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/g1CollectorState.hpp"
30 #include "gc_implementation/g1/g1EvacFailure.hpp"
31 #include "gc_implementation/g1/g1_globals.hpp"
32 #include "gc_implementation/g1/g1OopClosures.inline.hpp"
33 #include "gc_implementation/g1/heapRegion.hpp"
34 #include "gc_implementation/g1/heapRegionRemSet.hpp"
35
36 class UpdateRSetDeferred : public OopsInHeapRegionClosure {
37 private:
38 G1CollectedHeap* _g1;
39 DirtyCardQueue *_dcq;
40 G1SATBCardTableModRefBS* _ct_bs;
41
42 public:
43 UpdateRSetDeferred(G1CollectedHeap* g1, DirtyCardQueue* dcq) :
44 _g1(g1), _ct_bs(_g1->g1_barrier_set()), _dcq(dcq) {}
45
46 virtual void do_oop(narrowOop* p) { do_oop_work(p); }
47 virtual void do_oop( oop* p) { do_oop_work(p); }
48 template <class T> void do_oop_work(T* p) {
49 assert(_from->is_in_reserved(p), "paranoia");
50 if (!_from->is_in_reserved(oopDesc::load_decode_heap_oop(p)) &&
51 !_from->is_survivor()) {
52 size_t card_index = _ct_bs->index_for(p);
53 if (_ct_bs->mark_card_deferred(card_index)) {
54 _dcq->enqueue((jbyte*)_ct_bs->byte_for_index(card_index));
55 }
56 }
57 }
58 };
59
60 class RemoveSelfForwardPtrObjClosure: public ObjectClosure {
61 private:
62 G1CollectedHeap* _g1;
63 ConcurrentMark* _cm;
64 HeapRegion* _hr;
65 size_t _marked_bytes;
66 OopsInHeapRegionClosure *_update_rset_cl;
67 bool _during_initial_mark;
68 bool _during_conc_mark;
69 uint _worker_id;
70 HeapWord* _end_of_last_gap;
71 HeapWord* _last_gap_threshold;
72 HeapWord* _last_obj_threshold;
73
74 public:
75 RemoveSelfForwardPtrObjClosure(G1CollectedHeap* g1, ConcurrentMark* cm,
76 HeapRegion* hr,
77 OopsInHeapRegionClosure* update_rset_cl,
78 bool during_initial_mark,
79 bool during_conc_mark,
80 uint worker_id) :
81 _g1(g1), _cm(cm), _hr(hr), _marked_bytes(0),
82 _update_rset_cl(update_rset_cl),
83 _during_initial_mark(during_initial_mark),
84 _during_conc_mark(during_conc_mark),
85 _worker_id(worker_id),
86 _end_of_last_gap(hr->bottom()),
87 _last_gap_threshold(hr->bottom()),
88 _last_obj_threshold(hr->bottom()) { }
89
90 size_t marked_bytes() { return _marked_bytes; }
91
92 // <original comment>
93 // The original idea here was to coalesce evacuated and dead objects.
94 // However that caused complications with the block offset table (BOT).
95 // In particular if there were two TLABs, one of them partially refined.
96 // |----- TLAB_1--------|----TLAB_2-~~~(partially refined part)~~~|
97 // The BOT entries of the unrefined part of TLAB_2 point to the start
98 // of TLAB_2. If the last object of the TLAB_1 and the first object
99 // of TLAB_2 are coalesced, then the cards of the unrefined part
100 // would point into middle of the filler object.
101 // The current approach is to not coalesce and leave the BOT contents intact.
102 // </original comment>
103 //
104 // We now reset the BOT when we start the object iteration over the
105 // region and refine its entries for every object we come across. So
106 // the above comment is not really relevant and we should be able
107 // to coalesce dead objects if we want to.
108 void do_object(oop obj) {
109 HeapWord* obj_addr = (HeapWord*) obj;
110 assert(_hr->is_in(obj_addr), "sanity");
111 size_t obj_size = obj->size();
112 HeapWord* obj_end = obj_addr + obj_size;
113
114 if (_end_of_last_gap != obj_addr) {
115 // there was a gap before obj_addr
116 _last_gap_threshold = _hr->cross_threshold(_end_of_last_gap, obj_addr);
117 }
118
119 if (obj->is_forwarded() && obj->forwardee() == obj) {
120 // The object failed to move.
121
122 // We consider all objects that we find self-forwarded to be
123 // live. What we'll do is that we'll update the prev marking
124 // info so that they are all under PTAMS and explicitly marked.
125 if (!_cm->isPrevMarked(obj)) {
126 _cm->markPrev(obj);
127 }
128 if (_during_initial_mark) {
129 // For the next marking info we'll only mark the
130 // self-forwarded objects explicitly if we are during
131 // initial-mark (since, normally, we only mark objects pointed
132 // to by roots if we succeed in copying them). By marking all
133 // self-forwarded objects we ensure that we mark any that are
134 // still pointed to be roots. During concurrent marking, and
135 // after initial-mark, we don't need to mark any objects
136 // explicitly and all objects in the CSet are considered
137 // (implicitly) live. So, we won't mark them explicitly and
138 // we'll leave them over NTAMS.
139 _cm->grayRoot(obj, obj_size, _worker_id, _hr);
140 }
141 _marked_bytes += (obj_size * HeapWordSize);
142 obj->set_mark(markOopDesc::prototype());
143
144 // While we were processing RSet buffers during the collection,
145 // we actually didn't scan any cards on the collection set,
146 // since we didn't want to update remembered sets with entries
147 // that point into the collection set, given that live objects
148 // from the collection set are about to move and such entries
149 // will be stale very soon.
150 // This change also dealt with a reliability issue which
151 // involved scanning a card in the collection set and coming
152 // across an array that was being chunked and looking malformed.
153 // The problem is that, if evacuation fails, we might have
154 // remembered set entries missing given that we skipped cards on
155 // the collection set. So, we'll recreate such entries now.
156 obj->oop_iterate(_update_rset_cl);
157 } else {
158
159 // The object has been either evacuated or is dead. Fill it with a
160 // dummy object.
161 MemRegion mr(obj_addr, obj_size);
162 CollectedHeap::fill_with_object(mr);
163
164 // must nuke all dead objects which we skipped when iterating over the region
165 _cm->clearRangePrevBitmap(MemRegion(_end_of_last_gap, obj_end));
166 }
167 _end_of_last_gap = obj_end;
168 _last_obj_threshold = _hr->cross_threshold(obj_addr, obj_end);
169 }
170 };
171
172 class RemoveSelfForwardPtrHRClosure: public HeapRegionClosure {
173 G1CollectedHeap* _g1h;
174 ConcurrentMark* _cm;
175 uint _worker_id;
176 HeapRegionClaimer* _hrclaimer;
177
178 DirtyCardQueue _dcq;
179 UpdateRSetDeferred _update_rset_cl;
180
181 public:
182 RemoveSelfForwardPtrHRClosure(G1CollectedHeap* g1h,
183 uint worker_id,
184 HeapRegionClaimer* hrclaimer) :
185 _g1h(g1h), _dcq(&g1h->dirty_card_queue_set()), _update_rset_cl(g1h, &_dcq),
186 _worker_id(worker_id), _cm(_g1h->concurrent_mark()), _hrclaimer(hrclaimer) {
187 }
188
189 bool doHeapRegion(HeapRegion *hr) {
190 bool during_initial_mark = _g1h->collector_state()->during_initial_mark_pause();
191 bool during_conc_mark = _g1h->collector_state()->mark_in_progress();
192
193 assert(!hr->is_humongous(), "sanity");
194 assert(hr->in_collection_set(), "bad CS");
195
196 if (_hrclaimer->claim_region(hr->hrm_index())) {
197 if (hr->evacuation_failed()) {
198 RemoveSelfForwardPtrObjClosure rspc(_g1h, _cm, hr, &_update_rset_cl,
199 during_initial_mark,
200 during_conc_mark,
201 _worker_id);
202
203 hr->note_self_forwarding_removal_start(during_initial_mark,
204 during_conc_mark);
205 _g1h->check_bitmaps("Self-Forwarding Ptr Removal", hr);
206
207 // In the common case (i.e. when there is no evacuation
208 // failure) we make sure that the following is done when
209 // the region is freed so that it is "ready-to-go" when it's
210 // re-allocated. However, when evacuation failure happens, a
211 // region will remain in the heap and might ultimately be added
212 // to a CSet in the future. So we have to be careful here and
213 // make sure the region's RSet is ready for parallel iteration
214 // whenever this might be required in the future.
215 hr->rem_set()->reset_for_par_iteration();
216 hr->reset_bot();
217 _update_rset_cl.set_region(hr);
218 hr->object_iterate(&rspc);
219
220 hr->rem_set()->clean_strong_code_roots(hr);
221
222 hr->note_self_forwarding_removal_end(during_initial_mark,
223 during_conc_mark,
224 rspc.marked_bytes());
225 }
226 }
227 return false;
228 }
229 };
230
231 G1ParRemoveSelfForwardPtrsTask::G1ParRemoveSelfForwardPtrsTask(G1CollectedHeap* g1h) :
232 AbstractGangTask("G1 Remove Self-forwarding Pointers"), _g1h(g1h),
233 _hrclaimer(g1h->workers()->active_workers()) {}
234
235 void G1ParRemoveSelfForwardPtrsTask::work(uint worker_id) {
236 RemoveSelfForwardPtrHRClosure rsfp_cl(_g1h, worker_id, &_hrclaimer);
237
238 HeapRegion* hr = _g1h->start_cset_region_for_worker(worker_id);
239 _g1h->collection_set_iterate_from(hr, &rsfp_cl);
240 }