1 /*
   2  * Copyright (c) 2001, 2017, 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/concurrentG1Refine.hpp"
  27 #include "gc/g1/dirtyCardQueue.hpp"
  28 #include "gc/g1/g1BlockOffsetTable.inline.hpp"
  29 #include "gc/g1/g1CollectedHeap.inline.hpp"
  30 #include "gc/g1/g1FromCardCache.hpp"
  31 #include "gc/g1/g1GCPhaseTimes.hpp"
  32 #include "gc/g1/g1HotCardCache.hpp"
  33 #include "gc/g1/g1OopClosures.inline.hpp"
  34 #include "gc/g1/g1RemSet.inline.hpp"
  35 #include "gc/g1/g1SATBCardTableModRefBS.inline.hpp"
  36 #include "gc/g1/heapRegion.inline.hpp"
  37 #include "gc/g1/heapRegionManager.inline.hpp"
  38 #include "gc/g1/heapRegionRemSet.hpp"
  39 #include "gc/g1/suspendibleThreadSet.hpp"
  40 #include "gc/shared/gcTraceTime.inline.hpp"
  41 #include "memory/iterator.hpp"
  42 #include "memory/resourceArea.hpp"
  43 #include "oops/oop.inline.hpp"
  44 #include "utilities/align.hpp"
  45 #include "utilities/globalDefinitions.hpp"
  46 #include "utilities/intHisto.hpp"
  47 #include "utilities/stack.inline.hpp"
  48 
  49 // Collects information about the overall remembered set scan progress during an evacuation.
  50 class G1RemSetScanState : public CHeapObj<mtGC> {
  51 private:
  52   class G1ClearCardTableTask : public AbstractGangTask {
  53     G1CollectedHeap* _g1h;
  54     uint* _dirty_region_list;
  55     size_t _num_dirty_regions;
  56     size_t _chunk_length;
  57 
  58     size_t volatile _cur_dirty_regions;
  59   public:
  60     G1ClearCardTableTask(G1CollectedHeap* g1h,
  61                          uint* dirty_region_list,
  62                          size_t num_dirty_regions,
  63                          size_t chunk_length) :
  64       AbstractGangTask("G1 Clear Card Table Task"),
  65       _g1h(g1h),
  66       _dirty_region_list(dirty_region_list),
  67       _num_dirty_regions(num_dirty_regions),
  68       _chunk_length(chunk_length),
  69       _cur_dirty_regions(0) {
  70 
  71       assert(chunk_length > 0, "must be");
  72     }
  73 
  74     static size_t chunk_size() { return M; }
  75 
  76     void work(uint worker_id) {
  77       G1SATBCardTableModRefBS* ct_bs = _g1h->g1_barrier_set();
  78 
  79       while (_cur_dirty_regions < _num_dirty_regions) {
  80         size_t next = Atomic::add(_chunk_length, &_cur_dirty_regions) - _chunk_length;
  81         size_t max = MIN2(next + _chunk_length, _num_dirty_regions);
  82 
  83         for (size_t i = next; i < max; i++) {
  84           HeapRegion* r = _g1h->region_at(_dirty_region_list[i]);
  85           if (!r->is_survivor()) {
  86             ct_bs->clear(MemRegion(r->bottom(), r->end()));
  87           }
  88         }
  89       }
  90     }
  91   };
  92 
  93   size_t _max_regions;
  94 
  95   // Scan progress for the remembered set of a single region. Transitions from
  96   // Unclaimed -> Claimed -> Complete.
  97   // At each of the transitions the thread that does the transition needs to perform
  98   // some special action once. This is the reason for the extra "Claimed" state.
  99   typedef jint G1RemsetIterState;
 100 
 101   static const G1RemsetIterState Unclaimed = 0; // The remembered set has not been scanned yet.
 102   static const G1RemsetIterState Claimed = 1;   // The remembered set is currently being scanned.
 103   static const G1RemsetIterState Complete = 2;  // The remembered set has been completely scanned.
 104 
 105   G1RemsetIterState volatile* _iter_states;
 106   // The current location where the next thread should continue scanning in a region's
 107   // remembered set.
 108   size_t volatile* _iter_claims;
 109 
 110   // Temporary buffer holding the regions we used to store remembered set scan duplicate
 111   // information. These are also called "dirty". Valid entries are from [0.._cur_dirty_region)
 112   uint* _dirty_region_buffer;
 113 
 114   typedef jbyte IsDirtyRegionState;
 115   static const IsDirtyRegionState Clean = 0;
 116   static const IsDirtyRegionState Dirty = 1;
 117   // Holds a flag for every region whether it is in the _dirty_region_buffer already
 118   // to avoid duplicates. Uses jbyte since there are no atomic instructions for bools.
 119   IsDirtyRegionState* _in_dirty_region_buffer;
 120   size_t _cur_dirty_region;
 121 
 122   // Creates a snapshot of the current _top values at the start of collection to
 123   // filter out card marks that we do not want to scan.
 124   class G1ResetScanTopClosure : public HeapRegionClosure {
 125   private:
 126     HeapWord** _scan_top;
 127   public:
 128     G1ResetScanTopClosure(HeapWord** scan_top) : _scan_top(scan_top) { }
 129 
 130     virtual bool doHeapRegion(HeapRegion* r) {
 131       uint hrm_index = r->hrm_index();
 132       if (!r->in_collection_set() && r->is_old_or_humongous()) {
 133         _scan_top[hrm_index] = r->top();
 134       } else {
 135         _scan_top[hrm_index] = r->bottom();
 136       }
 137       return false;
 138     }
 139   };
 140 
 141   // For each region, contains the maximum top() value to be used during this garbage
 142   // collection. Subsumes common checks like filtering out everything but old and
 143   // humongous regions outside the collection set.
 144   // This is valid because we are not interested in scanning stray remembered set
 145   // entries from free or archive regions.
 146   HeapWord** _scan_top;
 147 public:
 148   G1RemSetScanState() :
 149     _max_regions(0),
 150     _iter_states(NULL),
 151     _iter_claims(NULL),
 152     _dirty_region_buffer(NULL),
 153     _in_dirty_region_buffer(NULL),
 154     _cur_dirty_region(0),
 155     _scan_top(NULL) {
 156   }
 157 
 158   ~G1RemSetScanState() {
 159     if (_iter_states != NULL) {
 160       FREE_C_HEAP_ARRAY(G1RemsetIterState, _iter_states);
 161     }
 162     if (_iter_claims != NULL) {
 163       FREE_C_HEAP_ARRAY(size_t, _iter_claims);
 164     }
 165     if (_dirty_region_buffer != NULL) {
 166       FREE_C_HEAP_ARRAY(uint, _dirty_region_buffer);
 167     }
 168     if (_in_dirty_region_buffer != NULL) {
 169       FREE_C_HEAP_ARRAY(IsDirtyRegionState, _in_dirty_region_buffer);
 170     }
 171     if (_scan_top != NULL) {
 172       FREE_C_HEAP_ARRAY(HeapWord*, _scan_top);
 173     }
 174   }
 175 
 176   void initialize(uint max_regions) {
 177     assert(_iter_states == NULL, "Must not be initialized twice");
 178     assert(_iter_claims == NULL, "Must not be initialized twice");
 179     _max_regions = max_regions;
 180     _iter_states = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_regions, mtGC);
 181     _iter_claims = NEW_C_HEAP_ARRAY(size_t, max_regions, mtGC);
 182     _dirty_region_buffer = NEW_C_HEAP_ARRAY(uint, max_regions, mtGC);
 183     _in_dirty_region_buffer = NEW_C_HEAP_ARRAY(IsDirtyRegionState, max_regions, mtGC);
 184     _scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_regions, mtGC);
 185   }
 186 
 187   void reset() {
 188     for (uint i = 0; i < _max_regions; i++) {
 189       _iter_states[i] = Unclaimed;
 190     }
 191 
 192     G1ResetScanTopClosure cl(_scan_top);
 193     G1CollectedHeap::heap()->heap_region_iterate(&cl);
 194 
 195     memset((void*)_iter_claims, 0, _max_regions * sizeof(size_t));
 196     memset(_in_dirty_region_buffer, Clean, _max_regions * sizeof(IsDirtyRegionState));
 197     _cur_dirty_region = 0;
 198   }
 199 
 200   // Attempt to claim the remembered set of the region for iteration. Returns true
 201   // if this call caused the transition from Unclaimed to Claimed.
 202   inline bool claim_iter(uint region) {
 203     assert(region < _max_regions, "Tried to access invalid region %u", region);
 204     if (_iter_states[region] != Unclaimed) {
 205       return false;
 206     }
 207     jint res = Atomic::cmpxchg(Claimed, (jint*)(&_iter_states[region]), Unclaimed);
 208     return (res == Unclaimed);
 209   }
 210 
 211   // Try to atomically sets the iteration state to "complete". Returns true for the
 212   // thread that caused the transition.
 213   inline bool set_iter_complete(uint region) {
 214     if (iter_is_complete(region)) {
 215       return false;
 216     }
 217     jint res = Atomic::cmpxchg(Complete, (jint*)(&_iter_states[region]), Claimed);
 218     return (res == Claimed);
 219   }
 220 
 221   // Returns true if the region's iteration is complete.
 222   inline bool iter_is_complete(uint region) const {
 223     assert(region < _max_regions, "Tried to access invalid region %u", region);
 224     return _iter_states[region] == Complete;
 225   }
 226 
 227   // The current position within the remembered set of the given region.
 228   inline size_t iter_claimed(uint region) const {
 229     assert(region < _max_regions, "Tried to access invalid region %u", region);
 230     return _iter_claims[region];
 231   }
 232 
 233   // Claim the next block of cards within the remembered set of the region with
 234   // step size.
 235   inline size_t iter_claimed_next(uint region, size_t step) {
 236     return Atomic::add(step, &_iter_claims[region]) - step;
 237   }
 238 
 239   void add_dirty_region(uint region) {
 240     if (_in_dirty_region_buffer[region] == Dirty) {
 241       return;
 242     }
 243 
 244     bool marked_as_dirty = Atomic::cmpxchg(Dirty, &_in_dirty_region_buffer[region], Clean) == Clean;
 245     if (marked_as_dirty) {
 246       size_t allocated = Atomic::add(1, &_cur_dirty_region) - 1;
 247       _dirty_region_buffer[allocated] = region;
 248     }
 249   }
 250 
 251   HeapWord* scan_top(uint region_idx) const {
 252     return _scan_top[region_idx];
 253   }
 254 
 255   // Clear the card table of "dirty" regions.
 256   void clear_card_table(WorkGang* workers) {
 257     if (_cur_dirty_region == 0) {
 258       return;
 259     }
 260 
 261     size_t const num_chunks = align_up(_cur_dirty_region * HeapRegion::CardsPerRegion, G1ClearCardTableTask::chunk_size()) / G1ClearCardTableTask::chunk_size();
 262     uint const num_workers = (uint)MIN2(num_chunks, (size_t)workers->active_workers());
 263     size_t const chunk_length = G1ClearCardTableTask::chunk_size() / HeapRegion::CardsPerRegion;
 264 
 265     // Iterate over the dirty cards region list.
 266     G1ClearCardTableTask cl(G1CollectedHeap::heap(), _dirty_region_buffer, _cur_dirty_region, chunk_length);
 267 
 268     log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " "
 269                         "units of work for " SIZE_FORMAT " regions.",
 270                         cl.name(), num_workers, num_chunks, _cur_dirty_region);
 271     workers->run_task(&cl, num_workers);
 272 
 273 #ifndef PRODUCT
 274     // Need to synchronize with concurrent cleanup since it needs to
 275     // finish its card table clearing before we can verify.
 276     G1CollectedHeap::heap()->wait_while_free_regions_coming();
 277     G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
 278 #endif
 279   }
 280 };
 281 
 282 G1RemSet::G1RemSet(G1CollectedHeap* g1,
 283                    CardTableModRefBS* ct_bs,
 284                    G1HotCardCache* hot_card_cache) :
 285   _g1(g1),
 286   _scan_state(new G1RemSetScanState()),
 287   _num_conc_refined_cards(0),
 288   _ct_bs(ct_bs),
 289   _g1p(_g1->g1_policy()),
 290   _hot_card_cache(hot_card_cache),
 291   _prev_period_summary()
 292 {
 293 }
 294 
 295 G1RemSet::~G1RemSet() {
 296   if (_scan_state != NULL) {
 297     delete _scan_state;
 298   }
 299 }
 300 
 301 uint G1RemSet::num_par_rem_sets() {
 302   return MAX2(DirtyCardQueueSet::num_par_ids() + ConcurrentG1Refine::thread_num(), ParallelGCThreads);
 303 }
 304 
 305 void G1RemSet::initialize(size_t capacity, uint max_regions) {
 306   G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
 307   _scan_state->initialize(max_regions);
 308   {
 309     GCTraceTime(Debug, gc, marking)("Initialize Card Live Data");
 310     _card_live_data.initialize(capacity, max_regions);
 311   }
 312   if (G1PretouchAuxiliaryMemory) {
 313     GCTraceTime(Debug, gc, marking)("Pre-Touch Card Live Data");
 314     _card_live_data.pretouch();
 315   }
 316 }
 317 
 318 G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state,
 319                                                    G1ScanObjsDuringScanRSClosure* scan_obj_on_card,
 320                                                    CodeBlobClosure* code_root_cl,
 321                                                    uint worker_i) :
 322   _scan_state(scan_state),
 323   _scan_objs_on_card_cl(scan_obj_on_card),
 324   _code_root_cl(code_root_cl),
 325   _strong_code_root_scan_time_sec(0.0),
 326   _cards_claimed(0),
 327   _cards_scanned(0),
 328   _cards_skipped(0),
 329   _worker_i(worker_i) {
 330   _g1h = G1CollectedHeap::heap();
 331   _bot = _g1h->bot();
 332   _ct_bs = _g1h->g1_barrier_set();
 333 }
 334 
 335 void G1ScanRSForRegionClosure::scan_card(MemRegion mr, uint region_idx_for_card) {
 336   HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
 337   _scan_objs_on_card_cl->set_region(card_region);
 338   card_region->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl);
 339   _cards_scanned++;
 340 }
 341 
 342 void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) {
 343   double scan_start = os::elapsedTime();
 344   r->strong_code_roots_do(_code_root_cl);
 345   _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
 346 }
 347 
 348 void G1ScanRSForRegionClosure::claim_card(size_t card_index, const uint region_idx_for_card){
 349   _ct_bs->set_card_claimed(card_index);
 350   _scan_state->add_dirty_region(region_idx_for_card);
 351 }
 352 
 353 bool G1ScanRSForRegionClosure::doHeapRegion(HeapRegion* r) {
 354   assert(r->in_collection_set(), "should only be called on elements of CS.");
 355   uint region_idx = r->hrm_index();
 356 
 357   if (_scan_state->iter_is_complete(region_idx)) {
 358     return false;
 359   }
 360   if (_scan_state->claim_iter(region_idx)) {
 361     // If we ever free the collection set concurrently, we should also
 362     // clear the card table concurrently therefore we won't need to
 363     // add regions of the collection set to the dirty cards region.
 364     _scan_state->add_dirty_region(region_idx);
 365   }
 366 
 367   // We claim cards in blocks so as to reduce the contention.
 368   size_t const block_size = G1RSetScanBlockSize;
 369 
 370   HeapRegionRemSetIterator iter(r->rem_set());
 371   size_t card_index;
 372 
 373   size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
 374   for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
 375     if (current_card >= claimed_card_block + block_size) {
 376       claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
 377     }
 378     if (current_card < claimed_card_block) {
 379       _cards_skipped++;
 380       continue;
 381     }
 382     _cards_claimed++;
 383 
 384     // If the card is dirty, then G1 will scan it during Update RS.
 385     if (_ct_bs->is_card_claimed(card_index) || _ct_bs->is_card_dirty(card_index)) {
 386       continue;
 387     }
 388 
 389     HeapWord* const card_start = _g1h->bot()->address_for_index(card_index);
 390     uint const region_idx_for_card = _g1h->addr_to_region(card_start);
 391 
 392     assert(_g1h->region_at(region_idx_for_card)->is_in_reserved(card_start),
 393            "Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index());
 394     HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
 395     if (card_start >= top) {
 396       continue;
 397     }
 398 
 399     // We claim lazily (so races are possible but they're benign), which reduces the
 400     // number of duplicate scans (the rsets of the regions in the cset can intersect).
 401     // Claim the card after checking bounds above: the remembered set may contain
 402     // random cards into current survivor, and we would then have an incorrectly
 403     // claimed card in survivor space. Card table clear does not reset the card table
 404     // of survivor space regions.
 405     claim_card(card_index, region_idx_for_card);
 406 
 407     MemRegion const mr(card_start, MIN2(card_start + BOTConstants::N_words, top));
 408 
 409     scan_card(mr, region_idx_for_card);
 410   }
 411   if (_scan_state->set_iter_complete(region_idx)) {
 412     // Scan the strong code root list attached to the current region
 413     scan_strong_code_roots(r);
 414   }
 415   return false;
 416 }
 417 
 418 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss,
 419                             CodeBlobClosure* heap_region_codeblobs,
 420                             uint worker_i) {
 421   double rs_time_start = os::elapsedTime();
 422 
 423   G1ScanObjsDuringScanRSClosure scan_cl(_g1, pss);
 424   G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, heap_region_codeblobs, worker_i);
 425   _g1->collection_set_iterate_from(&cl, worker_i);
 426 
 427   double scan_rs_time_sec = (os::elapsedTime() - rs_time_start) -
 428                              cl.strong_code_root_scan_time_sec();
 429 
 430   G1GCPhaseTimes* p = _g1p->phase_times();
 431 
 432   p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec);
 433   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards);
 434   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards);
 435   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards);
 436 
 437   p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time_sec());
 438 }
 439 
 440 // Closure used for updating rem sets. Only called during an evacuation pause.
 441 class G1RefineCardClosure: public CardTableEntryClosure {
 442   G1RemSet* _g1rs;
 443   G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
 444 
 445   size_t _cards_scanned;
 446   size_t _cards_skipped;
 447 public:
 448   G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
 449     _g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0)
 450   {}
 451 
 452   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
 453     assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
 454 
 455     bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
 456 
 457     if (card_scanned) {
 458       _cards_scanned++;
 459     } else {
 460       _cards_skipped++;
 461     }
 462     return true;
 463   }
 464 
 465   size_t cards_scanned() const { return _cards_scanned; }
 466   size_t cards_skipped() const { return _cards_skipped; }
 467 };
 468 
 469 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
 470   G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1, pss, worker_i);
 471   G1RefineCardClosure refine_card_cl(_g1, &update_rs_cl);
 472 
 473   G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i);
 474   if (G1HotCardCache::default_use_cache()) {
 475     // Apply the closure to the entries of the hot card cache.
 476     G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i);
 477     _g1->iterate_hcc_closure(&refine_card_cl, worker_i);
 478   }
 479   // Apply the closure to all remaining log entries.
 480   _g1->iterate_dirty_card_closure(&refine_card_cl, worker_i);
 481 
 482   G1GCPhaseTimes* p = _g1p->phase_times();
 483   p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards);
 484   p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards);
 485 }
 486 
 487 void G1RemSet::cleanupHRRS() {
 488   HeapRegionRemSet::cleanup();
 489 }
 490 
 491 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss,
 492                                            CodeBlobClosure* heap_region_codeblobs,
 493                                            uint worker_i) {
 494   update_rem_set(pss, worker_i);
 495   scan_rem_set(pss, heap_region_codeblobs, worker_i);;
 496 }
 497 
 498 void G1RemSet::prepare_for_oops_into_collection_set_do() {
 499   DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 500   dcqs.concatenate_logs();
 501 
 502   _scan_state->reset();
 503 }
 504 
 505 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
 506   G1GCPhaseTimes* phase_times = _g1->g1_policy()->phase_times();
 507 
 508   // Set all cards back to clean.
 509   double start = os::elapsedTime();
 510   _scan_state->clear_card_table(_g1->workers());
 511   phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
 512 }
 513 
 514 class G1ScrubRSClosure: public HeapRegionClosure {
 515   G1CollectedHeap* _g1h;
 516   G1CardLiveData* _live_data;
 517 public:
 518   G1ScrubRSClosure(G1CardLiveData* live_data) :
 519     _g1h(G1CollectedHeap::heap()),
 520     _live_data(live_data) { }
 521 
 522   bool doHeapRegion(HeapRegion* r) {
 523     if (!r->is_continues_humongous()) {
 524       r->rem_set()->scrub(_live_data);
 525     }
 526     return false;
 527   }
 528 };
 529 
 530 void G1RemSet::scrub(uint worker_num, HeapRegionClaimer *hrclaimer) {
 531   G1ScrubRSClosure scrub_cl(&_card_live_data);
 532   _g1->heap_region_par_iterate(&scrub_cl, worker_num, hrclaimer);
 533 }
 534 
 535 inline void check_card_ptr(jbyte* card_ptr, CardTableModRefBS* ct_bs) {
 536 #ifdef ASSERT
 537   G1CollectedHeap* g1 = G1CollectedHeap::heap();
 538   assert(g1->is_in_exact(ct_bs->addr_for(card_ptr)),
 539          "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
 540          p2i(card_ptr),
 541          ct_bs->index_for(ct_bs->addr_for(card_ptr)),
 542          p2i(ct_bs->addr_for(card_ptr)),
 543          g1->addr_to_region(ct_bs->addr_for(card_ptr)));
 544 #endif
 545 }
 546 
 547 void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
 548                                         uint worker_i) {
 549   assert(!_g1->is_gc_active(), "Only call concurrently");
 550 
 551   check_card_ptr(card_ptr, _ct_bs);
 552 
 553   // If the card is no longer dirty, nothing to do.
 554   if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 555     return;
 556   }
 557 
 558   // Construct the region representing the card.
 559   HeapWord* start = _ct_bs->addr_for(card_ptr);
 560   // And find the region containing it.
 561   HeapRegion* r = _g1->heap_region_containing(start);
 562 
 563   // This check is needed for some uncommon cases where we should
 564   // ignore the card.
 565   //
 566   // The region could be young.  Cards for young regions are
 567   // distinctly marked (set to g1_young_gen), so the post-barrier will
 568   // filter them out.  However, that marking is performed
 569   // concurrently.  A write to a young object could occur before the
 570   // card has been marked young, slipping past the filter.
 571   //
 572   // The card could be stale, because the region has been freed since
 573   // the card was recorded. In this case the region type could be
 574   // anything.  If (still) free or (reallocated) young, just ignore
 575   // it.  If (reallocated) old or humongous, the later card trimming
 576   // and additional checks in iteration may detect staleness.  At
 577   // worst, we end up processing a stale card unnecessarily.
 578   //
 579   // In the normal (non-stale) case, the synchronization between the
 580   // enqueueing of the card and processing it here will have ensured
 581   // we see the up-to-date region type here.
 582   if (!r->is_old_or_humongous()) {
 583     return;
 584   }
 585 
 586   // While we are processing RSet buffers during the collection, we
 587   // actually don't want to scan any cards on the collection set,
 588   // since we don't want to update remembered sets with entries that
 589   // point into the collection set, given that live objects from the
 590   // collection set are about to move and such entries will be stale
 591   // very soon. This change also deals with a reliability issue which
 592   // involves scanning a card in the collection set and coming across
 593   // an array that was being chunked and looking malformed. Note,
 594   // however, that if evacuation fails, we have to scan any objects
 595   // that were not moved and create any missing entries.
 596   if (r->in_collection_set()) {
 597     return;
 598   }
 599 
 600   // The result from the hot card cache insert call is either:
 601   //   * pointer to the current card
 602   //     (implying that the current card is not 'hot'),
 603   //   * null
 604   //     (meaning we had inserted the card ptr into the "hot" card cache,
 605   //     which had some headroom),
 606   //   * a pointer to a "hot" card that was evicted from the "hot" cache.
 607   //
 608 
 609   if (_hot_card_cache->use_cache()) {
 610     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
 611 
 612     const jbyte* orig_card_ptr = card_ptr;
 613     card_ptr = _hot_card_cache->insert(card_ptr);
 614     if (card_ptr == NULL) {
 615       // There was no eviction. Nothing to do.
 616       return;
 617     } else if (card_ptr != orig_card_ptr) {
 618       // Original card was inserted and an old card was evicted.
 619       start = _ct_bs->addr_for(card_ptr);
 620       r = _g1->heap_region_containing(start);
 621 
 622       // Check whether the region formerly in the cache should be
 623       // ignored, as discussed earlier for the original card.  The
 624       // region could have been freed while in the cache.  The cset is
 625       // not relevant here, since we're in concurrent phase.
 626       if (!r->is_old_or_humongous()) {
 627         return;
 628       }
 629     } // Else we still have the original card.
 630   }
 631 
 632   // Trim the region designated by the card to what's been allocated
 633   // in the region.  The card could be stale, or the card could cover
 634   // (part of) an object at the end of the allocated space and extend
 635   // beyond the end of allocation.
 636 
 637   // Non-humongous objects are only allocated in the old-gen during
 638   // GC, so if region is old then top is stable.  Humongous object
 639   // allocation sets top last; if top has not yet been set, this is
 640   // a stale card and we'll end up with an empty intersection.  If
 641   // this is not a stale card, the synchronization between the
 642   // enqueuing of the card and processing it here will have ensured
 643   // we see the up-to-date top here.
 644   HeapWord* scan_limit = r->top();
 645 
 646   if (scan_limit <= start) {
 647     // If the trimmed region is empty, the card must be stale.
 648     return;
 649   }
 650 
 651   // Okay to clean and process the card now.  There are still some
 652   // stale card cases that may be detected by iteration and dealt with
 653   // as iteration failure.
 654   *const_cast<volatile jbyte*>(card_ptr) = CardTableModRefBS::clean_card_val();
 655 
 656   // This fence serves two purposes.  First, the card must be cleaned
 657   // before processing the contents.  Second, we can't proceed with
 658   // processing until after the read of top, for synchronization with
 659   // possibly concurrent humongous object allocation.  It's okay that
 660   // reading top and reading type were racy wrto each other.  We need
 661   // both set, in any order, to proceed.
 662   OrderAccess::fence();
 663 
 664   // Don't use addr_for(card_ptr + 1) which can ask for
 665   // a card beyond the heap.
 666   HeapWord* end = start + CardTableModRefBS::card_size_in_words;
 667   MemRegion dirty_region(start, MIN2(scan_limit, end));
 668   assert(!dirty_region.is_empty(), "sanity");
 669 
 670   G1ConcurrentRefineOopClosure conc_refine_cl(_g1, worker_i);
 671 
 672   bool card_processed =
 673     r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
 674 
 675   // If unable to process the card then we encountered an unparsable
 676   // part of the heap (e.g. a partially allocated object) while
 677   // processing a stale card.  Despite the card being stale, redirty
 678   // and re-enqueue, because we've already cleaned the card.  Without
 679   // this we could incorrectly discard a non-stale card.
 680   if (!card_processed) {
 681     // The card might have gotten re-dirtied and re-enqueued while we
 682     // worked.  (In fact, it's pretty likely.)
 683     if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 684       *card_ptr = CardTableModRefBS::dirty_card_val();
 685       MutexLockerEx x(Shared_DirtyCardQ_lock,
 686                       Mutex::_no_safepoint_check_flag);
 687       DirtyCardQueue* sdcq =
 688         JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
 689       sdcq->enqueue(card_ptr);
 690     }
 691   } else {
 692     _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
 693   }
 694 }
 695 
 696 bool G1RemSet::refine_card_during_gc(jbyte* card_ptr,
 697                                      G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
 698   assert(_g1->is_gc_active(), "Only call during GC");
 699 
 700   check_card_ptr(card_ptr, _ct_bs);
 701 
 702   // If the card is no longer dirty, nothing to do. This covers cards that were already
 703   // scanned as parts of the remembered sets.
 704   if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 705     return false;
 706   }
 707 
 708   // During GC we can immediately clean the card since we will not re-enqueue stale
 709   // cards as we know they can be disregarded.
 710   *card_ptr = CardTableModRefBS::clean_card_val();
 711 
 712   // Construct the region representing the card.
 713   HeapWord* card_start = _ct_bs->addr_for(card_ptr);
 714   // And find the region containing it.
 715   HeapRegion* r = _g1->heap_region_containing(card_start);
 716 
 717   HeapWord* scan_limit = _scan_state->scan_top(r->hrm_index());
 718   if (scan_limit <= card_start) {
 719     // If the card starts above the area in the region containing objects to scan, skip it.
 720     return false;
 721   }
 722 
 723   // Don't use addr_for(card_ptr + 1) which can ask for
 724   // a card beyond the heap.
 725   HeapWord* card_end = card_start + CardTableModRefBS::card_size_in_words;
 726   MemRegion dirty_region(card_start, MIN2(scan_limit, card_end));
 727   assert(!dirty_region.is_empty(), "sanity");
 728 
 729   update_rs_cl->set_region(r);
 730   bool card_processed = r->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl);
 731   assert(card_processed, "must be");
 732   return true;
 733 }
 734 
 735 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
 736   if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
 737       (period_count % G1SummarizeRSetStatsPeriod == 0)) {
 738 
 739     G1RemSetSummary current(this);
 740     _prev_period_summary.subtract_from(&current);
 741 
 742     Log(gc, remset) log;
 743     log.trace("%s", header);
 744     ResourceMark rm;
 745     _prev_period_summary.print_on(log.trace_stream());
 746 
 747     _prev_period_summary.set(&current);
 748   }
 749 }
 750 
 751 void G1RemSet::print_summary_info() {
 752   Log(gc, remset, exit) log;
 753   if (log.is_trace()) {
 754     log.trace(" Cumulative RS summary");
 755     G1RemSetSummary current(this);
 756     ResourceMark rm;
 757     current.print_on(log.trace_stream());
 758   }
 759 }
 760 
 761 void G1RemSet::create_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
 762   _card_live_data.create(workers, mark_bitmap);
 763 }
 764 
 765 void G1RemSet::finalize_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
 766   _card_live_data.finalize(workers, mark_bitmap);
 767 }
 768 
 769 void G1RemSet::verify_card_live_data(WorkGang* workers, G1CMBitMap* bitmap) {
 770   _card_live_data.verify(workers, bitmap);
 771 }
 772 
 773 void G1RemSet::clear_card_live_data(WorkGang* workers) {
 774   _card_live_data.clear(workers);
 775 }
 776 
 777 #ifdef ASSERT
 778 void G1RemSet::verify_card_live_data_is_clear() {
 779   _card_live_data.verify_is_clear();
 780 }
 781 #endif