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->g1_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   r->strong_code_roots_do(_pss->closures()->weak_codeblobs());
 413   event.commit(GCId::current(), _worker_i, G1GCPhaseTimes::phase_name(G1GCPhaseTimes::CodeRoots));
 414 }
 415 
 416 bool G1ScanRSForRegionClosure::do_heap_region(HeapRegion* r) {
 417   assert(r->in_collection_set(),
 418          "Should only be called on elements of the collection set but region %u is not.",
 419          r->hrm_index());
 420   uint const region_idx = r->hrm_index();
 421 
 422   // Do an early out if we know we are complete.
 423   if (_scan_state->iter_is_complete(region_idx)) {
 424     return false;
 425   }
 426 
 427   {
 428     G1EvacPhaseWithTrimTimeTracker timer(_pss, _rem_set_root_scan_time, _rem_set_trim_partially_time);
 429     scan_rem_set_roots(r);
 430   }
 431 
 432   if (_scan_state->set_iter_complete(region_idx)) {
 433     G1EvacPhaseWithTrimTimeTracker timer(_pss, _strong_code_root_scan_time, _strong_code_trim_partially_time);
 434     // Scan the strong code root list attached to the current region
 435     scan_strong_code_roots(r);
 436   }
 437   return false;
 438 }
 439 
 440 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss, uint worker_i) {
 441   G1ScanObjsDuringScanRSClosure scan_cl(_g1h, pss);
 442   G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, pss, G1GCPhaseTimes::ScanRS, worker_i);
 443   _g1h->collection_set_iterate_from(&cl, worker_i);
 444 
 445   G1GCPhaseTimes* p = _g1p->phase_times();
 446 
 447   p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, cl.rem_set_root_scan_time().seconds());
 448   p->add_time_secs(G1GCPhaseTimes::ObjCopy, worker_i, cl.rem_set_trim_partially_time().seconds());
 449 
 450   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards);
 451   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards);
 452   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards);
 453 
 454   p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time().seconds());
 455   p->add_time_secs(G1GCPhaseTimes::ObjCopy, worker_i, cl.strong_code_root_trim_partially_time().seconds());
 456 }
 457 
 458 // Closure used for updating rem sets. Only called during an evacuation pause.
 459 class G1RefineCardClosure: public G1CardTableEntryClosure {
 460   G1RemSet* _g1rs;
 461   G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
 462 
 463   size_t _cards_scanned;
 464   size_t _cards_skipped;
 465 public:
 466   G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
 467     _g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0)
 468   {}
 469 
 470   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
 471     // The only time we care about recording cards that
 472     // contain references that point into the collection set
 473     // is during RSet updating within an evacuation pause.
 474     // In this case worker_i should be the id of a GC worker thread.
 475     assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
 476 
 477     bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
 478 
 479     if (card_scanned) {
 480       _update_rs_cl->trim_queue_partially();
 481       _cards_scanned++;
 482     } else {
 483       _cards_skipped++;
 484     }
 485     return true;
 486   }
 487 
 488   size_t cards_scanned() const { return _cards_scanned; }
 489   size_t cards_skipped() const { return _cards_skipped; }
 490 };
 491 
 492 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
 493   G1GCPhaseTimes* p = _g1p->phase_times();
 494 
 495   // Apply closure to log entries in the HCC.
 496   if (G1HotCardCache::default_use_cache()) {
 497     G1EvacPhaseTimesTracker x(p, pss, G1GCPhaseTimes::ScanHCC, worker_i);
 498 
 499     G1ScanObjsDuringUpdateRSClosure scan_hcc_cl(_g1h, pss);
 500     G1RefineCardClosure refine_card_cl(_g1h, &scan_hcc_cl);
 501     _g1h->iterate_hcc_closure(&refine_card_cl, worker_i);
 502   }
 503 
 504   // Now apply the closure to all remaining log entries.
 505   {
 506     G1EvacPhaseTimesTracker x(p, pss, G1GCPhaseTimes::UpdateRS, worker_i);
 507 
 508     G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1h, pss);
 509     G1RefineCardClosure refine_card_cl(_g1h, &update_rs_cl);
 510     _g1h->iterate_dirty_card_closure(&refine_card_cl, worker_i);
 511 
 512     p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards);
 513     p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards);
 514   }
 515 }
 516 
 517 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss, uint worker_i) {
 518   update_rem_set(pss, worker_i);
 519   scan_rem_set(pss, worker_i);;
 520 }
 521 
 522 void G1RemSet::prepare_for_oops_into_collection_set_do() {
 523   G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
 524   dcqs.concatenate_logs();
 525 
 526   _scan_state->reset();
 527 }
 528 
 529 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
 530   G1GCPhaseTimes* phase_times = _g1h->g1_policy()->phase_times();
 531 
 532   // Set all cards back to clean.
 533   double start = os::elapsedTime();
 534   _scan_state->clear_card_table(_g1h->workers());
 535   phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
 536 }
 537 
 538 inline void check_card_ptr(jbyte* card_ptr, G1CardTable* ct) {
 539 #ifdef ASSERT
 540   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 541   assert(g1h->is_in_exact(ct->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->index_for(ct->addr_for(card_ptr)),
 545          p2i(ct->addr_for(card_ptr)),
 546          g1h->addr_to_region(ct->addr_for(card_ptr)));
 547 #endif
 548 }
 549 
 550 void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
 551                                         uint worker_i) {
 552   assert(!_g1h->is_gc_active(), "Only call concurrently");
 553 
 554   // Construct the region representing the card.
 555   HeapWord* start = _ct->addr_for(card_ptr);
 556   // And find the region containing it.
 557   HeapRegion* r = _g1h->heap_region_containing_or_null(start);
 558 
 559   // If this is a (stale) card into an uncommitted region, exit.
 560   if (r == NULL) {
 561     return;
 562   }
 563 
 564   check_card_ptr(card_ptr, _ct);
 565 
 566   // If the card is no longer dirty, nothing to do.
 567   if (*card_ptr != G1CardTable::dirty_card_val()) {
 568     return;
 569   }
 570 
 571   // This check is needed for some uncommon cases where we should
 572   // ignore the card.
 573   //
 574   // The region could be young.  Cards for young regions are
 575   // distinctly marked (set to g1_young_gen), so the post-barrier will
 576   // filter them out.  However, that marking is performed
 577   // concurrently.  A write to a young object could occur before the
 578   // card has been marked young, slipping past the filter.
 579   //
 580   // The card could be stale, because the region has been freed since
 581   // the card was recorded. In this case the region type could be
 582   // anything.  If (still) free or (reallocated) young, just ignore
 583   // it.  If (reallocated) old or humongous, the later card trimming
 584   // and additional checks in iteration may detect staleness.  At
 585   // worst, we end up processing a stale card unnecessarily.
 586   //
 587   // In the normal (non-stale) case, the synchronization between the
 588   // enqueueing of the card and processing it here will have ensured
 589   // we see the up-to-date region type here.
 590   if (!r->is_old_or_humongous_or_archive()) {
 591     return;
 592   }
 593 
 594   // The result from the hot card cache insert call is either:
 595   //   * pointer to the current card
 596   //     (implying that the current card is not 'hot'),
 597   //   * null
 598   //     (meaning we had inserted the card ptr into the "hot" card cache,
 599   //     which had some headroom),
 600   //   * a pointer to a "hot" card that was evicted from the "hot" cache.
 601   //
 602 
 603   if (_hot_card_cache->use_cache()) {
 604     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
 605 
 606     const jbyte* orig_card_ptr = card_ptr;
 607     card_ptr = _hot_card_cache->insert(card_ptr);
 608     if (card_ptr == NULL) {
 609       // There was no eviction. Nothing to do.
 610       return;
 611     } else if (card_ptr != orig_card_ptr) {
 612       // Original card was inserted and an old card was evicted.
 613       start = _ct->addr_for(card_ptr);
 614       r = _g1h->heap_region_containing(start);
 615 
 616       // Check whether the region formerly in the cache should be
 617       // ignored, as discussed earlier for the original card.  The
 618       // region could have been freed while in the cache.
 619       if (!r->is_old_or_humongous_or_archive()) {
 620         return;
 621       }
 622     } // Else we still have the original card.
 623   }
 624 
 625   // Trim the region designated by the card to what's been allocated
 626   // in the region.  The card could be stale, or the card could cover
 627   // (part of) an object at the end of the allocated space and extend
 628   // beyond the end of allocation.
 629 
 630   // Non-humongous objects are only allocated in the old-gen during
 631   // GC, so if region is old then top is stable.  Humongous object
 632   // allocation sets top last; if top has not yet been set, this is
 633   // a stale card and we'll end up with an empty intersection.  If
 634   // this is not a stale card, the synchronization between the
 635   // enqueuing of the card and processing it here will have ensured
 636   // we see the up-to-date top here.
 637   HeapWord* scan_limit = r->top();
 638 
 639   if (scan_limit <= start) {
 640     // If the trimmed region is empty, the card must be stale.
 641     return;
 642   }
 643 
 644   // Okay to clean and process the card now.  There are still some
 645   // stale card cases that may be detected by iteration and dealt with
 646   // as iteration failure.
 647   *const_cast<volatile jbyte*>(card_ptr) = G1CardTable::clean_card_val();
 648 
 649   // This fence serves two purposes.  First, the card must be cleaned
 650   // before processing the contents.  Second, we can't proceed with
 651   // processing until after the read of top, for synchronization with
 652   // possibly concurrent humongous object allocation.  It's okay that
 653   // reading top and reading type were racy wrto each other.  We need
 654   // both set, in any order, to proceed.
 655   OrderAccess::fence();
 656 
 657   // Don't use addr_for(card_ptr + 1) which can ask for
 658   // a card beyond the heap.
 659   HeapWord* end = start + G1CardTable::card_size_in_words;
 660   MemRegion dirty_region(start, MIN2(scan_limit, end));
 661   assert(!dirty_region.is_empty(), "sanity");
 662 
 663   G1ConcurrentRefineOopClosure conc_refine_cl(_g1h, worker_i);
 664 
 665   bool card_processed =
 666     r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
 667 
 668   // If unable to process the card then we encountered an unparsable
 669   // part of the heap (e.g. a partially allocated object) while
 670   // processing a stale card.  Despite the card being stale, redirty
 671   // and re-enqueue, because we've already cleaned the card.  Without
 672   // this we could incorrectly discard a non-stale card.
 673   if (!card_processed) {
 674     // The card might have gotten re-dirtied and re-enqueued while we
 675     // worked.  (In fact, it's pretty likely.)
 676     if (*card_ptr != G1CardTable::dirty_card_val()) {
 677       *card_ptr = G1CardTable::dirty_card_val();
 678       MutexLockerEx x(Shared_DirtyCardQ_lock,
 679                       Mutex::_no_safepoint_check_flag);
 680       G1DirtyCardQueue* sdcq =
 681         G1BarrierSet::dirty_card_queue_set().shared_dirty_card_queue();
 682       sdcq->enqueue(card_ptr);
 683     }
 684   } else {
 685     _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
 686   }
 687 }
 688 
 689 bool G1RemSet::refine_card_during_gc(jbyte* card_ptr,
 690                                      G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
 691   assert(_g1h->is_gc_active(), "Only call during GC");
 692 
 693   // Construct the region representing the card.
 694   HeapWord* card_start = _ct->addr_for(card_ptr);
 695   // And find the region containing it.
 696   uint const card_region_idx = _g1h->addr_to_region(card_start);
 697 
 698   HeapWord* scan_limit = _scan_state->scan_top(card_region_idx);
 699   if (scan_limit == NULL) {
 700     // This is a card into an uncommitted region. We need to bail out early as we
 701     // should not access the corresponding card table entry.
 702     return false;
 703   }
 704 
 705   check_card_ptr(card_ptr, _ct);
 706 
 707   // If the card is no longer dirty, nothing to do. This covers cards that were already
 708   // scanned as parts of the remembered sets.
 709   if (*card_ptr != G1CardTable::dirty_card_val()) {
 710     return false;
 711   }
 712 
 713   // We claim lazily (so races are possible but they're benign), which reduces the
 714   // number of potential duplicate scans (multiple threads may enqueue the same card twice).
 715   *card_ptr = G1CardTable::clean_card_val() | G1CardTable::claimed_card_val();
 716 
 717   _scan_state->add_dirty_region(card_region_idx);
 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 + G1CardTable::card_size_in_words;
 726   MemRegion dirty_region(card_start, MIN2(scan_limit, card_end));
 727   assert(!dirty_region.is_empty(), "sanity");
 728 
 729   HeapRegion* const card_region = _g1h->region_at(card_region_idx);
 730   assert(!card_region->is_young(), "Should not scan card in young region %u", card_region_idx);
 731   bool card_processed = card_region->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl);
 732   assert(card_processed, "must be");
 733   return true;
 734 }
 735 
 736 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
 737   if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
 738       (period_count % G1SummarizeRSetStatsPeriod == 0)) {
 739 
 740     G1RemSetSummary current(this);
 741     _prev_period_summary.subtract_from(&current);
 742 
 743     Log(gc, remset) log;
 744     log.trace("%s", header);
 745     ResourceMark rm;
 746     LogStream ls(log.trace());
 747     _prev_period_summary.print_on(&ls);
 748 
 749     _prev_period_summary.set(&current);
 750   }
 751 }
 752 
 753 void G1RemSet::print_summary_info() {
 754   Log(gc, remset, exit) log;
 755   if (log.is_trace()) {
 756     log.trace(" Cumulative RS summary");
 757     G1RemSetSummary current(this);
 758     ResourceMark rm;
 759     LogStream ls(log.trace());
 760     current.print_on(&ls);
 761   }
 762 }
 763 
 764 class G1RebuildRemSetTask: public AbstractGangTask {
 765   // Aggregate the counting data that was constructed concurrently
 766   // with marking.
 767   class G1RebuildRemSetHeapRegionClosure : public HeapRegionClosure {
 768     G1ConcurrentMark* _cm;
 769     G1RebuildRemSetClosure _update_cl;
 770 
 771     // Applies _update_cl to the references of the given object, limiting objArrays
 772     // to the given MemRegion. Returns the amount of words actually scanned.
 773     size_t scan_for_references(oop const obj, MemRegion mr) {
 774       size_t const obj_size = obj->size();
 775       // All non-objArrays and objArrays completely within the mr
 776       // can be scanned without passing the mr.
 777       if (!obj->is_objArray() || mr.contains(MemRegion((HeapWord*)obj, obj_size))) {
 778         obj->oop_iterate(&_update_cl);
 779         return obj_size;
 780       }
 781       // This path is for objArrays crossing the given MemRegion. Only scan the
 782       // area within the MemRegion.
 783       obj->oop_iterate(&_update_cl, mr);
 784       return mr.intersection(MemRegion((HeapWord*)obj, obj_size)).word_size();
 785     }
 786 
 787     // A humongous object is live (with respect to the scanning) either
 788     // a) it is marked on the bitmap as such
 789     // b) its TARS is larger than TAMS, i.e. has been allocated during marking.
 790     bool is_humongous_live(oop const humongous_obj, const G1CMBitMap* const bitmap, HeapWord* tams, HeapWord* tars) const {
 791       return bitmap->is_marked(humongous_obj) || (tars > tams);
 792     }
 793 
 794     // Iterator over the live objects within the given MemRegion.
 795     class LiveObjIterator : public StackObj {
 796       const G1CMBitMap* const _bitmap;
 797       const HeapWord* _tams;
 798       const MemRegion _mr;
 799       HeapWord* _current;
 800 
 801       bool is_below_tams() const {
 802         return _current < _tams;
 803       }
 804 
 805       bool is_live(HeapWord* obj) const {
 806         return !is_below_tams() || _bitmap->is_marked(obj);
 807       }
 808 
 809       HeapWord* bitmap_limit() const {
 810         return MIN2(const_cast<HeapWord*>(_tams), _mr.end());
 811       }
 812 
 813       void move_if_below_tams() {
 814         if (is_below_tams() && has_next()) {
 815           _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
 816         }
 817       }
 818     public:
 819       LiveObjIterator(const G1CMBitMap* const bitmap, const HeapWord* tams, const MemRegion mr, HeapWord* first_oop_into_mr) :
 820           _bitmap(bitmap),
 821           _tams(tams),
 822           _mr(mr),
 823           _current(first_oop_into_mr) {
 824 
 825         assert(_current <= _mr.start(),
 826                "First oop " PTR_FORMAT " should extend into mr [" PTR_FORMAT ", " PTR_FORMAT ")",
 827                p2i(first_oop_into_mr), p2i(mr.start()), p2i(mr.end()));
 828 
 829         // Step to the next live object within the MemRegion if needed.
 830         if (is_live(_current)) {
 831           // Non-objArrays were scanned by the previous part of that region.
 832           if (_current < mr.start() && !oop(_current)->is_objArray()) {
 833             _current += oop(_current)->size();
 834             // We might have positioned _current on a non-live object. Reposition to the next
 835             // live one if needed.
 836             move_if_below_tams();
 837           }
 838         } else {
 839           // The object at _current can only be dead if below TAMS, so we can use the bitmap.
 840           // immediately.
 841           _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
 842           assert(_current == _mr.end() || is_live(_current),
 843                  "Current " PTR_FORMAT " should be live (%s) or beyond the end of the MemRegion (" PTR_FORMAT ")",
 844                  p2i(_current), BOOL_TO_STR(is_live(_current)), p2i(_mr.end()));
 845         }
 846       }
 847 
 848       void move_to_next() {
 849         _current += next()->size();
 850         move_if_below_tams();
 851       }
 852 
 853       oop next() const {
 854         oop result = oop(_current);
 855         assert(is_live(_current),
 856                "Object " PTR_FORMAT " must be live TAMS " PTR_FORMAT " below %d mr " PTR_FORMAT " " PTR_FORMAT " outside %d",
 857                p2i(_current), p2i(_tams), _tams > _current, p2i(_mr.start()), p2i(_mr.end()), _mr.contains(result));
 858         return result;
 859       }
 860 
 861       bool has_next() const {
 862         return _current < _mr.end();
 863       }
 864     };
 865 
 866     // Rebuild remembered sets in the part of the region specified by mr and hr.
 867     // Objects between the bottom of the region and the TAMS are checked for liveness
 868     // using the given bitmap. Objects between TAMS and TARS are assumed to be live.
 869     // Returns the number of live words between bottom and TAMS.
 870     size_t rebuild_rem_set_in_region(const G1CMBitMap* const bitmap,
 871                                      HeapWord* const top_at_mark_start,
 872                                      HeapWord* const top_at_rebuild_start,
 873                                      HeapRegion* hr,
 874                                      MemRegion mr) {
 875       size_t marked_words = 0;
 876 
 877       if (hr->is_humongous()) {
 878         oop const humongous_obj = oop(hr->humongous_start_region()->bottom());
 879         if (is_humongous_live(humongous_obj, bitmap, top_at_mark_start, top_at_rebuild_start)) {
 880           // We need to scan both [bottom, TAMS) and [TAMS, top_at_rebuild_start);
 881           // however in case of humongous objects it is sufficient to scan the encompassing
 882           // area (top_at_rebuild_start is always larger or equal to TAMS) as one of the
 883           // two areas will be zero sized. I.e. TAMS is either
 884           // the same as bottom or top(_at_rebuild_start). There is no way TAMS has a different
 885           // value: this would mean that TAMS points somewhere into the object.
 886           assert(hr->top() == top_at_mark_start || hr->top() == top_at_rebuild_start,
 887                  "More than one object in the humongous region?");
 888           humongous_obj->oop_iterate(&_update_cl, mr);
 889           return top_at_mark_start != hr->bottom() ? mr.intersection(MemRegion((HeapWord*)humongous_obj, humongous_obj->size())).byte_size() : 0;
 890         } else {
 891           return 0;
 892         }
 893       }
 894 
 895       for (LiveObjIterator it(bitmap, top_at_mark_start, mr, hr->block_start(mr.start())); it.has_next(); it.move_to_next()) {
 896         oop obj = it.next();
 897         size_t scanned_size = scan_for_references(obj, mr);
 898         if ((HeapWord*)obj < top_at_mark_start) {
 899           marked_words += scanned_size;
 900         }
 901       }
 902 
 903       return marked_words * HeapWordSize;
 904     }
 905 public:
 906   G1RebuildRemSetHeapRegionClosure(G1CollectedHeap* g1h,
 907                                    G1ConcurrentMark* cm,
 908                                    uint worker_id) :
 909     HeapRegionClosure(),
 910     _cm(cm),
 911     _update_cl(g1h, worker_id) { }
 912 
 913     bool do_heap_region(HeapRegion* hr) {
 914       if (_cm->has_aborted()) {
 915         return true;
 916       }
 917 
 918       uint const region_idx = hr->hrm_index();
 919       DEBUG_ONLY(HeapWord* const top_at_rebuild_start_check = _cm->top_at_rebuild_start(region_idx);)
 920       assert(top_at_rebuild_start_check == NULL ||
 921              top_at_rebuild_start_check > hr->bottom(),
 922              "A TARS (" PTR_FORMAT ") == bottom() (" PTR_FORMAT ") indicates the old region %u is empty (%s)",
 923              p2i(top_at_rebuild_start_check), p2i(hr->bottom()),  region_idx, hr->get_type_str());
 924 
 925       size_t total_marked_bytes = 0;
 926       size_t const chunk_size_in_words = G1RebuildRemSetChunkSize / HeapWordSize;
 927 
 928       HeapWord* const top_at_mark_start = hr->prev_top_at_mark_start();
 929 
 930       HeapWord* cur = hr->bottom();
 931       while (cur < hr->end()) {
 932         // After every iteration (yield point) we need to check whether the region's
 933         // TARS changed due to e.g. eager reclaim.
 934         HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);
 935         if (top_at_rebuild_start == NULL) {
 936           return false;
 937         }
 938 
 939         MemRegion next_chunk = MemRegion(hr->bottom(), top_at_rebuild_start).intersection(MemRegion(cur, chunk_size_in_words));
 940         if (next_chunk.is_empty()) {
 941           break;
 942         }
 943 
 944         const Ticks start = Ticks::now();
 945         size_t marked_bytes = rebuild_rem_set_in_region(_cm->prev_mark_bitmap(),
 946                                                         top_at_mark_start,
 947                                                         top_at_rebuild_start,
 948                                                         hr,
 949                                                         next_chunk);
 950         Tickspan time = Ticks::now() - start;
 951 
 952         log_trace(gc, remset, tracking)("Rebuilt region %u "
 953                                         "live " SIZE_FORMAT " "
 954                                         "time %.3fms "
 955                                         "marked bytes " SIZE_FORMAT " "
 956                                         "bot " PTR_FORMAT " "
 957                                         "TAMS " PTR_FORMAT " "
 958                                         "TARS " PTR_FORMAT,
 959                                         region_idx,
 960                                         _cm->liveness(region_idx) * HeapWordSize,
 961                                         time.seconds() * 1000.0,
 962                                         marked_bytes,
 963                                         p2i(hr->bottom()),
 964                                         p2i(top_at_mark_start),
 965                                         p2i(top_at_rebuild_start));
 966 
 967         if (marked_bytes > 0) {
 968           total_marked_bytes += marked_bytes;
 969         }
 970         cur += chunk_size_in_words;
 971 
 972         _cm->do_yield_check();
 973         if (_cm->has_aborted()) {
 974           return true;
 975         }
 976       }
 977       // In the final iteration of the loop the region might have been eagerly reclaimed.
 978       // Simply filter out those regions. We can not just use region type because there
 979       // might have already been new allocations into these regions.
 980       DEBUG_ONLY(HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);)
 981       assert(top_at_rebuild_start == NULL ||
 982              total_marked_bytes == hr->marked_bytes(),
 983              "Marked bytes " SIZE_FORMAT " for region %u (%s) in [bottom, TAMS) do not match calculated marked bytes " SIZE_FORMAT " "
 984              "(" PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT ")",
 985              total_marked_bytes, hr->hrm_index(), hr->get_type_str(), hr->marked_bytes(),
 986              p2i(hr->bottom()), p2i(top_at_mark_start), p2i(top_at_rebuild_start));
 987        // Abort state may have changed after the yield check.
 988       return _cm->has_aborted();
 989     }
 990   };
 991 
 992   HeapRegionClaimer _hr_claimer;
 993   G1ConcurrentMark* _cm;
 994 
 995   uint _worker_id_offset;
 996 public:
 997   G1RebuildRemSetTask(G1ConcurrentMark* cm,
 998                       uint n_workers,
 999                       uint worker_id_offset) :
1000       AbstractGangTask("G1 Rebuild Remembered Set"),
1001       _hr_claimer(n_workers),
1002       _cm(cm),
1003       _worker_id_offset(worker_id_offset) {
1004   }
1005 
1006   void work(uint worker_id) {
1007     SuspendibleThreadSetJoiner sts_join;
1008 
1009     G1CollectedHeap* g1h = G1CollectedHeap::heap();
1010 
1011     G1RebuildRemSetHeapRegionClosure cl(g1h, _cm, _worker_id_offset + worker_id);
1012     g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hr_claimer, worker_id);
1013   }
1014 };
1015 
1016 void G1RemSet::rebuild_rem_set(G1ConcurrentMark* cm,
1017                                WorkGang* workers,
1018                                uint worker_id_offset) {
1019   uint num_workers = workers->active_workers();
1020 
1021   G1RebuildRemSetTask cl(cm,
1022                          num_workers,
1023                          worker_id_offset);
1024   workers->run_task(&cl, num_workers);
1025 }