view src/share/vm/gc_implementation/g1/g1RemSet.cpp @ 2740:4dfb2df418f2

6484982: G1: process references during evacuation pauses Summary: G1 now uses two reference processors - one is used by concurrent marking and the other is used by STW GCs (both full and incremental evacuation pauses). In an evacuation pause, the reference processor is embedded into the closures used to scan objects. Doing so causes causes reference objects to be 'discovered' by the reference processor. At the end of the evacuation pause, these discovered reference objects are processed - preserving (and copying) referent objects (and their reachable graphs) as appropriate. Reviewed-by: ysr, jwilhelm, brutisso, stefank, tonyp
author johnc
date Thu, 22 Sep 2011 10:57:37 -0700
parents e8b0b0392037
children 811ec3d0833b
line wrap: on
line source
 * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.
 * 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 if you need additional information or have any
 * questions.

#include "precompiled.hpp"
#include "gc_implementation/g1/bufferingOopClosure.hpp"
#include "gc_implementation/g1/concurrentG1Refine.hpp"
#include "gc_implementation/g1/concurrentG1RefineThread.hpp"
#include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"
#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
#include "gc_implementation/g1/g1CollectorPolicy.hpp"
#include "gc_implementation/g1/g1OopClosures.inline.hpp"
#include "gc_implementation/g1/g1RemSet.inline.hpp"
#include "gc_implementation/g1/heapRegionSeq.inline.hpp"
#include "memory/iterator.hpp"
#include "oops/oop.inline.hpp"
#include "utilities/intHisto.hpp"


static size_t ct_freq_sz;
static jbyte* ct_freq = NULL;

void init_ct_freq_table(size_t heap_sz_bytes) {
  if (ct_freq == NULL) {
    ct_freq_sz = heap_sz_bytes/CardTableModRefBS::card_size;
    ct_freq = new jbyte[ct_freq_sz];
    for (size_t j = 0; j < ct_freq_sz; j++) ct_freq[j] = 0;

void ct_freq_note_card(size_t index) {
  assert(0 <= index && index < ct_freq_sz, "Bounds error.");
  if (ct_freq[index] < 100) { ct_freq[index]++; }

static IntHistogram card_repeat_count(10, 10);

void ct_freq_update_histo_and_reset() {
  for (size_t j = 0; j < ct_freq_sz; j++) {
    ct_freq[j] = 0;


G1RemSet::G1RemSet(G1CollectedHeap* g1, CardTableModRefBS* ct_bs)
  : _g1(g1), _conc_refine_cards(0),
    _ct_bs(ct_bs), _g1p(_g1->g1_policy()),
    _cards_scanned(NULL), _total_cards_scanned(0)
  _seq_task = new SubTasksDone(NumSeqTasks);
  guarantee(n_workers() > 0, "There should be some workers");
  _cset_rs_update_cl = NEW_C_HEAP_ARRAY(OopsInHeapRegionClosure*, n_workers());
  for (uint i = 0; i < n_workers(); i++) {
    _cset_rs_update_cl[i] = NULL;

G1RemSet::~G1RemSet() {
  delete _seq_task;
  for (uint i = 0; i < n_workers(); i++) {
    assert(_cset_rs_update_cl[i] == NULL, "it should be");
  FREE_C_HEAP_ARRAY(OopsInHeapRegionClosure*, _cset_rs_update_cl);

void CountNonCleanMemRegionClosure::do_MemRegion(MemRegion mr) {
  if (_g1->is_in_g1_reserved(mr.start())) {
    _n += (int) ((mr.byte_size() / CardTableModRefBS::card_size));
    if (_start_first == NULL) _start_first = mr.start();

class ScanRSClosure : public HeapRegionClosure {
  size_t _cards_done, _cards;
  G1CollectedHeap* _g1h;
  OopsInHeapRegionClosure* _oc;
  G1BlockOffsetSharedArray* _bot_shared;
  CardTableModRefBS *_ct_bs;
  int _worker_i;
  int _block_size;
  bool _try_claimed;
  ScanRSClosure(OopsInHeapRegionClosure* oc, int worker_i) :
    _g1h = G1CollectedHeap::heap();
    _bot_shared = _g1h->bot_shared();
    _ct_bs = (CardTableModRefBS*) (_g1h->barrier_set());
    _block_size = MAX2<int>(G1RSetScanBlockSize, 1);

  void set_try_claimed() { _try_claimed = true; }

  void scanCard(size_t index, HeapRegion *r) {
    DirtyCardToOopClosure* cl =

    // Set the "from" region in the closure.
    HeapWord* card_start = _bot_shared->address_for_index(index);
    HeapWord* card_end = card_start + G1BlockOffsetSharedArray::N_words;
    Space *sp = SharedHeap::heap()->space_containing(card_start);
    MemRegion sm_region = sp->used_region_at_save_marks();
    MemRegion mr = sm_region.intersection(MemRegion(card_start,card_end));
    if (!mr.is_empty() && !_ct_bs->is_card_claimed(index)) {
      // We make the card as "claimed" lazily (so races are possible
      // but they're benign), which reduces the number of duplicate
      // scans (the rsets of the regions in the cset can intersect).

  void printCard(HeapRegion* card_region, size_t card_index,
                 HeapWord* card_start) {
    gclog_or_tty->print_cr("T %d Region [" PTR_FORMAT ", " PTR_FORMAT ") "
                           "RS names card %p: "
                           "[" PTR_FORMAT ", " PTR_FORMAT ")",
                           card_region->bottom(), card_region->end(),
                           card_start, card_start + G1BlockOffsetSharedArray::N_words);

  bool doHeapRegion(HeapRegion* r) {
    assert(r->in_collection_set(), "should only be called on elements of CS.");
    HeapRegionRemSet* hrrs = r->rem_set();
    if (hrrs->iter_is_complete()) return false; // All done.
    if (!_try_claimed && !hrrs->claim_iter()) return false;
    // If we ever free the collection set concurrently, we should also
    // clear the card table concurrently therefore we won't need to
    // add regions of the collection set to the dirty cards region.
    // If we didn't return above, then
    //   _try_claimed || r->claim_iter()
    // is true: either we're supposed to work on claimed-but-not-complete
    // regions, or we successfully claimed the region.
    HeapRegionRemSetIterator* iter = _g1h->rem_set_iterator(_worker_i);
    size_t card_index;

    // We claim cards in block so as to recude the contention. The block size is determined by
    // the G1RSetScanBlockSize parameter.
    size_t jump_to_card = hrrs->iter_claimed_next(_block_size);
    for (size_t current_card = 0; iter->has_next(card_index); current_card++) {
      if (current_card >= jump_to_card + _block_size) {
        jump_to_card = hrrs->iter_claimed_next(_block_size);
      if (current_card < jump_to_card) continue;
      HeapWord* card_start = _g1h->bot_shared()->address_for_index(card_index);
#if 0
      gclog_or_tty->print("Rem set iteration yielded card [" PTR_FORMAT ", " PTR_FORMAT ").\n",
                          card_start, card_start + CardTableModRefBS::card_size_in_words);

      HeapRegion* card_region = _g1h->heap_region_containing(card_start);
      assert(card_region != NULL, "Yielding cards not in the heap?");

      if (!card_region->is_on_dirty_cards_region_list()) {

      // If the card is dirty, then we will scan it during updateRS.
      if (!card_region->in_collection_set() &&
          !_ct_bs->is_card_dirty(card_index)) {
        scanCard(card_index, card_region);
    if (!_try_claimed) {
    return false;
  size_t cards_done() { return _cards_done;}
  size_t cards_looked_up() { return _cards;}

// We want the parallel threads to start their scanning at
// different collection set regions to avoid contention.
// If we have:
//          n collection set regions
//          p threads
// Then thread t will start at region t * floor (n/p)

HeapRegion* G1RemSet::calculateStartRegion(int worker_i) {
  HeapRegion* result = _g1p->collection_set();
  if (ParallelGCThreads > 0) {
    size_t cs_size = _g1p->collection_set_size();
    int n_workers = _g1->workers()->total_workers();
    size_t cs_spans = cs_size / n_workers;
    size_t ind      = cs_spans * worker_i;
    for (size_t i = 0; i < ind; i++)
      result = result->next_in_collection_set();
  return result;

void G1RemSet::scanRS(OopsInHeapRegionClosure* oc, int worker_i) {
  double rs_time_start = os::elapsedTime();
  HeapRegion *startRegion = calculateStartRegion(worker_i);

  ScanRSClosure scanRScl(oc, worker_i);

  _g1->collection_set_iterate_from(startRegion, &scanRScl);
  _g1->collection_set_iterate_from(startRegion, &scanRScl);

  double scan_rs_time_sec = os::elapsedTime() - rs_time_start;

  assert( _cards_scanned != NULL, "invariant" );
  _cards_scanned[worker_i] = scanRScl.cards_done();

  _g1p->record_scan_rs_time(worker_i, scan_rs_time_sec * 1000.0);

// Closure used for updating RSets and recording references that
// point into the collection set. Only called during an
// evacuation pause.

class RefineRecordRefsIntoCSCardTableEntryClosure: public CardTableEntryClosure {
  G1RemSet* _g1rs;
  DirtyCardQueue* _into_cset_dcq;
  RefineRecordRefsIntoCSCardTableEntryClosure(G1CollectedHeap* g1h,
                                              DirtyCardQueue* into_cset_dcq) :
    _g1rs(g1h->g1_rem_set()), _into_cset_dcq(into_cset_dcq)
  bool do_card_ptr(jbyte* card_ptr, int worker_i) {
    // The only time we care about recording cards that
    // contain references that point into the collection set
    // is during RSet updating within an evacuation pause.
    // In this case worker_i should be the id of a GC worker thread.
    assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
    assert(worker_i < (int) (ParallelGCThreads == 0 ? 1 : ParallelGCThreads), "should be a GC worker");

    if (_g1rs->concurrentRefineOneCard(card_ptr, worker_i, true)) {
      // 'card_ptr' contains references that point into the collection
      // set. We need to record the card in the DCQS
      // (G1CollectedHeap::into_cset_dirty_card_queue_set())
      // that's used for that purpose.
      // Enqueue the card
    return true;

void G1RemSet::updateRS(DirtyCardQueue* into_cset_dcq, int worker_i) {
  double start = os::elapsedTime();
  // Apply the given closure to all remaining log entries.
  RefineRecordRefsIntoCSCardTableEntryClosure into_cset_update_rs_cl(_g1, into_cset_dcq);

  _g1->iterate_dirty_card_closure(&into_cset_update_rs_cl, into_cset_dcq, false, worker_i);

  // Now there should be no dirty cards.
  if (G1RSLogCheckCardTable) {
    CountNonCleanMemRegionClosure cl(_g1);
    // XXX This isn't true any more: keeping cards of young regions
    // marked dirty broke it.  Need some reasonable fix.
    guarantee(cl.n() == 0, "Card table should be clean.");

  _g1p->record_update_rs_time(worker_i, (os::elapsedTime() - start) * 1000.0);

class CountRSSizeClosure: public HeapRegionClosure {
  size_t _n;
  size_t _tot;
  size_t _max;
  HeapRegion* _max_r;
  enum {
    N = 20,
    MIN = 6
  int _histo[N];
  CountRSSizeClosure() : _n(0), _tot(0), _max(0), _max_r(NULL) {
    for (int i = 0; i < N; i++) _histo[i] = 0;
  bool doHeapRegion(HeapRegion* r) {
    if (!r->continuesHumongous()) {
      size_t occ = r->rem_set()->occupied();
      _tot += occ;
      if (occ > _max) {
        _max = occ;
        _max_r = r;
      // Fit it into a histo bin.
      int s = 1 << MIN;
      int i = 0;
      while (occ > (size_t) s && i < (N-1)) {
        s = s << 1;
    return false;
  size_t n() { return _n; }
  size_t tot() { return _tot; }
  size_t mx() { return _max; }
  HeapRegion* mxr() { return _max_r; }
  void print_histo() {
    int mx = N;
    while (mx >= 0) {
      if (_histo[mx-1] > 0) break;
    gclog_or_tty->print_cr("Number of regions with given RS sizes:");
    gclog_or_tty->print_cr("           <= %8d   %8d", 1 << MIN, _histo[0]);
    for (int i = 1; i < mx-1; i++) {
      gclog_or_tty->print_cr("  %8d  - %8d   %8d",
                    (1 << (MIN + i - 1)) + 1,
                    1 << (MIN + i),
    gclog_or_tty->print_cr("            > %8d   %8d", (1 << (MIN+mx-2))+1, _histo[mx-1]);

void G1RemSet::cleanupHRRS() {

void G1RemSet::oops_into_collection_set_do(OopsInHeapRegionClosure* oc,
                                             int worker_i) {
  if (worker_i == 0) {

  // Make this into a command-line flag...
  if (G1RSCountHisto && (ParallelGCThreads == 0 || worker_i == 0)) {
    CountRSSizeClosure count_cl;
    gclog_or_tty->print_cr("Avg of %d RS counts is %f, max is %d, "
                  "max region is " PTR_FORMAT,
                  count_cl.n(), (float)count_cl.tot()/(float)count_cl.n(),
        , count_cl.mxr());

  // We cache the value of 'oc' closure into the appropriate slot in the
  // _cset_rs_update_cl for this worker
  assert(worker_i < (int)n_workers(), "sanity");
  _cset_rs_update_cl[worker_i] = oc;

  // A DirtyCardQueue that is used to hold cards containing references
  // that point into the collection set. This DCQ is associated with a
  // special DirtyCardQueueSet (see g1CollectedHeap.hpp).  Under normal
  // circumstances (i.e. the pause successfully completes), these cards
  // are just discarded (there's no need to update the RSets of regions
  // that were in the collection set - after the pause these regions
  // are wholly 'free' of live objects. In the event of an evacuation
  // failure the cards/buffers in this queue set are:
  // * passed to the DirtyCardQueueSet that is used to manage deferred
  //   RSet updates, or
  // * scanned for references that point into the collection set
  //   and the RSet of the corresponding region in the collection set
  //   is updated immediately.
  DirtyCardQueue into_cset_dcq(&_g1->into_cset_dirty_card_queue_set());

  assert((ParallelGCThreads > 0) || worker_i == 0, "invariant");

  // The two flags below were introduced temporarily to serialize
  // the updating and scanning of remembered sets. There are some
  // race conditions when these two operations are done in parallel
  // and they are causing failures. When we resolve said race
  // conditions, we'll revert back to parallel remembered set
  // updating and scanning. See CRs 6677707 and 6677708.
  if (G1UseParallelRSetUpdating || (worker_i == 0)) {
    updateRS(&into_cset_dcq, worker_i);
  } else {
    _g1p->record_update_rs_processed_buffers(worker_i, 0.0);
    _g1p->record_update_rs_time(worker_i, 0.0);
  if (G1UseParallelRSetScanning || (worker_i == 0)) {
    scanRS(oc, worker_i);
  } else {
    _g1p->record_scan_rs_time(worker_i, 0.0);

  // We now clear the cached values of _cset_rs_update_cl for this worker
  _cset_rs_update_cl[worker_i] = NULL;

void G1RemSet::prepare_for_oops_into_collection_set_do() {
  ConcurrentG1Refine* cg1r = _g1->concurrent_g1_refine();
  DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();

  if (ParallelGCThreads > 0) {
  guarantee( _cards_scanned == NULL, "invariant" );
  _cards_scanned = NEW_C_HEAP_ARRAY(size_t, n_workers());
  for (uint i = 0; i < n_workers(); ++i) {
    _cards_scanned[i] = 0;
  _total_cards_scanned = 0;

// This closure, applied to a DirtyCardQueueSet, is used to immediately
// update the RSets for the regions in the CSet. For each card it iterates
// through the oops which coincide with that card. It scans the reference
// fields in each oop; when it finds an oop that points into the collection
// set, the RSet for the region containing the referenced object is updated.
class UpdateRSetCardTableEntryIntoCSetClosure: public CardTableEntryClosure {
  G1CollectedHeap* _g1;
  CardTableModRefBS* _ct_bs;
  UpdateRSetCardTableEntryIntoCSetClosure(G1CollectedHeap* g1,
                                          CardTableModRefBS* bs):
    _g1(g1), _ct_bs(bs)
  { }

  bool do_card_ptr(jbyte* card_ptr, int worker_i) {
    // Construct the region representing the card.
    HeapWord* start = _ct_bs->addr_for(card_ptr);
    // And find the region containing it.
    HeapRegion* r = _g1->heap_region_containing(start);
    assert(r != NULL, "unexpected null");

    // Scan oops in the card looking for references into the collection set
    HeapWord* end   = _ct_bs->addr_for(card_ptr + 1);
    MemRegion scanRegion(start, end);

    UpdateRSetImmediate update_rs_cl(_g1->g1_rem_set());
    FilterIntoCSClosure update_rs_cset_oop_cl(NULL, _g1, &update_rs_cl, NULL /* rp */);
    FilterOutOfRegionClosure filter_then_update_rs_cset_oop_cl(r, &update_rs_cset_oop_cl);

    // We can pass false as the "filter_young" parameter here as:
    // * we should be in a STW pause,
    // * the DCQS to which this closure is applied is used to hold
    //   references that point into the collection set from the prior
    //   RSet updating,
    // * the post-write barrier shouldn't be logging updates to young
    //   regions (but there is a situation where this can happen - see
    //   the comment in G1RemSet::concurrentRefineOneCard below -
    //   that should not be applicable here), and
    // * during actual RSet updating, the filtering of cards in young
    //   regions in HeapRegion::oops_on_card_seq_iterate_careful is
    //   employed.
    // As a result, when this closure is applied to "refs into cset"
    // DCQS, we shouldn't see any cards in young regions.
    HeapWord* stop_point =
                                          false /* filter_young */,
                                          NULL  /* card_ptr */);

    // Since this is performed in the event of an evacuation failure, we
    // we shouldn't see a non-null stop point
    assert(stop_point == NULL, "saw an unallocated region");
    return true;

void G1RemSet::cleanup_after_oops_into_collection_set_do() {
  guarantee( _cards_scanned != NULL, "invariant" );
  _total_cards_scanned = 0;
  for (uint i = 0; i < n_workers(); ++i) {
    _total_cards_scanned += _cards_scanned[i];
  FREE_C_HEAP_ARRAY(size_t, _cards_scanned);
  _cards_scanned = NULL;
  // Cleanup after copy
  // Set all cards back to clean.

  DirtyCardQueueSet& into_cset_dcqs = _g1->into_cset_dirty_card_queue_set();
  int into_cset_n_buffers = into_cset_dcqs.completed_buffers_num();

  if (_g1->evacuation_failed()) {
    // Restore remembered sets for the regions pointing into the collection set.

    if (G1DeferredRSUpdate) {
      // If deferred RS updates are enabled then we just need to transfer
      // the completed buffers from (a) the DirtyCardQueueSet used to hold
      // cards that contain references that point into the collection set
      // to (b) the DCQS used to hold the deferred RS updates
    } else {

      CardTableModRefBS* bs = (CardTableModRefBS*)_g1->barrier_set();
      UpdateRSetCardTableEntryIntoCSetClosure update_rs_cset_immediate(_g1, bs);

      int n_completed_buffers = 0;
      while (into_cset_dcqs.apply_closure_to_completed_buffer(&update_rs_cset_immediate,
                                                    0, 0, true)) {
      assert(n_completed_buffers == into_cset_n_buffers, "missed some buffers");

  // Free any completed buffers in the DirtyCardQueueSet used to hold cards
  // which contain references that point into the collection.
  assert(_g1->into_cset_dirty_card_queue_set().completed_buffers_num() == 0,
         "all buffers should be freed");

class ScrubRSClosure: public HeapRegionClosure {
  G1CollectedHeap* _g1h;
  BitMap* _region_bm;
  BitMap* _card_bm;
  CardTableModRefBS* _ctbs;
  ScrubRSClosure(BitMap* region_bm, BitMap* card_bm) :
    _region_bm(region_bm), _card_bm(card_bm),
    ModRefBarrierSet* bs = _g1h->mr_bs();
    guarantee(bs->is_a(BarrierSet::CardTableModRef), "Precondition");
    _ctbs = (CardTableModRefBS*)bs;

  bool doHeapRegion(HeapRegion* r) {
    if (!r->continuesHumongous()) {
      r->rem_set()->scrub(_ctbs, _region_bm, _card_bm);
    return false;

void G1RemSet::scrub(BitMap* region_bm, BitMap* card_bm) {
  ScrubRSClosure scrub_cl(region_bm, card_bm);

void G1RemSet::scrub_par(BitMap* region_bm, BitMap* card_bm,
                                int worker_num, int claim_val) {
  ScrubRSClosure scrub_cl(region_bm, card_bm);
  _g1->heap_region_par_iterate_chunked(&scrub_cl, worker_num, claim_val);

static IntHistogram out_of_histo(50, 50);

class TriggerClosure : public OopClosure {
  bool _trigger;
  TriggerClosure() : _trigger(false) { }
  bool value() const { return _trigger; }
  template <class T> void do_oop_nv(T* p) { _trigger = true; }
  virtual void do_oop(oop* p)        { do_oop_nv(p); }
  virtual void do_oop(narrowOop* p)  { do_oop_nv(p); }

class InvokeIfNotTriggeredClosure: public OopClosure {
  TriggerClosure* _t;
  OopClosure* _oc;
  InvokeIfNotTriggeredClosure(TriggerClosure* t, OopClosure* oc):
    _t(t), _oc(oc) { }
  template <class T> void do_oop_nv(T* p) {
    if (!_t->value()) _oc->do_oop(p);
  virtual void do_oop(oop* p)        { do_oop_nv(p); }
  virtual void do_oop(narrowOop* p)  { do_oop_nv(p); }

class Mux2Closure : public OopClosure {
  OopClosure* _c1;
  OopClosure* _c2;
  Mux2Closure(OopClosure *c1, OopClosure *c2) : _c1(c1), _c2(c2) { }
  template <class T> void do_oop_nv(T* p) {
    _c1->do_oop(p); _c2->do_oop(p);
  virtual void do_oop(oop* p)        { do_oop_nv(p); }
  virtual void do_oop(narrowOop* p)  { do_oop_nv(p); }

bool G1RemSet::concurrentRefineOneCard_impl(jbyte* card_ptr, int worker_i,
                                                   bool check_for_refs_into_cset) {
  // Construct the region representing the card.
  HeapWord* start = _ct_bs->addr_for(card_ptr);
  // And find the region containing it.
  HeapRegion* r = _g1->heap_region_containing(start);
  assert(r != NULL, "unexpected null");

  HeapWord* end   = _ct_bs->addr_for(card_ptr + 1);
  MemRegion dirtyRegion(start, end);


  assert(!check_for_refs_into_cset || _cset_rs_update_cl[worker_i] != NULL, "sanity");
  UpdateRSOrPushRefOopClosure update_rs_oop_cl(_g1,

  TriggerClosure trigger_cl;
  FilterIntoCSClosure into_cs_cl(NULL, _g1, &trigger_cl, NULL /* rp */);
  InvokeIfNotTriggeredClosure invoke_cl(&trigger_cl, &into_cs_cl);
  Mux2Closure mux(&invoke_cl, &update_rs_oop_cl);

  FilterOutOfRegionClosure filter_then_update_rs_oop_cl(r,
                        (check_for_refs_into_cset ?
                                (OopClosure*)&mux :

  // The region for the current card may be a young region. The
  // current card may have been a card that was evicted from the
  // card cache. When the card was inserted into the cache, we had
  // determined that its region was non-young. While in the cache,
  // the region may have been freed during a cleanup pause, reallocated
  // and tagged as young.
  // We wish to filter out cards for such a region but the current
  // thread, if we're running concurrently, may "see" the young type
  // change at any time (so an earlier "is_young" check may pass or
  // fail arbitrarily). We tell the iteration code to perform this
  // filtering when it has been determined that there has been an actual
  // allocation in this region and making it safe to check the young type.
  bool filter_young = true;

  HeapWord* stop_point =

  // If stop_point is non-null, then we encountered an unallocated region
  // (perhaps the unfilled portion of a TLAB.)  For now, we'll dirty the
  // card and re-enqueue: if we put off the card until a GC pause, then the
  // unallocated portion will be filled in.  Alternatively, we might try
  // the full complexity of the technique used in "regular" precleaning.
  if (stop_point != NULL) {
    // The card might have gotten re-dirtied and re-enqueued while we
    // worked.  (In fact, it's pretty likely.)
    if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
      *card_ptr = CardTableModRefBS::dirty_card_val();
      MutexLockerEx x(Shared_DirtyCardQ_lock,
      DirtyCardQueue* sdcq =
  } else {

  return trigger_cl.value();

bool G1RemSet::concurrentRefineOneCard(jbyte* card_ptr, int worker_i,
                                              bool check_for_refs_into_cset) {
  // If the card is no longer dirty, nothing to do.
  if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
    // No need to return that this card contains refs that point
    // into the collection set.
    return false;

  // Construct the region representing the card.
  HeapWord* start = _ct_bs->addr_for(card_ptr);
  // And find the region containing it.
  HeapRegion* r = _g1->heap_region_containing(start);
  if (r == NULL) {
    guarantee(_g1->is_in_permanent(start), "Or else where?");
    // Again no need to return that this card contains refs that
    // point into the collection set.
    return false;  // Not in the G1 heap (might be in perm, for example.)
  // Why do we have to check here whether a card is on a young region,
  // given that we dirty young regions and, as a result, the
  // post-barrier is supposed to filter them out and never to enqueue
  // them? When we allocate a new region as the "allocation region" we
  // actually dirty its cards after we release the lock, since card
  // dirtying while holding the lock was a performance bottleneck. So,
  // as a result, it is possible for other threads to actually
  // allocate objects in the region (after the acquire the lock)
  // before all the cards on the region are dirtied. This is unlikely,
  // and it doesn't happen often, but it can happen. So, the extra
  // check below filters out those cards.
  if (r->is_young()) {
    return false;
  // While we are processing RSet buffers during the collection, we
  // actually don't want to scan any cards on the collection set,
  // since we don't want to update remebered sets with entries that
  // point into the collection set, given that live objects from the
  // collection set are about to move and such entries will be stale
  // very soon. This change also deals with a reliability issue which
  // involves scanning a card in the collection set and coming across
  // an array that was being chunked and looking malformed. Note,
  // however, that if evacuation fails, we have to scan any objects
  // that were not moved and create any missing entries.
  if (r->in_collection_set()) {
    return false;

  // Should we defer processing the card?
  // Previously the result from the insert_cache call would be
  // either card_ptr (implying that card_ptr was currently "cold"),
  // null (meaning we had inserted the card ptr into the "hot"
  // cache, which had some headroom), or a "hot" card ptr
  // extracted from the "hot" cache.
  // Now that the _card_counts cache in the ConcurrentG1Refine
  // instance is an evicting hash table, the result we get back
  // could be from evicting the card ptr in an already occupied
  // bucket (in which case we have replaced the card ptr in the
  // bucket with card_ptr and "defer" is set to false). To avoid
  // having a data structure (updates to which would need a lock)
  // to hold these unprocessed dirty cards, we need to immediately
  // process card_ptr. The actions needed to be taken on return
  // from cache_insert are summarized in the following table:
  // res      defer   action
  // --------------------------------------------------------------
  // null     false   card evicted from _card_counts & replaced with
  //                  card_ptr; evicted ptr added to hot cache.
  //                  No need to process res; immediately process card_ptr
  // null     true    card not evicted from _card_counts; card_ptr added
  //                  to hot cache.
  //                  Nothing to do.
  // non-null false   card evicted from _card_counts & replaced with
  //                  card_ptr; evicted ptr is currently "cold" or
  //                  caused an eviction from the hot cache.
  //                  Immediately process res; process card_ptr.
  // non-null true    card not evicted from _card_counts; card_ptr is
  //                  currently cold, or caused an eviction from hot
  //                  cache.
  //                  Immediately process res; no need to process card_ptr.

  jbyte* res = card_ptr;
  bool defer = false;

  // This gets set to true if the card being refined has references
  // that point into the collection set.
  bool oops_into_cset = false;

  if (_cg1r->use_cache()) {
    jbyte* res = _cg1r->cache_insert(card_ptr, &defer);
    if (res != NULL && (res != card_ptr || defer)) {
      start = _ct_bs->addr_for(res);
      r = _g1->heap_region_containing(start);
      if (r == NULL) {
        assert(_g1->is_in_permanent(start), "Or else where?");
      } else {
        // Checking whether the region we got back from the cache
        // is young here is inappropriate. The region could have been
        // freed, reallocated and tagged as young while in the cache.
        // Hence we could see its young type change at any time.
        // Process card pointer we get back from the hot card cache. This
        // will check whether the region containing the card is young
        // _after_ checking that the region has been allocated from.
        oops_into_cset = concurrentRefineOneCard_impl(res, worker_i,
                                                      false /* check_for_refs_into_cset */);
        // The above call to concurrentRefineOneCard_impl is only
        // performed if the hot card cache is enabled. This cache is
        // disabled during an evacuation pause - which is the only
        // time when we need know if the card contains references
        // that point into the collection set. Also when the hot card
        // cache is enabled, this code is executed by the concurrent
        // refine threads - rather than the GC worker threads - and
        // concurrentRefineOneCard_impl will return false.
        assert(!oops_into_cset, "should not see true here");

  if (!defer) {
    oops_into_cset =
      concurrentRefineOneCard_impl(card_ptr, worker_i, check_for_refs_into_cset);
    // We should only be detecting that the card contains references
    // that point into the collection set if the current thread is
    // a GC worker thread.
    assert(!oops_into_cset || SafepointSynchronize::is_at_safepoint(),
           "invalid result at non safepoint");
  return oops_into_cset;

class HRRSStatsIter: public HeapRegionClosure {
  size_t _occupied;
  size_t _total_mem_sz;
  size_t _max_mem_sz;
  HeapRegion* _max_mem_sz_region;
  HRRSStatsIter() :

  bool doHeapRegion(HeapRegion* r) {
    if (r->continuesHumongous()) return false;
    size_t mem_sz = r->rem_set()->mem_size();
    if (mem_sz > _max_mem_sz) {
      _max_mem_sz = mem_sz;
      _max_mem_sz_region = r;
    _total_mem_sz += mem_sz;
    size_t occ = r->rem_set()->occupied();
    _occupied += occ;
    return false;
  size_t total_mem_sz() { return _total_mem_sz; }
  size_t max_mem_sz() { return _max_mem_sz; }
  size_t occupied() { return _occupied; }
  HeapRegion* max_mem_sz_region() { return _max_mem_sz_region; }

class PrintRSThreadVTimeClosure : public ThreadClosure {
  virtual void do_thread(Thread *t) {
    ConcurrentG1RefineThread* crt = (ConcurrentG1RefineThread*) t;
    gclog_or_tty->print("    %5.2f", crt->vtime_accum());

void G1RemSet::print_summary_info() {
  G1CollectedHeap* g1 = G1CollectedHeap::heap();

  gclog_or_tty->print_cr("\nG1 card_repeat count histogram: ");
  gclog_or_tty->print_cr("  # of repeats --> # of cards with that number.");

    gclog_or_tty->print_cr("\nG1 rem-set out-of-region histogram: ");
    gclog_or_tty->print_cr("  # of CS ptrs --> # of cards with that number.");
  gclog_or_tty->print_cr("\n Concurrent RS processed %d cards",
  DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
  jint tot_processed_buffers =
    dcqs.processed_buffers_mut() + dcqs.processed_buffers_rs_thread();
  gclog_or_tty->print_cr("  Of %d completed buffers:", tot_processed_buffers);
  gclog_or_tty->print_cr("     %8d (%5.1f%%) by conc RS threads.",
  gclog_or_tty->print_cr("     %8d (%5.1f%%) by mutator threads.",
  gclog_or_tty->print_cr("  Conc RS threads times(s)");
  PrintRSThreadVTimeClosure p;
  gclog_or_tty->print("     ");

  HRRSStatsIter blk;
  gclog_or_tty->print_cr("  Total heap region rem set sizes = " SIZE_FORMAT "K."
                         "  Max = " SIZE_FORMAT "K.",
                         blk.total_mem_sz()/K, blk.max_mem_sz()/K);
  gclog_or_tty->print_cr("  Static structures = " SIZE_FORMAT "K,"
                         " free_lists = " SIZE_FORMAT "K.",
  gclog_or_tty->print_cr("    %d occupied cards represented.",
  gclog_or_tty->print_cr("    Max sz region = [" PTR_FORMAT ", " PTR_FORMAT " )"
                         ", cap = " SIZE_FORMAT "K, occ = " SIZE_FORMAT "K.",
                         blk.max_mem_sz_region()->bottom(), blk.max_mem_sz_region()->end(),
                         (blk.max_mem_sz_region()->rem_set()->mem_size() + K - 1)/K,
                         (blk.max_mem_sz_region()->rem_set()->occupied() + K - 1)/K);
  gclog_or_tty->print_cr("    Did %d coarsenings.", HeapRegionRemSet::n_coarsenings());

void G1RemSet::prepare_for_verify() {
  if (G1HRRSFlushLogBuffersOnVerify &&
      (VerifyBeforeGC || VerifyAfterGC)
      &&  !_g1->full_collection()) {
    if (SafepointSynchronize::is_at_safepoint()) {
      DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
    bool cg1r_use_cache = _cg1r->use_cache();
    DirtyCardQueue into_cset_dcq(&_g1->into_cset_dirty_card_queue_set());
    updateRS(&into_cset_dcq, 0);

    assert(JavaThread::dirty_card_queue_set().completed_buffers_num() == 0, "All should be consumed");