1 /*
2 * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc_implementation/g1/concurrentMark.inline.hpp"
27 #include "gc_implementation/g1/dirtyCardQueue.hpp"
28 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
29 #include "gc_implementation/g1/g1EvacFailure.hpp"
30 #include "gc_implementation/g1/g1_globals.hpp"
31 #include "gc_implementation/g1/g1OopClosures.inline.hpp"
32 #include "gc_implementation/g1/heapRegion.hpp"
33 #include "gc_implementation/g1/heapRegionRemSet.hpp"
34
35 // Closures and tasks associated with any self-forwarding pointers
36 // installed as a result of an evacuation failure.
37
38 class UpdateRSetDeferred : public OopsInHeapRegionClosure {
39 private:
40 G1CollectedHeap* _g1;
41 DirtyCardQueue *_dcq;
42 G1SATBCardTableModRefBS* _ct_bs;
43
44 public:
45 UpdateRSetDeferred(G1CollectedHeap* g1, DirtyCardQueue* dcq) :
46 _g1(g1), _ct_bs(_g1->g1_barrier_set()), _dcq(dcq) {}
47
48 virtual void do_oop(narrowOop* p) { do_oop_work(p); }
49 virtual void do_oop( oop* p) { do_oop_work(p); }
50 template <class T> void do_oop_work(T* p) {
51 assert(_from->is_in_reserved(p), "paranoia");
52 if (!_from->is_in_reserved(oopDesc::load_decode_heap_oop(p)) &&
53 !_from->is_survivor()) {
54 size_t card_index = _ct_bs->index_for(p);
55 if (_ct_bs->mark_card_deferred(card_index)) {
56 _dcq->enqueue((jbyte*)_ct_bs->byte_for_index(card_index));
57 }
58 }
59 }
60 };
61
62 class RemoveSelfForwardPtrObjClosure: public ObjectClosure {
63 private:
64 G1CollectedHeap* _g1;
65 ConcurrentMark* _cm;
66 HeapRegion* _hr;
67 size_t _marked_bytes;
68 OopsInHeapRegionClosure *_update_rset_cl;
69 bool _during_initial_mark;
70 bool _during_conc_mark;
71 uint _worker_id;
72 HeapWord* _end_of_last_gap;
73 HeapWord* _last_gap_threshold;
74 HeapWord* _last_obj_threshold;
75
76 public:
77 RemoveSelfForwardPtrObjClosure(G1CollectedHeap* g1, ConcurrentMark* cm,
78 HeapRegion* hr,
79 OopsInHeapRegionClosure* update_rset_cl,
80 bool during_initial_mark,
81 bool during_conc_mark,
82 uint worker_id) :
83 _g1(g1), _cm(cm), _hr(hr), _marked_bytes(0),
84 _update_rset_cl(update_rset_cl),
85 _during_initial_mark(during_initial_mark),
86 _during_conc_mark(during_conc_mark),
87 _worker_id(worker_id),
88 _end_of_last_gap(hr->bottom()),
89 _last_gap_threshold(hr->bottom()),
90 _last_obj_threshold(hr->bottom()) { }
91
92 size_t marked_bytes() { return _marked_bytes; }
93
94 // <original comment>
95 // The original idea here was to coalesce evacuated and dead objects.
96 // However that caused complications with the block offset table (BOT).
97 // In particular if there were two TLABs, one of them partially refined.
98 // |----- TLAB_1--------|----TLAB_2-~~~(partially refined part)~~~|
99 // The BOT entries of the unrefined part of TLAB_2 point to the start
100 // of TLAB_2. If the last object of the TLAB_1 and the first object
101 // of TLAB_2 are coalesced, then the cards of the unrefined part
102 // would point into middle of the filler object.
103 // The current approach is to not coalesce and leave the BOT contents intact.
104 // </original comment>
105 //
106 // We now reset the BOT when we start the object iteration over the
107 // region and refine its entries for every object we come across. So
108 // the above comment is not really relevant and we should be able
109 // to coalesce dead objects if we want to.
110 void do_object(oop obj) {
111 HeapWord* obj_addr = (HeapWord*) obj;
112 assert(_hr->is_in(obj_addr), "sanity");
113 size_t obj_size = obj->size();
114 HeapWord* obj_end = obj_addr + obj_size;
115
116 if (_end_of_last_gap != obj_addr) {
117 // there was a gap before obj_addr
118 _last_gap_threshold = _hr->cross_threshold(_end_of_last_gap, obj_addr);
119 }
120
121 if (obj->is_forwarded() && obj->forwardee() == obj) {
122 // The object failed to move.
123
124 // We consider all objects that we find self-forwarded to be
125 // live. What we'll do is that we'll update the prev marking
126 // info so that they are all under PTAMS and explicitly marked.
127 if (!_cm->isPrevMarked(obj)) {
128 _cm->markPrev(obj);
129 }
130 if (_during_initial_mark) {
131 // For the next marking info we'll only mark the
132 // self-forwarded objects explicitly if we are during
133 // initial-mark (since, normally, we only mark objects pointed
134 // to by roots if we succeed in copying them). By marking all
135 // self-forwarded objects we ensure that we mark any that are
136 // still pointed to be roots. During concurrent marking, and
137 // after initial-mark, we don't need to mark any objects
138 // explicitly and all objects in the CSet are considered
139 // (implicitly) live. So, we won't mark them explicitly and
140 // we'll leave them over NTAMS.
141 _cm->grayRoot(obj, obj_size, _worker_id, _hr);
142 }
143 _marked_bytes += (obj_size * HeapWordSize);
144 obj->set_mark(markOopDesc::prototype());
145
146 // While we were processing RSet buffers during the collection,
147 // we actually didn't scan any cards on the collection set,
148 // since we didn't want to update remembered sets with entries
149 // that point into the collection set, given that live objects
150 // from the collection set are about to move and such entries
151 // will be stale very soon.
152 // This change also dealt with a reliability issue which
153 // involved scanning a card in the collection set and coming
154 // across an array that was being chunked and looking malformed.
155 // The problem is that, if evacuation fails, we might have
156 // remembered set entries missing given that we skipped cards on
157 // the collection set. So, we'll recreate such entries now.
158 obj->oop_iterate(_update_rset_cl);
159 } else {
160
161 // The object has been either evacuated or is dead. Fill it with a
162 // dummy object.
163 MemRegion mr(obj_addr, obj_size);
164 CollectedHeap::fill_with_object(mr);
165
166 // must nuke all dead objects which we skipped when iterating over the region
167 _cm->clearRangePrevBitmap(MemRegion(_end_of_last_gap, obj_end));
168 }
169 _end_of_last_gap = obj_end;
170 _last_obj_threshold = _hr->cross_threshold(obj_addr, obj_end);
171 }
172 };
173
174 class RemoveSelfForwardPtrHRClosure: public HeapRegionClosure {
175 G1CollectedHeap* _g1h;
176 ConcurrentMark* _cm;
177 uint _worker_id;
178 HeapRegionClaimer* _hrclaimer;
179
180 DirtyCardQueue _dcq;
181 UpdateRSetDeferred _update_rset_cl;
182
183 public:
184 RemoveSelfForwardPtrHRClosure(G1CollectedHeap* g1h,
185 uint worker_id,
186 HeapRegionClaimer* hrclaimer) :
187 _g1h(g1h), _dcq(&g1h->dirty_card_queue_set()), _update_rset_cl(g1h, &_dcq),
188 _worker_id(worker_id), _cm(_g1h->concurrent_mark()), _hrclaimer(hrclaimer) {
189 }
190
191 bool doHeapRegion(HeapRegion *hr) {
192 bool during_initial_mark = _g1h->g1_policy()->during_initial_mark_pause();
193 bool during_conc_mark = _g1h->mark_in_progress();
194
195 assert(!hr->is_humongous(), "sanity");
196 assert(hr->in_collection_set(), "bad CS");
197
198 if (_hrclaimer->claim_region(hr->hrm_index())) {
199 if (hr->evacuation_failed()) {
200 RemoveSelfForwardPtrObjClosure rspc(_g1h, _cm, hr, &_update_rset_cl,
201 during_initial_mark,
202 during_conc_mark,
203 _worker_id);
204
205 hr->note_self_forwarding_removal_start(during_initial_mark,
206 during_conc_mark);
207 _g1h->check_bitmaps("Self-Forwarding Ptr Removal", hr);
208
209 // In the common case (i.e. when there is no evacuation
210 // failure) we make sure that the following is done when
211 // the region is freed so that it is "ready-to-go" when it's
212 // re-allocated. However, when evacuation failure happens, a
213 // region will remain in the heap and might ultimately be added
214 // to a CSet in the future. So we have to be careful here and
215 // make sure the region's RSet is ready for parallel iteration
216 // whenever this might be required in the future.
217 hr->rem_set()->reset_for_par_iteration();
218 hr->reset_bot();
219 _update_rset_cl.set_region(hr);
220 hr->object_iterate(&rspc);
221
222 hr->rem_set()->clean_strong_code_roots(hr);
223
224 hr->note_self_forwarding_removal_end(during_initial_mark,
225 during_conc_mark,
226 rspc.marked_bytes());
227 }
228 }
229 return false;
230 }
231 };
232
233 G1ParRemoveSelfForwardPtrsTask::G1ParRemoveSelfForwardPtrsTask(G1CollectedHeap* g1h) :
234 AbstractGangTask("G1 Remove Self-forwarding Pointers"), _g1h(g1h),
235 _hrclaimer(g1h->workers()->active_workers()) {}
236
237 void G1ParRemoveSelfForwardPtrsTask::work(uint worker_id) {
238 RemoveSelfForwardPtrHRClosure rsfp_cl(_g1h, worker_id, &_hrclaimer);
239
240 HeapRegion* hr = _g1h->start_cset_region_for_worker(worker_id);
241 _g1h->collection_set_iterate_from(hr, &rsfp_cl);
242 }