g1EvacFailure.cpp revision 8413:92457dfb91bd 
1/*
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23 */
24
25#include "precompiled.hpp"
26#include "gc/g1/concurrentMark.inline.hpp"
27#include "gc/g1/dirtyCardQueue.hpp"
28#include "gc/g1/g1CollectedHeap.inline.hpp"
29#include "gc/g1/g1EvacFailure.hpp"
30#include "gc/g1/g1OopClosures.inline.hpp"
31#include "gc/g1/g1_globals.hpp"
32#include "gc/g1/heapRegion.hpp"
33#include "gc/g1/heapRegionRemSet.hpp"
34
35class UpdateRSetDeferred : public OopsInHeapRegionClosure {
36private:
37  G1CollectedHeap* _g1;
38  DirtyCardQueue *_dcq;
39  G1SATBCardTableModRefBS* _ct_bs;
40
41public:
42  UpdateRSetDeferred(G1CollectedHeap* g1, DirtyCardQueue* dcq) :
43    _g1(g1), _ct_bs(_g1->g1_barrier_set()), _dcq(dcq) {}
44
45  virtual void do_oop(narrowOop* p) { do_oop_work(p); }
46  virtual void do_oop(      oop* p) { do_oop_work(p); }
47  template <class T> void do_oop_work(T* p) {
48    assert(_from->is_in_reserved(p), "paranoia");
49    if (!_from->is_in_reserved(oopDesc::load_decode_heap_oop(p)) &&
50        !_from->is_survivor()) {
51      size_t card_index = _ct_bs->index_for(p);
52      if (_ct_bs->mark_card_deferred(card_index)) {
53        _dcq->enqueue((jbyte*)_ct_bs->byte_for_index(card_index));
54      }
55    }
56  }
57};
58
59class RemoveSelfForwardPtrObjClosure: public ObjectClosure {
60private:
61  G1CollectedHeap* _g1;
62  ConcurrentMark* _cm;
63  HeapRegion* _hr;
64  size_t _marked_bytes;
65  OopsInHeapRegionClosure *_update_rset_cl;
66  bool _during_initial_mark;
67  bool _during_conc_mark;
68  uint _worker_id;
69  HeapWord* _end_of_last_gap;
70  HeapWord* _last_gap_threshold;
71  HeapWord* _last_obj_threshold;
72
73public:
74  RemoveSelfForwardPtrObjClosure(G1CollectedHeap* g1, ConcurrentMark* cm,
75                                 HeapRegion* hr,
76                                 OopsInHeapRegionClosure* update_rset_cl,
77                                 bool during_initial_mark,
78                                 bool during_conc_mark,
79                                 uint worker_id) :
80    _g1(g1), _cm(cm), _hr(hr), _marked_bytes(0),
81    _update_rset_cl(update_rset_cl),
82    _during_initial_mark(during_initial_mark),
83    _during_conc_mark(during_conc_mark),
84    _worker_id(worker_id),
85    _end_of_last_gap(hr->bottom()),
86    _last_gap_threshold(hr->bottom()),
87    _last_obj_threshold(hr->bottom()) { }
88
89  size_t marked_bytes() { return _marked_bytes; }
90
91  // <original comment>
92  // The original idea here was to coalesce evacuated and dead objects.
93  // However that caused complications with the block offset table (BOT).
94  // In particular if there were two TLABs, one of them partially refined.
95  // |----- TLAB_1--------|----TLAB_2-~~~(partially refined part)~~~|
96  // The BOT entries of the unrefined part of TLAB_2 point to the start
97  // of TLAB_2. If the last object of the TLAB_1 and the first object
98  // of TLAB_2 are coalesced, then the cards of the unrefined part
99  // would point into middle of the filler object.
100  // The current approach is to not coalesce and leave the BOT contents intact.
101  // </original comment>
102  //
103  // We now reset the BOT when we start the object iteration over the
104  // region and refine its entries for every object we come across. So
105  // the above comment is not really relevant and we should be able
106  // to coalesce dead objects if we want to.
107  void do_object(oop obj) {
108    HeapWord* obj_addr = (HeapWord*) obj;
109    assert(_hr->is_in(obj_addr), "sanity");
110    size_t obj_size = obj->size();
111    HeapWord* obj_end = obj_addr + obj_size;
112
113    if (_end_of_last_gap != obj_addr) {
114      // there was a gap before obj_addr
115      _last_gap_threshold = _hr->cross_threshold(_end_of_last_gap, obj_addr);
116    }
117
118    if (obj->is_forwarded() && obj->forwardee() == obj) {
119      // The object failed to move.
120
121      // We consider all objects that we find self-forwarded to be
122      // live. What we'll do is that we'll update the prev marking
123      // info so that they are all under PTAMS and explicitly marked.
124      if (!_cm->isPrevMarked(obj)) {
125        _cm->markPrev(obj);
126      }
127      if (_during_initial_mark) {
128        // For the next marking info we'll only mark the
129        // self-forwarded objects explicitly if we are during
130        // initial-mark (since, normally, we only mark objects pointed
131        // to by roots if we succeed in copying them). By marking all
132        // self-forwarded objects we ensure that we mark any that are
133        // still pointed to be roots. During concurrent marking, and
134        // after initial-mark, we don't need to mark any objects
135        // explicitly and all objects in the CSet are considered
136        // (implicitly) live. So, we won't mark them explicitly and
137        // we'll leave them over NTAMS.
138        _cm->grayRoot(obj, obj_size, _worker_id, _hr);
139      }
140      _marked_bytes += (obj_size * HeapWordSize);
141      obj->set_mark(markOopDesc::prototype());
142
143      // While we were processing RSet buffers during the collection,
144      // we actually didn't scan any cards on the collection set,
145      // since we didn't want to update remembered sets with entries
146      // that point into the collection set, given that live objects
147      // from the collection set are about to move and such entries
148      // will be stale very soon.
149      // This change also dealt with a reliability issue which
150      // involved scanning a card in the collection set and coming
151      // across an array that was being chunked and looking malformed.
152      // The problem is that, if evacuation fails, we might have
153      // remembered set entries missing given that we skipped cards on
154      // the collection set. So, we'll recreate such entries now.
155      obj->oop_iterate(_update_rset_cl);
156    } else {
157
158      // The object has been either evacuated or is dead. Fill it with a
159      // dummy object.
160      MemRegion mr(obj_addr, obj_size);
161      CollectedHeap::fill_with_object(mr);
162
163      // must nuke all dead objects which we skipped when iterating over the region
164      _cm->clearRangePrevBitmap(MemRegion(_end_of_last_gap, obj_end));
165    }
166    _end_of_last_gap = obj_end;
167    _last_obj_threshold = _hr->cross_threshold(obj_addr, obj_end);
168  }
169};
170
171class RemoveSelfForwardPtrHRClosure: public HeapRegionClosure {
172  G1CollectedHeap* _g1h;
173  ConcurrentMark* _cm;
174  uint _worker_id;
175  HeapRegionClaimer* _hrclaimer;
176
177  DirtyCardQueue _dcq;
178  UpdateRSetDeferred _update_rset_cl;
179
180public:
181  RemoveSelfForwardPtrHRClosure(G1CollectedHeap* g1h,
182                                uint worker_id,
183                                HeapRegionClaimer* hrclaimer) :
184      _g1h(g1h), _dcq(&g1h->dirty_card_queue_set()), _update_rset_cl(g1h, &_dcq),
185      _worker_id(worker_id), _cm(_g1h->concurrent_mark()), _hrclaimer(hrclaimer) {
186  }
187
188  bool doHeapRegion(HeapRegion *hr) {
189    bool during_initial_mark = _g1h->g1_policy()->during_initial_mark_pause();
190    bool during_conc_mark = _g1h->mark_in_progress();
191
192    assert(!hr->is_humongous(), "sanity");
193    assert(hr->in_collection_set(), "bad CS");
194
195    if (_hrclaimer->claim_region(hr->hrm_index())) {
196      if (hr->evacuation_failed()) {
197        RemoveSelfForwardPtrObjClosure rspc(_g1h, _cm, hr, &_update_rset_cl,
198                                            during_initial_mark,
199                                            during_conc_mark,
200                                            _worker_id);
201
202        hr->note_self_forwarding_removal_start(during_initial_mark,
203                                               during_conc_mark);
204        _g1h->check_bitmaps("Self-Forwarding Ptr Removal", hr);
205
206        // In the common case (i.e. when there is no evacuation
207        // failure) we make sure that the following is done when
208        // the region is freed so that it is "ready-to-go" when it's
209        // re-allocated. However, when evacuation failure happens, a
210        // region will remain in the heap and might ultimately be added
211        // to a CSet in the future. So we have to be careful here and
212        // make sure the region's RSet is ready for parallel iteration
213        // whenever this might be required in the future.
214        hr->rem_set()->reset_for_par_iteration();
215        hr->reset_bot();
216        _update_rset_cl.set_region(hr);
217        hr->object_iterate(&rspc);
218
219        hr->rem_set()->clean_strong_code_roots(hr);
220
221        hr->note_self_forwarding_removal_end(during_initial_mark,
222                                             during_conc_mark,
223                                             rspc.marked_bytes());
224      }
225    }
226    return false;
227  }
228};
229
230G1ParRemoveSelfForwardPtrsTask::G1ParRemoveSelfForwardPtrsTask(G1CollectedHeap* g1h) :
231    AbstractGangTask("G1 Remove Self-forwarding Pointers"), _g1h(g1h),
232    _hrclaimer(g1h->workers()->active_workers()) {}
233
234void G1ParRemoveSelfForwardPtrsTask::work(uint worker_id) {
235  RemoveSelfForwardPtrHRClosure rsfp_cl(_g1h, worker_id, &_hrclaimer);
236
237  HeapRegion* hr = _g1h->start_cset_region_for_worker(worker_id);
238  _g1h->collection_set_iterate_from(hr, &rsfp_cl);
239}
240