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/g1/concurrentMark.inline.hpp"
  27 #include "gc/g1/dirtyCardQueue.hpp"
  28 #include "gc/g1/g1CollectedHeap.inline.hpp"
  29 #include "gc/g1/g1CollectorState.hpp"
  30 #include "gc/g1/g1EvacFailure.hpp"
  31 #include "gc/g1/g1OopClosures.inline.hpp"
  32 #include "gc/g1/g1_globals.hpp"
  33 #include "gc/g1/heapRegion.hpp"
  34 #include "gc/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(DirtyCardQueue* dcq) :
  44     _g1(G1CollectedHeap::heap()), _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   uint _worker_id;
  69   HeapWord* _last_forwarded_object_end;
  70 
  71 public:
  72   RemoveSelfForwardPtrObjClosure(HeapRegion* hr,
  73                                  OopsInHeapRegionClosure* update_rset_cl,
  74                                  bool during_initial_mark,
  75                                  uint worker_id) :
  76     _g1(G1CollectedHeap::heap()),
  77     _cm(_g1->concurrent_mark()),
  78     _hr(hr),
  79     _marked_bytes(0),
  80     _update_rset_cl(update_rset_cl),
  81     _during_initial_mark(during_initial_mark),
  82     _worker_id(worker_id),
  83     _last_forwarded_object_end(hr->bottom()) { }
  84 
  85   size_t marked_bytes() { return _marked_bytes; }
  86 
  87   // Iterate over the live objects in the region to find self-forwarded objects
  88   // that need to be kept live. We need to update the remembered sets of these
  89   // objects. Further update the BOT and marks.
  90   // We can coalesce and overwrite the remaining heap contents with dummy objects
  91   // as they have either been dead or evacuated (which are unreferenced now, i.e.
  92   // dead too) already.
  93   void do_object(oop obj) {
  94     HeapWord* obj_addr = (HeapWord*) obj;
  95     assert(_hr->is_in(obj_addr), "sanity");
  96     size_t obj_size = obj->size();
  97     HeapWord* obj_end = obj_addr + obj_size;
  98 
  99     if (obj->is_forwarded() && obj->forwardee() == obj) {
 100       // The object failed to move.
 101 
 102       zap_dead_objects(_last_forwarded_object_end, obj_addr);
 103       // We consider all objects that we find self-forwarded to be
 104       // live. What we'll do is that we'll update the prev marking
 105       // info so that they are all under PTAMS and explicitly marked.
 106       if (!_cm->isPrevMarked(obj)) {
 107         _cm->markPrev(obj);
 108       }
 109       if (_during_initial_mark) {
 110         // For the next marking info we'll only mark the
 111         // self-forwarded objects explicitly if we are during
 112         // initial-mark (since, normally, we only mark objects pointed
 113         // to by roots if we succeed in copying them). By marking all
 114         // self-forwarded objects we ensure that we mark any that are
 115         // still pointed to be roots. During concurrent marking, and
 116         // after initial-mark, we don't need to mark any objects
 117         // explicitly and all objects in the CSet are considered
 118         // (implicitly) live. So, we won't mark them explicitly and
 119         // we'll leave them over NTAMS.
 120         _cm->grayRoot(obj, obj_size, _worker_id, _hr);
 121       }
 122       _marked_bytes += (obj_size * HeapWordSize);
 123       obj->set_mark(markOopDesc::prototype());
 124 
 125       // While we were processing RSet buffers during the collection,
 126       // we actually didn't scan any cards on the collection set,
 127       // since we didn't want to update remembered sets with entries
 128       // that point into the collection set, given that live objects
 129       // from the collection set are about to move and such entries
 130       // will be stale very soon.
 131       // This change also dealt with a reliability issue which
 132       // involved scanning a card in the collection set and coming
 133       // across an array that was being chunked and looking malformed.
 134       // The problem is that, if evacuation fails, we might have
 135       // remembered set entries missing given that we skipped cards on
 136       // the collection set. So, we'll recreate such entries now.
 137       obj->oop_iterate(_update_rset_cl);
 138 
 139       _last_forwarded_object_end = obj_end;
 140       _hr->cross_threshold(obj_addr, obj_end);
 141     }
 142   }
 143 
 144   // Fill the memory area from start to end with filler objects, and update the BOT
 145   // and the mark bitmap accordingly.
 146   void zap_dead_objects(HeapWord* start, HeapWord* end) {
 147     if (start == end) {
 148       return;
 149     }
 150 
 151     size_t gap_size = pointer_delta(end, start);
 152     MemRegion mr(start, gap_size);
 153     if (gap_size >= CollectedHeap::min_fill_size()) {
 154       G1CollectedHeap::fill_with_non_humongous_objects(start, gap_size);
 155 
 156       HeapWord* end_first_obj = start + ((oop)start)->size();
 157       _hr->cross_threshold(start, end_first_obj);
 158       // Fill_with_objects() may have created multiple (i.e. two)
 159       // objects, as the max_fill_size() is half a region.
 160       // After updating the BOT for the first object, also update the
 161       // BOT for the second object to make the BOT complete.
 162       if (end_first_obj != end) {
 163         _hr->cross_threshold(end_first_obj, end);
 164 #ifdef ASSERT
 165         size_t size_second_obj = ((oop)end_first_obj)->size();
 166         HeapWord* end_of_second_obj = end_first_obj + size_second_obj;
 167         assert(end == end_of_second_obj,
 168                "More than two objects were used to fill the area from " PTR_FORMAT " to " PTR_FORMAT ", "
 169                "second objects size " SIZE_FORMAT " ends at " PTR_FORMAT,
 170                p2i(start), p2i(end), size_second_obj, p2i(end_of_second_obj));
 171 #endif
 172       }
 173     }
 174     _cm->clearRangePrevBitmap(mr);
 175   }
 176 
 177   void zap_remainder() {
 178     zap_dead_objects(_last_forwarded_object_end, _hr->top());
 179   }
 180 };
 181 
 182 class RemoveSelfForwardPtrHRClosure: public HeapRegionClosure {
 183   G1CollectedHeap* _g1h;
 184   uint _worker_id;
 185   HeapRegionClaimer* _hrclaimer;
 186 
 187   DirtyCardQueue _dcq;
 188   UpdateRSetDeferred _update_rset_cl;
 189 
 190 public:
 191   RemoveSelfForwardPtrHRClosure(uint worker_id,
 192                                 HeapRegionClaimer* hrclaimer) :
 193     _g1h(G1CollectedHeap::heap()),
 194     _dcq(&_g1h->dirty_card_queue_set()),
 195     _update_rset_cl(&_dcq),
 196     _worker_id(worker_id),
 197     _hrclaimer(hrclaimer) {
 198   }
 199 
 200   size_t remove_self_forward_ptr_by_walking_hr(HeapRegion* hr,
 201                                                bool during_initial_mark) {
 202     RemoveSelfForwardPtrObjClosure rspc(hr,
 203                                         &_update_rset_cl,
 204                                         during_initial_mark,
 205                                         _worker_id);
 206     _update_rset_cl.set_region(hr);
 207     hr->object_iterate(&rspc);
 208     // Need to zap the remainder area of the processed region.
 209     rspc.zap_remainder();
 210 
 211     return rspc.marked_bytes();
 212   }
 213 
 214   bool doHeapRegion(HeapRegion *hr) {
 215     bool during_initial_mark = _g1h->collector_state()->during_initial_mark_pause();
 216     bool during_conc_mark = _g1h->collector_state()->mark_in_progress();
 217 
 218     assert(!hr->is_pinned(), "Unexpected pinned region at index %u", hr->hrm_index());
 219     assert(hr->in_collection_set(), "bad CS");
 220 
 221     if (_hrclaimer->claim_region(hr->hrm_index())) {
 222       if (hr->evacuation_failed()) {
 223         hr->note_self_forwarding_removal_start(during_initial_mark,
 224                                                during_conc_mark);
 225         _g1h->check_bitmaps("Self-Forwarding Ptr Removal", hr);
 226 
 227         // In the common case (i.e. when there is no evacuation
 228         // failure) we make sure that the following is done when
 229         // the region is freed so that it is "ready-to-go" when it's
 230         // re-allocated. However, when evacuation failure happens, a
 231         // region will remain in the heap and might ultimately be added
 232         // to a CSet in the future. So we have to be careful here and
 233         // make sure the region's RSet is ready for parallel iteration
 234         // whenever this might be required in the future.
 235         hr->rem_set()->reset_for_par_iteration();
 236         hr->reset_bot();
 237 
 238         size_t live_bytes = remove_self_forward_ptr_by_walking_hr(hr, during_initial_mark);
 239 
 240         hr->rem_set()->clean_strong_code_roots(hr);
 241 
 242         hr->note_self_forwarding_removal_end(during_initial_mark,
 243                                              during_conc_mark,
 244                                              live_bytes);
 245       }
 246     }
 247     return false;
 248   }
 249 };
 250 
 251 G1ParRemoveSelfForwardPtrsTask::G1ParRemoveSelfForwardPtrsTask() :
 252   AbstractGangTask("G1 Remove Self-forwarding Pointers"),
 253   _g1h(G1CollectedHeap::heap()),
 254   _hrclaimer(_g1h->workers()->active_workers()) { }
 255 
 256 void G1ParRemoveSelfForwardPtrsTask::work(uint worker_id) {
 257   RemoveSelfForwardPtrHRClosure rsfp_cl(worker_id, &_hrclaimer);
 258 
 259   HeapRegion* hr = _g1h->start_cset_region_for_worker(worker_id);
 260   _g1h->collection_set_iterate_from(hr, &rsfp_cl);
 261 }