration::adjust_for_thread_increase(size_t new_size_candidate,
                                                    size_t new_size_before,
                                                    size_t alignment) const {
  size_t desired_new_size = new_size_before;

  if (NewSizeThreadIncrease > 0) {
    int threads_count;
    size_t thread_increase_size = 0;

    // 1. Check an overflow at 'threads_count * NewSizeThreadIncrease'.
    threads_count = Threads::number_of_non_daemon_threads();
    if (threads_count > 0 && NewSizeThreadIncrease <= max_uintx / threads_count) {
      thread_increase_size = threads_count * NewSizeThreadIncrease;

      // 2. Check an overflow at 'new_size_candidate + thread_increase_size'.
      if (new_size_candidate <= max_uintx - thread_increase_size) {
        new_size_candidate += thread_increase_size;

        // 3. Check an overflow at 'align_up'.
        size_t aligned_max = ((max_uintx - alignment) & ~(alignment-1));
        if (new_size_candidate <= aligned_max) {
          desired_new_size = align_up(new_size_candidate, alignment);
        }
      }
    }
  }

  return desired_new_size;
}

void DefNewGeneration::compute_new_size() {
  // This is called after a GC that includes the old generation, so from-space
  // will normally be empty.
  // Note that we check both spaces, since if scavenge failed they revert roles.
  // If not we bail out (otherwise we would have to relocate the objects).
  if (!from()->is_empty() || !to()->is_empty()) {
    return;
  }

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  size_t old_size = gch->old_gen()->capacity();
  size_t new_size_before = _virtual_space.committed_size();
  size_t min_new_size = initial_size();
  size_t max_new_size = reserved().byte_size();
  assert(min_new_size <= new_size_before &&
         new_size_before <= max_new_size,
         "just checking");
  // All space sizes must be multiples of Generation::GenGrain.
  size_t alignment = Generation::GenGrain;

  int threads_count = 0;
  size_t thread_increase_size = 0;

  size_t new_size_candidate = old_size / NewRatio;
  // Compute desired new generation size based on NewRatio and NewSizeThreadIncrease
  // and reverts to previous value if any overflow happens
  size_t desired_new_size = adjust_for_thread_increase(new_size_candidate, new_size_before, alignment);

  // Adjust new generation size
  desired_new_size = MAX2(MIN2(desired_new_size, max_new_size), min_new_size);
  assert(desired_new_size <= max_new_size, "just checking");

  bool changed = false;
  if (desired_new_size > new_size_before) {
    size_t change = desired_new_size - new_size_before;
    assert(change % alignment == 0, "just checking");
    if (expand(change)) {
       changed = true;
    }
    // If the heap failed to expand to the desired size,
    // "changed" will be false.  If the expansion failed
    // (and at this point it was expected to succeed),
    // ignore the failure (leaving "changed" as false).
  }
  if (desired_new_size < new_size_before && eden()->is_empty()) {
    // bail out of shrinking if objects in eden
    size_t change = new_size_before - desired_new_size;
    assert(change % alignment == 0, "just checking");
    _virtual_space.shrink_by(change);
    changed = true;
  }
  if (changed) {
    // The spaces have already been mangled at this point but
    // may not have been cleared (set top = bottom) and should be.
    // Mangling was done when the heap was being expanded.
    compute_space_boundaries(eden()->used(),
                             SpaceDecorator::Clear,
                             SpaceDecorator::DontMangle);
    MemRegion cmr((HeapWord*)_virtual_space.low(),
                  (HeapWord*)_virtual_space.high());
    gch->rem_set()->resize_covered_region(cmr);

    log_debug(gc, ergo, heap)(
        "New generation size " SIZE_FORMAT "K->" SIZE_FORMAT "K [eden=" SIZE_FORMAT "K,survivor=" SIZE_FORMAT "K]",
        new_size_before/K, _virtual_space.committed_size()/K,
        eden()->capacity()/K, from()->capacity()/K);
    log_trace(gc, ergo, heap)(
        "  [allowed " SIZE_FORMAT "K extra for %d threads]",
          thread_increase_size/K, threads_count);
      }
}

void DefNewGeneration::younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) {
  assert(false, "NYI -- are you sure you want to call this?");
}


size_t DefNewGeneration::capacity() const {
  return eden()->capacity()
       + from()->capacity();  // to() is only used during scavenge
}


size_t DefNewGeneration::used() const {
  return eden()->used()
       + from()->used();      // to() is only used during scavenge
}


size_t DefNewGeneration::free() const {
  return eden()->free()
       + from()->free();      // to() is only used during scavenge
}

size_t DefNewGeneration::max_capacity() const {
  const size_t alignment = GenCollectedHeap::heap()->collector_policy()->space_alignment();
  const size_t reserved_bytes = reserved().byte_size();
  return reserved_bytes - compute_survivor_size(reserved_bytes, alignment);
}

size_t DefNewGeneration::unsafe_max_alloc_nogc() const {
  return eden()->free();
}

size_t DefNewGeneration::capacity_before_gc() const {
  return eden()->capacity();
}

size_t DefNewGeneration::contiguous_available() const {
  return eden()->free();
}


HeapWord* volatile* DefNewGeneration::top_addr() const { return eden()->top_addr(); }
HeapWord** DefNewGeneration::end_addr() const { return eden()->end_addr(); }

void DefNewGeneration::object_iterate(ObjectClosure* blk) {
  eden()->object_iterate(blk);
  from()->object_iterate(blk);
}


void DefNewGeneration::space_iterate(SpaceClosure* blk,
                                     bool usedOnly) {
  blk->do_space(eden());
  blk->do_space(from());
  blk->do_space(to());
}

// The last collection bailed out, we are running out of heap space,
// so we try to allocate the from-space, too.
HeapWord* DefNewGeneration::allocate_from_space(size_t size) {
  bool should_try_alloc = should_allocate_from_space() || GCLocker::is_active_and_needs_gc();

  // If the Heap_lock is not locked by this thread, this will be called
  // again later with the Heap_lock held.
  bool do_alloc = should_try_alloc && (Heap_lock->owned_by_self() || (SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread()));

  HeapWord* result = NULL;
  if (do_alloc) {
    result = from()->allocate(size);
  }

  log_trace(gc, alloc)("DefNewGeneration::allocate_from_space(" SIZE_FORMAT "):  will_fail: %s  heap_lock: %s  free: " SIZE_FORMAT "%s%s returns %s",
                        size,
                        GenCollectedHeap::heap()->incremental_collection_will_fail(false /* don't consult_young */) ?
                          "true" : "false",
                        Heap_lock->is_locked() ? "locked" : "unlocked",
                        from()->free(),
                        should_try_alloc ? "" : "  should_allocate_from_space: NOT",
                        do_alloc ? "  Heap_lock is not owned by self" : "",
                        result == NULL ? "NULL" : "object");

  return result;
}

HeapWord* DefNewGeneration::expand_and_allocate(size_t size,
                                                bool   is_tlab,
                                                bool   parallel) {
  // We don't attempt to expand the young generation (but perhaps we should.)
  return allocate(size, is_tlab);
}

void DefNewGeneration::adjust_desired_tenuring_threshold() {
  // Set the desired survivor size to half the real survivor space
  size_t const survivor_capacity = to()->capacity() / HeapWordSize;
  size_t const desired_survivor_size = (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);

  _tenuring_threshold = age_table()->compute_tenuring_threshold(desired_survivor_size);

  if (UsePerfData) {
    GCPolicyCounters* gc_counters = GenCollectedHeap::heap()->counters();
    gc_counters->tenuring_threshold()->set_value(_tenuring_threshold);
    gc_counters->desired_survivor_size()->set_value(desired_survivor_size * oopSize);
  }

  age_table()->print_age_table(_tenuring_threshold);
}

void DefNewGeneration::collect(bool   full,
                               bool   clear_all_soft_refs,
                               size_t size,
                               bool   is_tlab) {
  assert(full || size > 0, "otherwise we don't want to collect");

  SerialHeap* heap = SerialHeap::heap();

  _gc_timer->register_gc_start();
  DefNewTracer gc_tracer;
  gc_tracer.report_gc_start(heap->gc_cause(), _gc_timer->gc_start());

  _old_gen = heap->old_gen();

  // If the next generation is too full to accommodate promotion
  // from this generation, pass on collection; let the next generation
  // do it.
  if (!collection_attempt_is_safe()) {
    log_trace(gc)(":: Collection attempt not safe ::");
    heap->set_incremental_collection_failed(); // Slight lie: we did not even attempt one
    return;
  }
  assert(to()->is_empty(), "Else not collection_attempt_is_safe");

  init_assuming_no_promotion_failure();

  GCTraceTime(Trace, gc, phases) tm("DefNew", NULL, heap->gc_cause());

  heap->trace_heap_before_gc(&gc_tracer);

  // These can be shared for all code paths
  IsAliveClosure is_alive(this);
  ScanWeakRefClosure scan_weak_ref(this);

  age_table()->clear();
  to()->clear(SpaceDecorator::Mangle);
  // The preserved marks should be empty at the start of the GC.
  _preserved_marks_set.init(1);

  heap->rem_set()->prepare_for_younger_refs_iterate(false);

  assert(heap->no_allocs_since_save_marks(),
         "save marks have not been newly set.");

  FastScanClosure fsc_with_no_gc_barrier(this, false);
  FastScanClosure fsc_with_gc_barrier(this, true);

  CLDScanClosure cld_scan_closure(&fsc_with_no_gc_barrier,
                                  heap->rem_set()->cld_rem_set()->accumulate_modified_oops());

  set_promo_failure_scan_stack_closure(&fsc_with_no_gc_barrier);
  FastEvacuateFollowersClosure evacuate_followers(heap,
                                                  &fsc_with_no_gc_barrier,
                                                  &fsc_with_gc_barrier);

  assert(heap->no_allocs_since_save_marks(),
         "save marks have not been newly set.");

  {
    // DefNew needs to run with n_threads == 0, to make sure the serial
    // version of the card table scanning code is used.
    // See: CardTableRS::non_clean_card_iterate_possibly_parallel.
    StrongRootsScope srs(0);

    heap->young_process_roots(&srs,
                              &fsc_with_no_gc_barrier,
                              &fsc_with_gc_barrier,
                              &cld_scan_closure);
  }

  // "evacuate followers".
  evacuate_followers.do_void();

  FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
  BarrierEnqueueDiscoveredFieldClosure enqueue;
  ReferenceProcessor* rp = ref_processor();
  rp->setup_policy(clear_all_soft_refs);
  ReferenceProcessorPhaseTimes pt(_gc_timer, rp->max_num_queues());
  const ReferenceProcessorStats& stats =
  rp->process_discovered_references(&is_alive, &keep_alive, &enqueue, &evacuate_followers,
                                    NULL, &pt);
  gc_tracer.report_gc_reference_stats(stats);
  gc_tracer.report_tenuring_threshold(tenuring_threshold());
  pt.print_all_references();

  assert(heap->no_allocs_since_save_marks(), "save marks have not been newly set.");

  WeakProcessor::weak_oops_do(&is_alive, &keep_alive);

  // Verify that the usage of keep_alive didn't copy any objects.
  assert(heap->no_allocs_since_save_marks(), "save marks have not been newly set.");

  if (!_promotion_failed) {
    // Swap the survivor spaces.
    eden()->clear(SpaceDecorator::Mangle);
    from()->clear(SpaceDecorator::Mangle);
    if (ZapUnusedHeapArea) {
      // This is now done here because of the piece-meal mangling which
      // can check for valid mangling at intermediate points in the
      // collection(s).  When a young collection fails to collect
      // sufficient space resizing of the young generation can occur
      // an redistribute the spaces in the young generation.  Mangle
      // here so that unzapped regions don't get distributed to
      // other spaces.
      to()->mangle_unused_area();
    }
    swap_spaces();

    assert(to()->is_empty(), "to space should be empty now");

    adjust_desired_tenuring_threshold();

    // A successful scavenge should restart the GC time limit count which is
    // for full GC's.
    AdaptiveSizePolicy* size_policy = heap->size_policy();
    size_policy->reset_gc_overhead_limit_count();
    assert(!heap->incremental_collection_failed(), "Should be clear");
  } else {
    assert(_promo_failure_scan_stack.is_empty(), "post condition");
    _promo_failure_scan_stack.clear(true); // Clear cached segments.

    remove_forwarding_pointers();
    log_info(gc, promotion)("Promotion failed");
    // Add to-space to the list of space to compact
    // when a promotion failure has occurred.  In that
    // case there can be live objects in to-space
    // as a result of a partial evacuation of eden
    // and from-space.
    swap_spaces();   // For uniformity wrt ParNewGeneration.
    from()->set_next_compaction_space(to());
    heap->set_incremental_collection_failed();

    // Inform the next generation that a promotion failure occurred.
    _old_gen->promotion_failure_occurred();
    gc_tracer.report_promotion_failed(_promotion_failed_info);

    // Reset the PromotionFailureALot counters.
    NOT_PRODUCT(heap->reset_promotion_should_fail();)
  }
  // We should have processed and cleared all the preserved marks.
  _preserved_marks_set.reclaim();
  // set new iteration safe limit for the survivor spaces
  from()->set_concurrent_iteration_safe_limit(from()->top());
  to()->set_concurrent_iteration_safe_limit(to()->top());

  // We need to use a monotonically non-decreasing time in ms
  // or we will see time-warp warnings and os::javaTimeMillis()
  // does not guarantee monotonicity.
  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
  update_time_of_last_gc(now);

  heap->trace_heap_after_gc(&gc_tracer);

  _gc_timer->register_gc_end();

  gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
}

void DefNewGeneration::init_assuming_no_promotion_failure() {
  _promotion_failed = false;
  _promotion_failed_info.reset();
  from()->set_next_compaction_space(NULL);
}

void DefNewGeneration::remove_forwarding_pointers() {
  RemoveForwardedPointerClosure rspc;
  eden()->object_iterate(&rspc);
  from()->object_iterate(&rspc);
  restore_preserved_marks();
}

void DefNewGeneration::restore_preserved_marks() {
  SharedRestorePreservedMarksTaskExecutor task_executor(NULL);
  _preserved_marks_set.restore(&task_executor);
}

void DefNewGeneration::handle_promotion_failure(oop old) {
  log_debug(gc, promotion)("Promotion failure size = %d) ", old->size());

  _promotion_failed = true;
  _promotion_failed_info.register_copy_failure(old->size());
  _preserved_marks_set.get()->push_if_necessary(old, old->mark_raw());
  // forward to self
  old->forward_to(old);

  _promo_failure_scan_stack.push(old);

  if (!_promo_failure_drain_in_progress) {
    // prevent recursion in copy_to_survivor_space()
    _promo_failure_drain_in_progress = true;
    drain_promo_failure_scan_stack();
    _promo_failure_drain_in_progress = false;
  }
}

oop DefNewGeneration::copy_to_survivor_space(oop old) {
  assert(is_in_reserved(old) && !old->is_forwarded(),
         "shouldn't be scavenging this oop");
  size_t s = old->size();
  oop obj = NULL;

  // Try allocating obj in to-space (unless too old)
  if (old->age() < tenuring_threshold()) {
    obj = (oop) to()->allocate_aligned(s);
  }

  // Otherwise try allocating obj tenured
  if (obj == NULL) {
    obj = _old_gen->promote(old, s);
    if (obj == NULL) {
      handle_promotion_failure(old);
      return old;
    }
  } else {
    // Prefetch beyond obj
    const intx interval = PrefetchCopyIntervalInBytes;
    Prefetch::write(obj, interval);

    // Copy obj
    Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)obj, s);

    // Increment age if obj still in new generation
    obj->incr_age();
    age_table()->add(obj, s);
  }

  // Done, insert forward pointer to obj in this header
  old->forward_to(obj);

  return obj;
}

void DefNewGeneration::drain_promo_failure_scan_stack() {
  while (!_promo_failure_scan_stack.is_empty()) {
     oop obj = _promo_failure_scan_stack.pop();
     obj->oop_iterate(_promo_failure_scan_stack_closure);
  }
}

void DefNewGeneration::save_marks() {
  eden()->set_saved_mark();
  to()->set_saved_mark();
  from()->set_saved_mark();
}


void DefNewGeneration::reset_saved_marks() {
  eden()->reset_saved_mark();
  to()->reset_saved_mark();
  from()->reset_saved_mark();
}


bool DefNewGeneration::no_allocs_since_save_marks() {
  assert(eden()->saved_mark_at_top(), "Violated spec - alloc in eden");
  assert(from()->saved_mark_at_top(), "Violated spec - alloc in from");
  return to()->saved_mark_at_top();
}

void DefNewGeneration::contribute_scratch(ScratchBlock*& list, Generation* requestor,
                                         size_t max_alloc_words) {
  if (requestor == this || _promotion_failed) {
    return;
  }
  assert(GenCollectedHeap::heap()->is_old_gen(requestor), "We should not call our own generation");

  /* $$$ Assert this?  "trace" is a "MarkSweep" function so that's not appropriate.
  if (to_space->top() > to_space->bottom()) {
    trace("to_space not empty when contribute_scratch called");
  }
  */

  ContiguousSpace* to_space = to();
  assert(to_space->end() >= to_space->top(), "pointers out of order");
  size_t free_words = pointer_delta(to_space->end(), to_space->top());
  if (free_words >= MinFreeScratchWords) {
    ScratchBlock* sb = (ScratchBlock*)to_space->top();
    sb->num_words = free_words;
    sb->next = list;
    list = sb;
  }
}

void DefNewGeneration::reset_scratch() {
  // If contributing scratch in to_space, mangle all of
  // to_space if ZapUnusedHeapArea.  This is needed because
  // top is not maintained while using to-space as scratch.
  if (ZapUnusedHeapArea) {
    to()->mangle_unused_area_complete();
  }
}

bool DefNewGeneration::collection_attempt_is_safe() {
  if (!to()->is_empty()) {
    log_trace(gc)(":: to is not empty ::");
    return false;
  }
  if (_old_gen == NULL) {
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    _old_gen = gch->old_gen();
  }
  return _old_gen->promotion_attempt_is_safe(used());
}

void DefNewGeneration::gc_epilogue(bool full) {
  DEBUG_ONLY(static bool seen_incremental_collection_failed = false;)

  assert(!GCLocker::is_active(), "We should not be executing here");
  // Check if the heap is approaching full after a collection has
  // been done.  Generally the young generation is empty at
  // a minimum at the end of a collection.  If it is not, then
  // the heap is approaching full.
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  if (full) {
    DEBUG_ONLY(seen_incremental_collection_failed = false;)
    if (!collection_attempt_is_safe() && !_eden_space->is_empty()) {
      log_trace(gc)("DefNewEpilogue: cause(%s), full, not safe, set_failed, set_alloc_from, clear_seen",
                            GCCause::to_string(gch->gc_cause()));
      gch->set_incremental_collection_failed(); // Slight lie: a full gc left us in that state
      set_should_allocate_from_space(); // we seem to be running out of space
    } else {
      log_trace(gc)("DefNewEpilogue: cause(%s), full, safe, clear_failed, clear_alloc_from, clear_seen",
                            GCCause::to_string(gch->gc_cause()));
      gch->clear_incremental_collection_failed(); // We just did a full collection
      clear_should_allocate_from_space(); // if set
    }
  } else {
#ifdef ASSERT
    // It is possible that incremental_collection_failed() == true
    // here, because an attempted scavenge did not succeed. The policy
    // is normally expected to cause a full collection which should
    // clear that condition, so we should not be here twice in a row
    // with incremental_collection_failed() == true without having done
    // a full collection in between.
    if (!seen_incremental_collection_failed &&
        gch->incremental_collection_failed()) {
      log_trace(gc)("DefNewEpilogue: cause(%s), not full, not_seen_failed, failed, set_seen_failed",
                            GCCause::to_string(gch->gc_cause()));
      seen_incremental_collection_failed = true;
    } else if (seen_incremental_collection_failed) {
      log_trace(gc)("DefNewEpilogue: cause(%s), not full, seen_failed, will_clear_seen_failed",
                            GCCause::to_string(gch->gc_cause()));
      seen_incremental_collection_failed = false;
    }
#endif // ASSERT
  }

  if (ZapUnusedHeapArea) {
    eden()->check_mangled_unused_area_complete();
    from()->check_mangled_unused_area_complete();
    to()->check_mangled_unused_area_complete();
  }

  if (!CleanChunkPoolAsync) {
    Chunk::clean_chunk_pool();
  }

  // update the generation and space performance counters
  update_counters();
  gch->counters()->update_counters();
}

void DefNewGeneration::record_spaces_top() {
  assert(ZapUnusedHeapArea, "Not mangling unused space");
  eden()->set_top_for_allocations();
  to()->set_top_for_allocations();
  from()->set_top_for_allocations();
}

void DefNewGeneration::ref_processor_init() {
  Generation::ref_processor_init();
}


void DefNewGeneration::update_counters() {
  if (UsePerfData) {
    _eden_counters->update_all();
    _from_counters->update_all();
    _to_counters->update_all();
    _gen_counters->update_all();
  }
}

void DefNewGeneration::verify() {
  eden()->verify();
  from()->verify();
    to()->verify();
}

void DefNewGeneration::print_on(outputStream* st) const {
  Generation::print_on(st);
  st->print("  eden");
  eden()->print_on(st);
  st->print("  from");
  from()->print_on(st);
  st->print("  to  ");
  to()->print_on(st);
}


const char* DefNewGeneration::name() const {
  return "def new generation";
}

// Moved from inline file as they are not called inline
CompactibleSpace* DefNewGeneration::first_compaction_space() const {
  return eden();
}

HeapWord* DefNewGeneration::allocate(size_t word_size, bool is_tlab) {
  // This is the slow-path allocation for the DefNewGeneration.
  // Most allocations are fast-path in compiled code.
  // We try to allocate from the eden.  If that works, we are happy.
  // Note that since DefNewGeneration supports lock-free allocation, we
  // have to use it here, as well.
  HeapWord* result = eden()->par_allocate(word_size);
  if (result != NULL) {
    if (_old_gen != NULL) {
      _old_gen->sample_eden_chunk();
    }
  } else {
    // If the eden is full and the last collection bailed out, we are running
    // out of heap space, and we try to allocate the from-space, too.
    // allocate_from_space can't be inlined because that would introduce a
    // circular dependency at compile time.
    result = allocate_from_space(word_size);
  }
  return result;
}

HeapWord* DefNewGeneration::par_allocate(size_t word_size,
                                         bool is_tlab) {
  HeapWord* res = eden()->par_allocate(word_size);
  if (_old_gen != NULL) {
    _old_gen->sample_eden_chunk();
  }
  return res;
}

size_t DefNewGeneration::tlab_capacity() const {
  return eden()->capacity();
}

size_t DefNewGeneration::tlab_used() const {
  return eden()->used();
}

size_t DefNewGeneration::unsafe_max_tlab_alloc() const {
  return unsafe_max_alloc_nogc();
}