1 /*
   2  * Copyright (c) 2001, 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/g1BarrierSet.hpp"
  27 #include "gc/g1/g1BlockOffsetTable.inline.hpp"
  28 #include "gc/g1/g1CardTable.inline.hpp"
  29 #include "gc/g1/g1CollectedHeap.inline.hpp"
  30 #include "gc/g1/g1ConcurrentRefine.hpp"
  31 #include "gc/g1/g1DirtyCardQueue.hpp"
  32 #include "gc/g1/g1FromCardCache.hpp"
  33 #include "gc/g1/g1GCPhaseTimes.hpp"
  34 #include "gc/g1/g1HotCardCache.hpp"
  35 #include "gc/g1/g1OopClosures.inline.hpp"
  36 #include "gc/g1/g1RootClosures.hpp"
  37 #include "gc/g1/g1RemSet.hpp"
  38 #include "gc/g1/heapRegion.inline.hpp"
  39 #include "gc/g1/heapRegionManager.inline.hpp"
  40 #include "gc/g1/heapRegionRemSet.hpp"
  41 #include "gc/shared/gcTraceTime.inline.hpp"
  42 #include "gc/shared/suspendibleThreadSet.hpp"
  43 #include "jfr/jfrEvents.hpp"
  44 #include "memory/iterator.hpp"
  45 #include "memory/resourceArea.hpp"
  46 #include "oops/access.inline.hpp"
  47 #include "oops/oop.inline.hpp"
  48 #include "runtime/os.hpp"
  49 #include "utilities/align.hpp"
  50 #include "utilities/globalDefinitions.hpp"
  51 #include "utilities/intHisto.hpp"
  52 #include "utilities/stack.inline.hpp"
  53 #include "utilities/ticks.hpp"
  54 
  55 // Collects information about the overall remembered set scan progress during an evacuation.
  56 class G1RemSetScanState : public CHeapObj<mtGC> {
  57 private:
  58   class G1ClearCardTableTask : public AbstractGangTask {
  59     G1CollectedHeap* _g1h;
  60     uint* _dirty_region_list;
  61     size_t _num_dirty_regions;
  62     size_t _chunk_length;
  63 
  64     size_t volatile _cur_dirty_regions;
  65   public:
  66     G1ClearCardTableTask(G1CollectedHeap* g1h,
  67                          uint* dirty_region_list,
  68                          size_t num_dirty_regions,
  69                          size_t chunk_length) :
  70       AbstractGangTask("G1 Clear Card Table Task"),
  71       _g1h(g1h),
  72       _dirty_region_list(dirty_region_list),
  73       _num_dirty_regions(num_dirty_regions),
  74       _chunk_length(chunk_length),
  75       _cur_dirty_regions(0) {
  76 
  77       assert(chunk_length > 0, "must be");
  78     }
  79 
  80     static size_t chunk_size() { return M; }
  81 
  82     void work(uint worker_id) {
  83       while (_cur_dirty_regions < _num_dirty_regions) {
  84         size_t next = Atomic::add(_chunk_length, &_cur_dirty_regions) - _chunk_length;
  85         size_t max = MIN2(next + _chunk_length, _num_dirty_regions);
  86 
  87         for (size_t i = next; i < max; i++) {
  88           HeapRegion* r = _g1h->region_at(_dirty_region_list[i]);
  89           if (!r->is_survivor()) {
  90             r->clear_cardtable();
  91           }
  92         }
  93       }
  94     }
  95   };
  96 
  97   size_t _max_regions;
  98 
  99   // Scan progress for the remembered set of a single region. Transitions from
 100   // Unclaimed -> Claimed -> Complete.
 101   // At each of the transitions the thread that does the transition needs to perform
 102   // some special action once. This is the reason for the extra "Claimed" state.
 103   typedef jint G1RemsetIterState;
 104 
 105   static const G1RemsetIterState Unclaimed = 0; // The remembered set has not been scanned yet.
 106   static const G1RemsetIterState Claimed = 1;   // The remembered set is currently being scanned.
 107   static const G1RemsetIterState Complete = 2;  // The remembered set has been completely scanned.
 108 
 109   G1RemsetIterState volatile* _iter_states;
 110   // The current location where the next thread should continue scanning in a region's
 111   // remembered set.
 112   size_t volatile* _iter_claims;
 113 
 114   // Temporary buffer holding the regions we used to store remembered set scan duplicate
 115   // information. These are also called "dirty". Valid entries are from [0.._cur_dirty_region)
 116   uint* _dirty_region_buffer;
 117 
 118   typedef jbyte IsDirtyRegionState;
 119   static const IsDirtyRegionState Clean = 0;
 120   static const IsDirtyRegionState Dirty = 1;
 121   // Holds a flag for every region whether it is in the _dirty_region_buffer already
 122   // to avoid duplicates. Uses jbyte since there are no atomic instructions for bools.
 123   IsDirtyRegionState* _in_dirty_region_buffer;
 124   size_t _cur_dirty_region;
 125 
 126   // Creates a snapshot of the current _top values at the start of collection to
 127   // filter out card marks that we do not want to scan.
 128   class G1ResetScanTopClosure : public HeapRegionClosure {
 129   private:
 130     HeapWord** _scan_top;
 131   public:
 132     G1ResetScanTopClosure(HeapWord** scan_top) : _scan_top(scan_top) { }
 133 
 134     virtual bool do_heap_region(HeapRegion* r) {
 135       uint hrm_index = r->hrm_index();
 136       if (!r->in_collection_set() && r->is_old_or_humongous_or_archive() && !r->is_empty()) {
 137         _scan_top[hrm_index] = r->top();
 138       } else {
 139         _scan_top[hrm_index] = NULL;
 140       }
 141       return false;
 142     }
 143   };
 144 
 145   // For each region, contains the maximum top() value to be used during this garbage
 146   // collection. Subsumes common checks like filtering out everything but old and
 147   // humongous regions outside the collection set.
 148   // This is valid because we are not interested in scanning stray remembered set
 149   // entries from free or archive regions.
 150   HeapWord** _scan_top;
 151 public:
 152   G1RemSetScanState() :
 153     _max_regions(0),
 154     _iter_states(NULL),
 155     _iter_claims(NULL),
 156     _dirty_region_buffer(NULL),
 157     _in_dirty_region_buffer(NULL),
 158     _cur_dirty_region(0),
 159     _scan_top(NULL) {
 160   }
 161 
 162   ~G1RemSetScanState() {
 163     if (_iter_states != NULL) {
 164       FREE_C_HEAP_ARRAY(G1RemsetIterState, _iter_states);
 165     }
 166     if (_iter_claims != NULL) {
 167       FREE_C_HEAP_ARRAY(size_t, _iter_claims);
 168     }
 169     if (_dirty_region_buffer != NULL) {
 170       FREE_C_HEAP_ARRAY(uint, _dirty_region_buffer);
 171     }
 172     if (_in_dirty_region_buffer != NULL) {
 173       FREE_C_HEAP_ARRAY(IsDirtyRegionState, _in_dirty_region_buffer);
 174     }
 175     if (_scan_top != NULL) {
 176       FREE_C_HEAP_ARRAY(HeapWord*, _scan_top);
 177     }
 178   }
 179 
 180   void initialize(uint max_regions) {
 181     assert(_iter_states == NULL, "Must not be initialized twice");
 182     assert(_iter_claims == NULL, "Must not be initialized twice");
 183     _max_regions = max_regions;
 184     _iter_states = NEW_C_HEAP_ARRAY(G1RemsetIterState, max_regions, mtGC);
 185     _iter_claims = NEW_C_HEAP_ARRAY(size_t, max_regions, mtGC);
 186     _dirty_region_buffer = NEW_C_HEAP_ARRAY(uint, max_regions, mtGC);
 187     _in_dirty_region_buffer = NEW_C_HEAP_ARRAY(IsDirtyRegionState, max_regions, mtGC);
 188     _scan_top = NEW_C_HEAP_ARRAY(HeapWord*, max_regions, mtGC);
 189   }
 190 
 191   void reset() {
 192     for (uint i = 0; i < _max_regions; i++) {
 193       _iter_states[i] = Unclaimed;
 194       _scan_top[i] = NULL;
 195     }
 196 
 197     G1ResetScanTopClosure cl(_scan_top);
 198     G1CollectedHeap::heap()->heap_region_iterate(&cl);
 199 
 200     memset((void*)_iter_claims, 0, _max_regions * sizeof(size_t));
 201     memset(_in_dirty_region_buffer, Clean, _max_regions * sizeof(IsDirtyRegionState));
 202     _cur_dirty_region = 0;
 203   }
 204 
 205   // Attempt to claim the remembered set of the region for iteration. Returns true
 206   // if this call caused the transition from Unclaimed to Claimed.
 207   inline bool claim_iter(uint region) {
 208     assert(region < _max_regions, "Tried to access invalid region %u", region);
 209     if (_iter_states[region] != Unclaimed) {
 210       return false;
 211     }
 212     G1RemsetIterState res = Atomic::cmpxchg(Claimed, &_iter_states[region], Unclaimed);
 213     return (res == Unclaimed);
 214   }
 215 
 216   // Try to atomically sets the iteration state to "complete". Returns true for the
 217   // thread that caused the transition.
 218   inline bool set_iter_complete(uint region) {
 219     if (iter_is_complete(region)) {
 220       return false;
 221     }
 222     G1RemsetIterState res = Atomic::cmpxchg(Complete, &_iter_states[region], Claimed);
 223     return (res == Claimed);
 224   }
 225 
 226   // Returns true if the region's iteration is complete.
 227   inline bool iter_is_complete(uint region) const {
 228     assert(region < _max_regions, "Tried to access invalid region %u", region);
 229     return _iter_states[region] == Complete;
 230   }
 231 
 232   // The current position within the remembered set of the given region.
 233   inline size_t iter_claimed(uint region) const {
 234     assert(region < _max_regions, "Tried to access invalid region %u", region);
 235     return _iter_claims[region];
 236   }
 237 
 238   // Claim the next block of cards within the remembered set of the region with
 239   // step size.
 240   inline size_t iter_claimed_next(uint region, size_t step) {
 241     return Atomic::add(step, &_iter_claims[region]) - step;
 242   }
 243 
 244   void add_dirty_region(uint region) {
 245     if (_in_dirty_region_buffer[region] == Dirty) {
 246       return;
 247     }
 248 
 249     bool marked_as_dirty = Atomic::cmpxchg(Dirty, &_in_dirty_region_buffer[region], Clean) == Clean;
 250     if (marked_as_dirty) {
 251       size_t allocated = Atomic::add(1u, &_cur_dirty_region) - 1;
 252       _dirty_region_buffer[allocated] = region;
 253     }
 254   }
 255 
 256   HeapWord* scan_top(uint region_idx) const {
 257     return _scan_top[region_idx];
 258   }
 259 
 260   // Clear the card table of "dirty" regions.
 261   void clear_card_table(WorkGang* workers) {
 262     if (_cur_dirty_region == 0) {
 263       return;
 264     }
 265 
 266     size_t const num_chunks = align_up(_cur_dirty_region * HeapRegion::CardsPerRegion, G1ClearCardTableTask::chunk_size()) / G1ClearCardTableTask::chunk_size();
 267     uint const num_workers = (uint)MIN2(num_chunks, (size_t)workers->active_workers());
 268     size_t const chunk_length = G1ClearCardTableTask::chunk_size() / HeapRegion::CardsPerRegion;
 269 
 270     // Iterate over the dirty cards region list.
 271     G1ClearCardTableTask cl(G1CollectedHeap::heap(), _dirty_region_buffer, _cur_dirty_region, chunk_length);
 272 
 273     log_debug(gc, ergo)("Running %s using %u workers for " SIZE_FORMAT " "
 274                         "units of work for " SIZE_FORMAT " regions.",
 275                         cl.name(), num_workers, num_chunks, _cur_dirty_region);
 276     workers->run_task(&cl, num_workers);
 277 
 278 #ifndef PRODUCT
 279     G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
 280 #endif
 281   }
 282 };
 283 
 284 G1RemSet::G1RemSet(G1CollectedHeap* g1h,
 285                    G1CardTable* ct,
 286                    G1HotCardCache* hot_card_cache) :
 287   _scan_state(new G1RemSetScanState()),
 288   _prev_period_summary(),
 289   _g1h(g1h),
 290   _num_conc_refined_cards(0),
 291   _ct(ct),
 292   _g1p(_g1h->policy()),
 293   _hot_card_cache(hot_card_cache) {
 294 }
 295 
 296 G1RemSet::~G1RemSet() {
 297   if (_scan_state != NULL) {
 298     delete _scan_state;
 299   }
 300 }
 301 
 302 uint G1RemSet::num_par_rem_sets() {
 303   return G1DirtyCardQueueSet::num_par_ids() + G1ConcurrentRefine::max_num_threads() + MAX2(ConcGCThreads, ParallelGCThreads);
 304 }
 305 
 306 void G1RemSet::initialize(size_t capacity, uint max_regions) {
 307   G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
 308   _scan_state->initialize(max_regions);
 309 }
 310 
 311 G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state,
 312                                                    G1ScanObjsDuringScanRSClosure* scan_obj_on_card,
 313                                                    G1ParScanThreadState* pss,
 314                                                    G1GCPhaseTimes::GCParPhases phase,
 315                                                    uint worker_i) :
 316   _g1h(G1CollectedHeap::heap()),
 317   _ct(_g1h->card_table()),
 318   _pss(pss),
 319   _scan_objs_on_card_cl(scan_obj_on_card),
 320   _scan_state(scan_state),
 321   _phase(phase),
 322   _worker_i(worker_i),
 323   _cards_scanned(0),
 324   _cards_claimed(0),
 325   _cards_skipped(0),
 326   _rem_set_root_scan_time(),
 327   _rem_set_trim_partially_time(),
 328   _strong_code_root_scan_time(),
 329   _strong_code_trim_partially_time() {
 330 }
 331 
 332 void G1ScanRSForRegionClosure::claim_card(size_t card_index, const uint region_idx_for_card){
 333   _ct->set_card_claimed(card_index);
 334   _scan_state->add_dirty_region(region_idx_for_card);
 335 }
 336 
 337 void G1ScanRSForRegionClosure::scan_card(MemRegion mr, uint region_idx_for_card) {
 338   HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
 339   assert(!card_region->is_young(), "Should not scan card in young region %u", region_idx_for_card);
 340   card_region->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl);
 341   _scan_objs_on_card_cl->trim_queue_partially();
 342   _cards_scanned++;
 343 }
 344 
 345 void G1ScanRSForRegionClosure::scan_rem_set_roots(HeapRegion* r) {
 346   EventGCPhaseParallel event;
 347   uint const region_idx = r->hrm_index();
 348 
 349   if (_scan_state->claim_iter(region_idx)) {
 350     // If we ever free the collection set concurrently, we should also
 351     // clear the card table concurrently therefore we won't need to
 352     // add regions of the collection set to the dirty cards region.
 353     _scan_state->add_dirty_region(region_idx);
 354   }
 355 
 356   if (r->rem_set()->cardset_is_empty()) {
 357     return;
 358   }
 359 
 360   // We claim cards in blocks so as to reduce the contention.
 361   size_t const block_size = G1RSetScanBlockSize;
 362 
 363   HeapRegionRemSetIterator iter(r->rem_set());
 364   size_t card_index;
 365 
 366   size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
 367   for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
 368     if (current_card >= claimed_card_block + block_size) {
 369       claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
 370     }
 371     if (current_card < claimed_card_block) {
 372       _cards_skipped++;
 373       continue;
 374     }
 375     _cards_claimed++;
 376 
 377     HeapWord* const card_start = _g1h->bot()->address_for_index_raw(card_index);
 378     uint const region_idx_for_card = _g1h->addr_to_region(card_start);
 379 
 380 #ifdef ASSERT
 381     HeapRegion* hr = _g1h->region_at_or_null(region_idx_for_card);
 382     assert(hr == NULL || hr->is_in_reserved(card_start),
 383            "Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index());
 384 #endif
 385     HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
 386     if (card_start >= top) {
 387       continue;
 388     }
 389 
 390     // If the card is dirty, then G1 will scan it during Update RS.
 391     if (_ct->is_card_claimed(card_index) || _ct->is_card_dirty(card_index)) {
 392       continue;
 393     }
 394 
 395     // We claim lazily (so races are possible but they're benign), which reduces the
 396     // number of duplicate scans (the rsets of the regions in the cset can intersect).
 397     // Claim the card after checking bounds above: the remembered set may contain
 398     // random cards into current survivor, and we would then have an incorrectly
 399     // claimed card in survivor space. Card table clear does not reset the card table
 400     // of survivor space regions.
 401     claim_card(card_index, region_idx_for_card);
 402 
 403     MemRegion const mr(card_start, MIN2(card_start + BOTConstants::N_words, top));
 404 
 405     scan_card(mr, region_idx_for_card);
 406   }
 407   event.commit(GCId::current(), _worker_i, G1GCPhaseTimes::phase_name(_phase));
 408 }
 409 
 410 void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) {
 411   EventGCPhaseParallel event;
 412   // We pass a weak code blobs closure to the remembered set scanning because we want to avoid
 413   // treating the nmethods visited to act as roots for concurrent marking.
 414   // We only want to make sure that the oops in the nmethods are adjusted with regard to the
 415   // objects copied by the current evacuation.
 416   r->strong_code_roots_do(_pss->closures()->weak_codeblobs());
 417   event.commit(GCId::current(), _worker_i, G1GCPhaseTimes::phase_name(G1GCPhaseTimes::CodeRoots));
 418 }
 419 
 420 bool G1ScanRSForRegionClosure::do_heap_region(HeapRegion* r) {
 421   assert(r->in_collection_set(),
 422          "Should only be called on elements of the collection set but region %u is not.",
 423          r->hrm_index());
 424   uint const region_idx = r->hrm_index();
 425 
 426   // Do an early out if we know we are complete.
 427   if (_scan_state->iter_is_complete(region_idx)) {
 428     return false;
 429   }
 430 
 431   {
 432     G1EvacPhaseWithTrimTimeTracker timer(_pss, _rem_set_root_scan_time, _rem_set_trim_partially_time);
 433     scan_rem_set_roots(r);
 434   }
 435 
 436   if (_scan_state->set_iter_complete(region_idx)) {
 437     G1EvacPhaseWithTrimTimeTracker timer(_pss, _strong_code_root_scan_time, _strong_code_trim_partially_time);
 438     // Scan the strong code root list attached to the current region
 439     scan_strong_code_roots(r);
 440   }
 441   return false;
 442 }
 443 
 444 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss, uint worker_i) {
 445   G1ScanObjsDuringScanRSClosure scan_cl(_g1h, pss);
 446   G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, pss, G1GCPhaseTimes::ScanRS, worker_i);
 447   _g1h->collection_set_iterate_from(&cl, worker_i);
 448 
 449   G1GCPhaseTimes* p = _g1p->phase_times();
 450 
 451   p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, cl.rem_set_root_scan_time().seconds());
 452   p->add_time_secs(G1GCPhaseTimes::ObjCopy, worker_i, cl.rem_set_trim_partially_time().seconds());
 453 
 454   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards);
 455   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards);
 456   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards);
 457 
 458   p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time().seconds());
 459   p->add_time_secs(G1GCPhaseTimes::ObjCopy, worker_i, cl.strong_code_root_trim_partially_time().seconds());
 460 }
 461 
 462 // Closure used for updating rem sets. Only called during an evacuation pause.
 463 class G1RefineCardClosure: public G1CardTableEntryClosure {
 464   G1RemSet* _g1rs;
 465   G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
 466 
 467   size_t _cards_scanned;
 468   size_t _cards_skipped;
 469 public:
 470   G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
 471     _g1rs(g1h->rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0)
 472   {}
 473 
 474   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
 475     // The only time we care about recording cards that
 476     // contain references that point into the collection set
 477     // is during RSet updating within an evacuation pause.
 478     // In this case worker_i should be the id of a GC worker thread.
 479     assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
 480 
 481     bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
 482 
 483     if (card_scanned) {
 484       _update_rs_cl->trim_queue_partially();
 485       _cards_scanned++;
 486     } else {
 487       _cards_skipped++;
 488     }
 489     return true;
 490   }
 491 
 492   size_t cards_scanned() const { return _cards_scanned; }
 493   size_t cards_skipped() const { return _cards_skipped; }
 494 };
 495 
 496 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
 497   G1GCPhaseTimes* p = _g1p->phase_times();
 498 
 499   // Apply closure to log entries in the HCC.
 500   if (G1HotCardCache::default_use_cache()) {
 501     G1EvacPhaseTimesTracker x(p, pss, G1GCPhaseTimes::ScanHCC, worker_i);
 502 
 503     G1ScanObjsDuringUpdateRSClosure scan_hcc_cl(_g1h, pss);
 504     G1RefineCardClosure refine_card_cl(_g1h, &scan_hcc_cl);
 505     _g1h->iterate_hcc_closure(&refine_card_cl, worker_i);
 506   }
 507 
 508   // Now apply the closure to all remaining log entries.
 509   {
 510     G1EvacPhaseTimesTracker x(p, pss, G1GCPhaseTimes::UpdateRS, worker_i);
 511 
 512     G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1h, pss);
 513     G1RefineCardClosure refine_card_cl(_g1h, &update_rs_cl);
 514     _g1h->iterate_dirty_card_closure(&refine_card_cl, worker_i);
 515 
 516     p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards);
 517     p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards);
 518   }
 519 }
 520 
 521 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss, uint worker_i) {
 522   update_rem_set(pss, worker_i);
 523   scan_rem_set(pss, worker_i);;
 524 }
 525 
 526 void G1RemSet::prepare_for_oops_into_collection_set_do() {
 527   G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
 528   dcqs.concatenate_logs();
 529 
 530   _scan_state->reset();
 531 }
 532 
 533 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
 534   G1GCPhaseTimes* phase_times = _g1h->phase_times();
 535 
 536   // Set all cards back to clean.
 537   double start = os::elapsedTime();
 538   _scan_state->clear_card_table(_g1h->workers());
 539   phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
 540 }
 541 
 542 inline void check_card_ptr(jbyte* card_ptr, G1CardTable* ct) {
 543 #ifdef ASSERT
 544   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 545   assert(g1h->is_in_exact(ct->addr_for(card_ptr)),
 546          "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
 547          p2i(card_ptr),
 548          ct->index_for(ct->addr_for(card_ptr)),
 549          p2i(ct->addr_for(card_ptr)),
 550          g1h->addr_to_region(ct->addr_for(card_ptr)));
 551 #endif
 552 }
 553 
 554 void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
 555                                         uint worker_i) {
 556   assert(!_g1h->is_gc_active(), "Only call concurrently");
 557 
 558   // Construct the region representing the card.
 559   HeapWord* start = _ct->addr_for(card_ptr);
 560   // And find the region containing it.
 561   HeapRegion* r = _g1h->heap_region_containing_or_null(start);
 562 
 563   // If this is a (stale) card into an uncommitted region, exit.
 564   if (r == NULL) {
 565     return;
 566   }
 567 
 568   check_card_ptr(card_ptr, _ct);
 569 
 570   // If the card is no longer dirty, nothing to do.
 571   if (*card_ptr != G1CardTable::dirty_card_val()) {
 572     return;
 573   }
 574 
 575   // This check is needed for some uncommon cases where we should
 576   // ignore the card.
 577   //
 578   // The region could be young.  Cards for young regions are
 579   // distinctly marked (set to g1_young_gen), so the post-barrier will
 580   // filter them out.  However, that marking is performed
 581   // concurrently.  A write to a young object could occur before the
 582   // card has been marked young, slipping past the filter.
 583   //
 584   // The card could be stale, because the region has been freed since
 585   // the card was recorded. In this case the region type could be
 586   // anything.  If (still) free or (reallocated) young, just ignore
 587   // it.  If (reallocated) old or humongous, the later card trimming
 588   // and additional checks in iteration may detect staleness.  At
 589   // worst, we end up processing a stale card unnecessarily.
 590   //
 591   // In the normal (non-stale) case, the synchronization between the
 592   // enqueueing of the card and processing it here will have ensured
 593   // we see the up-to-date region type here.
 594   if (!r->is_old_or_humongous_or_archive()) {
 595     return;
 596   }
 597 
 598   // The result from the hot card cache insert call is either:
 599   //   * pointer to the current card
 600   //     (implying that the current card is not 'hot'),
 601   //   * null
 602   //     (meaning we had inserted the card ptr into the "hot" card cache,
 603   //     which had some headroom),
 604   //   * a pointer to a "hot" card that was evicted from the "hot" cache.
 605   //
 606 
 607   if (_hot_card_cache->use_cache()) {
 608     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
 609 
 610     const jbyte* orig_card_ptr = card_ptr;
 611     card_ptr = _hot_card_cache->insert(card_ptr);
 612     if (card_ptr == NULL) {
 613       // There was no eviction. Nothing to do.
 614       return;
 615     } else if (card_ptr != orig_card_ptr) {
 616       // Original card was inserted and an old card was evicted.
 617       start = _ct->addr_for(card_ptr);
 618       r = _g1h->heap_region_containing(start);
 619 
 620       // Check whether the region formerly in the cache should be
 621       // ignored, as discussed earlier for the original card.  The
 622       // region could have been freed while in the cache.
 623       if (!r->is_old_or_humongous_or_archive()) {
 624         return;
 625       }
 626     } // Else we still have the original card.
 627   }
 628 
 629   // Trim the region designated by the card to what's been allocated
 630   // in the region.  The card could be stale, or the card could cover
 631   // (part of) an object at the end of the allocated space and extend
 632   // beyond the end of allocation.
 633 
 634   // Non-humongous objects are only allocated in the old-gen during
 635   // GC, so if region is old then top is stable.  Humongous object
 636   // allocation sets top last; if top has not yet been set, this is
 637   // a stale card and we'll end up with an empty intersection.  If
 638   // this is not a stale card, the synchronization between the
 639   // enqueuing of the card and processing it here will have ensured
 640   // we see the up-to-date top here.
 641   HeapWord* scan_limit = r->top();
 642 
 643   if (scan_limit <= start) {
 644     // If the trimmed region is empty, the card must be stale.
 645     return;
 646   }
 647 
 648   // Okay to clean and process the card now.  There are still some
 649   // stale card cases that may be detected by iteration and dealt with
 650   // as iteration failure.
 651   *const_cast<volatile jbyte*>(card_ptr) = G1CardTable::clean_card_val();
 652 
 653   // This fence serves two purposes.  First, the card must be cleaned
 654   // before processing the contents.  Second, we can't proceed with
 655   // processing until after the read of top, for synchronization with
 656   // possibly concurrent humongous object allocation.  It's okay that
 657   // reading top and reading type were racy wrto each other.  We need
 658   // both set, in any order, to proceed.
 659   OrderAccess::fence();
 660 
 661   // Don't use addr_for(card_ptr + 1) which can ask for
 662   // a card beyond the heap.
 663   HeapWord* end = start + G1CardTable::card_size_in_words;
 664   MemRegion dirty_region(start, MIN2(scan_limit, end));
 665   assert(!dirty_region.is_empty(), "sanity");
 666 
 667   G1ConcurrentRefineOopClosure conc_refine_cl(_g1h, worker_i);
 668 
 669   bool card_processed =
 670     r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
 671 
 672   // If unable to process the card then we encountered an unparsable
 673   // part of the heap (e.g. a partially allocated object) while
 674   // processing a stale card.  Despite the card being stale, redirty
 675   // and re-enqueue, because we've already cleaned the card.  Without
 676   // this we could incorrectly discard a non-stale card.
 677   if (!card_processed) {
 678     // The card might have gotten re-dirtied and re-enqueued while we
 679     // worked.  (In fact, it's pretty likely.)
 680     if (*card_ptr != G1CardTable::dirty_card_val()) {
 681       *card_ptr = G1CardTable::dirty_card_val();
 682       MutexLockerEx x(Shared_DirtyCardQ_lock,
 683                       Mutex::_no_safepoint_check_flag);
 684       G1DirtyCardQueue* sdcq =
 685         G1BarrierSet::dirty_card_queue_set().shared_dirty_card_queue();
 686       sdcq->enqueue(card_ptr);
 687     }
 688   } else {
 689     _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
 690   }
 691 }
 692 
 693 bool G1RemSet::refine_card_during_gc(jbyte* card_ptr,
 694                                      G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
 695   assert(_g1h->is_gc_active(), "Only call during GC");
 696 
 697   // Construct the region representing the card.
 698   HeapWord* card_start = _ct->addr_for(card_ptr);
 699   // And find the region containing it.
 700   uint const card_region_idx = _g1h->addr_to_region(card_start);
 701 
 702   HeapWord* scan_limit = _scan_state->scan_top(card_region_idx);
 703   if (scan_limit == NULL) {
 704     // This is a card into an uncommitted region. We need to bail out early as we
 705     // should not access the corresponding card table entry.
 706     return false;
 707   }
 708 
 709   check_card_ptr(card_ptr, _ct);
 710 
 711   // If the card is no longer dirty, nothing to do. This covers cards that were already
 712   // scanned as parts of the remembered sets.
 713   if (*card_ptr != G1CardTable::dirty_card_val()) {
 714     return false;
 715   }
 716 
 717   // We claim lazily (so races are possible but they're benign), which reduces the
 718   // number of potential duplicate scans (multiple threads may enqueue the same card twice).
 719   *card_ptr = G1CardTable::clean_card_val() | G1CardTable::claimed_card_val();
 720 
 721   _scan_state->add_dirty_region(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 + G1CardTable::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 = _g1h->region_at(card_region_idx);
 734   assert(!card_region->is_young(), "Should not scan card in young region %u", card_region_idx);
 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 class G1RebuildRemSetTask: public AbstractGangTask {
 769   // Aggregate the counting data that was constructed concurrently
 770   // with marking.
 771   class G1RebuildRemSetHeapRegionClosure : public HeapRegionClosure {
 772     G1ConcurrentMark* _cm;
 773     G1RebuildRemSetClosure _update_cl;
 774 
 775     // Applies _update_cl to the references of the given object, limiting objArrays
 776     // to the given MemRegion. Returns the amount of words actually scanned.
 777     size_t scan_for_references(oop const obj, MemRegion mr) {
 778       size_t const obj_size = obj->size();
 779       // All non-objArrays and objArrays completely within the mr
 780       // can be scanned without passing the mr.
 781       if (!obj->is_objArray() || mr.contains(MemRegion((HeapWord*)obj, obj_size))) {
 782         obj->oop_iterate(&_update_cl);
 783         return obj_size;
 784       }
 785       // This path is for objArrays crossing the given MemRegion. Only scan the
 786       // area within the MemRegion.
 787       obj->oop_iterate(&_update_cl, mr);
 788       return mr.intersection(MemRegion((HeapWord*)obj, obj_size)).word_size();
 789     }
 790 
 791     // A humongous object is live (with respect to the scanning) either
 792     // a) it is marked on the bitmap as such
 793     // b) its TARS is larger than TAMS, i.e. has been allocated during marking.
 794     bool is_humongous_live(oop const humongous_obj, const G1CMBitMap* const bitmap, HeapWord* tams, HeapWord* tars) const {
 795       return bitmap->is_marked(humongous_obj) || (tars > tams);
 796     }
 797 
 798     // Iterator over the live objects within the given MemRegion.
 799     class LiveObjIterator : public StackObj {
 800       const G1CMBitMap* const _bitmap;
 801       const HeapWord* _tams;
 802       const MemRegion _mr;
 803       HeapWord* _current;
 804 
 805       bool is_below_tams() const {
 806         return _current < _tams;
 807       }
 808 
 809       bool is_live(HeapWord* obj) const {
 810         return !is_below_tams() || _bitmap->is_marked(obj);
 811       }
 812 
 813       HeapWord* bitmap_limit() const {
 814         return MIN2(const_cast<HeapWord*>(_tams), _mr.end());
 815       }
 816 
 817       void move_if_below_tams() {
 818         if (is_below_tams() && has_next()) {
 819           _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
 820         }
 821       }
 822     public:
 823       LiveObjIterator(const G1CMBitMap* const bitmap, const HeapWord* tams, const MemRegion mr, HeapWord* first_oop_into_mr) :
 824           _bitmap(bitmap),
 825           _tams(tams),
 826           _mr(mr),
 827           _current(first_oop_into_mr) {
 828 
 829         assert(_current <= _mr.start(),
 830                "First oop " PTR_FORMAT " should extend into mr [" PTR_FORMAT ", " PTR_FORMAT ")",
 831                p2i(first_oop_into_mr), p2i(mr.start()), p2i(mr.end()));
 832 
 833         // Step to the next live object within the MemRegion if needed.
 834         if (is_live(_current)) {
 835           // Non-objArrays were scanned by the previous part of that region.
 836           if (_current < mr.start() && !oop(_current)->is_objArray()) {
 837             _current += oop(_current)->size();
 838             // We might have positioned _current on a non-live object. Reposition to the next
 839             // live one if needed.
 840             move_if_below_tams();
 841           }
 842         } else {
 843           // The object at _current can only be dead if below TAMS, so we can use the bitmap.
 844           // immediately.
 845           _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
 846           assert(_current == _mr.end() || is_live(_current),
 847                  "Current " PTR_FORMAT " should be live (%s) or beyond the end of the MemRegion (" PTR_FORMAT ")",
 848                  p2i(_current), BOOL_TO_STR(is_live(_current)), p2i(_mr.end()));
 849         }
 850       }
 851 
 852       void move_to_next() {
 853         _current += next()->size();
 854         move_if_below_tams();
 855       }
 856 
 857       oop next() const {
 858         oop result = oop(_current);
 859         assert(is_live(_current),
 860                "Object " PTR_FORMAT " must be live TAMS " PTR_FORMAT " below %d mr " PTR_FORMAT " " PTR_FORMAT " outside %d",
 861                p2i(_current), p2i(_tams), _tams > _current, p2i(_mr.start()), p2i(_mr.end()), _mr.contains(result));
 862         return result;
 863       }
 864 
 865       bool has_next() const {
 866         return _current < _mr.end();
 867       }
 868     };
 869 
 870     // Rebuild remembered sets in the part of the region specified by mr and hr.
 871     // Objects between the bottom of the region and the TAMS are checked for liveness
 872     // using the given bitmap. Objects between TAMS and TARS are assumed to be live.
 873     // Returns the number of live words between bottom and TAMS.
 874     size_t rebuild_rem_set_in_region(const G1CMBitMap* const bitmap,
 875                                      HeapWord* const top_at_mark_start,
 876                                      HeapWord* const top_at_rebuild_start,
 877                                      HeapRegion* hr,
 878                                      MemRegion mr) {
 879       size_t marked_words = 0;
 880 
 881       if (hr->is_humongous()) {
 882         oop const humongous_obj = oop(hr->humongous_start_region()->bottom());
 883         if (is_humongous_live(humongous_obj, bitmap, top_at_mark_start, top_at_rebuild_start)) {
 884           // We need to scan both [bottom, TAMS) and [TAMS, top_at_rebuild_start);
 885           // however in case of humongous objects it is sufficient to scan the encompassing
 886           // area (top_at_rebuild_start is always larger or equal to TAMS) as one of the
 887           // two areas will be zero sized. I.e. TAMS is either
 888           // the same as bottom or top(_at_rebuild_start). There is no way TAMS has a different
 889           // value: this would mean that TAMS points somewhere into the object.
 890           assert(hr->top() == top_at_mark_start || hr->top() == top_at_rebuild_start,
 891                  "More than one object in the humongous region?");
 892           humongous_obj->oop_iterate(&_update_cl, mr);
 893           return top_at_mark_start != hr->bottom() ? mr.intersection(MemRegion((HeapWord*)humongous_obj, humongous_obj->size())).byte_size() : 0;
 894         } else {
 895           return 0;
 896         }
 897       }
 898 
 899       for (LiveObjIterator it(bitmap, top_at_mark_start, mr, hr->block_start(mr.start())); it.has_next(); it.move_to_next()) {
 900         oop obj = it.next();
 901         size_t scanned_size = scan_for_references(obj, mr);
 902         if ((HeapWord*)obj < top_at_mark_start) {
 903           marked_words += scanned_size;
 904         }
 905       }
 906 
 907       return marked_words * HeapWordSize;
 908     }
 909 public:
 910   G1RebuildRemSetHeapRegionClosure(G1CollectedHeap* g1h,
 911                                    G1ConcurrentMark* cm,
 912                                    uint worker_id) :
 913     HeapRegionClosure(),
 914     _cm(cm),
 915     _update_cl(g1h, worker_id) { }
 916 
 917     bool do_heap_region(HeapRegion* hr) {
 918       if (_cm->has_aborted()) {
 919         return true;
 920       }
 921 
 922       uint const region_idx = hr->hrm_index();
 923       DEBUG_ONLY(HeapWord* const top_at_rebuild_start_check = _cm->top_at_rebuild_start(region_idx);)
 924       assert(top_at_rebuild_start_check == NULL ||
 925              top_at_rebuild_start_check > hr->bottom(),
 926              "A TARS (" PTR_FORMAT ") == bottom() (" PTR_FORMAT ") indicates the old region %u is empty (%s)",
 927              p2i(top_at_rebuild_start_check), p2i(hr->bottom()),  region_idx, hr->get_type_str());
 928 
 929       size_t total_marked_bytes = 0;
 930       size_t const chunk_size_in_words = G1RebuildRemSetChunkSize / HeapWordSize;
 931 
 932       HeapWord* const top_at_mark_start = hr->prev_top_at_mark_start();
 933 
 934       HeapWord* cur = hr->bottom();
 935       while (cur < hr->end()) {
 936         // After every iteration (yield point) we need to check whether the region's
 937         // TARS changed due to e.g. eager reclaim.
 938         HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);
 939         if (top_at_rebuild_start == NULL) {
 940           return false;
 941         }
 942 
 943         MemRegion next_chunk = MemRegion(hr->bottom(), top_at_rebuild_start).intersection(MemRegion(cur, chunk_size_in_words));
 944         if (next_chunk.is_empty()) {
 945           break;
 946         }
 947 
 948         const Ticks start = Ticks::now();
 949         size_t marked_bytes = rebuild_rem_set_in_region(_cm->prev_mark_bitmap(),
 950                                                         top_at_mark_start,
 951                                                         top_at_rebuild_start,
 952                                                         hr,
 953                                                         next_chunk);
 954         Tickspan time = Ticks::now() - start;
 955 
 956         log_trace(gc, remset, tracking)("Rebuilt region %u "
 957                                         "live " SIZE_FORMAT " "
 958                                         "time %.3fms "
 959                                         "marked bytes " SIZE_FORMAT " "
 960                                         "bot " PTR_FORMAT " "
 961                                         "TAMS " PTR_FORMAT " "
 962                                         "TARS " PTR_FORMAT,
 963                                         region_idx,
 964                                         _cm->liveness(region_idx) * HeapWordSize,
 965                                         time.seconds() * 1000.0,
 966                                         marked_bytes,
 967                                         p2i(hr->bottom()),
 968                                         p2i(top_at_mark_start),
 969                                         p2i(top_at_rebuild_start));
 970 
 971         if (marked_bytes > 0) {
 972           total_marked_bytes += marked_bytes;
 973         }
 974         cur += chunk_size_in_words;
 975 
 976         _cm->do_yield_check();
 977         if (_cm->has_aborted()) {
 978           return true;
 979         }
 980       }
 981       // In the final iteration of the loop the region might have been eagerly reclaimed.
 982       // Simply filter out those regions. We can not just use region type because there
 983       // might have already been new allocations into these regions.
 984       DEBUG_ONLY(HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);)
 985       assert(top_at_rebuild_start == NULL ||
 986              total_marked_bytes == hr->marked_bytes(),
 987              "Marked bytes " SIZE_FORMAT " for region %u (%s) in [bottom, TAMS) do not match calculated marked bytes " SIZE_FORMAT " "
 988              "(" PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT ")",
 989              total_marked_bytes, hr->hrm_index(), hr->get_type_str(), hr->marked_bytes(),
 990              p2i(hr->bottom()), p2i(top_at_mark_start), p2i(top_at_rebuild_start));
 991        // Abort state may have changed after the yield check.
 992       return _cm->has_aborted();
 993     }
 994   };
 995 
 996   HeapRegionClaimer _hr_claimer;
 997   G1ConcurrentMark* _cm;
 998 
 999   uint _worker_id_offset;
1000 public:
1001   G1RebuildRemSetTask(G1ConcurrentMark* cm,
1002                       uint n_workers,
1003                       uint worker_id_offset) :
1004       AbstractGangTask("G1 Rebuild Remembered Set"),
1005       _hr_claimer(n_workers),
1006       _cm(cm),
1007       _worker_id_offset(worker_id_offset) {
1008   }
1009 
1010   void work(uint worker_id) {
1011     SuspendibleThreadSetJoiner sts_join;
1012 
1013     G1CollectedHeap* g1h = G1CollectedHeap::heap();
1014 
1015     G1RebuildRemSetHeapRegionClosure cl(g1h, _cm, _worker_id_offset + worker_id);
1016     g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hr_claimer, worker_id);
1017   }
1018 };
1019 
1020 void G1RemSet::rebuild_rem_set(G1ConcurrentMark* cm,
1021                                WorkGang* workers,
1022                                uint worker_id_offset) {
1023   uint num_workers = workers->active_workers();
1024 
1025   G1RebuildRemSetTask cl(cm,
1026                          num_workers,
1027                          worker_id_offset);
1028   workers->run_task(&cl, num_workers);
1029 }