rev 49539 : imported patch 8178105-switch-at-remark
rev 49542 : imported patch 8178105-8200371-assert-problem

   1 /*
   2  * Copyright (c) 2001, 2018, 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/dirtyCardQueue.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/g1FromCardCache.hpp"
  32 #include "gc/g1/g1GCPhaseTimes.hpp"
  33 #include "gc/g1/g1HotCardCache.hpp"
  34 #include "gc/g1/g1OopClosures.inline.hpp"
  35 #include "gc/g1/g1RemSet.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/access.inline.hpp"
  44 #include "oops/oop.inline.hpp"
  45 #include "utilities/align.hpp"
  46 #include "utilities/globalDefinitions.hpp"
  47 #include "utilities/intHisto.hpp"
  48 #include "utilities/stack.inline.hpp"
  49 #include "utilities/ticks.inline.hpp"
  50 
  51 // Collects information about the overall remembered set scan progress during an evacuation.
  52 class G1RemSetScanState : public CHeapObj<mtGC> {
  53 private:
  54   class G1ClearCardTableTask : public AbstractGangTask {
  55     G1CollectedHeap* _g1h;
  56     uint* _dirty_region_list;
  57     size_t _num_dirty_regions;
  58     size_t _chunk_length;
  59 
  60     size_t volatile _cur_dirty_regions;
  61   public:
  62     G1ClearCardTableTask(G1CollectedHeap* g1h,
  63                          uint* dirty_region_list,
  64                          size_t num_dirty_regions,
  65                          size_t chunk_length) :
  66       AbstractGangTask("G1 Clear Card Table Task"),
  67       _g1h(g1h),
  68       _dirty_region_list(dirty_region_list),
  69       _num_dirty_regions(num_dirty_regions),
  70       _chunk_length(chunk_length),
  71       _cur_dirty_regions(0) {
  72 
  73       assert(chunk_length > 0, "must be");
  74     }
  75 
  76     static size_t chunk_size() { return M; }
  77 
  78     void work(uint worker_id) {
  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             r->clear_cardtable();
  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 do_heap_region(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     G1RemsetIterState res = Atomic::cmpxchg(Claimed, &_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     G1RemsetIterState res = Atomic::cmpxchg(Complete, &_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     G1CollectedHeap::heap()->verifier()->verify_card_table_cleanup();
 275 #endif
 276   }
 277 };
 278 
 279 G1RemSet::G1RemSet(G1CollectedHeap* g1,
 280                    G1CardTable* ct,
 281                    G1HotCardCache* hot_card_cache) :
 282   _g1(g1),
 283   _scan_state(new G1RemSetScanState()),
 284   _num_conc_refined_cards(0),
 285   _ct(ct),
 286   _g1p(_g1->g1_policy()),
 287   _hot_card_cache(hot_card_cache),
 288   _prev_period_summary() {
 289 }
 290 
 291 G1RemSet::~G1RemSet() {
 292   if (_scan_state != NULL) {
 293     delete _scan_state;
 294   }
 295 }
 296 
 297 uint G1RemSet::num_par_rem_sets() {
 298   return DirtyCardQueueSet::num_par_ids() + G1ConcurrentRefine::max_num_threads() + MAX2(ConcGCThreads, ParallelGCThreads);
 299 }
 300 
 301 void G1RemSet::initialize(size_t capacity, uint max_regions) {
 302   G1FromCardCache::initialize(num_par_rem_sets(), max_regions);
 303   _scan_state->initialize(max_regions);
 304 }
 305 
 306 G1ScanRSForRegionClosure::G1ScanRSForRegionClosure(G1RemSetScanState* scan_state,
 307                                                    G1ScanObjsDuringScanRSClosure* scan_obj_on_card,
 308                                                    CodeBlobClosure* code_root_cl,
 309                                                    uint worker_i) :
 310   _scan_state(scan_state),
 311   _scan_objs_on_card_cl(scan_obj_on_card),
 312   _code_root_cl(code_root_cl),
 313   _strong_code_root_scan_time_sec(0.0),
 314   _cards_claimed(0),
 315   _cards_scanned(0),
 316   _cards_skipped(0),
 317   _worker_i(worker_i) {
 318   _g1h = G1CollectedHeap::heap();
 319   _bot = _g1h->bot();
 320   _ct = _g1h->card_table();
 321 }
 322 
 323 void G1ScanRSForRegionClosure::scan_card(MemRegion mr, uint region_idx_for_card) {
 324   HeapRegion* const card_region = _g1h->region_at(region_idx_for_card);
 325   _scan_objs_on_card_cl->set_region(card_region);
 326   card_region->oops_on_card_seq_iterate_careful<true>(mr, _scan_objs_on_card_cl);
 327   _cards_scanned++;
 328 }
 329 
 330 void G1ScanRSForRegionClosure::scan_strong_code_roots(HeapRegion* r) {
 331   double scan_start = os::elapsedTime();
 332   r->strong_code_roots_do(_code_root_cl);
 333   _strong_code_root_scan_time_sec += (os::elapsedTime() - scan_start);
 334 }
 335 
 336 void G1ScanRSForRegionClosure::claim_card(size_t card_index, const uint region_idx_for_card){
 337   _ct->set_card_claimed(card_index);
 338   _scan_state->add_dirty_region(region_idx_for_card);
 339 }
 340 
 341 bool G1ScanRSForRegionClosure::do_heap_region(HeapRegion* r) {
 342   assert(r->in_collection_set(), "should only be called on elements of CS.");
 343   uint region_idx = r->hrm_index();
 344 
 345   if (_scan_state->iter_is_complete(region_idx)) {
 346     return false;
 347   }
 348   if (_scan_state->claim_iter(region_idx)) {
 349     // If we ever free the collection set concurrently, we should also
 350     // clear the card table concurrently therefore we won't need to
 351     // add regions of the collection set to the dirty cards region.
 352     _scan_state->add_dirty_region(region_idx);
 353   }
 354 
 355   // We claim cards in blocks so as to reduce the contention.
 356   size_t const block_size = G1RSetScanBlockSize;
 357 
 358   HeapRegionRemSetIterator iter(r->rem_set());
 359   size_t card_index;
 360 
 361   size_t claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
 362   for (size_t current_card = 0; iter.has_next(card_index); current_card++) {
 363     if (current_card >= claimed_card_block + block_size) {
 364       claimed_card_block = _scan_state->iter_claimed_next(region_idx, block_size);
 365     }
 366     if (current_card < claimed_card_block) {
 367       _cards_skipped++;
 368       continue;
 369     }
 370     _cards_claimed++;
 371 
 372     // If the card is dirty, then G1 will scan it during Update RS.
 373     if (_ct->is_card_claimed(card_index) || _ct->is_card_dirty(card_index)) {
 374       continue;
 375     }
 376 
 377     HeapWord* const card_start = _g1h->bot()->address_for_index(card_index);
 378     uint const region_idx_for_card = _g1h->addr_to_region(card_start);
 379 
 380     assert(_g1h->region_at(region_idx_for_card)->is_in_reserved(card_start),
 381            "Card start " PTR_FORMAT " to scan outside of region %u", p2i(card_start), _g1h->region_at(region_idx_for_card)->hrm_index());
 382     HeapWord* const top = _scan_state->scan_top(region_idx_for_card);
 383     if (card_start >= top) {
 384       continue;
 385     }
 386 
 387     // We claim lazily (so races are possible but they're benign), which reduces the
 388     // number of duplicate scans (the rsets of the regions in the cset can intersect).
 389     // Claim the card after checking bounds above: the remembered set may contain
 390     // random cards into current survivor, and we would then have an incorrectly
 391     // claimed card in survivor space. Card table clear does not reset the card table
 392     // of survivor space regions.
 393     claim_card(card_index, region_idx_for_card);
 394 
 395     MemRegion const mr(card_start, MIN2(card_start + BOTConstants::N_words, top));
 396 
 397     scan_card(mr, region_idx_for_card);
 398   }
 399   if (_scan_state->set_iter_complete(region_idx)) {
 400     // Scan the strong code root list attached to the current region
 401     scan_strong_code_roots(r);
 402   }
 403   return false;
 404 }
 405 
 406 void G1RemSet::scan_rem_set(G1ParScanThreadState* pss,
 407                             CodeBlobClosure* heap_region_codeblobs,
 408                             uint worker_i) {
 409   double rs_time_start = os::elapsedTime();
 410 
 411   G1ScanObjsDuringScanRSClosure scan_cl(_g1, pss);
 412   G1ScanRSForRegionClosure cl(_scan_state, &scan_cl, heap_region_codeblobs, worker_i);
 413   _g1->collection_set_iterate_from(&cl, worker_i);
 414 
 415   double scan_rs_time_sec = (os::elapsedTime() - rs_time_start) -
 416                              cl.strong_code_root_scan_time_sec();
 417 
 418   G1GCPhaseTimes* p = _g1p->phase_times();
 419 
 420   p->record_time_secs(G1GCPhaseTimes::ScanRS, worker_i, scan_rs_time_sec);
 421   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_scanned(), G1GCPhaseTimes::ScanRSScannedCards);
 422   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_claimed(), G1GCPhaseTimes::ScanRSClaimedCards);
 423   p->record_thread_work_item(G1GCPhaseTimes::ScanRS, worker_i, cl.cards_skipped(), G1GCPhaseTimes::ScanRSSkippedCards);
 424 
 425   p->record_time_secs(G1GCPhaseTimes::CodeRoots, worker_i, cl.strong_code_root_scan_time_sec());
 426 }
 427 
 428 // Closure used for updating rem sets. Only called during an evacuation pause.
 429 class G1RefineCardClosure: public CardTableEntryClosure {
 430   G1RemSet* _g1rs;
 431   G1ScanObjsDuringUpdateRSClosure* _update_rs_cl;
 432 
 433   size_t _cards_scanned;
 434   size_t _cards_skipped;
 435 public:
 436   G1RefineCardClosure(G1CollectedHeap* g1h, G1ScanObjsDuringUpdateRSClosure* update_rs_cl) :
 437     _g1rs(g1h->g1_rem_set()), _update_rs_cl(update_rs_cl), _cards_scanned(0), _cards_skipped(0)
 438   {}
 439 
 440   bool do_card_ptr(jbyte* card_ptr, uint worker_i) {
 441     // The only time we care about recording cards that
 442     // contain references that point into the collection set
 443     // is during RSet updating within an evacuation pause.
 444     // In this case worker_i should be the id of a GC worker thread.
 445     assert(SafepointSynchronize::is_at_safepoint(), "not during an evacuation pause");
 446 
 447     bool card_scanned = _g1rs->refine_card_during_gc(card_ptr, _update_rs_cl);
 448 
 449     if (card_scanned) {
 450       _cards_scanned++;
 451     } else {
 452       _cards_skipped++;
 453     }
 454     return true;
 455   }
 456 
 457   size_t cards_scanned() const { return _cards_scanned; }
 458   size_t cards_skipped() const { return _cards_skipped; }
 459 };
 460 
 461 void G1RemSet::update_rem_set(G1ParScanThreadState* pss, uint worker_i) {
 462   G1ScanObjsDuringUpdateRSClosure update_rs_cl(_g1, pss, worker_i);
 463   G1RefineCardClosure refine_card_cl(_g1, &update_rs_cl);
 464 
 465   G1GCParPhaseTimesTracker x(_g1p->phase_times(), G1GCPhaseTimes::UpdateRS, worker_i);
 466   if (G1HotCardCache::default_use_cache()) {
 467     // Apply the closure to the entries of the hot card cache.
 468     G1GCParPhaseTimesTracker y(_g1p->phase_times(), G1GCPhaseTimes::ScanHCC, worker_i);
 469     _g1->iterate_hcc_closure(&refine_card_cl, worker_i);
 470   }
 471   // Apply the closure to all remaining log entries.
 472   _g1->iterate_dirty_card_closure(&refine_card_cl, worker_i);
 473 
 474   G1GCPhaseTimes* p = _g1p->phase_times();
 475   p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_scanned(), G1GCPhaseTimes::UpdateRSScannedCards);
 476   p->record_thread_work_item(G1GCPhaseTimes::UpdateRS, worker_i, refine_card_cl.cards_skipped(), G1GCPhaseTimes::UpdateRSSkippedCards);
 477 }
 478 
 479 void G1RemSet::cleanupHRRS() {
 480   HeapRegionRemSet::cleanup();
 481 }
 482 
 483 void G1RemSet::oops_into_collection_set_do(G1ParScanThreadState* pss,
 484                                            CodeBlobClosure* heap_region_codeblobs,
 485                                            uint worker_i) {
 486   update_rem_set(pss, worker_i);
 487   scan_rem_set(pss, heap_region_codeblobs, worker_i);;
 488 }
 489 
 490 void G1RemSet::prepare_for_oops_into_collection_set_do() {
 491   DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
 492   dcqs.concatenate_logs();
 493 
 494   _scan_state->reset();
 495 }
 496 
 497 void G1RemSet::cleanup_after_oops_into_collection_set_do() {
 498   G1GCPhaseTimes* phase_times = _g1->g1_policy()->phase_times();
 499 
 500   // Set all cards back to clean.
 501   double start = os::elapsedTime();
 502   _scan_state->clear_card_table(_g1->workers());
 503   phase_times->record_clear_ct_time((os::elapsedTime() - start) * 1000.0);
 504 }
 505 
 506 inline void check_card_ptr(jbyte* card_ptr, G1CardTable* ct) {
 507 #ifdef ASSERT
 508   G1CollectedHeap* g1 = G1CollectedHeap::heap();
 509   assert(g1->is_in_exact(ct->addr_for(card_ptr)),
 510          "Card at " PTR_FORMAT " index " SIZE_FORMAT " representing heap at " PTR_FORMAT " (%u) must be in committed heap",
 511          p2i(card_ptr),
 512          ct->index_for(ct->addr_for(card_ptr)),
 513          p2i(ct->addr_for(card_ptr)),
 514          g1->addr_to_region(ct->addr_for(card_ptr)));
 515 #endif
 516 }
 517 
 518 void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
 519                                         uint worker_i) {
 520   assert(!_g1->is_gc_active(), "Only call concurrently");
 521 
 522   check_card_ptr(card_ptr, _ct);
 523 
 524   // If the card is no longer dirty, nothing to do.
 525   if (*card_ptr != G1CardTable::dirty_card_val()) {
 526     return;
 527   }
 528 
 529   // Construct the region representing the card.
 530   HeapWord* start = _ct->addr_for(card_ptr);
 531   // And find the region containing it.
 532   HeapRegion* r = _g1->heap_region_containing(start);
 533 
 534   // This check is needed for some uncommon cases where we should
 535   // ignore the card.
 536   //
 537   // The region could be young.  Cards for young regions are
 538   // distinctly marked (set to g1_young_gen), so the post-barrier will
 539   // filter them out.  However, that marking is performed
 540   // concurrently.  A write to a young object could occur before the
 541   // card has been marked young, slipping past the filter.
 542   //
 543   // The card could be stale, because the region has been freed since
 544   // the card was recorded. In this case the region type could be
 545   // anything.  If (still) free or (reallocated) young, just ignore
 546   // it.  If (reallocated) old or humongous, the later card trimming
 547   // and additional checks in iteration may detect staleness.  At
 548   // worst, we end up processing a stale card unnecessarily.
 549   //
 550   // In the normal (non-stale) case, the synchronization between the
 551   // enqueueing of the card and processing it here will have ensured
 552   // we see the up-to-date region type here.
 553   if (!r->is_old_or_humongous()) {
 554     return;
 555   }
 556 
 557   // The result from the hot card cache insert call is either:
 558   //   * pointer to the current card
 559   //     (implying that the current card is not 'hot'),
 560   //   * null
 561   //     (meaning we had inserted the card ptr into the "hot" card cache,
 562   //     which had some headroom),
 563   //   * a pointer to a "hot" card that was evicted from the "hot" cache.
 564   //
 565 
 566   if (_hot_card_cache->use_cache()) {
 567     assert(!SafepointSynchronize::is_at_safepoint(), "sanity");
 568 
 569     const jbyte* orig_card_ptr = card_ptr;
 570     card_ptr = _hot_card_cache->insert(card_ptr);
 571     if (card_ptr == NULL) {
 572       // There was no eviction. Nothing to do.
 573       return;
 574     } else if (card_ptr != orig_card_ptr) {
 575       // Original card was inserted and an old card was evicted.
 576       start = _ct->addr_for(card_ptr);
 577       r = _g1->heap_region_containing(start);
 578 
 579       // Check whether the region formerly in the cache should be
 580       // ignored, as discussed earlier for the original card.  The
 581       // region could have been freed while in the cache.
 582       if (!r->is_old_or_humongous()) {
 583         return;
 584       }
 585     } // Else we still have the original card.
 586   }
 587 
 588   // Trim the region designated by the card to what's been allocated
 589   // in the region.  The card could be stale, or the card could cover
 590   // (part of) an object at the end of the allocated space and extend
 591   // beyond the end of allocation.
 592 
 593   // Non-humongous objects are only allocated in the old-gen during
 594   // GC, so if region is old then top is stable.  Humongous object
 595   // allocation sets top last; if top has not yet been set, this is
 596   // a stale card and we'll end up with an empty intersection.  If
 597   // this is not a stale card, the synchronization between the
 598   // enqueuing of the card and processing it here will have ensured
 599   // we see the up-to-date top here.
 600   HeapWord* scan_limit = r->top();
 601 
 602   if (scan_limit <= start) {
 603     // If the trimmed region is empty, the card must be stale.
 604     return;
 605   }
 606 
 607   // Okay to clean and process the card now.  There are still some
 608   // stale card cases that may be detected by iteration and dealt with
 609   // as iteration failure.
 610   *const_cast<volatile jbyte*>(card_ptr) = G1CardTable::clean_card_val();
 611 
 612   // This fence serves two purposes.  First, the card must be cleaned
 613   // before processing the contents.  Second, we can't proceed with
 614   // processing until after the read of top, for synchronization with
 615   // possibly concurrent humongous object allocation.  It's okay that
 616   // reading top and reading type were racy wrto each other.  We need
 617   // both set, in any order, to proceed.
 618   OrderAccess::fence();
 619 
 620   // Don't use addr_for(card_ptr + 1) which can ask for
 621   // a card beyond the heap.
 622   HeapWord* end = start + G1CardTable::card_size_in_words;
 623   MemRegion dirty_region(start, MIN2(scan_limit, end));
 624   assert(!dirty_region.is_empty(), "sanity");
 625 
 626   G1ConcurrentRefineOopClosure conc_refine_cl(_g1, worker_i);
 627 
 628   bool card_processed =
 629     r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
 630 
 631   // If unable to process the card then we encountered an unparsable
 632   // part of the heap (e.g. a partially allocated object) while
 633   // processing a stale card.  Despite the card being stale, redirty
 634   // and re-enqueue, because we've already cleaned the card.  Without
 635   // this we could incorrectly discard a non-stale card.
 636   if (!card_processed) {
 637     // The card might have gotten re-dirtied and re-enqueued while we
 638     // worked.  (In fact, it's pretty likely.)
 639     if (*card_ptr != G1CardTable::dirty_card_val()) {
 640       *card_ptr = G1CardTable::dirty_card_val();
 641       MutexLockerEx x(Shared_DirtyCardQ_lock,
 642                       Mutex::_no_safepoint_check_flag);
 643       DirtyCardQueue* sdcq =
 644         JavaThread::dirty_card_queue_set().shared_dirty_card_queue();
 645       sdcq->enqueue(card_ptr);
 646     }
 647   } else {
 648     _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
 649   }
 650 }
 651 
 652 bool G1RemSet::refine_card_during_gc(jbyte* card_ptr,
 653                                      G1ScanObjsDuringUpdateRSClosure* update_rs_cl) {
 654   assert(_g1->is_gc_active(), "Only call during GC");
 655 
 656   check_card_ptr(card_ptr, _ct);
 657 
 658   // If the card is no longer dirty, nothing to do. This covers cards that were already
 659   // scanned as parts of the remembered sets.
 660   if (*card_ptr != G1CardTable::dirty_card_val()) {
 661     return false;
 662   }
 663 
 664   // We claim lazily (so races are possible but they're benign), which reduces the
 665   // number of potential duplicate scans (multiple threads may enqueue the same card twice).
 666   *card_ptr = G1CardTable::clean_card_val() | G1CardTable::claimed_card_val();
 667 
 668   // Construct the region representing the card.
 669   HeapWord* card_start = _ct->addr_for(card_ptr);
 670   // And find the region containing it.
 671   uint const card_region_idx = _g1->addr_to_region(card_start);
 672 
 673   _scan_state->add_dirty_region(card_region_idx);
 674   HeapWord* scan_limit = _scan_state->scan_top(card_region_idx);
 675   if (scan_limit <= card_start) {
 676     // If the card starts above the area in the region containing objects to scan, skip it.
 677     return false;
 678   }
 679 
 680   // Don't use addr_for(card_ptr + 1) which can ask for
 681   // a card beyond the heap.
 682   HeapWord* card_end = card_start + G1CardTable::card_size_in_words;
 683   MemRegion dirty_region(card_start, MIN2(scan_limit, card_end));
 684   assert(!dirty_region.is_empty(), "sanity");
 685 
 686   HeapRegion* const card_region = _g1->region_at(card_region_idx);
 687   update_rs_cl->set_region(card_region);
 688   bool card_processed = card_region->oops_on_card_seq_iterate_careful<true>(dirty_region, update_rs_cl);
 689   assert(card_processed, "must be");
 690   return true;
 691 }
 692 
 693 void G1RemSet::print_periodic_summary_info(const char* header, uint period_count) {
 694   if ((G1SummarizeRSetStatsPeriod > 0) && log_is_enabled(Trace, gc, remset) &&
 695       (period_count % G1SummarizeRSetStatsPeriod == 0)) {
 696 
 697     G1RemSetSummary current(this);
 698     _prev_period_summary.subtract_from(&current);
 699 
 700     Log(gc, remset) log;
 701     log.trace("%s", header);
 702     ResourceMark rm;
 703     LogStream ls(log.trace());
 704     _prev_period_summary.print_on(&ls);
 705 
 706     _prev_period_summary.set(&current);
 707   }
 708 }
 709 
 710 void G1RemSet::print_summary_info() {
 711   Log(gc, remset, exit) log;
 712   if (log.is_trace()) {
 713     log.trace(" Cumulative RS summary");
 714     G1RemSetSummary current(this);
 715     ResourceMark rm;
 716     LogStream ls(log.trace());
 717     current.print_on(&ls);
 718   }
 719 }
 720 
 721 class G1RebuildRemSetTask: public AbstractGangTask {
 722   // Aggregate the counting data that was constructed concurrently
 723   // with marking.
 724   class G1RebuildRemSetHeapRegionClosure : public HeapRegionClosure {
 725     G1ConcurrentMark* _cm;
 726     G1RebuildRemSetClosure _update_cl;
 727 
 728     // Applies _update_cl to the references of the given object, limiting objArrays
 729     // to the given MemRegion. Returns the amount of words actually scanned.
 730     size_t scan_for_references(oop const obj, MemRegion mr) {
 731       size_t const obj_size = obj->size();
 732       // All non-objArrays and objArrays completely within the mr
 733       // can be scanned without passing the mr.
 734       if (!obj->is_objArray() || mr.contains(MemRegion((HeapWord*)obj, obj_size))) {
 735         obj->oop_iterate(&_update_cl);
 736         return obj_size;
 737       }
 738       // This path is for objArrays crossing the given MemRegion. Only scan the
 739       // area within the MemRegion.
 740       obj->oop_iterate(&_update_cl, mr);
 741       return mr.intersection(MemRegion((HeapWord*)obj, obj_size)).word_size();
 742     }
 743 
 744     // A humongous object is live (with respect to the scanning) either
 745     // a) it is marked on the bitmap as such
 746     // b) its TARS is larger than TAMS, i.e. has been allocated during marking.
 747     bool is_humongous_live(oop const humongous_obj, const G1CMBitMap* const bitmap, HeapWord* tams, HeapWord* tars) const {
 748       return bitmap->is_marked(humongous_obj) || (tars > tams);
 749     }
 750 
 751     // Iterator over the live objects within the given MemRegion.
 752     class LiveObjIterator : public StackObj {
 753       const G1CMBitMap* const _bitmap;
 754       const HeapWord* _tams;
 755       const MemRegion _mr;
 756       HeapWord* _current;
 757 
 758       bool is_below_tams() const {
 759         return _current < _tams;
 760       }
 761 
 762       bool is_live(HeapWord* obj) const {
 763         return !is_below_tams() || _bitmap->is_marked(obj);
 764       }
 765 
 766       HeapWord* bitmap_limit() const {
 767         return MIN2(const_cast<HeapWord*>(_tams), _mr.end());
 768       }
 769 
 770       void move_if_below_tams() {
 771         if (is_below_tams() && has_next()) {
 772           _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
 773         }
 774       }
 775     public:
 776       LiveObjIterator(const G1CMBitMap* const bitmap, const HeapWord* tams, const MemRegion mr, HeapWord* first_oop_into_mr) :
 777           _bitmap(bitmap),
 778           _tams(tams),
 779           _mr(mr),
 780           _current(first_oop_into_mr) {
 781 
 782         assert(_current <= _mr.start(),
 783                "First oop " PTR_FORMAT " should extend into mr [" PTR_FORMAT ", " PTR_FORMAT ")",
 784                p2i(first_oop_into_mr), p2i(mr.start()), p2i(mr.end()));
 785 
 786         // Step to the next live object within the MemRegion if needed.
 787         if (is_live(_current)) {
 788           // Non-objArrays were scanned by the previous part of that region.
 789           if (_current < mr.start() && !oop(_current)->is_objArray()) {
 790             _current += oop(_current)->size();
 791             // We might have positioned _current on a non-live object. Reposition to the next
 792             // live one if needed.
 793             move_if_below_tams();
 794           }
 795         } else {
 796           // The object at _current can only be dead if below TAMS, so we can use the bitmap.
 797           // immediately.
 798           _current = _bitmap->get_next_marked_addr(_current, bitmap_limit());
 799           assert(_current == _mr.end() || is_live(_current),
 800                  "Current " PTR_FORMAT " should be live (%s) or beyond the end of the MemRegion (" PTR_FORMAT ")",
 801                  p2i(_current), BOOL_TO_STR(is_live(_current)), p2i(_mr.end()));
 802         }
 803       }
 804 
 805       void move_to_next() {
 806         _current += next()->size();
 807         move_if_below_tams();
 808       }
 809 
 810       oop next() const {
 811         oop result = oop(_current);
 812         assert(is_live(_current),
 813                "Object " PTR_FORMAT " must be live TAMS " PTR_FORMAT " below %d mr " PTR_FORMAT " " PTR_FORMAT " outside %d",
 814                p2i(_current), p2i(_tams), _tams > _current, p2i(_mr.start()), p2i(_mr.end()), _mr.contains(result));
 815         return result;
 816       }
 817 
 818       bool has_next() const {
 819         return _current < _mr.end();
 820       }
 821     };
 822 
 823     // Rebuild remembered sets in the part of the region specified by mr and hr.
 824     // Objects between the bottom of the region and the TAMS are checked for liveness
 825     // using the given bitmap. Objects between TAMS and TARS are assumed to be live.
 826     // Returns the number of live words between bottom and TAMS.
 827     size_t rebuild_rem_set_in_region(const G1CMBitMap* const bitmap,
 828                                      HeapWord* const top_at_mark_start,
 829                                      HeapWord* const top_at_rebuild_start,
 830                                      HeapRegion* hr,
 831                                      MemRegion mr) {
 832       size_t marked_words = 0;
 833 
 834       if (hr->is_humongous()) {
 835         oop const humongous_obj = oop(hr->humongous_start_region()->bottom());
 836         if (is_humongous_live(humongous_obj, bitmap, top_at_mark_start, top_at_rebuild_start)) {
 837           // We need to scan both [bottom, TAMS) and [TAMS, top_at_rebuild_start);
 838           // however in case of humongous objects it is sufficient to scan the encompassing
 839           // area (top_at_rebuild_start is always larger or equal to TAMS) as one of the
 840           // two areas will be zero sized. I.e. TAMS is either
 841           // the same as bottom or top(_at_rebuild_start). There is no way TAMS has a different
 842           // value: this would mean that TAMS points somewhere into the object.
 843           assert(hr->top() == top_at_mark_start || hr->top() == top_at_rebuild_start,
 844                  "More than one object in the humongous region?");
 845           humongous_obj->oop_iterate(&_update_cl, mr);
 846           return top_at_mark_start != hr->bottom() ? mr.intersection(MemRegion((HeapWord*)humongous_obj, humongous_obj->size())).byte_size() : 0;
 847         } else {
 848           return 0;
 849         }
 850       }
 851 
 852       for (LiveObjIterator it(bitmap, top_at_mark_start, mr, hr->block_start(mr.start())); it.has_next(); it.move_to_next()) {
 853         oop obj = it.next();
 854         size_t scanned_size = scan_for_references(obj, mr);
 855         if ((HeapWord*)obj < top_at_mark_start) {
 856           marked_words += scanned_size;
 857         }
 858       }
 859 
 860       return marked_words * HeapWordSize;
 861     }
 862 public:
 863   G1RebuildRemSetHeapRegionClosure(G1CollectedHeap* g1h,
 864                                    G1ConcurrentMark* cm,
 865                                    uint worker_id) :
 866     HeapRegionClosure(),
 867     _cm(cm),
 868     _update_cl(g1h, worker_id) { }
 869 
 870     bool do_heap_region(HeapRegion* hr) {
 871       if (_cm->has_aborted()) {
 872         return true;
 873       }
 874 
 875       uint const region_idx = hr->hrm_index();
 876       DEBUG_ONLY(HeapWord* const top_at_rebuild_start_check = _cm->top_at_rebuild_start(region_idx);)
 877       assert(top_at_rebuild_start_check == NULL ||
 878              top_at_rebuild_start_check > hr->bottom(),
 879              "A TARS (" PTR_FORMAT ") == bottom() (" PTR_FORMAT ") indicates the old region %u is empty (%s)",
 880              p2i(top_at_rebuild_start_check), p2i(hr->bottom()),  region_idx, hr->get_type_str());
 881 
 882       size_t total_marked_bytes = 0;
 883       size_t const chunk_size_in_words = G1RebuildRemSetChunkSize / HeapWordSize;
 884 
 885       HeapWord* const top_at_mark_start = hr->prev_top_at_mark_start();
 886 
 887       HeapWord* cur = hr->bottom();
 888       while (cur < hr->end()) {
 889         // After every iteration (yield point) we need to check whether the region's
 890         // TARS changed due to e.g. eager reclaim.
 891         HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);
 892         if (top_at_rebuild_start == NULL) {
 893           return false;
 894         }
 895 
 896         MemRegion next_chunk = MemRegion(hr->bottom(), top_at_rebuild_start).intersection(MemRegion(cur, chunk_size_in_words));
 897         if (next_chunk.is_empty()) {
 898           break;
 899         }
 900 
 901         const Ticks start = Ticks::now();
 902         size_t marked_bytes = rebuild_rem_set_in_region(_cm->prev_mark_bitmap(),
 903                                                         top_at_mark_start,
 904                                                         top_at_rebuild_start,
 905                                                         hr,
 906                                                         next_chunk);
 907         Tickspan time = Ticks::now() - start;
 908 
 909         log_trace(gc, remset, tracking)("Rebuilt region %u "
 910                                         "live " SIZE_FORMAT " "
 911                                         "time %.3fms "
 912                                         "marked bytes " SIZE_FORMAT " "
 913                                         "bot " PTR_FORMAT " "
 914                                         "TAMS " PTR_FORMAT " "
 915                                         "TARS " PTR_FORMAT,
 916                                         region_idx,
 917                                         _cm->liveness(region_idx) * HeapWordSize,
 918                                         TicksToTimeHelper::seconds(time) * 1000.0,
 919                                         marked_bytes,
 920                                         p2i(hr->bottom()),
 921                                         p2i(top_at_mark_start),
 922                                         p2i(top_at_rebuild_start));
 923 
 924         if (marked_bytes > 0) {
 925           total_marked_bytes += marked_bytes;
 926         }
 927         cur += chunk_size_in_words;
 928 
 929         _cm->do_yield_check();
 930         if (_cm->has_aborted()) {
 931           return true;
 932         }
 933       }
 934       // In the final iteration of the loop the region might have been eagerly reclaimed.
 935       // Simply filter out those regions. We can not just use region type because there
 936       // might have already been new allocations into these regions.
 937       DEBUG_ONLY(HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);)
 938       assert(top_at_rebuild_start == NULL ||
 939              total_marked_bytes == hr->marked_bytes(),
 940              "Marked bytes " SIZE_FORMAT " for region %u (%s) in [bottom, TAMS) do not match liveness during mark " SIZE_FORMAT " "
 941              "(" PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT ")",
 942              total_marked_bytes, hr->hrm_index(), hr->get_type_str(), _cm->liveness(region_idx) * HeapWordSize,
 943              p2i(hr->bottom()), p2i(top_at_mark_start), p2i(top_at_rebuild_start));
 944        // Abort state may have changed after the yield check.
 945       return _cm->has_aborted();
 946     }
 947   };
 948 
 949   HeapRegionClaimer _hr_claimer;
 950   G1ConcurrentMark* _cm;
 951 
 952   uint _worker_id_offset;
 953 public:
 954   G1RebuildRemSetTask(G1ConcurrentMark* cm,
 955                       uint n_workers,
 956                       uint worker_id_offset) :
 957       AbstractGangTask("G1 Rebuild Remembered Set"),
 958       _cm(cm),
 959       _hr_claimer(n_workers),
 960       _worker_id_offset(worker_id_offset) {
 961   }
 962 
 963   void work(uint worker_id) {
 964     SuspendibleThreadSetJoiner sts_join;
 965 
 966     G1CollectedHeap* g1h = G1CollectedHeap::heap();
 967 
 968     G1RebuildRemSetHeapRegionClosure cl(g1h, _cm, _worker_id_offset + worker_id);
 969     g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hr_claimer, worker_id);
 970   }
 971 };
 972 
 973 void G1RemSet::rebuild_rem_set(G1ConcurrentMark* cm,
 974                                WorkGang* workers,
 975                                uint worker_id_offset) {
 976   uint num_workers = workers->active_workers();
 977 
 978   G1RebuildRemSetTask cl(cm,
 979                          num_workers,
 980                          worker_id_offset);
 981   workers->run_task(&cl, num_workers);
 982 }
--- EOF ---