Thu, 21 Aug 2014 16:44:41 +0200
8055098: WB API should be extended to provide information about size and age of object.
Summary: Extend the WhiteBox API to provide information about the size and age of objects. Further add a mechanism to trigger a young GC.
Reviewed-by: tschatzl, sjohanss
Contributed-by: Leonid Mesnik <leonid.mesnik@oracle.com>
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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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 *
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23 */
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1EVACFAILURE_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1EVACFAILURE_HPP
28 #include "gc_implementation/g1/concurrentMark.inline.hpp"
29 #include "gc_implementation/g1/dirtyCardQueue.hpp"
30 #include "gc_implementation/g1/g1CollectedHeap.inline.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 #include "utilities/workgroup.hpp"
37 // Closures and tasks associated with any self-forwarding pointers
38 // installed as a result of an evacuation failure.
40 class UpdateRSetDeferred : public OopsInHeapRegionClosure {
41 private:
42 G1CollectedHeap* _g1;
43 DirtyCardQueue *_dcq;
44 G1SATBCardTableModRefBS* _ct_bs;
46 public:
47 UpdateRSetDeferred(G1CollectedHeap* g1, DirtyCardQueue* dcq) :
48 _g1(g1), _ct_bs(_g1->g1_barrier_set()), _dcq(dcq) {}
50 virtual void do_oop(narrowOop* p) { do_oop_work(p); }
51 virtual void do_oop( oop* p) { do_oop_work(p); }
52 template <class T> void do_oop_work(T* p) {
53 assert(_from->is_in_reserved(p), "paranoia");
54 if (!_from->is_in_reserved(oopDesc::load_decode_heap_oop(p)) &&
55 !_from->is_survivor()) {
56 size_t card_index = _ct_bs->index_for(p);
57 if (_ct_bs->mark_card_deferred(card_index)) {
58 _dcq->enqueue((jbyte*)_ct_bs->byte_for_index(card_index));
59 }
60 }
61 }
62 };
64 class RemoveSelfForwardPtrObjClosure: public ObjectClosure {
65 private:
66 G1CollectedHeap* _g1;
67 ConcurrentMark* _cm;
68 HeapRegion* _hr;
69 size_t _marked_bytes;
70 OopsInHeapRegionClosure *_update_rset_cl;
71 bool _during_initial_mark;
72 bool _during_conc_mark;
73 uint _worker_id;
74 HeapWord* _end_of_last_gap;
75 HeapWord* _last_gap_threshold;
76 HeapWord* _last_obj_threshold;
78 public:
79 RemoveSelfForwardPtrObjClosure(G1CollectedHeap* g1, ConcurrentMark* cm,
80 HeapRegion* hr,
81 OopsInHeapRegionClosure* update_rset_cl,
82 bool during_initial_mark,
83 bool during_conc_mark,
84 uint worker_id) :
85 _g1(g1), _cm(cm), _hr(hr), _marked_bytes(0),
86 _update_rset_cl(update_rset_cl),
87 _during_initial_mark(during_initial_mark),
88 _during_conc_mark(during_conc_mark),
89 _worker_id(worker_id),
90 _end_of_last_gap(hr->bottom()),
91 _last_gap_threshold(hr->bottom()),
92 _last_obj_threshold(hr->bottom()) { }
94 size_t marked_bytes() { return _marked_bytes; }
96 // <original comment>
97 // The original idea here was to coalesce evacuated and dead objects.
98 // However that caused complications with the block offset table (BOT).
99 // In particular if there were two TLABs, one of them partially refined.
100 // |----- TLAB_1--------|----TLAB_2-~~~(partially refined part)~~~|
101 // The BOT entries of the unrefined part of TLAB_2 point to the start
102 // of TLAB_2. If the last object of the TLAB_1 and the first object
103 // of TLAB_2 are coalesced, then the cards of the unrefined part
104 // would point into middle of the filler object.
105 // The current approach is to not coalesce and leave the BOT contents intact.
106 // </original comment>
107 //
108 // We now reset the BOT when we start the object iteration over the
109 // region and refine its entries for every object we come across. So
110 // the above comment is not really relevant and we should be able
111 // to coalesce dead objects if we want to.
112 void do_object(oop obj) {
113 HeapWord* obj_addr = (HeapWord*) obj;
114 assert(_hr->is_in(obj_addr), "sanity");
115 size_t obj_size = obj->size();
116 HeapWord* obj_end = obj_addr + obj_size;
118 if (_end_of_last_gap != obj_addr) {
119 // there was a gap before obj_addr
120 _last_gap_threshold = _hr->cross_threshold(_end_of_last_gap, obj_addr);
121 }
123 if (obj->is_forwarded() && obj->forwardee() == obj) {
124 // The object failed to move.
126 // We consider all objects that we find self-forwarded to be
127 // live. What we'll do is that we'll update the prev marking
128 // info so that they are all under PTAMS and explicitly marked.
129 if (!_cm->isPrevMarked(obj)) {
130 _cm->markPrev(obj);
131 }
132 if (_during_initial_mark) {
133 // For the next marking info we'll only mark the
134 // self-forwarded objects explicitly if we are during
135 // initial-mark (since, normally, we only mark objects pointed
136 // to by roots if we succeed in copying them). By marking all
137 // self-forwarded objects we ensure that we mark any that are
138 // still pointed to be roots. During concurrent marking, and
139 // after initial-mark, we don't need to mark any objects
140 // explicitly and all objects in the CSet are considered
141 // (implicitly) live. So, we won't mark them explicitly and
142 // we'll leave them over NTAMS.
143 _cm->grayRoot(obj, obj_size, _worker_id, _hr);
144 }
145 _marked_bytes += (obj_size * HeapWordSize);
146 obj->set_mark(markOopDesc::prototype());
148 // While we were processing RSet buffers during the collection,
149 // we actually didn't scan any cards on the collection set,
150 // since we didn't want to update remembered sets with entries
151 // that point into the collection set, given that live objects
152 // from the collection set are about to move and such entries
153 // will be stale very soon.
154 // This change also dealt with a reliability issue which
155 // involved scanning a card in the collection set and coming
156 // across an array that was being chunked and looking malformed.
157 // The problem is that, if evacuation fails, we might have
158 // remembered set entries missing given that we skipped cards on
159 // the collection set. So, we'll recreate such entries now.
160 obj->oop_iterate(_update_rset_cl);
161 } else {
163 // The object has been either evacuated or is dead. Fill it with a
164 // dummy object.
165 MemRegion mr(obj_addr, obj_size);
166 CollectedHeap::fill_with_object(mr);
168 // must nuke all dead objects which we skipped when iterating over the region
169 _cm->clearRangePrevBitmap(MemRegion(_end_of_last_gap, obj_end));
170 }
171 _end_of_last_gap = obj_end;
172 _last_obj_threshold = _hr->cross_threshold(obj_addr, obj_end);
173 }
174 };
176 class RemoveSelfForwardPtrHRClosure: public HeapRegionClosure {
177 G1CollectedHeap* _g1h;
178 ConcurrentMark* _cm;
179 OopsInHeapRegionClosure *_update_rset_cl;
180 uint _worker_id;
182 public:
183 RemoveSelfForwardPtrHRClosure(G1CollectedHeap* g1h,
184 OopsInHeapRegionClosure* update_rset_cl,
185 uint worker_id) :
186 _g1h(g1h), _update_rset_cl(update_rset_cl),
187 _worker_id(worker_id), _cm(_g1h->concurrent_mark()) { }
189 bool doHeapRegion(HeapRegion *hr) {
190 bool during_initial_mark = _g1h->g1_policy()->during_initial_mark_pause();
191 bool during_conc_mark = _g1h->mark_in_progress();
193 assert(!hr->isHumongous(), "sanity");
194 assert(hr->in_collection_set(), "bad CS");
196 if (hr->claimHeapRegion(HeapRegion::ParEvacFailureClaimValue)) {
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);
203 hr->note_self_forwarding_removal_start(during_initial_mark,
204 during_conc_mark);
205 _g1h->check_bitmaps("Self-Forwarding Ptr Removal", hr);
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);
220 hr->note_self_forwarding_removal_end(during_initial_mark,
221 during_conc_mark,
222 rspc.marked_bytes());
223 }
224 }
225 return false;
226 }
227 };
229 class G1ParRemoveSelfForwardPtrsTask: public AbstractGangTask {
230 protected:
231 G1CollectedHeap* _g1h;
233 public:
234 G1ParRemoveSelfForwardPtrsTask(G1CollectedHeap* g1h) :
235 AbstractGangTask("G1 Remove Self-forwarding Pointers"),
236 _g1h(g1h) { }
238 void work(uint worker_id) {
239 UpdateRSetImmediate immediate_update(_g1h->g1_rem_set());
240 DirtyCardQueue dcq(&_g1h->dirty_card_queue_set());
241 UpdateRSetDeferred deferred_update(_g1h, &dcq);
243 OopsInHeapRegionClosure *update_rset_cl = &deferred_update;
244 if (!G1DeferredRSUpdate) {
245 update_rset_cl = &immediate_update;
246 }
248 RemoveSelfForwardPtrHRClosure rsfp_cl(_g1h, update_rset_cl, worker_id);
250 HeapRegion* hr = _g1h->start_cset_region_for_worker(worker_id);
251 _g1h->collection_set_iterate_from(hr, &rsfp_cl);
252 }
253 };
255 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1EVACFAILURE_HPP