1 /*
   2  * Copyright (c) 2012, 2019, 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/g1CollectedHeap.inline.hpp"
  27 #include "gc/g1/g1CollectorState.hpp"
  28 #include "gc/g1/g1ConcurrentMark.inline.hpp"
  29 #include "gc/g1/g1DirtyCardQueue.hpp"
  30 #include "gc/g1/g1EvacFailure.hpp"
  31 #include "gc/g1/g1HeapVerifier.hpp"
  32 #include "gc/g1/g1OopClosures.inline.hpp"
  33 #include "gc/g1/heapRegion.hpp"
  34 #include "gc/g1/heapRegionRemSet.hpp"
  35 #include "gc/shared/preservedMarks.inline.hpp"
  36 #include "oops/access.inline.hpp"
  37 #include "oops/compressedOops.inline.hpp"
  38 #include "oops/oop.inline.hpp"
  39 
  40 class UpdateRSetDeferred : public BasicOopIterateClosure {
  41 private:
  42   G1CollectedHeap* _g1h;
  43   G1DirtyCardQueue* _dcq;
  44   G1CardTable*    _ct;
  45 
  46 public:
  47   UpdateRSetDeferred(G1DirtyCardQueue* dcq) :
  48     _g1h(G1CollectedHeap::heap()), _dcq(dcq), _ct(_g1h->card_table()) {}
  49 
  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(_g1h->heap_region_containing(p)->is_in_reserved(p), "paranoia");
  54     assert(!_g1h->heap_region_containing(p)->is_survivor(), "Unexpected evac failure in survivor region");
  55 
  56     T const o = RawAccess<>::oop_load(p);
  57     if (CompressedOops::is_null(o)) {
  58       return;
  59     }
  60 
  61     if (HeapRegion::is_in_same_region(p, CompressedOops::decode(o))) {
  62       return;
  63     }
  64     size_t card_index = _ct->index_for(p);
  65     if (_ct->mark_card_deferred(card_index)) {
  66       _dcq->enqueue(_ct->byte_for_index(card_index));
  67     }
  68   }
  69 };
  70 
  71 class RemoveSelfForwardPtrObjClosure: public ObjectClosure {
  72   G1CollectedHeap* _g1h;
  73   G1ConcurrentMark* _cm;
  74   HeapRegion* _hr;
  75   size_t _marked_bytes;
  76   UpdateRSetDeferred* _update_rset_cl;
  77   bool _during_initial_mark;
  78   uint _worker_id;
  79   HeapWord* _last_forwarded_object_end;
  80 
  81 public:
  82   RemoveSelfForwardPtrObjClosure(HeapRegion* hr,
  83                                  UpdateRSetDeferred* update_rset_cl,
  84                                  bool during_initial_mark,
  85                                  uint worker_id) :
  86     _g1h(G1CollectedHeap::heap()),
  87     _cm(_g1h->concurrent_mark()),
  88     _hr(hr),
  89     _marked_bytes(0),
  90     _update_rset_cl(update_rset_cl),
  91     _during_initial_mark(during_initial_mark),
  92     _worker_id(worker_id),
  93     _last_forwarded_object_end(hr->bottom()) { }
  94 
  95   size_t marked_bytes() { return _marked_bytes; }
  96 
  97   // Iterate over the live objects in the region to find self-forwarded objects
  98   // that need to be kept live. We need to update the remembered sets of these
  99   // objects. Further update the BOT and marks.
 100   // We can coalesce and overwrite the remaining heap contents with dummy objects
 101   // as they have either been dead or evacuated (which are unreferenced now, i.e.
 102   // dead too) already.
 103   void do_object(oop obj) {
 104     HeapWord* obj_addr = (HeapWord*) obj;
 105     assert(_hr->is_in(obj_addr), "sanity");
 106 
 107     if (obj->is_forwarded() && obj->forwardee() == obj) {
 108       // The object failed to move.
 109 
 110       zap_dead_objects(_last_forwarded_object_end, obj_addr);
 111       // We consider all objects that we find self-forwarded to be
 112       // live. What we'll do is that we'll update the prev marking
 113       // info so that they are all under PTAMS and explicitly marked.
 114       if (!_cm->is_marked_in_prev_bitmap(obj)) {
 115         _cm->mark_in_prev_bitmap(obj);
 116       }
 117       if (_during_initial_mark) {
 118         // For the next marking info we'll only mark the
 119         // self-forwarded objects explicitly if we are during
 120         // initial-mark (since, normally, we only mark objects pointed
 121         // to by roots if we succeed in copying them). By marking all
 122         // self-forwarded objects we ensure that we mark any that are
 123         // still pointed to be roots. During concurrent marking, and
 124         // after initial-mark, we don't need to mark any objects
 125         // explicitly and all objects in the CSet are considered
 126         // (implicitly) live. So, we won't mark them explicitly and
 127         // we'll leave them over NTAMS.
 128         _cm->mark_in_next_bitmap(_worker_id, _hr, obj);
 129       }
 130       size_t obj_size = obj->size();
 131 
 132       _marked_bytes += (obj_size * HeapWordSize);
 133       PreservedMarks::init_forwarded_mark(obj);
 134 
 135       // While we were processing RSet buffers during the collection,
 136       // we actually didn't scan any cards on the collection set,
 137       // since we didn't want to update remembered sets with entries
 138       // that point into the collection set, given that live objects
 139       // from the collection set are about to move and such entries
 140       // will be stale very soon.
 141       // This change also dealt with a reliability issue which
 142       // involved scanning a card in the collection set and coming
 143       // across an array that was being chunked and looking malformed.
 144       // The problem is that, if evacuation fails, we might have
 145       // remembered set entries missing given that we skipped cards on
 146       // the collection set. So, we'll recreate such entries now.
 147       obj->oop_iterate(_update_rset_cl);
 148 
 149       HeapWord* obj_end = obj_addr + obj_size;
 150       _last_forwarded_object_end = obj_end;
 151       _hr->cross_threshold(obj_addr, obj_end);
 152     }
 153   }
 154 
 155   // Fill the memory area from start to end with filler objects, and update the BOT
 156   // and the mark bitmap accordingly.
 157   void zap_dead_objects(HeapWord* start, HeapWord* end) {
 158     if (start == end) {
 159       return;
 160     }
 161 
 162     size_t gap_size = pointer_delta(end, start);
 163     MemRegion mr(start, gap_size);
 164     if (gap_size >= CollectedHeap::min_fill_size()) {
 165       CollectedHeap::fill_with_objects(start, gap_size);
 166 
 167       HeapWord* end_first_obj = start + ((oop)start)->size();
 168       _hr->cross_threshold(start, end_first_obj);
 169       // Fill_with_objects() may have created multiple (i.e. two)
 170       // objects, as the max_fill_size() is half a region.
 171       // After updating the BOT for the first object, also update the
 172       // BOT for the second object to make the BOT complete.
 173       if (end_first_obj != end) {
 174         _hr->cross_threshold(end_first_obj, end);
 175 #ifdef ASSERT
 176         size_t size_second_obj = ((oop)end_first_obj)->size();
 177         HeapWord* end_of_second_obj = end_first_obj + size_second_obj;
 178         assert(end == end_of_second_obj,
 179                "More than two objects were used to fill the area from " PTR_FORMAT " to " PTR_FORMAT ", "
 180                "second objects size " SIZE_FORMAT " ends at " PTR_FORMAT,
 181                p2i(start), p2i(end), size_second_obj, p2i(end_of_second_obj));
 182 #endif
 183       }
 184     }
 185     _cm->clear_range_in_prev_bitmap(mr);
 186   }
 187 
 188   void zap_remainder() {
 189     zap_dead_objects(_last_forwarded_object_end, _hr->top());
 190   }
 191 };
 192 
 193 class RemoveSelfForwardPtrHRClosure: public HeapRegionClosure {
 194   G1CollectedHeap* _g1h;
 195   uint _worker_id;
 196   HeapRegionClaimer* _hrclaimer;
 197 
 198   G1DirtyCardQueue _dcq;
 199   UpdateRSetDeferred _update_rset_cl;
 200 
 201 public:
 202   RemoveSelfForwardPtrHRClosure(uint worker_id,
 203                                 HeapRegionClaimer* hrclaimer) :
 204     _g1h(G1CollectedHeap::heap()),
 205     _worker_id(worker_id),
 206     _hrclaimer(hrclaimer),
 207     _dcq(&_g1h->dirty_card_queue_set()),
 208     _update_rset_cl(&_dcq){
 209   }
 210 
 211   size_t remove_self_forward_ptr_by_walking_hr(HeapRegion* hr,
 212                                                bool during_initial_mark) {
 213     RemoveSelfForwardPtrObjClosure rspc(hr,
 214                                         &_update_rset_cl,
 215                                         during_initial_mark,
 216                                         _worker_id);
 217     hr->object_iterate(&rspc);
 218     // Need to zap the remainder area of the processed region.
 219     rspc.zap_remainder();
 220 
 221     return rspc.marked_bytes();
 222   }
 223 
 224   bool do_heap_region(HeapRegion *hr) {
 225     assert(!hr->is_pinned(), "Unexpected pinned region at index %u", hr->hrm_index());
 226     assert(hr->in_collection_set(), "bad CS");
 227 
 228     if (_hrclaimer->claim_region(hr->hrm_index())) {
 229       if (hr->evacuation_failed()) {
 230         hr->clear_index_in_opt_cset();
 231 
 232         bool during_initial_mark = _g1h->collector_state()->in_initial_mark_gc();
 233         bool during_conc_mark = _g1h->collector_state()->mark_or_rebuild_in_progress();
 234 
 235         hr->note_self_forwarding_removal_start(during_initial_mark,
 236                                                during_conc_mark);
 237         _g1h->verifier()->check_bitmaps("Self-Forwarding Ptr Removal", hr);
 238 
 239         hr->reset_bot();
 240 
 241         size_t live_bytes = remove_self_forward_ptr_by_walking_hr(hr, during_initial_mark);
 242 
 243         hr->rem_set()->clean_strong_code_roots(hr);
 244         hr->rem_set()->clear_locked(true);
 245 
 246         hr->note_self_forwarding_removal_end(live_bytes);
 247       }
 248     }
 249     return false;
 250   }
 251 };
 252 
 253 G1ParRemoveSelfForwardPtrsTask::G1ParRemoveSelfForwardPtrsTask() :
 254   AbstractGangTask("G1 Remove Self-forwarding Pointers"),
 255   _g1h(G1CollectedHeap::heap()),
 256   _hrclaimer(_g1h->workers()->active_workers()) { }
 257 
 258 void G1ParRemoveSelfForwardPtrsTask::work(uint worker_id) {
 259   RemoveSelfForwardPtrHRClosure rsfp_cl(worker_id, &_hrclaimer);
 260 
 261   _g1h->collection_set_iterate_increment_from(&rsfp_cl, worker_id);
 262 }