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/shared/gcTraceTime.inline.hpp"
  40 #include "gc/shared/suspendibleThreadSet.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(1u, &_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 G1RemSet::~G1RemSet() {
 295   if (_scan_state != NULL) {
 296     delete _scan_state;
 297   }
 298 }
 299 
 300 uint G1RemSet::num_par_rem_sets() {
 301   return MAX2(DirtyCardQueueSet::num_par_ids() + ConcurrentG1Refine::thread_num(), ParallelGCThreads);
 302 }
 303 
 304 void G1RemSet::initialize(size_t capacity, uint max_regions) {
 305   G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
 306   _scan_state->initialize(max_regions);
 307   {
 308     GCTraceTime(Debug, gc, marking)("Initialize Card Live Data");
 309     _card_live_data.initialize(capacity, max_regions);
 310   }
 311   if (G1PretouchAuxiliaryMemory) {
 312     GCTraceTime(Debug, gc, marking)("Pre-Touch Card Live Data");
 313     _card_live_data.pretouch();
 314   }
 315 }
 316 
 317 G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state,
 318                                                    G1ScanObjsDuringScanRSClosure* scan_obj_on_card,
 319                                                    CodeBlobClosure* code_root_cl,
 320                                                    uint worker_i) :
 321   _scan_state(scan_state),
 322   _scan_objs_on_card_cl(scan_obj_on_card),
 323   _code_root_cl(code_root_cl),
 324   _strong_code_root_scan_time_sec(0.0),
 325   _cards_claimed(0),
 326   _cards_scanned(0),
 327   _cards_skipped(0),
 328   _worker_i(worker_i) {
 329   _g1h = G1CollectedHeap::heap();
 330   _bot = _g1h->bot();
 331   _ct_bs = _g1h->g1_barrier_set();
 332 }
 333 
 334 void G1ScanRSForRegionClosure::scan_card(MemRegion mr, uint region_idx_for_card) {
 335   HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
 336   _scan_objs_on_card_cl->set_region(card_region);
 337   card_region->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl);
 338   _cards_scanned++;
 339 }
 340 
 341 void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) {
 342   double scan_start = os::elapsedTime();
 343   r->strong_code_roots_do(_code_root_cl);
 344   _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
 345 }
 346 
 347 void G1ScanRSForRegionClosure::claim_card(size_t card_index, const uint region_idx_for_card){
 348   _ct_bs->set_card_claimed(card_index);
 349   _scan_state->add_dirty_region(region_idx_for_card);
 350 }
 351 
 352 bool G1ScanRSForRegionClosure::doHeapRegion(HeapRegion* r) {
 353   assert(r->in_collection_set(), "should only be called on elements of CS.");
 354   uint region_idx = r->hrm_index();
 355 
 356   if (_scan_state->iter_is_complete(region_idx)) {
 357     return false;
 358   }
 359   if (_scan_state->claim_iter(region_idx)) {
 360     // If we ever free the collection set concurrently, we should also
 361     // clear the card table concurrently therefore we won't need to
 362     // add regions of the collection set to the dirty cards region.
 363     _scan_state->add_dirty_region(region_idx);
 364   }
 365 
 366   // We claim cards in blocks so as to reduce the contention.
 367   size_t const block_size = G1RSetScanBlockSize;
 368 
 369   HeapRegionRemSetIterator iter(r->rem_set());
 370   size_t card_index;
 371 
 372   size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
 373   for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
 374     if (current_card >= claimed_card_block + block_size) {
 375       claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
 376     }
 377     if (current_card < claimed_card_block) {
 378       _cards_skipped++;
 379       continue;
 380     }
 381     _cards_claimed++;
 382 
 383     // If the card is dirty, then G1 will scan it during Update RS.
 384     if (_ct_bs->is_card_claimed(card_index) || _ct_bs->is_card_dirty(card_index)) {
 385       continue;
 386     }
 387 
 388     HeapWord* const card_start = _g1h->bot()->address_for_index(card_index);
 389     uint const region_idx_for_card = _g1h->addr_to_region(card_start);
 390 
 391     assert(_g1h->region_at(region_idx_for_card)->is_in_reserved(card_start),
 392            "Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index());
 393     HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
 394     if (card_start >= top) {
 395       continue;
 396     }
 397 
 398     // We claim lazily (so races are possible but they're benign), which reduces the
 399     // number of duplicate scans (the rsets of the regions in the cset can intersect).
 400     // Claim the card after checking bounds above: the remembered set may contain
 401     // random cards into current survivor, and we would then have an incorrectly
 402     // claimed card in survivor space. Card table clear does not reset the card table
 403     // of survivor space regions.
 404     claim_card(card_index, region_idx_for_card);
 405 
 406     MemRegion const mr(card_start, MIN2(card_start + BOTConstants::N_words, top));
 407 
 408     scan_card(mr, region_idx_for_card);
 409   }
 410   if (_scan_state->set_iter_complete(region_idx)) {
 411     // Scan the strong code root list attached to the current region
 412     scan_strong_code_roots(r);
 413   }
 414   return false;
 415 }
 416 
 417 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss,
 418                             CodeBlobClosure* heap_region_codeblobs,
 419                             uint worker_i) {
 420   double rs_time_start = os::elapsedTime();
 421 
 422   G1ScanObjsDuringScanRSClosure scan_cl(_g1, pss);
 423   G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, heap_region_codeblobs, worker_i);
 424   _g1->collection_set_iterate_from(&cl, worker_i);
 425 
 426   double scan_rs_time_sec = (os::elapsedTime() - rs_time_start) -
 427                              cl.strong_code_root_scan_time_sec();
 428 
 429   G1GCPhaseTimes* p = _g1p->phase_times();
 430 
 431   p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec);
 432   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards);
 433   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards);
 434   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards);
 435 
 436   p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time_sec());
 437 }
 438 
 439 // Closure used for updating rem sets. Only called during an evacuation pause.
 440 class G1RefineCardClosure: public CardTableEntryClosure {
 441   G1RemSet* _g1rs;
 442   G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
 443 
 444   size_t _cards_scanned;
 445   size_t _cards_skipped;
 446 public:
 447   G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
 448     _g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0)
 449   {}
 450 
 451   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
 452     // The only time we care about recording cards that
 453     // contain references that point into the collection set
 454     // is during RSet updating within an evacuation pause.
 455     // In this case worker_i should be the id of a GC worker thread.
 456     assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
 457 
 458     bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
 459 
 460     if (card_scanned) {
 461       _cards_scanned++;
 462     } else {
 463       _cards_skipped++;
 464     }
 465     return true;
 466   }
 467 
 468   size_t cards_scanned() const { return _cards_scanned; }
 469   size_t cards_skipped() const { return _cards_skipped; }
 470 };
 471 
 472 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
 473   G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1, pss, worker_i);
 474   G1RefineCardClosure refine_card_cl(_g1, &update_rs_cl);
 475 
 476   G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i);
 477   if (G1HotCardCache::default_use_cache()) {
 478     // Apply the closure to the entries of the hot card cache.
 479     G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i);
 480     _g1->iterate_hcc_closure(&refine_card_cl, worker_i);
 481   }
 482   // Apply the closure to all remaining log entries.
 483   _g1->iterate_dirty_card_closure(&refine_card_cl, worker_i);
 484 
 485   G1GCPhaseTimes* p = _g1p->phase_times();
 486   p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards);
 487   p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards);
 488 }
 489 
 490 void G1RemSet::cleanupHRRS() {
 491   HeapRegionRemSet::cleanup();
 492 }
 493 
 494 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss,
 495                                            CodeBlobClosure* heap_region_codeblobs,
 496                                            uint worker_i) {
 497   update_rem_set(pss, worker_i);
 498   scan_rem_set(pss, heap_region_codeblobs, worker_i);;
 499 }
 500 
 501 void G1RemSet::prepare_for_oops_into_collection_set_do() {
 502   DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 503   dcqs.concatenate_logs();
 504 
 505   _scan_state->reset();
 506 }
 507 
 508 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
 509   G1GCPhaseTimes* phase_times = _g1->g1_policy()->phase_times();
 510 
 511   // Set all cards back to clean.
 512   double start = os::elapsedTime();
 513   _scan_state->clear_card_table(_g1->workers());
 514   phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
 515 }
 516 
 517 class G1ScrubRSClosure: public HeapRegionClosure {
 518   G1CollectedHeap* _g1h;
 519   G1CardLiveData* _live_data;
 520 public:
 521   G1ScrubRSClosure(G1CardLiveData* live_data) :
 522     _g1h(G1CollectedHeap::heap()),
 523     _live_data(live_data) { }
 524 
 525   bool doHeapRegion(HeapRegion* r) {
 526     if (!r->is_continues_humongous()) {
 527       r->rem_set()->scrub(_live_data);
 528     }
 529     return false;
 530   }
 531 };
 532 
 533 void G1RemSet::scrub(uint worker_num, HeapRegionClaimer *hrclaimer) {
 534   G1ScrubRSClosure scrub_cl(&_card_live_data);
 535   _g1->heap_region_par_iterate(&scrub_cl, worker_num, hrclaimer);
 536 }
 537 
 538 inline void check_card_ptr(jbyte* card_ptr, CardTableModRefBS* ct_bs) {
 539 #ifdef ASSERT
 540   G1CollectedHeap* g1 = G1CollectedHeap::heap();
 541   assert(g1->is_in_exact(ct_bs->addr_for(card_ptr)),
 542          "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
 543          p2i(card_ptr),
 544          ct_bs->index_for(ct_bs->addr_for(card_ptr)),
 545          p2i(ct_bs->addr_for(card_ptr)),
 546          g1->addr_to_region(ct_bs->addr_for(card_ptr)));
 547 #endif
 548 }
 549 
 550 void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
 551                                         uint worker_i) {
 552   assert(!_g1->is_gc_active(), "Only call concurrently");
 553 
 554   check_card_ptr(card_ptr, _ct_bs);
 555 
 556   // If the card is no longer dirty, nothing to do.
 557   if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 558     return;
 559   }
 560 
 561   // Construct the region representing the card.
 562   HeapWord* start = _ct_bs->addr_for(card_ptr);
 563   // And find the region containing it.
 564   HeapRegion* r = _g1->heap_region_containing(start);
 565 
 566   // This check is needed for some uncommon cases where we should
 567   // ignore the card.
 568   //
 569   // The region could be young.  Cards for young regions are
 570   // distinctly marked (set to g1_young_gen), so the post-barrier will
 571   // filter them out.  However, that marking is performed
 572   // concurrently.  A write to a young object could occur before the
 573   // card has been marked young, slipping past the filter.
 574   //
 575   // The card could be stale, because the region has been freed since
 576   // the card was recorded. In this case the region type could be
 577   // anything.  If (still) free or (reallocated) young, just ignore
 578   // it.  If (reallocated) old or humongous, the later card trimming
 579   // and additional checks in iteration may detect staleness.  At
 580   // worst, we end up processing a stale card unnecessarily.
 581   //
 582   // In the normal (non-stale) case, the synchronization between the
 583   // enqueueing of the card and processing it here will have ensured
 584   // we see the up-to-date region type here.
 585   if (!r->is_old_or_humongous()) {
 586     return;
 587   }
 588 
 589   // While we are processing RSet buffers during the collection, we
 590   // actually don't want to scan any cards on the collection set,
 591   // since we don't want to update remembered sets with entries that
 592   // point into the collection set, given that live objects from the
 593   // collection set are about to move and such entries will be stale
 594   // very soon. This change also deals with a reliability issue which
 595   // involves scanning a card in the collection set and coming across
 596   // an array that was being chunked and looking malformed. Note,
 597   // however, that if evacuation fails, we have to scan any objects
 598   // that were not moved and create any missing entries.
 599   if (r->in_collection_set()) {
 600     return;
 601   }
 602 
 603   // The result from the hot card cache insert call is either:
 604   //   * pointer to the current card
 605   //     (implying that the current card is not 'hot'),
 606   //   * null
 607   //     (meaning we had inserted the card ptr into the "hot" card cache,
 608   //     which had some headroom),
 609   //   * a pointer to a "hot" card that was evicted from the "hot" cache.
 610   //
 611 
 612   if (_hot_card_cache->use_cache()) {
 613     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
 614 
 615     const jbyte* orig_card_ptr = card_ptr;
 616     card_ptr = _hot_card_cache->insert(card_ptr);
 617     if (card_ptr == NULL) {
 618       // There was no eviction. Nothing to do.
 619       return;
 620     } else if (card_ptr != orig_card_ptr) {
 621       // Original card was inserted and an old card was evicted.
 622       start = _ct_bs->addr_for(card_ptr);
 623       r = _g1->heap_region_containing(start);
 624 
 625       // Check whether the region formerly in the cache should be
 626       // ignored, as discussed earlier for the original card.  The
 627       // region could have been freed while in the cache.  The cset is
 628       // not relevant here, since we're in concurrent phase.
 629       if (!r->is_old_or_humongous()) {
 630         return;
 631       }
 632     } // Else we still have the original card.
 633   }
 634 
 635   // Trim the region designated by the card to what's been allocated
 636   // in the region.  The card could be stale, or the card could cover
 637   // (part of) an object at the end of the allocated space and extend
 638   // beyond the end of allocation.
 639 
 640   // Non-humongous objects are only allocated in the old-gen during
 641   // GC, so if region is old then top is stable.  Humongous object
 642   // allocation sets top last; if top has not yet been set, this is
 643   // a stale card and we'll end up with an empty intersection.  If
 644   // this is not a stale card, the synchronization between the
 645   // enqueuing of the card and processing it here will have ensured
 646   // we see the up-to-date top here.
 647   HeapWord* scan_limit = r->top();
 648 
 649   if (scan_limit <= start) {
 650     // If the trimmed region is empty, the card must be stale.
 651     return;
 652   }
 653 
 654   // Okay to clean and process the card now.  There are still some
 655   // stale card cases that may be detected by iteration and dealt with
 656   // as iteration failure.
 657   *const_cast<volatile jbyte*>(card_ptr) = CardTableModRefBS::clean_card_val();
 658 
 659   // This fence serves two purposes.  First, the card must be cleaned
 660   // before processing the contents.  Second, we can't proceed with
 661   // processing until after the read of top, for synchronization with
 662   // possibly concurrent humongous object allocation.  It's okay that
 663   // reading top and reading type were racy wrto each other.  We need
 664   // both set, in any order, to proceed.
 665   OrderAccess::fence();
 666 
 667   // Don't use addr_for(card_ptr + 1) which can ask for
 668   // a card beyond the heap.
 669   HeapWord* end = start + CardTableModRefBS::card_size_in_words;
 670   MemRegion dirty_region(start, MIN2(scan_limit, end));
 671   assert(!dirty_region.is_empty(), "sanity");
 672 
 673   G1ConcurrentRefineOopClosure conc_refine_cl(_g1, worker_i);
 674 
 675   bool card_processed =
 676     r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
 677 
 678   // If unable to process the card then we encountered an unparsable
 679   // part of the heap (e.g. a partially allocated object) while
 680   // processing a stale card.  Despite the card being stale, redirty
 681   // and re-enqueue, because we've already cleaned the card.  Without
 682   // this we could incorrectly discard a non-stale card.
 683   if (!card_processed) {
 684     // The card might have gotten re-dirtied and re-enqueued while we
 685     // worked.  (In fact, it's pretty likely.)
 686     if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 687       *card_ptr = CardTableModRefBS::dirty_card_val();
 688       MutexLockerEx x(Shared_DirtyCardQ_lock,
 689                       Mutex::_no_safepoint_check_flag);
 690       DirtyCardQueue* sdcq =
 691         JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
 692       sdcq->enqueue(card_ptr);
 693     }
 694   } else {
 695     _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
 696   }
 697 }
 698 
 699 bool G1RemSet::refine_card_during_gc(jbyte* card_ptr,
 700                                      G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
 701   assert(_g1->is_gc_active(), "Only call during GC");
 702 
 703   check_card_ptr(card_ptr, _ct_bs);
 704 
 705   // If the card is no longer dirty, nothing to do. This covers cards that were already
 706   // scanned as parts of the remembered sets.
 707   if (*card_ptr != CardTableModRefBS::dirty_card_val()) {
 708     return false;
 709   }
 710 
 711   // We claim lazily (so races are possible but they're benign), which reduces the
 712   // number of potential duplicate scans (multiple threads may enqueue the same card twice).
 713   *card_ptr = CardTableModRefBS::clean_card_val() | CardTableModRefBS::claimed_card_val();
 714 
 715   // Construct the region representing the card.
 716   HeapWord* card_start = _ct_bs->addr_for(card_ptr);
 717   // And find the region containing it.
 718   uint const card_region_idx = _g1->addr_to_region(card_start);
 719 
 720   _scan_state->add_dirty_region(card_region_idx);
 721   HeapWord* scan_limit = _scan_state->scan_top(card_region_idx);
 722   if (scan_limit <= card_start) {
 723     // If the card starts above the area in the region containing objects to scan, skip it.
 724     return false;
 725   }
 726 
 727   // Don't use addr_for(card_ptr + 1) which can ask for
 728   // a card beyond the heap.
 729   HeapWord* card_end = card_start + CardTableModRefBS::card_size_in_words;
 730   MemRegion dirty_region(card_start, MIN2(scan_limit, card_end));
 731   assert(!dirty_region.is_empty(), "sanity");
 732 
 733   HeapRegion* const card_region = _g1->region_at(card_region_idx);
 734   update_rs_cl->set_region(card_region);
 735   bool card_processed = card_region->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl);
 736   assert(card_processed, "must be");
 737   return true;
 738 }
 739 
 740 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
 741   if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
 742       (period_count % G1SummarizeRSetStatsPeriod == 0)) {
 743 
 744     G1RemSetSummary current(this);
 745     _prev_period_summary.subtract_from(&current);
 746 
 747     Log(gc, remset) log;
 748     log.trace("%s", header);
 749     ResourceMark rm;
 750     LogStream ls(log.trace());
 751     _prev_period_summary.print_on(&ls);
 752 
 753     _prev_period_summary.set(&current);
 754   }
 755 }
 756 
 757 void G1RemSet::print_summary_info() {
 758   Log(gc, remset, exit) log;
 759   if (log.is_trace()) {
 760     log.trace(" Cumulative RS summary");
 761     G1RemSetSummary current(this);
 762     ResourceMark rm;
 763     LogStream ls(log.trace());
 764     current.print_on(&ls);
 765   }
 766 }
 767 
 768 void G1RemSet::create_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
 769   _card_live_data.create(workers, mark_bitmap);
 770 }
 771 
 772 void G1RemSet::finalize_card_live_data(WorkGang* workers, G1CMBitMap* mark_bitmap) {
 773   _card_live_data.finalize(workers, mark_bitmap);
 774 }
 775 
 776 void G1RemSet::verify_card_live_data(WorkGang* workers, G1CMBitMap* bitmap) {
 777   _card_live_data.verify(workers, bitmap);
 778 }
 779 
 780 void G1RemSet::clear_card_live_data(WorkGang* workers) {
 781   _card_live_data.clear(workers);
 782 }
 783 
 784 #ifdef ASSERT
 785 void G1RemSet::verify_card_live_data_is_clear() {
 786   _card_live_data.verify_is_clear();
 787 }
 788 #endif