view hotspot/src/share/vm/gc_implementation/g1/g1EvacFailure.hpp @ 26701:f8ff74a6c058

8052172: Evacuation failure handling in G1 does not evacuate all objects if -XX:-G1DeferredRSUpdate is set Summary: Remove -XX:-G1DeferredRSUpdate functionality as it is racy. During evacuation failure handling, threads where evacuation failure handling occurred may try to add remembered sets to regions which remembered sets are currently being scanned. The iterator to handle the remembered set scan does not support addition of entries during scan and so may skip valid references. Reviewed-by: iveresov, brutisso, mgerdin
author tschatzl
date Tue, 16 Sep 2014 10:28:15 +0200
parents 4ee5901e205e
children 7d4376f8560e
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 * Copyright (c) 2012, 2013, 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;
  G1SATBCardTableModRefBS* _ct_bs;

  UpdateRSetDeferred(G1CollectedHeap* g1, DirtyCardQueue* dcq) :
    _g1(g1), _ct_bs(_g1->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;
  uint _worker_id;
  HeapWord* _end_of_last_gap;
  HeapWord* _last_gap_threshold;
  HeapWord* _last_obj_threshold;

  RemoveSelfForwardPtrObjClosure(G1CollectedHeap* g1, ConcurrentMark* cm,
                                 HeapRegion* hr,
                                 OopsInHeapRegionClosure* update_rset_cl,
                                 bool during_initial_mark,
                                 bool during_conc_mark,
                                 uint worker_id) :
    _g1(g1), _cm(cm), _hr(hr), _marked_bytes(0),
    _last_obj_threshold(hr->bottom()) { }

  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();
    HeapWord* obj_end = obj_addr + obj_size;

    if (_end_of_last_gap != obj_addr) {
      // there was a gap before obj_addr
      _last_gap_threshold = _hr->cross_threshold(_end_of_last_gap, obj_addr);

    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 (!_cm->isPrevMarked(obj)) {
      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.
        _cm->grayRoot(obj, obj_size, _worker_id, _hr);
      _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.
    } else {

      // The object has been either evacuated or is dead. Fill it with a
      // dummy object.
      MemRegion mr(obj_addr, obj_size);

      // must nuke all dead objects which we skipped when iterating over the region
      _cm->clearRangePrevBitmap(MemRegion(_end_of_last_gap, obj_end));
    _end_of_last_gap = obj_end;
    _last_obj_threshold = _hr->cross_threshold(obj_addr, obj_end);

class RemoveSelfForwardPtrHRClosure: public HeapRegionClosure {
  G1CollectedHeap* _g1h;
  ConcurrentMark* _cm;
  uint _worker_id;

  DirtyCardQueue _dcq;
  UpdateRSetDeferred _update_rset_cl;

  RemoveSelfForwardPtrHRClosure(G1CollectedHeap* g1h,
                                uint worker_id) :
    _g1h(g1h), _dcq(&g1h->dirty_card_queue_set()), _update_rset_cl(g1h, &_dcq),
    _worker_id(worker_id), _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,

        _g1h->check_bitmaps("Self-Forwarding Ptr Removal", hr);

        // 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) {
    RemoveSelfForwardPtrHRClosure rsfp_cl(_g1h, worker_id);

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