src/hotspot/share/gc/shared/cardTable.cpp - platform/libcore - Git at Google

 /*
  * Copyright (c) 2000, 2018, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */

 #include "precompiled.hpp"
 #include "gc/shared/cardTable.hpp"
 #include "gc/shared/collectedHeap.hpp"
 #include "gc/shared/space.inline.hpp"
 #include "logging/log.hpp"
 #include "memory/virtualspace.hpp"
 #include "runtime/java.hpp"
 #include "runtime/os.hpp"
 #include "services/memTracker.hpp"
 #include "utilities/align.hpp"

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

 CardTable::CardTable(MemRegion whole_heap, bool conc_scan) :
   _scanned_concurrently(conc_scan),
   _whole_heap(whole_heap),
   _guard_index(0),
   _guard_region(),
   _last_valid_index(0),
   _page_size(os::vm_page_size()),
   _byte_map_size(0),
   _covered(NULL),
   _committed(NULL),
   _cur_covered_regions(0),
   _byte_map(NULL),
   _byte_map_base(NULL)
 {
   assert((uintptr_t(_whole_heap.start())  & (card_size - 1))  == 0, "heap must start at card boundary");
   assert((uintptr_t(_whole_heap.end()) & (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];
   if (_covered == NULL) {
     vm_exit_during_initialization("Could not allocate card table covered region set.");
   }
 }

 CardTable::~CardTable() {
   if (_covered) {
     delete[] _covered;
     _covered = NULL;
   }
   if (_committed) {
     delete[] _committed;
     _committed = NULL;
   }
 }

 void CardTable::initialize() {
   _guard_index = cards_required(_whole_heap.word_size()) - 1;
   _last_valid_index = _guard_index - 1;

   _byte_map_size = compute_byte_map_size();

   HeapWord* low_bound  = _whole_heap.start();
   HeapWord* high_bound = _whole_heap.end();

   _cur_covered_regions = 0;
   _committed = new MemRegion[_max_covered_regions];
   if (_committed == NULL) {
     vm_exit_during_initialization("Could not allocate card table committed region set.");
   }

   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);

   MemTracker::record_virtual_memory_type((address)heap_rs.base(), mtGC);

   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 assembler 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];
   HeapWord* guard_page = align_down((HeapWord*)guard_card, _page_size);
   _guard_region = MemRegion(guard_page, _page_size);
   os::commit_memory_or_exit((char*)guard_page, _page_size, _page_size,
                             !ExecMem, "card table last card");
   *guard_card = last_card;

   log_trace(gc, barrier)("CardTable::CardTable: ");
   log_trace(gc, barrier)("    &_byte_map[0]: " INTPTR_FORMAT "  &_byte_map[_last_valid_index]: " INTPTR_FORMAT,
                   p2i(&_byte_map[0]), p2i(&_byte_map[_last_valid_index]));
   log_trace(gc, barrier)("    _byte_map_base: " INTPTR_FORMAT, p2i(_byte_map_base));
 }

 int CardTable::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);
   HeapWord* ct_start_aligned = align_down((HeapWord*)ct_start, _page_size);
   _committed[res].set_start(ct_start_aligned);
   _committed[res].set_word_size(0);
   return res;
 }

 int CardTable::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* CardTable::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 CardTable::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 CardTable::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 _committed 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).
     HeapWord* new_end = (HeapWord*) byte_after(new_region.last());
     HeapWord* new_end_aligned = align_up(new_end, _page_size);
     assert(new_end_aligned >= 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 = ind + 1; ri < _cur_covered_regions; ri++) {
       if (new_end_aligned > _committed[ri].start()) {
         assert(new_end_aligned <= _committed[ri].end(),
                "An earlier committed region can't cover a later committed region");
         // 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");
       os::commit_memory_or_exit((char*)new_committed.start(),
                                 new_committed.byte_size(), _page_size,
                                 !ExecMem, "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()) {
         // It is not safe to uncommit cards if the boundary between
         // the generations is moving.  A shrink can uncommit cards
         // owned by generation A but being used by generation B.
         if (!UseAdaptiveGCBoundary) {
           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();
           }
         } else {
           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);

 #ifdef ASSERT
     // Check that the last card in the new region is committed according
     // to the tables.
     bool covered = false;
     for (int cr = 0; cr < _cur_covered_regions; cr++) {
       if (_committed[cr].contains(new_end - 1)) {
         covered = true;
         break;
       }
     }
     assert(covered, "Card for end of new region not committed");
 #endif

     // 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());

   log_trace(gc, barrier)("CardTable::resize_covered_region: ");
   log_trace(gc, barrier)("    _covered[%d].start(): " INTPTR_FORMAT " _covered[%d].last(): " INTPTR_FORMAT,
                          ind, p2i(_covered[ind].start()), ind, p2i(_covered[ind].last()));
   log_trace(gc, barrier)("    _committed[%d].start(): " INTPTR_FORMAT "  _committed[%d].last(): " INTPTR_FORMAT,
                          ind, p2i(_committed[ind].start()), ind, p2i(_committed[ind].last()));
   log_trace(gc, barrier)("    byte_for(start): " INTPTR_FORMAT "  byte_for(last): " INTPTR_FORMAT,
                          p2i(byte_for(_covered[ind].start())),  p2i(byte_for(_covered[ind].last())));
   log_trace(gc, barrier)("    addr_for(start): " INTPTR_FORMAT "  addr_for(last): " INTPTR_FORMAT,
                          p2i(addr_for((jbyte*) _committed[ind].start())),  p2i(addr_for((jbyte*) _committed[ind].last())));

   // Touch the last card of the covered region to show that it
   // is committed (or SEGV).
   debug_only((void) (*byte_for(_covered[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 CardTable::dirty_MemRegion(MemRegion mr) {
   assert(align_down(mr.start(), HeapWordSize) == mr.start(), "Unaligned start");
   assert(align_up  (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 CardTable::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 CardTable::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 CardTable::dirty(MemRegion mr) {
   jbyte* first = byte_for(mr.start());
   jbyte* last  = byte_after(mr.last());
   memset(first, dirty_card, last-first);
 }

 // Unlike several other card table methods, dirty_card_iterate()
 // iterates over dirty cards ranges in increasing address order.
 void CardTable::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 CardTable::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());
 }

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

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

 void CardTable::invalidate(MemRegion mr) {
   assert(align_down(mr.start(), HeapWordSize) == mr.start(), "Unaligned start");
   assert(align_up  (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 CardTable::verify() {
   verify_guard();
 }

 #ifndef PRODUCT
 void CardTable::verify_region(MemRegion mr,
                                       jbyte val, bool val_equals) {
   jbyte* start    = byte_for(mr.start());
   jbyte* end      = byte_for(mr.last());
   bool failures = false;
   for (jbyte* curr = start; curr <= end; ++curr) {
     jbyte curr_val = *curr;
     bool failed = (val_equals) ? (curr_val != val) : (curr_val == val);
     if (failed) {
       if (!failures) {
         log_error(gc, verify)("== CT verification failed: [" INTPTR_FORMAT "," INTPTR_FORMAT "]", p2i(start), p2i(end));
         log_error(gc, verify)("==   %sexpecting value: %d", (val_equals) ? "" : "not ", val);
         failures = true;
       }
       log_error(gc, verify)("==   card " PTR_FORMAT " [" PTR_FORMAT "," PTR_FORMAT "], val: %d",
                             p2i(curr), p2i(addr_for(curr)),
                             p2i((HeapWord*) (((size_t) addr_for(curr)) + card_size)),
                             (int) curr_val);
     }
   }
   guarantee(!failures, "there should not have been any failures");
 }

 void CardTable::verify_not_dirty_region(MemRegion mr) {
   verify_region(mr, dirty_card, false /* val_equals */);
 }

 void CardTable::verify_dirty_region(MemRegion mr) {
   verify_region(mr, dirty_card, true /* val_equals */);
 }
 #endif

 void CardTable::print_on(outputStream* st) const {
   st->print_cr("Card table byte_map: [" INTPTR_FORMAT "," INTPTR_FORMAT "] _byte_map_base: " INTPTR_FORMAT,
                p2i(_byte_map), p2i(_byte_map + _byte_map_size), p2i(_byte_map_base));
 }
	/*
	* Copyright (c) 2000, 2018, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*
	*/

	#include "precompiled.hpp"
	#include "gc/shared/cardTable.hpp"
	#include "gc/shared/collectedHeap.hpp"
	#include "gc/shared/space.inline.hpp"
	#include "logging/log.hpp"
	#include "memory/virtualspace.hpp"
	#include "runtime/java.hpp"
	#include "runtime/os.hpp"
	#include "services/memTracker.hpp"
	#include "utilities/align.hpp"

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

	CardTable::CardTable(MemRegion whole_heap, bool conc_scan) :
	_scanned_concurrently(conc_scan),
	_whole_heap(whole_heap),
	_guard_index(0),
	_guard_region(),
	_last_valid_index(0),
	_page_size(os::vm_page_size()),
	_byte_map_size(0),
	_covered(NULL),
	_committed(NULL),
	_cur_covered_regions(0),
	_byte_map(NULL),
	_byte_map_base(NULL)
	{
	assert((uintptr_t(_whole_heap.start()) & (card_size - 1)) == 0, "heap must start at card boundary");
	assert((uintptr_t(_whole_heap.end()) & (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];
	if (_covered == NULL) {
	vm_exit_during_initialization("Could not allocate card table covered region set.");
	}
	}

	CardTable::~CardTable() {
	if (_covered) {
	delete[] _covered;
	_covered = NULL;
	}
	if (_committed) {
	delete[] _committed;
	_committed = NULL;
	}
	}

	void CardTable::initialize() {
	_guard_index = cards_required(_whole_heap.word_size()) - 1;
	_last_valid_index = _guard_index - 1;

	_byte_map_size = compute_byte_map_size();

	HeapWord* low_bound = _whole_heap.start();
	HeapWord* high_bound = _whole_heap.end();

	_cur_covered_regions = 0;
	_committed = new MemRegion[_max_covered_regions];
	if (_committed == NULL) {
	vm_exit_during_initialization("Could not allocate card table committed region set.");
	}

	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);

	MemTracker::record_virtual_memory_type((address)heap_rs.base(), mtGC);

	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 assembler 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];
	HeapWord* guard_page = align_down((HeapWord*)guard_card, _page_size);
	_guard_region = MemRegion(guard_page, _page_size);
	os::commit_memory_or_exit((char*)guard_page, _page_size, _page_size,
	!ExecMem, "card table last card");
	*guard_card = last_card;

	log_trace(gc, barrier)("CardTable::CardTable: ");
	log_trace(gc, barrier)(" &_byte_map[0]: " INTPTR_FORMAT " &_byte_map[_last_valid_index]: " INTPTR_FORMAT,
	p2i(&_byte_map[0]), p2i(&_byte_map[_last_valid_index]));
	log_trace(gc, barrier)(" _byte_map_base: " INTPTR_FORMAT, p2i(_byte_map_base));
	}

	int CardTable::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);
	HeapWord* ct_start_aligned = align_down((HeapWord*)ct_start, _page_size);
	_committed[res].set_start(ct_start_aligned);
	_committed[res].set_word_size(0);
	return res;
	}

	int CardTable::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* CardTable::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 CardTable::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 CardTable::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 _committed 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).
	HeapWord* new_end = (HeapWord*) byte_after(new_region.last());
	HeapWord* new_end_aligned = align_up(new_end, _page_size);
	assert(new_end_aligned >= 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 = ind + 1; ri < _cur_covered_regions; ri++) {
	if (new_end_aligned > _committed[ri].start()) {
	assert(new_end_aligned <= _committed[ri].end(),
	"An earlier committed region can't cover a later committed region");
	// 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");
	os::commit_memory_or_exit((char*)new_committed.start(),
	new_committed.byte_size(), _page_size,
	!ExecMem, "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()) {
	// It is not safe to uncommit cards if the boundary between
	// the generations is moving. A shrink can uncommit cards
	// owned by generation A but being used by generation B.
	if (!UseAdaptiveGCBoundary) {
	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();
	}
	} else {
	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);

	#ifdef ASSERT
	// Check that the last card in the new region is committed according
	// to the tables.
	bool covered = false;
	for (int cr = 0; cr < _cur_covered_regions; cr++) {
	if (_committed[cr].contains(new_end - 1)) {
	covered = true;
	break;
	}
	}
	assert(covered, "Card for end of new region not committed");
	#endif

	// 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());

	log_trace(gc, barrier)("CardTable::resize_covered_region: ");
	log_trace(gc, barrier)(" _covered[%d].start(): " INTPTR_FORMAT " _covered[%d].last(): " INTPTR_FORMAT,
	ind, p2i(_covered[ind].start()), ind, p2i(_covered[ind].last()));
	log_trace(gc, barrier)(" _committed[%d].start(): " INTPTR_FORMAT " _committed[%d].last(): " INTPTR_FORMAT,
	ind, p2i(_committed[ind].start()), ind, p2i(_committed[ind].last()));
	log_trace(gc, barrier)(" byte_for(start): " INTPTR_FORMAT " byte_for(last): " INTPTR_FORMAT,
	p2i(byte_for(_covered[ind].start())), p2i(byte_for(_covered[ind].last())));
	log_trace(gc, barrier)(" addr_for(start): " INTPTR_FORMAT " addr_for(last): " INTPTR_FORMAT,
	p2i(addr_for((jbyte) _committed[ind].start())), p2i(addr_for((jbyte) _committed[ind].last())));

	// Touch the last card of the covered region to show that it
	// is committed (or SEGV).
	debug_only((void) (*byte_for(_covered[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 CardTable::dirty_MemRegion(MemRegion mr) {
	assert(align_down(mr.start(), HeapWordSize) == mr.start(), "Unaligned start");
	assert(align_up (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 CardTable::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 CardTable::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 CardTable::dirty(MemRegion mr) {
	jbyte* first = byte_for(mr.start());
	jbyte* last = byte_after(mr.last());
	memset(first, dirty_card, last-first);
	}

	// Unlike several other card table methods, dirty_card_iterate()
	// iterates over dirty cards ranges in increasing address order.
	void CardTable::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 CardTable::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());
	}

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

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

	void CardTable::invalidate(MemRegion mr) {
	assert(align_down(mr.start(), HeapWordSize) == mr.start(), "Unaligned start");
	assert(align_up (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 CardTable::verify() {
	verify_guard();
	}

	#ifndef PRODUCT
	void CardTable::verify_region(MemRegion mr,
	jbyte val, bool val_equals) {
	jbyte* start = byte_for(mr.start());
	jbyte* end = byte_for(mr.last());
	bool failures = false;
	for (jbyte* curr = start; curr <= end; ++curr) {
	jbyte curr_val = *curr;
	bool failed = (val_equals) ? (curr_val != val) : (curr_val == val);
	if (failed) {
	if (!failures) {
	log_error(gc, verify)("== CT verification failed: [" INTPTR_FORMAT "," INTPTR_FORMAT "]", p2i(start), p2i(end));
	log_error(gc, verify)("== %sexpecting value: %d", (val_equals) ? "" : "not ", val);
	failures = true;
	}
	log_error(gc, verify)("== card " PTR_FORMAT " [" PTR_FORMAT "," PTR_FORMAT "], val: %d",
	p2i(curr), p2i(addr_for(curr)),
	p2i((HeapWord*) (((size_t) addr_for(curr)) + card_size)),
	(int) curr_val);
	}
	}
	guarantee(!failures, "there should not have been any failures");
	}

	void CardTable::verify_not_dirty_region(MemRegion mr) {
	verify_region(mr, dirty_card, false /* val_equals */);
	}

	void CardTable::verify_dirty_region(MemRegion mr) {
	verify_region(mr, dirty_card, true /* val_equals */);
	}
	#endif

	void CardTable::print_on(outputStream* st) const {
	st->print_cr("Card table byte_map: [" INTPTR_FORMAT "," INTPTR_FORMAT "] _byte_map_base: " INTPTR_FORMAT,
	p2i(_byte_map), p2i(_byte_map + _byte_map_size), p2i(_byte_map_base));
	}