view src/share/vm/gc_implementation/g1/g1EvacFailure.hpp @ 2981:2ace1c4ee8da

6888336: G1: avoid explicitly marking and pushing objects in survivor spaces Summary: This change simplifies the interaction between GC and concurrent marking. By disabling survivor spaces during the initial-mark pause we don't need to propagate marks of objects we copy during each GC (since we never need to copy an explicitly marked object). Reviewed-by: johnc, brutisso
author tonyp
date Tue, 10 Jan 2012 18:58:13 -0500
parents 023652e49ac0
children d30fa85f9994
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 * Copyright (c) 2012, 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 "gc_implementation/g1/concurrentMark.inline.hpp"
#include "gc_implementation/g1/dirtyCardQueue.hpp"
#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
#include "gc_implementation/g1/g1_globals.hpp"
#include "gc_implementation/g1/g1OopClosures.inline.hpp"
#include "gc_implementation/g1/heapRegion.hpp"
#include "gc_implementation/g1/heapRegionRemSet.hpp"
#include "utilities/workgroup.hpp"

// Closures and tasks associated with any self-forwarding pointers
// installed as a result of an evacuation failure.

class UpdateRSetDeferred : public OopsInHeapRegionClosure {
  G1CollectedHeap* _g1;
  DirtyCardQueue *_dcq;
  CardTableModRefBS* _ct_bs;

  UpdateRSetDeferred(G1CollectedHeap* g1, DirtyCardQueue* dcq) :
    _g1(g1), _ct_bs((CardTableModRefBS*)_g1->barrier_set()), _dcq(dcq) {}

  virtual void do_oop(narrowOop* p) { do_oop_work(p); }
  virtual void do_oop(      oop* p) { do_oop_work(p); }
  template <class T> void do_oop_work(T* p) {
    assert(_from->is_in_reserved(p), "paranoia");
    if (!_from->is_in_reserved(oopDesc::load_decode_heap_oop(p)) &&
        !_from->is_survivor()) {
      size_t card_index = _ct_bs->index_for(p);
      if (_ct_bs->mark_card_deferred(card_index)) {

class RemoveSelfForwardPtrObjClosure: public ObjectClosure {
  G1CollectedHeap* _g1;
  ConcurrentMark* _cm;
  HeapRegion* _hr;
  size_t _marked_bytes;
  OopsInHeapRegionClosure *_update_rset_cl;
  bool _during_initial_mark;
  bool _during_conc_mark;
  RemoveSelfForwardPtrObjClosure(G1CollectedHeap* g1, ConcurrentMark* cm,
                                 HeapRegion* hr,
                                 OopsInHeapRegionClosure* update_rset_cl,
                                 bool during_initial_mark,
                                 bool during_conc_mark) :
    _g1(g1), _cm(cm), _hr(hr), _marked_bytes(0),
    _during_conc_mark(during_conc_mark) { }

  size_t marked_bytes() { return _marked_bytes; }

  // <original comment>
  // The original idea here was to coalesce evacuated and dead objects.
  // However that caused complications with the block offset table (BOT).
  // In particular if there were two TLABs, one of them partially refined.
  // |----- TLAB_1--------|----TLAB_2-~~~(partially refined part)~~~|
  // The BOT entries of the unrefined part of TLAB_2 point to the start
  // of TLAB_2. If the last object of the TLAB_1 and the first object
  // of TLAB_2 are coalesced, then the cards of the unrefined part
  // would point into middle of the filler object.
  // The current approach is to not coalesce and leave the BOT contents intact.
  // </original comment>
  // We now reset the BOT when we start the object iteration over the
  // region and refine its entries for every object we come across. So
  // the above comment is not really relevant and we should be able
  // to coalesce dead objects if we want to.
  void do_object(oop obj) {
    HeapWord* obj_addr = (HeapWord*) obj;
    assert(_hr->is_in(obj_addr), "sanity");
    size_t obj_size = obj->size();
    _hr->update_bot_for_object(obj_addr, obj_size);

    if (obj->is_forwarded() && obj->forwardee() == obj) {
      // The object failed to move.

      // We consider all objects that we find self-forwarded to be
      // live. What we'll do is that we'll update the prev marking
      // info so that they are all under PTAMS and explicitly marked.
      if (_during_initial_mark) {
        // For the next marking info we'll only mark the
        // self-forwarded objects explicitly if we are during
        // initial-mark (since, normally, we only mark objects pointed
        // to by roots if we succeed in copying them). By marking all
        // self-forwarded objects we ensure that we mark any that are
        // still pointed to be roots. During concurrent marking, and
        // after initial-mark, we don't need to mark any objects
        // explicitly and all objects in the CSet are considered
        // (implicitly) live. So, we won't mark them explicitly and
        // we'll leave them over NTAMS.
      _marked_bytes += (obj_size * HeapWordSize);

      // While we were processing RSet buffers during the collection,
      // we actually didn't scan any cards on the collection set,
      // since we didn't want to update remembered 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 dealt with a reliability issue which
      // involved scanning a card in the collection set and coming
      // across an array that was being chunked and looking malformed.
      // The problem is that, if evacuation fails, we might have
      // remembered set entries missing given that we skipped cards on
      // the collection set. So, we'll recreate such entries now.
      assert(_cm->isPrevMarked(obj), "Should be marked!");
    } else {
      // The object has been either evacuated or is dead. Fill it with a
      // dummy object.
      MemRegion mr((HeapWord*) obj, obj_size);

class RemoveSelfForwardPtrHRClosure: public HeapRegionClosure {
  G1CollectedHeap* _g1h;
  ConcurrentMark* _cm;
  OopsInHeapRegionClosure *_update_rset_cl;

  RemoveSelfForwardPtrHRClosure(G1CollectedHeap* g1h,
                                OopsInHeapRegionClosure* update_rset_cl) :
    _g1h(g1h), _update_rset_cl(update_rset_cl),
    _cm(_g1h->concurrent_mark()) { }

  bool doHeapRegion(HeapRegion *hr) {
    bool during_initial_mark = _g1h->g1_policy()->during_initial_mark_pause();
    bool during_conc_mark = _g1h->mark_in_progress();

    assert(!hr->isHumongous(), "sanity");
    assert(hr->in_collection_set(), "bad CS");

    if (hr->claimHeapRegion(HeapRegion::ParEvacFailureClaimValue)) {
      if (hr->evacuation_failed()) {
        RemoveSelfForwardPtrObjClosure rspc(_g1h, _cm, hr, _update_rset_cl,

        MemRegion mr(hr->bottom(), hr->end());
        // We'll recreate the prev marking info so we'll first clear
        // the prev bitmap range for this region. We never mark any
        // CSet objects explicitly so the next bitmap range should be
        // cleared anyway.


        // In the common case (i.e. when there is no evacuation
        // failure) we make sure that the following is done when
        // the region is freed so that it is "ready-to-go" when it's
        // re-allocated. However, when evacuation failure happens, a
        // region will remain in the heap and might ultimately be added
        // to a CSet in the future. So we have to be careful here and
        // make sure the region's RSet is ready for parallel iteration
        // whenever this might be required in the future.

    return false;

class G1ParRemoveSelfForwardPtrsTask: public AbstractGangTask {
  G1CollectedHeap* _g1h;

  G1ParRemoveSelfForwardPtrsTask(G1CollectedHeap* g1h) :
    AbstractGangTask("G1 Remove Self-forwarding Pointers"),
    _g1h(g1h) { }

  void work(uint worker_id) {
    UpdateRSetImmediate immediate_update(_g1h->g1_rem_set());
    DirtyCardQueue dcq(&_g1h->dirty_card_queue_set());
    UpdateRSetDeferred deferred_update(_g1h, &dcq);

    OopsInHeapRegionClosure *update_rset_cl = &deferred_update;
    if (!G1DeferredRSUpdate) {
      update_rset_cl = &immediate_update;

    RemoveSelfForwardPtrHRClosure rsfp_cl(_g1h, update_rset_cl);

    HeapRegion* hr = _g1h->start_cset_region_for_worker(worker_id);
    _g1h->collection_set_iterate_from(hr, &rsfp_cl);