1 /*
   2  * Copyright (c) 2016, 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/g1CollectedHeap.inline.hpp"
  27 #include "gc/g1/g1ConcurrentMark.inline.hpp"
  28 #include "gc/g1/g1CardLiveData.inline.hpp"
  29 #include "gc/g1/suspendibleThreadSet.hpp"
  30 #include "gc/shared/workgroup.hpp"
  31 #include "logging/log.hpp"
  32 #include "memory/universe.hpp"
  33 #include "runtime/atomic.inline.hpp"
  34 #include "runtime/globals.hpp"
  35 #include "runtime/os.hpp"
  36 #include "utilities/bitMap.inline.hpp"
  37 #include "utilities/debug.hpp"
  38 
  39 G1CardLiveData::G1CardLiveData() :
  40   _max_capacity(0),
  41   _cards_per_region(0),
  42   _gc_timestamp_at_create(0),
  43   _live_regions(NULL),
  44   _live_regions_size_in_bits(0),
  45   _live_cards(NULL),
  46   _live_cards_size_in_bits(0) {
  47 }
  48 
  49 G1CardLiveData::~G1CardLiveData()  {
  50   free_large_bitmap(_live_cards, _live_cards_size_in_bits);
  51   free_large_bitmap(_live_regions, _live_regions_size_in_bits);
  52 }
  53 
  54 G1CardLiveData::bm_word_t* G1CardLiveData::allocate_large_bitmap(size_t size_in_bits) {
  55   size_t size_in_words = BitMap::calc_size_in_words(size_in_bits);
  56 
  57   bm_word_t* map = MmapArrayAllocator<bm_word_t, mtGC>::allocate(size_in_words);
  58 
  59   return map;
  60 }
  61 
  62 void G1CardLiveData::free_large_bitmap(bm_word_t* bitmap, size_t size_in_bits) {
  63   MmapArrayAllocator<bm_word_t, mtGC>::free(bitmap, size_in_bits / BitsPerWord);
  64 }
  65 
  66 void G1CardLiveData::initialize(size_t max_capacity, uint num_max_regions) {
  67   assert(max_capacity % num_max_regions == 0,
  68          "Given capacity must be evenly divisible by region size.");
  69   size_t region_size = max_capacity / num_max_regions;
  70   assert(region_size % (G1SATBCardTableModRefBS::card_size * BitsPerWord) == 0,
  71          "Region size must be evenly divisible by area covered by a single word.");
  72   _max_capacity = max_capacity;
  73   _cards_per_region = region_size / G1SATBCardTableModRefBS::card_size;
  74 
  75   _live_regions_size_in_bits = live_region_bitmap_size_in_bits();
  76   _live_regions = allocate_large_bitmap(_live_regions_size_in_bits);
  77   _live_cards_size_in_bits = live_card_bitmap_size_in_bits();
  78   _live_cards = allocate_large_bitmap(_live_cards_size_in_bits);
  79 }
  80 
  81 void G1CardLiveData::pretouch() {
  82   live_cards_bm().pretouch();
  83   live_regions_bm().pretouch();
  84 }
  85 
  86 size_t G1CardLiveData::live_region_bitmap_size_in_bits() const {
  87   return _max_capacity / (_cards_per_region << G1SATBCardTableModRefBS::card_shift);
  88 }
  89 
  90 size_t G1CardLiveData::live_card_bitmap_size_in_bits() const {
  91   return _max_capacity >> G1SATBCardTableModRefBS::card_shift;
  92 }
  93 
  94 // Helper class that provides functionality to generate the Live Data Count
  95 // information.
  96 class G1CardLiveDataHelper VALUE_OBJ_CLASS_SPEC {
  97 private:
  98   BitMap _region_bm;
  99   BitMap _card_bm;
 100 
 101   // The card number of the bottom of the G1 heap.
 102   // Used in biasing indices into accounting card bitmaps.
 103   BitMap::idx_t _heap_card_bias;
 104 
 105   // Utility routine to set an exclusive range of bits on the given
 106   // bitmap, optimized for very small ranges.
 107   // There must be at least one bit to set.
 108   void set_card_bitmap_range(BitMap::idx_t start_idx,
 109                              BitMap::idx_t end_idx) {
 110 
 111     // Set the exclusive bit range [start_idx, end_idx).
 112     assert((end_idx - start_idx) > 0, "at least one bit");
 113 
 114     // For small ranges use a simple loop; otherwise use set_range.
 115     // The range is made up of the cards that are spanned by an object/mem
 116     // region so 8 cards will allow up to object sizes up to 4K to be handled
 117     // using the loop.
 118     if ((end_idx - start_idx) <= 8) {
 119       for (BitMap::idx_t i = start_idx; i < end_idx; i += 1) {
 120         _card_bm.set_bit(i);
 121       }
 122     } else {
 123       _card_bm.set_range(start_idx, end_idx);
 124     }
 125   }
 126 
 127   // We cache the last mark set. This avoids setting the same bit multiple times.
 128   // This is particularly interesting for dense bitmaps, as this avoids doing
 129   // lots of work most of the time.
 130   BitMap::idx_t _last_marked_bit_idx;
 131 
 132   void clear_card_bitmap_range(HeapWord* start, HeapWord* end) {
 133     BitMap::idx_t start_idx = card_live_bitmap_index_for(start);
 134     BitMap::idx_t end_idx = card_live_bitmap_index_for((HeapWord*)align_ptr_up(end, CardTableModRefBS::card_size));
 135 
 136     _card_bm.clear_range(start_idx, end_idx);
 137   }
 138   
 139   // Mark the card liveness bitmap for the object spanning from start to end.
 140   void mark_card_bitmap_range(HeapWord* start, HeapWord* end) {
 141     BitMap::idx_t start_idx = card_live_bitmap_index_for(start);
 142     BitMap::idx_t end_idx = card_live_bitmap_index_for((HeapWord*)align_ptr_up(end, CardTableModRefBS::card_size));
 143 
 144     assert((end_idx - start_idx) > 0, "Trying to mark zero sized range.");
 145 
 146     if (start_idx == _last_marked_bit_idx) {
 147       start_idx++;
 148     }
 149     if (start_idx == end_idx) {
 150       return;
 151     }
 152 
 153     // Set the bits in the card bitmap for the cards spanned by this object.
 154     set_card_bitmap_range(start_idx, end_idx);
 155     _last_marked_bit_idx = end_idx - 1;
 156   }
 157 
 158   void reset_mark_cache() {
 159     _last_marked_bit_idx = (BitMap::idx_t)-1;
 160   }
 161 
 162 public:
 163   // Returns the index in the per-card liveness count bitmap
 164   // for the given address
 165   inline BitMap::idx_t card_live_bitmap_index_for(HeapWord* addr) {
 166     // Below, the term "card num" means the result of shifting an address
 167     // by the card shift -- address 0 corresponds to card number 0.  One
 168     // must subtract the card num of the bottom of the heap to obtain a
 169     // card table index.
 170     BitMap::idx_t card_num = uintptr_t(addr) >> CardTableModRefBS::card_shift;
 171     return card_num - _heap_card_bias;
 172   }
 173 
 174   // Takes a region that's not empty (i.e., it has at least one
 175   // live object in it and sets its corresponding bit on the region
 176   // bitmap to 1.
 177   void set_bit_for_region(HeapRegion* hr) {
 178     _region_bm.par_set_bit(hr->hrm_index());
 179   }
 180 
 181   void reset_live_data(HeapRegion* hr) {
 182     clear_card_bitmap_range(hr->next_top_at_mark_start(), hr->end());
 183   }
 184 
 185   // Mark the range of bits covered by allocations done since the last marking
 186   // in the given heap region, i.e. from NTAMS to top of the given region.
 187   // Returns if there has been some allocation in this region since the last marking.
 188   bool mark_allocated_since_marking(HeapRegion* hr) {
 189     reset_mark_cache();
 190 
 191     HeapWord* ntams = hr->next_top_at_mark_start();
 192     HeapWord* top   = hr->top();
 193 
 194     assert(hr->bottom() <= ntams && ntams <= hr->end(), "Preconditions.");
 195 
 196     // Mark the allocated-since-marking portion...
 197     if (ntams < top) {
 198       mark_card_bitmap_range(ntams, top);
 199       return true;
 200     } else {
 201       return false;
 202     }
 203   }
 204 
 205   // Mark the range of bits covered by live objects on the mark bitmap between
 206   // bottom and NTAMS of the given region.
 207   // Returns the number of live bytes marked within that area for the given
 208   // heap region.
 209   size_t mark_marked_during_marking(G1CMBitMap* mark_bitmap, HeapRegion* hr) {
 210     reset_mark_cache();
 211 
 212     size_t marked_bytes = 0;
 213 
 214     HeapWord* ntams = hr->next_top_at_mark_start();
 215     HeapWord* start = hr->bottom();
 216 
 217     if (ntams <= start) {
 218       // Skip empty regions.
 219       return 0;
 220     }
 221     if (hr->is_humongous()) {
 222       mark_card_bitmap_range(start, hr->top());
 223       return pointer_delta(hr->top(), start, 1);
 224     }
 225 
 226     assert(start <= hr->end() && start <= ntams && ntams <= hr->end(),
 227            "Preconditions not met - "
 228            "start: " PTR_FORMAT ", ntams: " PTR_FORMAT ", end: " PTR_FORMAT,
 229            p2i(start), p2i(ntams), p2i(hr->end()));
 230 
 231     // Find the first marked object at or after "start".
 232     start = mark_bitmap->getNextMarkedWordAddress(start, ntams);
 233     while (start < ntams) {
 234       oop obj = oop(start);
 235       size_t obj_size = obj->size();
 236       HeapWord* obj_end = start + obj_size;
 237 
 238       assert(obj_end <= hr->end(), "Humongous objects must have been handled elsewhere.");
 239 
 240       mark_card_bitmap_range(start, obj_end);
 241 
 242       // Add the size of this object to the number of marked bytes.
 243       marked_bytes += obj_size * HeapWordSize;
 244 
 245       // Find the next marked object after this one.
 246       start = mark_bitmap->getNextMarkedWordAddress(obj_end, ntams);
 247     }
 248 
 249     return marked_bytes;
 250   }
 251 
 252   G1CardLiveDataHelper(G1CardLiveData* live_data, HeapWord* base_address) :
 253     _region_bm(live_data->live_regions_bm()),
 254     _card_bm(live_data->live_cards_bm()) {
 255     // Calculate the card number for the bottom of the heap. Used
 256     // in biasing indexes into the accounting card bitmaps.
 257     _heap_card_bias =
 258       uintptr_t(base_address) >> CardTableModRefBS::card_shift;
 259   }
 260 };
 261 
 262 class G1CreateCardLiveDataTask: public AbstractGangTask {
 263   // Aggregate the counting data that was constructed concurrently
 264   // with marking.
 265   class G1CreateLiveDataClosure : public HeapRegionClosure {
 266     G1CardLiveDataHelper _helper;
 267 
 268     G1CMBitMap* _mark_bitmap;
 269 
 270     G1ConcurrentMark* _cm;
 271   public:
 272     G1CreateLiveDataClosure(G1CollectedHeap* g1h,
 273                             G1ConcurrentMark* cm,
 274                             G1CMBitMap* mark_bitmap,
 275                             G1CardLiveData* live_data) :
 276       HeapRegionClosure(),
 277       _helper(live_data, g1h->reserved_region().start()),
 278       _mark_bitmap(mark_bitmap),
 279       _cm(cm) { }
 280 
 281     bool doHeapRegion(HeapRegion* hr) {
 282       size_t marked_bytes = _helper.mark_marked_during_marking(_mark_bitmap, hr);
 283       if (marked_bytes > 0) {
 284         hr->add_to_marked_bytes(marked_bytes);
 285       }
 286 
 287       return (_cm->do_yield_check() && _cm->has_aborted());
 288     }
 289   };
 290 
 291   G1ConcurrentMark* _cm;
 292   G1CardLiveData* _live_data;
 293   HeapRegionClaimer _hr_claimer;
 294 
 295 public:
 296   G1CreateCardLiveDataTask(G1CMBitMap* bitmap,
 297                            G1CardLiveData* live_data,
 298                            uint n_workers) :
 299       AbstractGangTask("G1 Create Live Data"),
 300       _live_data(live_data),
 301       _hr_claimer(n_workers) {
 302   }
 303 
 304   void work(uint worker_id) {
 305     SuspendibleThreadSetJoiner sts_join;
 306 
 307     G1CollectedHeap* g1h = G1CollectedHeap::heap();
 308     G1ConcurrentMark* cm = g1h->concurrent_mark();
 309     G1CreateLiveDataClosure cl(g1h, cm, cm->nextMarkBitMap(), _live_data);
 310     g1h->heap_region_par_iterate(&cl, worker_id, &_hr_claimer);
 311   }
 312 };
 313 
 314 void G1CardLiveData::create(WorkGang* workers, G1CMBitMap* mark_bitmap) {
 315   _gc_timestamp_at_create = G1CollectedHeap::heap()->get_gc_time_stamp();
 316 
 317   uint n_workers = workers->active_workers();
 318 
 319   G1CreateCardLiveDataTask cl(mark_bitmap,
 320                               this,
 321                               n_workers);
 322   workers->run_task(&cl);
 323 }
 324 
 325 class G1FinalizeCardLiveDataTask: public AbstractGangTask {
 326   // Finalizes the liveness counting data.
 327   // Sets the bits corresponding to the interval [NTAMS, top]
 328   // (which contains the implicitly live objects) in the
 329   // card liveness bitmap. Also sets the bit for each region
 330   // containing live data, in the region liveness bitmap.
 331   class G1FinalizeCardLiveDataClosure: public HeapRegionClosure {
 332   private:
 333     G1CardLiveDataHelper _helper;
 334 
 335     uint _gc_timestamp_at_create;
 336 
 337     bool has_been_reclaimed(HeapRegion* hr) const {
 338       return hr->get_gc_time_stamp() > _gc_timestamp_at_create;
 339     }
 340   public:
 341     G1FinalizeCardLiveDataClosure(G1CollectedHeap* g1h,
 342                                   G1CMBitMap* bitmap,
 343                                   G1CardLiveData* live_data) :
 344       HeapRegionClosure(),
 345       _helper(live_data, g1h->reserved_region().start()),
 346       _gc_timestamp_at_create(live_data->gc_timestamp_at_create()) { }
 347 
 348     bool doHeapRegion(HeapRegion* hr) {
 349       if (has_been_reclaimed(hr)) {
 350         _helper.reset_live_data(hr);
 351       }
 352       bool allocated_since_marking = _helper.mark_allocated_since_marking(hr);
 353       if (allocated_since_marking || hr->next_marked_bytes() > 0) {
 354         _helper.set_bit_for_region(hr);
 355       }
 356       return false;
 357     }
 358   };
 359 
 360   G1CMBitMap* _bitmap;
 361 
 362   G1CardLiveData* _live_data;
 363 
 364   HeapRegionClaimer _hr_claimer;
 365 
 366 public:
 367   G1FinalizeCardLiveDataTask(G1CMBitMap* bitmap, G1CardLiveData* live_data, uint n_workers) :
 368     AbstractGangTask("G1 Finalize Card Live Data"),
 369     _bitmap(bitmap),
 370     _live_data(live_data),
 371     _hr_claimer(n_workers) {
 372   }
 373 
 374   void work(uint worker_id) {
 375     G1FinalizeCardLiveDataClosure cl(G1CollectedHeap::heap(), _bitmap, _live_data);
 376 
 377     G1CollectedHeap::heap()->heap_region_par_iterate(&cl, worker_id, &_hr_claimer);
 378   }
 379 };
 380 
 381 void G1CardLiveData::finalize(WorkGang* workers, G1CMBitMap* mark_bitmap) {
 382   // Finalize the live data.
 383   G1FinalizeCardLiveDataTask cl(mark_bitmap,
 384                                 this,
 385                                 workers->active_workers());
 386   workers->run_task(&cl);
 387 }
 388 
 389 class G1ClearCardLiveDataTask : public AbstractGangTask {
 390   BitMap _bitmap;
 391   size_t _num_chunks;
 392   size_t _cur_chunk;
 393 public:
 394   G1ClearCardLiveDataTask(BitMap bitmap, size_t num_tasks) :
 395     AbstractGangTask("G1 Clear Card Live Data"),
 396     _bitmap(bitmap),
 397     _num_chunks(num_tasks),
 398     _cur_chunk(0) {
 399   }
 400 
 401   static size_t chunk_size() { return M; }
 402 
 403   virtual void work(uint worker_id) {
 404     while (true) {
 405       size_t to_process = Atomic::add(1, &_cur_chunk) - 1;
 406       if (to_process >= _num_chunks) {
 407         break;
 408       }
 409 
 410       BitMap::idx_t start = M * BitsPerByte * to_process;
 411       BitMap::idx_t end = MIN2(start + M * BitsPerByte, _bitmap.size());
 412       _bitmap.clear_range(start, end);
 413     }
 414   }
 415 };
 416 
 417 void G1CardLiveData::clear(WorkGang* workers) {
 418   guarantee(Universe::is_fully_initialized(), "Should not call this during initialization.");
 419 
 420   size_t const num_chunks = align_size_up(live_cards_bm().size_in_bytes(), G1ClearCardLiveDataTask::chunk_size()) / G1ClearCardLiveDataTask::chunk_size();
 421 
 422   G1ClearCardLiveDataTask cl(live_cards_bm(), num_chunks);
 423   workers->run_task(&cl);
 424 
 425   // The region live bitmap is always very small, even for huge heaps. Clear
 426   // directly.
 427   live_regions_bm().clear();
 428 }
 429 
 430 class G1VerifyCardLiveDataTask: public AbstractGangTask {
 431   // Heap region closure used for verifying the live count data
 432   // that was created concurrently and finalized during
 433   // the remark pause. This closure is applied to the heap
 434   // regions during the STW cleanup pause.
 435   class G1VerifyCardLiveDataClosure: public HeapRegionClosure {
 436   private:
 437     G1CollectedHeap* _g1h;
 438     G1CMBitMap* _mark_bitmap;
 439     G1CardLiveDataHelper _helper;
 440 
 441     G1CardLiveData* _act_live_data;
 442 
 443     G1CardLiveData* _exp_live_data;
 444 
 445     int _failures;
 446 
 447     // Completely recreates the live data count for the given heap region and
 448     // returns the number of bytes marked.
 449     size_t create_live_data_count(HeapRegion* hr) {
 450       size_t bytes_marked = _helper.mark_marked_during_marking(_mark_bitmap, hr);
 451       bool allocated_since_marking = _helper.mark_allocated_since_marking(hr);
 452       if (allocated_since_marking || bytes_marked > 0) {
 453         _helper.set_bit_for_region(hr);
 454       }
 455       return bytes_marked;
 456     }
 457   public:
 458     G1VerifyCardLiveDataClosure(G1CollectedHeap* g1h,
 459                                 G1CMBitMap* mark_bitmap,
 460                                 G1CardLiveData* act_live_data,
 461                                 G1CardLiveData* exp_live_data) :
 462       _g1h(g1h),
 463       _mark_bitmap(mark_bitmap),
 464       _helper(exp_live_data, g1h->reserved_region().start()),
 465       _act_live_data(act_live_data),
 466       _exp_live_data(exp_live_data),
 467       _failures(0) { }
 468 
 469     int failures() const { return _failures; }
 470 
 471     bool doHeapRegion(HeapRegion* hr) {
 472       int failures = 0;
 473 
 474       // Walk the marking bitmap for this region and set the corresponding bits
 475       // in the expected region and card bitmaps.
 476       size_t exp_marked_bytes = create_live_data_count(hr);
 477       size_t act_marked_bytes = hr->next_marked_bytes();
 478       // Verify the marked bytes for this region.
 479 
 480       if (exp_marked_bytes != act_marked_bytes) {
 481         log_error(gc)("Expected marked bytes " SIZE_FORMAT " != actual marked bytes " SIZE_FORMAT " in region %u", exp_marked_bytes, act_marked_bytes, hr->hrm_index());
 482         failures += 1;
 483       } else if (exp_marked_bytes > HeapRegion::GrainBytes) {
 484         log_error(gc)("Expected marked bytes " SIZE_FORMAT " larger than possible " SIZE_FORMAT " in region %u", exp_marked_bytes, HeapRegion::GrainBytes, hr->hrm_index());
 485         failures += 1;
 486       }
 487 
 488       // Verify the bit, for this region, in the actual and expected
 489       // (which was just calculated) region bit maps.
 490       // We're not OK if the bit in the calculated expected region
 491       // bitmap is set and the bit in the actual region bitmap is not.
 492       uint index = hr->hrm_index();
 493 
 494       bool expected = _exp_live_data->is_region_live(index);
 495       bool actual = _act_live_data->is_region_live(index);
 496       if (expected != actual) {
 497         log_error(gc)("Expected liveness %d not equal actual %d in region %u", expected, actual, hr->hrm_index());
 498         failures += 1;
 499       }
 500 
 501       // Verify that the card bit maps for the cards spanned by the current
 502       // region match. We have an error if we have a set bit in the expected
 503       // bit map and the corresponding bit in the actual bitmap is not set.
 504 
 505       BitMap::idx_t start_idx = _helper.card_live_bitmap_index_for(hr->bottom());
 506       BitMap::idx_t end_idx = _helper.card_live_bitmap_index_for(hr->top());
 507 
 508       for (BitMap::idx_t i = start_idx; i < end_idx; i+=1) {
 509         expected = _exp_live_data->is_card_live_at(i);
 510         actual = _act_live_data->is_card_live_at(i);
 511 
 512         if (expected != actual) {
 513           log_error(gc)("Expected card liveness %d not equal actual card liveness %d at card " SIZE_FORMAT " in region %u", expected, actual, i, hr->hrm_index());
 514           failures += 1;
 515         }
 516       }
 517 
 518       _failures += failures;
 519 
 520       // We could stop iteration over the heap when we
 521       // find the first violating region by returning true.
 522       return false;
 523     }
 524   };
 525 protected:
 526   G1CollectedHeap* _g1h;
 527   G1CMBitMap* _mark_bitmap;
 528 
 529   G1CardLiveData* _act_live_data;
 530 
 531   G1CardLiveData _exp_live_data;
 532 
 533   int  _failures;
 534 
 535   HeapRegionClaimer _hr_claimer;
 536 
 537 public:
 538   G1VerifyCardLiveDataTask(G1CMBitMap* bitmap,
 539                            G1CardLiveData* act_live_data,
 540                            uint n_workers)
 541   : AbstractGangTask("G1 Verify Card Live Data"),
 542     _g1h(G1CollectedHeap::heap()),
 543     _mark_bitmap(bitmap),
 544     _act_live_data(act_live_data),
 545     _exp_live_data(),
 546     _failures(0),
 547     _hr_claimer(n_workers) {
 548     assert(VerifyDuringGC, "don't call this otherwise");
 549     _exp_live_data.initialize(_g1h->max_capacity(), _g1h->max_regions());
 550   }
 551 
 552   void work(uint worker_id) {
 553     G1VerifyCardLiveDataClosure cl(_g1h,
 554                                    _mark_bitmap,
 555                                    _act_live_data,
 556                                    &_exp_live_data);
 557     _g1h->heap_region_par_iterate(&cl, worker_id, &_hr_claimer);
 558 
 559     Atomic::add(cl.failures(), &_failures);
 560   }
 561 
 562   int failures() const { return _failures; }
 563 };
 564 
 565 void G1CardLiveData::verify(WorkGang* workers, G1CMBitMap* actual_bitmap) {
 566     ResourceMark rm;
 567 
 568     G1VerifyCardLiveDataTask cl(actual_bitmap,
 569                                 this,
 570                                 workers->active_workers());
 571     workers->run_task(&cl);
 572 
 573     guarantee(cl.failures() == 0, "Unexpected accounting failures");
 574 }
 575 
 576 #ifndef PRODUCT
 577 void G1CardLiveData::verify_is_clear() {
 578   assert(live_cards_bm().count_one_bits() == 0, "Live cards bitmap must be clear.");
 579   assert(live_regions_bm().count_one_bits() == 0, "Live regions bitmap must be clear.");
 580 }
 581 #endif