cardTableModRefBS.cpp

/*
 * Copyright 2000-2009 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 */

// This kind of "BarrierSet" allows a "CollectedHeap" to detect and
// enumerate ref fields that have been modified (since the last
// enumeration.)

# include "incls/_precompiled.incl"
# include "incls/_cardTableModRefBS.cpp.incl"

size_t CardTableModRefBS::cards_required(size_t covered_words)
{
  // Add one for a guard card, used to detect errors.
  const size_t words = align_size_up(covered_words, card_size_in_words);
  return words / card_size_in_words + 1;
}

size_t CardTableModRefBS::compute_byte_map_size()
{
  assert(_guard_index == cards_required(_whole_heap.word_size()) - 1,
                                        "unitialized, check declaration order");
  assert(_page_size != 0, "unitialized, check declaration order");
  const size_t granularity = os::vm_allocation_granularity();
  return align_size_up(_guard_index + 1, MAX2(_page_size, granularity));
}

CardTableModRefBS::CardTableModRefBS(MemRegion whole_heap,
                                     int max_covered_regions):
  ModRefBarrierSet(max_covered_regions),
  _whole_heap(whole_heap),
  _guard_index(cards_required(whole_heap.word_size()) - 1),
  _last_valid_index(_guard_index - 1),
  _page_size(os::vm_page_size()),
  _byte_map_size(compute_byte_map_size())
{
  _kind = BarrierSet::CardTableModRef;

  HeapWord* low_bound  = _whole_heap.start();
  HeapWord* high_bound = _whole_heap.end();
  assert((uintptr_t(low_bound)  & (card_size - 1))  == 0, "heap must start at card boundary");
  assert((uintptr_t(high_bound) & (card_size - 1))  == 0, "heap must end at card boundary");

  assert(card_size <= 512, "card_size must be less than 512"); // why?

  _covered   = new MemRegion[max_covered_regions];
  _committed = new MemRegion[max_covered_regions];
  if (_covered == NULL || _committed == NULL)
    vm_exit_during_initialization("couldn't alloc card table covered region set.");
  int i;
  for (i = 0; i < max_covered_regions; i++) {
    _covered[i].set_word_size(0);
    _committed[i].set_word_size(0);
  }
  _cur_covered_regions = 0;

  const size_t rs_align = _page_size == (size_t) os::vm_page_size() ? 0 :
    MAX2(_page_size, (size_t) os::vm_allocation_granularity());
  ReservedSpace heap_rs(_byte_map_size, rs_align, false);
  os::trace_page_sizes("card table", _guard_index + 1, _guard_index + 1,
                       _page_size, heap_rs.base(), heap_rs.size());
  if (!heap_rs.is_reserved()) {
    vm_exit_during_initialization("Could not reserve enough space for the "
                                  "card marking array");
  }

  // The assember store_check code will do an unsigned shift of the oop,
  // then add it to byte_map_base, i.e.
  //
  //   _byte_map = byte_map_base + (uintptr_t(low_bound) >> card_shift)
  _byte_map = (jbyte*) heap_rs.base();
  byte_map_base = _byte_map - (uintptr_t(low_bound) >> card_shift);
  assert(byte_for(low_bound) == &_byte_map[0], "Checking start of map");
  assert(byte_for(high_bound-1) <= &_byte_map[_last_valid_index], "Checking end of map");

  jbyte* guard_card = &_byte_map[_guard_index];
  uintptr_t guard_page = align_size_down((uintptr_t)guard_card, _page_size);
  _guard_region = MemRegion((HeapWord*)guard_page, _page_size);
  if (!os::commit_memory((char*)guard_page, _page_size, _page_size)) {
    // Do better than this for Merlin
    vm_exit_out_of_memory(_page_size, "card table last card");
  }
  *guard_card = last_card;

   _lowest_non_clean =
    NEW_C_HEAP_ARRAY(CardArr, max_covered_regions);
  _lowest_non_clean_chunk_size =
    NEW_C_HEAP_ARRAY(size_t, max_covered_regions);
  _lowest_non_clean_base_chunk_index =
    NEW_C_HEAP_ARRAY(uintptr_t, max_covered_regions);
  _last_LNC_resizing_collection =
    NEW_C_HEAP_ARRAY(int, max_covered_regions);
  if (_lowest_non_clean == NULL
      || _lowest_non_clean_chunk_size == NULL
      || _lowest_non_clean_base_chunk_index == NULL
      || _last_LNC_resizing_collection == NULL)
    vm_exit_during_initialization("couldn't allocate an LNC array.");
  for (i = 0; i < max_covered_regions; i++) {
    _lowest_non_clean[i] = NULL;
    _lowest_non_clean_chunk_size[i] = 0;
    _last_LNC_resizing_collection[i] = -1;
  }

  if (TraceCardTableModRefBS) {
    gclog_or_tty->print_cr("CardTableModRefBS::CardTableModRefBS: ");
    gclog_or_tty->print_cr("  "
                  "  &_byte_map[0]: " INTPTR_FORMAT
                  "  &_byte_map[_last_valid_index]: " INTPTR_FORMAT,
                  &_byte_map[0],
                  &_byte_map[_last_valid_index]);
    gclog_or_tty->print_cr("  "
                  "  byte_map_base: " INTPTR_FORMAT,
                  byte_map_base);
  }
}

int CardTableModRefBS::find_covering_region_by_base(HeapWord* base) {
  int i;
  for (i = 0; i < _cur_covered_regions; i++) {
    if (_covered[i].start() == base) return i;
    if (_covered[i].start() > base) break;
  }
  // If we didn't find it, create a new one.
  assert(_cur_covered_regions < _max_covered_regions,
         "too many covered regions");
  // Move the ones above up, to maintain sorted order.
  for (int j = _cur_covered_regions; j > i; j--) {
    _covered[j] = _covered[j-1];
    _committed[j] = _committed[j-1];
  }
  int res = i;
  _cur_covered_regions++;
  _covered[res].set_start(base);
  _covered[res].set_word_size(0);
  jbyte* ct_start = byte_for(base);
  uintptr_t ct_start_aligned = align_size_down((uintptr_t)ct_start, _page_size);
  _committed[res].set_start((HeapWord*)ct_start_aligned);
  _committed[res].set_word_size(0);
  return res;
}

int CardTableModRefBS::find_covering_region_containing(HeapWord* addr) {
  for (int i = 0; i < _cur_covered_regions; i++) {
    if (_covered[i].contains(addr)) {
      return i;
    }
  }
  assert(0, "address outside of heap?");
  return -1;
}

HeapWord* CardTableModRefBS::largest_prev_committed_end(int ind) const {
  HeapWord* max_end = NULL;
  for (int j = 0; j < ind; j++) {
    HeapWord* this_end = _committed[j].end();
    if (this_end > max_end) max_end = this_end;
  }
  return max_end;
}

MemRegion CardTableModRefBS::committed_unique_to_self(int self,
                                                      MemRegion mr) const {
  MemRegion result = mr;
  for (int r = 0; r < _cur_covered_regions; r += 1) {
    if (r != self) {
      result = result.minus(_committed[r]);
    }
  }
  // Never include the guard page.
  result = result.minus(_guard_region);
  return result;
}

void CardTableModRefBS::resize_covered_region(MemRegion new_region) {
  // We don't change the start of a region, only the end.
  assert(_whole_heap.contains(new_region),
           "attempt to cover area not in reserved area");
  debug_only(verify_guard();)
  // collided is true if the expansion would push into another committed region
  debug_only(bool collided = false;)
  int const ind = find_covering_region_by_base(new_region.start());
  MemRegion const old_region = _covered[ind];
  assert(old_region.start() == new_region.start(), "just checking");
  if (new_region.word_size() != old_region.word_size()) {
    // Commit new or uncommit old pages, if necessary.
    MemRegion cur_committed = _committed[ind];
    // Extend the end of this _commited region
    // to cover the end of any lower _committed regions.
    // This forms overlapping regions, but never interior regions.
    HeapWord* const max_prev_end = largest_prev_committed_end(ind);
    if (max_prev_end > cur_committed.end()) {
      cur_committed.set_end(max_prev_end);
    }
    // Align the end up to a page size (starts are already aligned).
    jbyte* const new_end = byte_after(new_region.last());
    HeapWord* new_end_aligned =
      (HeapWord*) align_size_up((uintptr_t)new_end, _page_size);
    assert(new_end_aligned >= (HeapWord*) new_end,
           "align up, but less");
    // Check the other regions (excludes "ind") to ensure that
    // the new_end_aligned does not intrude onto the committed
    // space of another region.
    int ri = 0;
    for (ri = 0; ri < _cur_covered_regions; ri++) {
      if (ri != ind) {
        if (_committed[ri].contains(new_end_aligned)) {
          // The prior check included in the assert
          // (new_end_aligned >= _committed[ri].start())
          // is redundant with the "contains" test.
          // Any region containing the new end
          // should start at or beyond the region found (ind)
          // for the new end (committed regions are not expected to
          // be proper subsets of other committed regions).
          assert(_committed[ri].start() >= _committed[ind].start(),
                 "New end of committed region is inconsistent");
          new_end_aligned = _committed[ri].start();
          // new_end_aligned can be equal to the start of its
          // committed region (i.e., of "ind") if a second
          // region following "ind" also start at the same location
          // as "ind".
          assert(new_end_aligned >= _committed[ind].start(),
            "New end of committed region is before start");
          debug_only(collided = true;)
          // Should only collide with 1 region
          break;
        }
      }
    }
#ifdef ASSERT
    for (++ri; ri < _cur_covered_regions; ri++) {
      assert(!_committed[ri].contains(new_end_aligned),
        "New end of committed region is in a second committed region");
    }
#endif
    // The guard page is always committed and should not be committed over.
    // "guarded" is used for assertion checking below and recalls the fact
    // that the would-be end of the new committed region would have
    // penetrated the guard page.
    HeapWord* new_end_for_commit = new_end_aligned;

    DEBUG_ONLY(bool guarded = false;)
    if (new_end_for_commit > _guard_region.start()) {
      new_end_for_commit = _guard_region.start();
      DEBUG_ONLY(guarded = true;)
    }

    if (new_end_for_commit > cur_committed.end()) {
      // Must commit new pages.
      MemRegion const new_committed =
        MemRegion(cur_committed.end(), new_end_for_commit);

      assert(!new_committed.is_empty(), "Region should not be empty here");
      if (!os::commit_memory((char*)new_committed.start(),
                             new_committed.byte_size(), _page_size)) {
        // Do better than this for Merlin
        vm_exit_out_of_memory(new_committed.byte_size(),
                "card table expansion");
      }
    // Use new_end_aligned (as opposed to new_end_for_commit) because
    // the cur_committed region may include the guard region.
    } else if (new_end_aligned < cur_committed.end()) {
      // Must uncommit pages.
      MemRegion const uncommit_region =
        committed_unique_to_self(ind, MemRegion(new_end_aligned,
                                                cur_committed.end()));
      if (!uncommit_region.is_empty()) {
        if (!os::uncommit_memory((char*)uncommit_region.start(),
                                 uncommit_region.byte_size())) {
          assert(false, "Card table contraction failed");
          // The call failed so don't change the end of the
          // committed region.  This is better than taking the
          // VM down.
          new_end_aligned = _committed[ind].end();
        }
      }
    }
    // In any case, we can reset the end of the current committed entry.
    _committed[ind].set_end(new_end_aligned);

    // The default of 0 is not necessarily clean cards.
    jbyte* entry;
    if (old_region.last() < _whole_heap.start()) {
      entry = byte_for(_whole_heap.start());
    } else {
      entry = byte_after(old_region.last());
    }
    assert(index_for(new_region.last()) <  _guard_index,
      "The guard card will be overwritten");
    // This line commented out cleans the newly expanded region and
    // not the aligned up expanded region.
    // jbyte* const end = byte_after(new_region.last());
    jbyte* const end = (jbyte*) new_end_for_commit;
    assert((end >= byte_after(new_region.last())) || collided || guarded,
      "Expect to be beyond new region unless impacting another region");
    // do nothing if we resized downward.
#ifdef ASSERT
    for (int ri = 0; ri < _cur_covered_regions; ri++) {
      if (ri != ind) {
        // The end of the new committed region should not
        // be in any existing region unless it matches
        // the start of the next region.
        assert(!_committed[ri].contains(end) ||
               (_committed[ri].start() == (HeapWord*) end),
               "Overlapping committed regions");
      }
    }
#endif
    if (entry < end) {
      memset(entry, clean_card, pointer_delta(end, entry, sizeof(jbyte)));
    }
  }
  // In any case, the covered size changes.
  _covered[ind].set_word_size(new_region.word_size());
  if (TraceCardTableModRefBS) {
    gclog_or_tty->print_cr("CardTableModRefBS::resize_covered_region: ");
    gclog_or_tty->print_cr("  "
                  "  _covered[%d].start(): " INTPTR_FORMAT
                  "  _covered[%d].last(): " INTPTR_FORMAT,
                  ind, _covered[ind].start(),
                  ind, _covered[ind].last());
    gclog_or_tty->print_cr("  "
                  "  _committed[%d].start(): " INTPTR_FORMAT
                  "  _committed[%d].last(): " INTPTR_FORMAT,
                  ind, _committed[ind].start(),
                  ind, _committed[ind].last());
    gclog_or_tty->print_cr("  "
                  "  byte_for(start): " INTPTR_FORMAT
                  "  byte_for(last): " INTPTR_FORMAT,
                  byte_for(_covered[ind].start()),
                  byte_for(_covered[ind].last()));
    gclog_or_tty->print_cr("  "
                  "  addr_for(start): " INTPTR_FORMAT
                  "  addr_for(last): " INTPTR_FORMAT,
                  addr_for((jbyte*) _committed[ind].start()),
                  addr_for((jbyte*) _committed[ind].last()));
  }
  debug_only(verify_guard();)
}

// Note that these versions are precise!  The scanning code has to handle the
// fact that the write barrier may be either precise or imprecise.

void CardTableModRefBS::write_ref_field_work(void* field, oop newVal) {
  inline_write_ref_field(field, newVal);
}

/*
   Claimed and deferred bits are used together in G1 during the evacuation
   pause. These bits can have the following state transitions:
   1. The claimed bit can be put over any other card state. Except that
      the "dirty -> dirty and claimed" transition is checked for in
      G1 code and is not used.
   2. Deferred bit can be set only if the previous state of the card
      was either clean or claimed. mark_card_deferred() is wait-free.
      We do not care if the operation is be successful because if
      it does not it will only result in duplicate entry in the update
      buffer because of the "cache-miss". So it's not worth spinning.
 */


bool CardTableModRefBS::claim_card(size_t card_index) {
  jbyte val = _byte_map[card_index];
  assert(val != dirty_card_val(), "Shouldn't claim a dirty card");
  while (val == clean_card_val() ||
         (val & (clean_card_mask_val() | claimed_card_val())) != claimed_card_val()) {
    jbyte new_val = val;
    if (val == clean_card_val()) {
      new_val = (jbyte)claimed_card_val();
    } else {
      new_val = val | (jbyte)claimed_card_val();
    }
    jbyte res = Atomic::cmpxchg(new_val, &_byte_map[card_index], val);
    if (res == val) {
      return true;
    }
    val = res;
  }
  return false;
}

bool CardTableModRefBS::mark_card_deferred(size_t card_index) {
  jbyte val = _byte_map[card_index];
  // It's already processed
  if ((val & (clean_card_mask_val() | deferred_card_val())) == deferred_card_val()) {
    return false;
  }
  // Cached bit can be installed either on a clean card or on a claimed card.
  jbyte new_val = val;
  if (val == clean_card_val()) {
    new_val = (jbyte)deferred_card_val();
  } else {
    if (val & claimed_card_val()) {
      new_val = val | (jbyte)deferred_card_val();
    }
  }
  if (new_val != val) {
    Atomic::cmpxchg(new_val, &_byte_map[card_index], val);
  }
  return true;
}


void CardTableModRefBS::non_clean_card_iterate(Space* sp,
                                               MemRegion mr,
                                               DirtyCardToOopClosure* dcto_cl,
                                               MemRegionClosure* cl,
                                               bool clear) {
  if (!mr.is_empty()) {
    int n_threads = SharedHeap::heap()->n_par_threads();
    if (n_threads > 0) {
#ifndef SERIALGC
      par_non_clean_card_iterate_work(sp, mr, dcto_cl, cl, clear, n_threads);
#else  // SERIALGC
      fatal("Parallel gc not supported here.");
#endif // SERIALGC
    } else {
      non_clean_card_iterate_work(mr, cl, clear);
    }
  }
}

// NOTE: For this to work correctly, it is important that
// we look for non-clean cards below (so as to catch those
// marked precleaned), rather than look explicitly for dirty
// cards (and miss those marked precleaned). In that sense,
// the name precleaned is currently somewhat of a misnomer.
void CardTableModRefBS::non_clean_card_iterate_work(MemRegion mr,
                                                    MemRegionClosure* cl,
                                                    bool clear) {
  // Figure out whether we have to worry about parallelism.
  bool is_par = (SharedHeap::heap()->n_par_threads() > 1);
  for (int i = 0; i < _cur_covered_regions; i++) {
    MemRegion mri = mr.intersection(_covered[i]);
    if (mri.word_size() > 0) {
      jbyte* cur_entry = byte_for(mri.last());
      jbyte* limit = byte_for(mri.start());
      while (cur_entry >= limit) {
        jbyte* next_entry = cur_entry - 1;
        if (*cur_entry != clean_card) {
          size_t non_clean_cards = 1;
          // Should the next card be included in this range of dirty cards.
          while (next_entry >= limit && *next_entry != clean_card) {
            non_clean_cards++;
            cur_entry = next_entry;
            next_entry--;
          }
          // The memory region may not be on a card boundary.  So that
          // objects beyond the end of the region are not processed, make
          // cur_cards precise with regard to the end of the memory region.
          MemRegion cur_cards(addr_for(cur_entry),
                              non_clean_cards * card_size_in_words);
          MemRegion dirty_region = cur_cards.intersection(mri);
          if (clear) {
            for (size_t i = 0; i < non_clean_cards; i++) {
              // Clean the dirty cards (but leave the other non-clean
              // alone.)  If parallel, do the cleaning atomically.
              jbyte cur_entry_val = cur_entry[i];
              if (card_is_dirty_wrt_gen_iter(cur_entry_val)) {
                if (is_par) {
                  jbyte res = Atomic::cmpxchg(clean_card, &cur_entry[i], cur_entry_val);
                  assert(res != clean_card,
                         "Dirty card mysteriously cleaned");
                } else {
                  cur_entry[i] = clean_card;
                }
              }
            }
          }
          cl->do_MemRegion(dirty_region);
        }
        cur_entry = next_entry;
      }
    }
  }
}

void CardTableModRefBS::mod_oop_in_space_iterate(Space* sp,
                                                 OopClosure* cl,
                                                 bool clear,
                                                 bool before_save_marks) {
  // Note that dcto_cl is resource-allocated, so there is no
  // corresponding "delete".
  DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision());
  MemRegion used_mr;
  if (before_save_marks) {
    used_mr = sp->used_region_at_save_marks();
  } else {
    used_mr = sp->used_region();
  }
  non_clean_card_iterate(sp, used_mr, dcto_cl, dcto_cl, clear);
}

void CardTableModRefBS::dirty_MemRegion(MemRegion mr) {
  assert((HeapWord*)align_size_down((uintptr_t)mr.start(), HeapWordSize) == mr.start(), "Unaligned start");
  assert((HeapWord*)align_size_up  ((uintptr_t)mr.end(),   HeapWordSize) == mr.end(),   "Unaligned end"  );
  jbyte* cur  = byte_for(mr.start());
  jbyte* last = byte_after(mr.last());
  while (cur < last) {
    *cur = dirty_card;
    cur++;
  }
}

void CardTableModRefBS::invalidate(MemRegion mr, bool whole_heap) {
  assert((HeapWord*)align_size_down((uintptr_t)mr.start(), HeapWordSize) == mr.start(), "Unaligned start");
  assert((HeapWord*)align_size_up  ((uintptr_t)mr.end(),   HeapWordSize) == mr.end(),   "Unaligned end"  );
  for (int i = 0; i < _cur_covered_regions; i++) {
    MemRegion mri = mr.intersection(_covered[i]);
    if (!mri.is_empty()) dirty_MemRegion(mri);
  }
}

void CardTableModRefBS::clear_MemRegion(MemRegion mr) {
  // Be conservative: only clean cards entirely contained within the
  // region.
  jbyte* cur;
  if (mr.start() == _whole_heap.start()) {
    cur = byte_for(mr.start());
  } else {
    assert(mr.start() > _whole_heap.start(), "mr is not covered.");
    cur = byte_after(mr.start() - 1);
  }
  jbyte* last = byte_after(mr.last());
  memset(cur, clean_card, pointer_delta(last, cur, sizeof(jbyte)));
}

void CardTableModRefBS::clear(MemRegion mr) {
  for (int i = 0; i < _cur_covered_regions; i++) {
    MemRegion mri = mr.intersection(_covered[i]);
    if (!mri.is_empty()) clear_MemRegion(mri);
  }
}

void CardTableModRefBS::dirty(MemRegion mr) {
  jbyte* first = byte_for(mr.start());
  jbyte* last  = byte_after(mr.last());
  memset(first, dirty_card, last-first);
}

// NOTES:
// (1) Unlike mod_oop_in_space_iterate() above, dirty_card_iterate()
//     iterates over dirty cards ranges in increasing address order.
void CardTableModRefBS::dirty_card_iterate(MemRegion mr,
                                           MemRegionClosure* cl) {
  for (int i = 0; i < _cur_covered_regions; i++) {
    MemRegion mri = mr.intersection(_covered[i]);
    if (!mri.is_empty()) {
      jbyte *cur_entry, *next_entry, *limit;
      for (cur_entry = byte_for(mri.start()), limit = byte_for(mri.last());
           cur_entry <= limit;
           cur_entry  = next_entry) {
        next_entry = cur_entry + 1;
        if (*cur_entry == dirty_card) {
          size_t dirty_cards;
          // Accumulate maximal dirty card range, starting at cur_entry
          for (dirty_cards = 1;
               next_entry <= limit && *next_entry == dirty_card;
               dirty_cards++, next_entry++);
          MemRegion cur_cards(addr_for(cur_entry),
                              dirty_cards*card_size_in_words);
          cl->do_MemRegion(cur_cards);
        }
      }
    }
  }
}

MemRegion CardTableModRefBS::dirty_card_range_after_reset(MemRegion mr,
                                                          bool reset,
                                                          int reset_val) {
  for (int i = 0; i < _cur_covered_regions; i++) {
    MemRegion mri = mr.intersection(_covered[i]);
    if (!mri.is_empty()) {
      jbyte* cur_entry, *next_entry, *limit;
      for (cur_entry = byte_for(mri.start()), limit = byte_for(mri.last());
           cur_entry <= limit;
           cur_entry  = next_entry) {
        next_entry = cur_entry + 1;
        if (*cur_entry == dirty_card) {
          size_t dirty_cards;
          // Accumulate maximal dirty card range, starting at cur_entry
          for (dirty_cards = 1;
               next_entry <= limit && *next_entry == dirty_card;
               dirty_cards++, next_entry++);
          MemRegion cur_cards(addr_for(cur_entry),
                              dirty_cards*card_size_in_words);
          if (reset) {
            for (size_t i = 0; i < dirty_cards; i++) {
              cur_entry[i] = reset_val;
            }
          }
          return cur_cards;
        }
      }
    }
  }
  return MemRegion(mr.end(), mr.end());
}

// Set all the dirty cards in the given region to "precleaned" state.
void CardTableModRefBS::preclean_dirty_cards(MemRegion mr) {
  for (int i = 0; i < _cur_covered_regions; i++) {
    MemRegion mri = mr.intersection(_covered[i]);
    if (!mri.is_empty()) {
      jbyte *cur_entry, *limit;
      for (cur_entry = byte_for(mri.start()), limit = byte_for(mri.last());
           cur_entry <= limit;
           cur_entry++) {
        if (*cur_entry == dirty_card) {
          *cur_entry = precleaned_card;
        }
      }
    }
  }
}

uintx CardTableModRefBS::ct_max_alignment_constraint() {
  return card_size * os::vm_page_size();
}

void CardTableModRefBS::verify_guard() {
  // For product build verification
  guarantee(_byte_map[_guard_index] == last_card,
            "card table guard has been modified");
}

void CardTableModRefBS::verify() {
  verify_guard();
}

#ifndef PRODUCT
class GuaranteeNotModClosure: public MemRegionClosure {
  CardTableModRefBS* _ct;
public:
  GuaranteeNotModClosure(CardTableModRefBS* ct) : _ct(ct) {}
  void do_MemRegion(MemRegion mr) {
    jbyte* entry = _ct->byte_for(mr.start());
    guarantee(*entry != CardTableModRefBS::clean_card,
              "Dirty card in region that should be clean");
  }
};

void CardTableModRefBS::verify_clean_region(MemRegion mr) {
  GuaranteeNotModClosure blk(this);
  non_clean_card_iterate_work(mr, &blk, false);
}

// To verify a MemRegion is entirely dirty this closure is passed to
// dirty_card_iterate. If the region is dirty do_MemRegion will be
// invoked only once with a MemRegion equal to the one being
// verified.
class GuaranteeDirtyClosure: public MemRegionClosure {
  CardTableModRefBS* _ct;
  MemRegion _mr;
  bool _result;
public:
  GuaranteeDirtyClosure(CardTableModRefBS* ct, MemRegion mr)
    : _ct(ct), _mr(mr), _result(false) {}
  void do_MemRegion(MemRegion mr) {
    _result = _mr.equals(mr);
  }
  bool result() const { return _result; }
};

void CardTableModRefBS::verify_dirty_region(MemRegion mr) {
  GuaranteeDirtyClosure blk(this, mr);
  dirty_card_iterate(mr, &blk);
  guarantee(blk.result(), "Non-dirty cards in region that should be dirty");
}
#endif

bool CardTableModRefBSForCTRS::card_will_be_scanned(jbyte cv) {
  return
    CardTableModRefBS::card_will_be_scanned(cv) ||
    _rs->is_prev_nonclean_card_val(cv);
};

bool CardTableModRefBSForCTRS::card_may_have_been_dirty(jbyte cv) {
  return
    cv != clean_card &&
    (CardTableModRefBS::card_may_have_been_dirty(cv) ||
     CardTableRS::youngergen_may_have_been_dirty(cv));
};