Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 2001, 2014, 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.

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  */

 #include "precompiled.hpp"

 #include "gc_implementation/g1/concurrentG1Refine.hpp"

 #include "gc_implementation/g1/g1BlockOffsetTable.inline.hpp"

 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"

 #include "gc_implementation/g1/heapRegionRemSet.hpp"

 #include "gc_implementation/g1/heapRegionSeq.inline.hpp"

 #include "memory/allocation.hpp"

 #include "memory/padded.inline.hpp"

 #include "memory/space.inline.hpp"

 #include "oops/oop.inline.hpp"

 #include "utilities/bitMap.inline.hpp"

 #include "utilities/globalDefinitions.hpp"

 #include "utilities/growableArray.hpp"

 class PerRegionTable: public CHeapObj<mtGC> {

   friend class OtherRegionsTable;

   friend class HeapRegionRemSetIterator;

   HeapRegion*     _hr;

   BitMap          _bm;

   jint            _occupied;

   // next pointer for free/allocated 'all' list

   PerRegionTable* _next;

   // prev pointer for the allocated 'all' list

   PerRegionTable* _prev;

   // next pointer in collision list

   PerRegionTable * _collision_list_next;

   // Global free list of PRTs

   static PerRegionTable* _free_list;

 protected:

   // We need access in order to union things into the base table.

   BitMap* bm() { return &_bm; }

   void recount_occupied() {

     _occupied = (jint) bm()->count_one_bits();

   }

   PerRegionTable(HeapRegion* hr) :

     _hr(hr),

     _occupied(0),

     _bm(HeapRegion::CardsPerRegion, false /* in-resource-area */),

     _collision_list_next(NULL), _next(NULL), _prev(NULL)

   {}

   void add_card_work(CardIdx_t from_card, bool par) {

     if (!_bm.at(from_card)) {

       if (par) {

         if (_bm.par_at_put(from_card, 1)) {

           Atomic::inc(&_occupied);

         }

       } else {

         _bm.at_put(from_card, 1);

         _occupied++;

       }

     }

   }

   void add_reference_work(OopOrNarrowOopStar from, bool par) {

     // Must make this robust in case "from" is not in "_hr", because of

     // concurrency.

     if (G1TraceHeapRegionRememberedSet) {

       gclog_or_tty->print_cr("    PRT::Add_reference_work(" PTR_FORMAT "->" PTR_FORMAT").",

                              from,

                              UseCompressedOops

                              ? (void *)oopDesc::load_decode_heap_oop((narrowOop*)from)

                              : (void *)oopDesc::load_decode_heap_oop((oop*)from));

     }

     HeapRegion* loc_hr = hr();

     // If the test below fails, then this table was reused concurrently

     // with this operation.  This is OK, since the old table was coarsened,

     // and adding a bit to the new table is never incorrect.

     // If the table used to belong to a continues humongous region and is

     // now reused for the corresponding start humongous region, we need to

     // make sure that we detect this. Thus, we call is_in_reserved_raw()

     // instead of just is_in_reserved() here.

     if (loc_hr->is_in_reserved_raw(from)) {

       size_t hw_offset = pointer_delta((HeapWord*)from, loc_hr->bottom());

       CardIdx_t from_card = (CardIdx_t)

           hw_offset >> (CardTableModRefBS::card_shift - LogHeapWordSize);

       assert(0 <= from_card && (size_t)from_card < HeapRegion::CardsPerRegion,

              "Must be in range.");

       add_card_work(from_card, par);

     }

   }

 public:

   HeapRegion* hr() const { return _hr; }

   jint occupied() const {

     // Overkill, but if we ever need it...

     // guarantee(_occupied == _bm.count_one_bits(), "Check");

     return _occupied;

   }

   void init(HeapRegion* hr, bool clear_links_to_all_list) {

     if (clear_links_to_all_list) {

       set_next(NULL);

       set_prev(NULL);

     }

     _hr = hr;

     _collision_list_next = NULL;

     _occupied = 0;

     _bm.clear();

   }

   void add_reference(OopOrNarrowOopStar from) {

     add_reference_work(from, /*parallel*/ true);

   }

   void seq_add_reference(OopOrNarrowOopStar from) {

     add_reference_work(from, /*parallel*/ false);

   }

   void scrub(CardTableModRefBS* ctbs, BitMap* card_bm) {

     HeapWord* hr_bot = hr()->bottom();

     size_t hr_first_card_index = ctbs->index_for(hr_bot);

     bm()->set_intersection_at_offset(*card_bm, hr_first_card_index);

     recount_occupied();

   }

   void add_card(CardIdx_t from_card_index) {

     add_card_work(from_card_index, /*parallel*/ true);

   }

   void seq_add_card(CardIdx_t from_card_index) {

     add_card_work(from_card_index, /*parallel*/ false);

   }

   // (Destructively) union the bitmap of the current table into the given

   // bitmap (which is assumed to be of the same size.)

   void union_bitmap_into(BitMap* bm) {

     bm->set_union(_bm);

   }

   // Mem size in bytes.

   size_t mem_size() const {

     return sizeof(this) + _bm.size_in_words() * HeapWordSize;

   }

   // Requires "from" to be in "hr()".

   bool contains_reference(OopOrNarrowOopStar from) const {

     assert(hr()->is_in_reserved(from), "Precondition.");

     size_t card_ind = pointer_delta(from, hr()->bottom(),

                                     CardTableModRefBS::card_size);

     return _bm.at(card_ind);

   }

   // Bulk-free the PRTs from prt to last, assumes that they are

   // linked together using their _next field.

   static void bulk_free(PerRegionTable* prt, PerRegionTable* last) {

     while (true) {

       PerRegionTable* fl = _free_list;

       last->set_next(fl);

       PerRegionTable* res = (PerRegionTable*) Atomic::cmpxchg_ptr(prt, &_free_list, fl);

       if (res == fl) {

         return;

       }

     }

     ShouldNotReachHere();

   }

   static void free(PerRegionTable* prt) {

     bulk_free(prt, prt);

   }

   // Returns an initialized PerRegionTable instance.

   static PerRegionTable* alloc(HeapRegion* hr) {

     PerRegionTable* fl = _free_list;

     while (fl != NULL) {

       PerRegionTable* nxt = fl->next();

       PerRegionTable* res =

         (PerRegionTable*)

         Atomic::cmpxchg_ptr(nxt, &_free_list, fl);

       if (res == fl) {

         fl->init(hr, true);

         return fl;

       } else {

         fl = _free_list;

       }

     }

     assert(fl == NULL, "Loop condition.");

     return new PerRegionTable(hr);

   }

   PerRegionTable* next() const { return _next; }

   void set_next(PerRegionTable* next) { _next = next; }

   PerRegionTable* prev() const { return _prev; }

   void set_prev(PerRegionTable* prev) { _prev = prev; }

   // Accessor and Modification routines for the pointer for the

   // singly linked collision list that links the PRTs within the

   // OtherRegionsTable::_fine_grain_regions hash table.

   //

   // It might be useful to also make the collision list doubly linked

   // to avoid iteration over the collisions list during scrubbing/deletion.

   // OTOH there might not be many collisions.

   PerRegionTable* collision_list_next() const {

     return _collision_list_next;

   }

   void set_collision_list_next(PerRegionTable* next) {

     _collision_list_next = next;

   }

   PerRegionTable** collision_list_next_addr() {

     return &_collision_list_next;

   }

   static size_t fl_mem_size() {

     PerRegionTable* cur = _free_list;

     size_t res = 0;

     while (cur != NULL) {

       res += cur->mem_size();

       cur = cur->next();

     }

     return res;

   }

   static void test_fl_mem_size();

 };

 PerRegionTable* PerRegionTable::_free_list = NULL;

 size_t OtherRegionsTable::_max_fine_entries = 0;

 size_t OtherRegionsTable::_mod_max_fine_entries_mask = 0;

 size_t OtherRegionsTable::_fine_eviction_stride = 0;

 size_t OtherRegionsTable::_fine_eviction_sample_size = 0;

 OtherRegionsTable::OtherRegionsTable(HeapRegion* hr, Mutex* m) :

   _g1h(G1CollectedHeap::heap()),

   _hr(hr), _m(m),

   _coarse_map(G1CollectedHeap::heap()->max_regions(),

               false /* in-resource-area */),

   _fine_grain_regions(NULL),

   _first_all_fine_prts(NULL), _last_all_fine_prts(NULL),

   _n_fine_entries(0), _n_coarse_entries(0),

   _fine_eviction_start(0),

   _sparse_table(hr)

 {

   typedef PerRegionTable* PerRegionTablePtr;

   if (_max_fine_entries == 0) {

     assert(_mod_max_fine_entries_mask == 0, "Both or none.");

     size_t max_entries_log = (size_t)log2_long((jlong)G1RSetRegionEntries);

     _max_fine_entries = (size_t)1 << max_entries_log;

     _mod_max_fine_entries_mask = _max_fine_entries - 1;

     assert(_fine_eviction_sample_size == 0

            && _fine_eviction_stride == 0, "All init at same time.");

     _fine_eviction_sample_size = MAX2((size_t)4, max_entries_log);

     _fine_eviction_stride = _max_fine_entries / _fine_eviction_sample_size;

   }

   _fine_grain_regions = NEW_C_HEAP_ARRAY3(PerRegionTablePtr, _max_fine_entries,

                         mtGC, 0, AllocFailStrategy::RETURN_NULL);

   if (_fine_grain_regions == NULL) {

     vm_exit_out_of_memory(sizeof(void*)*_max_fine_entries, OOM_MALLOC_ERROR,

                           "Failed to allocate _fine_grain_entries.");

   }

   for (size_t i = 0; i < _max_fine_entries; i++) {

     _fine_grain_regions[i] = NULL;

   }

 }

 void OtherRegionsTable::link_to_all(PerRegionTable* prt) {

   // We always append to the beginning of the list for convenience;

   // the order of entries in this list does not matter.

   if (_first_all_fine_prts != NULL) {

     assert(_first_all_fine_prts->prev() == NULL, "invariant");

     _first_all_fine_prts->set_prev(prt);

     prt->set_next(_first_all_fine_prts);

   } else {

     // this is the first element we insert. Adjust the "last" pointer

     _last_all_fine_prts = prt;

     assert(prt->next() == NULL, "just checking");

   }

   // the new element is always the first element without a predecessor

   prt->set_prev(NULL);

   _first_all_fine_prts = prt;

   assert(prt->prev() == NULL, "just checking");

   assert(_first_all_fine_prts == prt, "just checking");

   assert((_first_all_fine_prts == NULL && _last_all_fine_prts == NULL) ||

          (_first_all_fine_prts != NULL && _last_all_fine_prts != NULL),

          "just checking");

   assert(_last_all_fine_prts == NULL || _last_all_fine_prts->next() == NULL,

          "just checking");

   assert(_first_all_fine_prts == NULL || _first_all_fine_prts->prev() == NULL,

          "just checking");

 }

 void OtherRegionsTable::unlink_from_all(PerRegionTable* prt) {

   if (prt->prev() != NULL) {

     assert(_first_all_fine_prts != prt, "just checking");

     prt->prev()->set_next(prt->next());

     // removing the last element in the list?

     if (_last_all_fine_prts == prt) {

       _last_all_fine_prts = prt->prev();

     }

   } else {

     assert(_first_all_fine_prts == prt, "just checking");

     _first_all_fine_prts = prt->next();

     // list is empty now?

     if (_first_all_fine_prts == NULL) {

       _last_all_fine_prts = NULL;

     }

   }

   if (prt->next() != NULL) {

     prt->next()->set_prev(prt->prev());

   }

   prt->set_next(NULL);

   prt->set_prev(NULL);

   assert((_first_all_fine_prts == NULL && _last_all_fine_prts == NULL) ||

          (_first_all_fine_prts != NULL && _last_all_fine_prts != NULL),

          "just checking");

   assert(_last_all_fine_prts == NULL || _last_all_fine_prts->next() == NULL,

          "just checking");

   assert(_first_all_fine_prts == NULL || _first_all_fine_prts->prev() == NULL,

          "just checking");

 }

 int**  OtherRegionsTable::_from_card_cache = NULL;

 uint   OtherRegionsTable::_from_card_cache_max_regions = 0;

 size_t OtherRegionsTable::_from_card_cache_mem_size = 0;

 void OtherRegionsTable::init_from_card_cache(uint max_regions) {

   guarantee(_from_card_cache == NULL, "Should not call this multiple times");

   uint n_par_rs = HeapRegionRemSet::num_par_rem_sets();

   _from_card_cache_max_regions = max_regions;

   _from_card_cache = Padded2DArray<int, mtGC>::create_unfreeable(n_par_rs,

                                                                  _from_card_cache_max_regions,

                                                                  &_from_card_cache_mem_size);

   for (uint i = 0; i < n_par_rs; i++) {

     for (uint j = 0; j < _from_card_cache_max_regions; j++) {

       _from_card_cache[i][j] = -1;  // An invalid value.

     }

   }

 }

 void OtherRegionsTable::shrink_from_card_cache(uint new_n_regs) {

   for (uint i = 0; i < HeapRegionRemSet::num_par_rem_sets(); i++) {

     assert(new_n_regs <= _from_card_cache_max_regions, "Must be within max.");

     for (uint j = new_n_regs; j < _from_card_cache_max_regions; j++) {

       _from_card_cache[i][j] = -1;  // An invalid value.

     }

   }

 }

 #ifndef PRODUCT

 void OtherRegionsTable::print_from_card_cache() {

   for (uint i = 0; i < HeapRegionRemSet::num_par_rem_sets(); i++) {

     for (uint j = 0; j < _from_card_cache_max_regions; j++) {

       gclog_or_tty->print_cr("_from_card_cache[%d][%d] = %d.",

                     i, j, _from_card_cache[i][j]);

     }

   }

 }

 #endif

 void OtherRegionsTable::add_reference(OopOrNarrowOopStar from, int tid) {

   size_t cur_hrs_ind = (size_t) hr()->hrs_index();

   if (G1TraceHeapRegionRememberedSet) {

     gclog_or_tty->print_cr("ORT::add_reference_work(" PTR_FORMAT "->" PTR_FORMAT ").",

                                                     from,

                                                     UseCompressedOops

                                                     ? (void *)oopDesc::load_decode_heap_oop((narrowOop*)from)

                                                     : (void *)oopDesc::load_decode_heap_oop((oop*)from));

   }

   int from_card = (int)(uintptr_t(from) >> CardTableModRefBS::card_shift);

   if (G1TraceHeapRegionRememberedSet) {

     gclog_or_tty->print_cr("Table for [" PTR_FORMAT "...): card %d (cache = %d)",

                   hr()->bottom(), from_card,

                   _from_card_cache[tid][cur_hrs_ind]);

   }

   if (from_card == _from_card_cache[tid][cur_hrs_ind]) {

     if (G1TraceHeapRegionRememberedSet) {

       gclog_or_tty->print_cr("  from-card cache hit.");

     }

     assert(contains_reference(from), "We just added it!");

     return;

   } else {

     _from_card_cache[tid][cur_hrs_ind] = from_card;

   }

   // Note that this may be a continued H region.

   HeapRegion* from_hr = _g1h->heap_region_containing_raw(from);

   RegionIdx_t from_hrs_ind = (RegionIdx_t) from_hr->hrs_index();

   // If the region is already coarsened, return.

   if (_coarse_map.at(from_hrs_ind)) {

     if (G1TraceHeapRegionRememberedSet) {

       gclog_or_tty->print_cr("  coarse map hit.");

     }

     assert(contains_reference(from), "We just added it!");

     return;

   }

   // Otherwise find a per-region table to add it to.

   size_t ind = from_hrs_ind & _mod_max_fine_entries_mask;

   PerRegionTable* prt = find_region_table(ind, from_hr);

   if (prt == NULL) {

     MutexLockerEx x(_m, Mutex::_no_safepoint_check_flag);

     // Confirm that it's really not there...

     prt = find_region_table(ind, from_hr);

     if (prt == NULL) {

       uintptr_t from_hr_bot_card_index =

         uintptr_t(from_hr->bottom())

           >> CardTableModRefBS::card_shift;

       CardIdx_t card_index = from_card - from_hr_bot_card_index;

       assert(0 <= card_index && (size_t)card_index < HeapRegion::CardsPerRegion,

              "Must be in range.");

       if (G1HRRSUseSparseTable &&

           _sparse_table.add_card(from_hrs_ind, card_index)) {

         if (G1RecordHRRSOops) {

           HeapRegionRemSet::record(hr(), from);

           if (G1TraceHeapRegionRememberedSet) {

             gclog_or_tty->print("   Added card " PTR_FORMAT " to region "

                                 "[" PTR_FORMAT "...) for ref " PTR_FORMAT ".\n",

                                 align_size_down(uintptr_t(from),

                                                 CardTableModRefBS::card_size),

                                 hr()->bottom(), from);

           }

         }

         if (G1TraceHeapRegionRememberedSet) {

           gclog_or_tty->print_cr("   added card to sparse table.");

         }

         assert(contains_reference_locked(from), "We just added it!");

         return;

       } else {

         if (G1TraceHeapRegionRememberedSet) {

           gclog_or_tty->print_cr("   [tid %d] sparse table entry "

                         "overflow(f: %d, t: %d)",

                         tid, from_hrs_ind, cur_hrs_ind);

         }

       }

       if (_n_fine_entries == _max_fine_entries) {

         prt = delete_region_table();

         // There is no need to clear the links to the 'all' list here:

         // prt will be reused immediately, i.e. remain in the 'all' list.

         prt->init(from_hr, false /* clear_links_to_all_list */);

       } else {

         prt = PerRegionTable::alloc(from_hr);

         link_to_all(prt);

       }

       PerRegionTable* first_prt = _fine_grain_regions[ind];

       prt->set_collision_list_next(first_prt);

       _fine_grain_regions[ind] = prt;

       _n_fine_entries++;

       if (G1HRRSUseSparseTable) {

         // Transfer from sparse to fine-grain.

         SparsePRTEntry *sprt_entry = _sparse_table.get_entry(from_hrs_ind);

         assert(sprt_entry != NULL, "There should have been an entry");

         for (int i = 0; i < SparsePRTEntry::cards_num(); i++) {

           CardIdx_t c = sprt_entry->card(i);

           if (c != SparsePRTEntry::NullEntry) {

             prt->add_card(c);

           }

         }

         // Now we can delete the sparse entry.

         bool res = _sparse_table.delete_entry(from_hrs_ind);

         assert(res, "It should have been there.");

       }

     }

     assert(prt != NULL && prt->hr() == from_hr, "consequence");

   }

   // Note that we can't assert "prt->hr() == from_hr", because of the

   // possibility of concurrent reuse.  But see head comment of

   // OtherRegionsTable for why this is OK.

   assert(prt != NULL, "Inv");

   prt->add_reference(from);

   if (G1RecordHRRSOops) {

     HeapRegionRemSet::record(hr(), from);

     if (G1TraceHeapRegionRememberedSet) {

       gclog_or_tty->print("Added card " PTR_FORMAT " to region "

                           "[" PTR_FORMAT "...) for ref " PTR_FORMAT ".\n",

                           align_size_down(uintptr_t(from),

                                           CardTableModRefBS::card_size),

                           hr()->bottom(), from);

     }

   }

   assert(contains_reference(from), "We just added it!");

 }

 PerRegionTable*

 OtherRegionsTable::find_region_table(size_t ind, HeapRegion* hr) const {

   assert(0 <= ind && ind < _max_fine_entries, "Preconditions.");

   PerRegionTable* prt = _fine_grain_regions[ind];

   while (prt != NULL && prt->hr() != hr) {

     prt = prt->collision_list_next();

   }

   // Loop postcondition is the method postcondition.

   return prt;

 }

 jint OtherRegionsTable::_n_coarsenings = 0;

 PerRegionTable* OtherRegionsTable::delete_region_table() {

   assert(_m->owned_by_self(), "Precondition");

   assert(_n_fine_entries == _max_fine_entries, "Precondition");

   PerRegionTable* max = NULL;

   jint max_occ = 0;

   PerRegionTable** max_prev;

   size_t max_ind;

   size_t i = _fine_eviction_start;

   for (size_t k = 0; k < _fine_eviction_sample_size; k++) {

     size_t ii = i;

     // Make sure we get a non-NULL sample.

     while (_fine_grain_regions[ii] == NULL) {

       ii++;

       if (ii == _max_fine_entries) ii = 0;

       guarantee(ii != i, "We must find one.");

     }

     PerRegionTable** prev = &_fine_grain_regions[ii];

     PerRegionTable* cur = *prev;

     while (cur != NULL) {

       jint cur_occ = cur->occupied();

       if (max == NULL || cur_occ > max_occ) {

         max = cur;

         max_prev = prev;

         max_ind = i;

         max_occ = cur_occ;

       }

       prev = cur->collision_list_next_addr();

       cur = cur->collision_list_next();

     }

     i = i + _fine_eviction_stride;

     if (i >= _n_fine_entries) i = i - _n_fine_entries;

   }

   _fine_eviction_start++;

   if (_fine_eviction_start >= _n_fine_entries) {

     _fine_eviction_start -= _n_fine_entries;

   }

   guarantee(max != NULL, "Since _n_fine_entries > 0");

   // Set the corresponding coarse bit.

   size_t max_hrs_index = (size_t) max->hr()->hrs_index();

   if (!_coarse_map.at(max_hrs_index)) {

     _coarse_map.at_put(max_hrs_index, true);

     _n_coarse_entries++;

     if (G1TraceHeapRegionRememberedSet) {

       gclog_or_tty->print("Coarsened entry in region [" PTR_FORMAT "...] "

                  "for region [" PTR_FORMAT "...] (%d coarse entries).\n",

                  hr()->bottom(),

                  max->hr()->bottom(),

                  _n_coarse_entries);

     }

   }

   // Unsplice.

   *max_prev = max->collision_list_next();

   Atomic::inc(&_n_coarsenings);

   _n_fine_entries--;

   return max;

 }

 // At present, this must be called stop-world single-threaded.

 void OtherRegionsTable::scrub(CardTableModRefBS* ctbs,

                               BitMap* region_bm, BitMap* card_bm) {

   // First eliminated garbage regions from the coarse map.

   if (G1RSScrubVerbose) {

     gclog_or_tty->print_cr("Scrubbing region %u:", hr()->hrs_index());

   }

   assert(_coarse_map.size() == region_bm->size(), "Precondition");

   if (G1RSScrubVerbose) {

     gclog_or_tty->print("   Coarse map: before = "SIZE_FORMAT"...",

                         _n_coarse_entries);

   }

   _coarse_map.set_intersection(*region_bm);

   _n_coarse_entries = _coarse_map.count_one_bits();

   if (G1RSScrubVerbose) {

     gclog_or_tty->print_cr("   after = "SIZE_FORMAT".", _n_coarse_entries);

   }

   // Now do the fine-grained maps.

   for (size_t i = 0; i < _max_fine_entries; i++) {

     PerRegionTable* cur = _fine_grain_regions[i];

     PerRegionTable** prev = &_fine_grain_regions[i];

     while (cur != NULL) {

       PerRegionTable* nxt = cur->collision_list_next();

       // If the entire region is dead, eliminate.

       if (G1RSScrubVerbose) {

         gclog_or_tty->print_cr("     For other region %u:",

                                cur->hr()->hrs_index());

       }

       if (!region_bm->at((size_t) cur->hr()->hrs_index())) {

         *prev = nxt;

         cur->set_collision_list_next(NULL);

         _n_fine_entries--;

         if (G1RSScrubVerbose) {

           gclog_or_tty->print_cr("          deleted via region map.");

         }

         unlink_from_all(cur);

         PerRegionTable::free(cur);

       } else {

         // Do fine-grain elimination.

         if (G1RSScrubVerbose) {

           gclog_or_tty->print("          occ: before = %4d.", cur->occupied());

         }

         cur->scrub(ctbs, card_bm);

         if (G1RSScrubVerbose) {

           gclog_or_tty->print_cr("          after = %4d.", cur->occupied());

         }

         // Did that empty the table completely?

         if (cur->occupied() == 0) {

           *prev = nxt;

           cur->set_collision_list_next(NULL);

           _n_fine_entries--;

           unlink_from_all(cur);

           PerRegionTable::free(cur);

         } else {

           prev = cur->collision_list_next_addr();

         }

       }

       cur = nxt;

     }

   }

   // Since we may have deleted a from_card_cache entry from the RS, clear

   // the FCC.

   clear_fcc();

 }

 size_t OtherRegionsTable::occupied() const {

   size_t sum = occ_fine();

   sum += occ_sparse();

   sum += occ_coarse();

   return sum;

 }

 size_t OtherRegionsTable::occ_fine() const {

   size_t sum = 0;

   size_t num = 0;

   PerRegionTable * cur = _first_all_fine_prts;

   while (cur != NULL) {

     sum += cur->occupied();

     cur = cur->next();

     num++;

   }

   guarantee(num == _n_fine_entries, "just checking");

   return sum;

 }

 size_t OtherRegionsTable::occ_coarse() const {

   return (_n_coarse_entries * HeapRegion::CardsPerRegion);

 }

 size_t OtherRegionsTable::occ_sparse() const {

   return _sparse_table.occupied();

 }

 size_t OtherRegionsTable::mem_size() const {

   size_t sum = 0;

   // all PRTs are of the same size so it is sufficient to query only one of them.

   if (_first_all_fine_prts != NULL) {

     assert(_last_all_fine_prts != NULL &&

       _first_all_fine_prts->mem_size() == _last_all_fine_prts->mem_size(), "check that mem_size() is constant");

     sum += _first_all_fine_prts->mem_size() * _n_fine_entries;

   }

   sum += (sizeof(PerRegionTable*) * _max_fine_entries);

   sum += (_coarse_map.size_in_words() * HeapWordSize);

   sum += (_sparse_table.mem_size());

   sum += sizeof(*this) - sizeof(_sparse_table); // Avoid double counting above.

   return sum;

 }

 size_t OtherRegionsTable::static_mem_size() {

   return _from_card_cache_mem_size;

 }

 size_t OtherRegionsTable::fl_mem_size() {

   return PerRegionTable::fl_mem_size();

 }

 void OtherRegionsTable::clear_fcc() {

   uint hrs_idx = hr()->hrs_index();

   for (uint i = 0; i < HeapRegionRemSet::num_par_rem_sets(); i++) {

     _from_card_cache[i][hrs_idx] = -1;

   }

 }

 void OtherRegionsTable::clear() {

   // if there are no entries, skip this step

   if (_first_all_fine_prts != NULL) {

     guarantee(_first_all_fine_prts != NULL && _last_all_fine_prts != NULL, "just checking");

     PerRegionTable::bulk_free(_first_all_fine_prts, _last_all_fine_prts);

     memset(_fine_grain_regions, 0, _max_fine_entries * sizeof(_fine_grain_regions[0]));

   } else {

     guarantee(_first_all_fine_prts == NULL && _last_all_fine_prts == NULL, "just checking");

   }

   _first_all_fine_prts = _last_all_fine_prts = NULL;

   _sparse_table.clear();

   _coarse_map.clear();

   _n_fine_entries = 0;

   _n_coarse_entries = 0;

   clear_fcc();

 }

 void OtherRegionsTable::clear_incoming_entry(HeapRegion* from_hr) {

   MutexLockerEx x(_m, Mutex::_no_safepoint_check_flag);

   size_t hrs_ind = (size_t) from_hr->hrs_index();

   size_t ind = hrs_ind & _mod_max_fine_entries_mask;

   if (del_single_region_table(ind, from_hr)) {

     assert(!_coarse_map.at(hrs_ind), "Inv");

   } else {

     _coarse_map.par_at_put(hrs_ind, 0);

   }

   // Check to see if any of the fcc entries come from here.

   uint hr_ind = hr()->hrs_index();

   for (uint tid = 0; tid < HeapRegionRemSet::num_par_rem_sets(); tid++) {

     int fcc_ent = _from_card_cache[tid][hr_ind];

     if (fcc_ent != -1) {

       HeapWord* card_addr = (HeapWord*)

         (uintptr_t(fcc_ent) << CardTableModRefBS::card_shift);

       if (hr()->is_in_reserved(card_addr)) {

         // Clear the from card cache.

         _from_card_cache[tid][hr_ind] = -1;

       }

     }

   }

 }

 bool OtherRegionsTable::del_single_region_table(size_t ind,

                                                 HeapRegion* hr) {

   assert(0 <= ind && ind < _max_fine_entries, "Preconditions.");

   PerRegionTable** prev_addr = &_fine_grain_regions[ind];

   PerRegionTable* prt = *prev_addr;

   while (prt != NULL && prt->hr() != hr) {

     prev_addr = prt->collision_list_next_addr();

     prt = prt->collision_list_next();

   }

   if (prt != NULL) {

     assert(prt->hr() == hr, "Loop postcondition.");

     *prev_addr = prt->collision_list_next();

     unlink_from_all(prt);

     PerRegionTable::free(prt);

     _n_fine_entries--;

     return true;

   } else {

     return false;

   }

 }

 bool OtherRegionsTable::contains_reference(OopOrNarrowOopStar from) const {

   // Cast away const in this case.

   MutexLockerEx x((Mutex*)_m, Mutex::_no_safepoint_check_flag);

   return contains_reference_locked(from);

 }

 bool OtherRegionsTable::contains_reference_locked(OopOrNarrowOopStar from) const {

   HeapRegion* hr = _g1h->heap_region_containing_raw(from);

   if (hr == NULL) return false;

   RegionIdx_t hr_ind = (RegionIdx_t) hr->hrs_index();

   // Is this region in the coarse map?

   if (_coarse_map.at(hr_ind)) return true;

   PerRegionTable* prt = find_region_table(hr_ind & _mod_max_fine_entries_mask,

                                      hr);

   if (prt != NULL) {

     return prt->contains_reference(from);

   } else {

     uintptr_t from_card =

       (uintptr_t(from) >> CardTableModRefBS::card_shift);

     uintptr_t hr_bot_card_index =

       uintptr_t(hr->bottom()) >> CardTableModRefBS::card_shift;

     assert(from_card >= hr_bot_card_index, "Inv");

     CardIdx_t card_index = from_card - hr_bot_card_index;

     assert(0 <= card_index && (size_t)card_index < HeapRegion::CardsPerRegion,

            "Must be in range.");

     return _sparse_table.contains_card(hr_ind, card_index);

   }

 }

 void

 OtherRegionsTable::do_cleanup_work(HRRSCleanupTask* hrrs_cleanup_task) {

   _sparse_table.do_cleanup_work(hrrs_cleanup_task);

 }

 // Determines how many threads can add records to an rset in parallel.

 // This can be done by either mutator threads together with the

 // concurrent refinement threads or GC threads.

 uint HeapRegionRemSet::num_par_rem_sets() {

   return (uint)MAX2(DirtyCardQueueSet::num_par_ids() + ConcurrentG1Refine::thread_num(), ParallelGCThreads);

 }

 HeapRegionRemSet::HeapRegionRemSet(G1BlockOffsetSharedArray* bosa,

                                    HeapRegion* hr)

   : _bosa(bosa),

     _m(Mutex::leaf, FormatBuffer<128>("HeapRegionRemSet lock #"UINT32_FORMAT, hr->hrs_index()), true),

     _code_roots(), _other_regions(hr, &_m) {

   reset_for_par_iteration();

 }

 void HeapRegionRemSet::setup_remset_size() {

   // Setup sparse and fine-grain tables sizes.

   // table_size = base * (log(region_size / 1M) + 1)

   const int LOG_M = 20;

   int region_size_log_mb = MAX2(HeapRegion::LogOfHRGrainBytes - LOG_M, 0);

   if (FLAG_IS_DEFAULT(G1RSetSparseRegionEntries)) {

     G1RSetSparseRegionEntries = G1RSetSparseRegionEntriesBase * (region_size_log_mb + 1);

   }

   if (FLAG_IS_DEFAULT(G1RSetRegionEntries)) {

     G1RSetRegionEntries = G1RSetRegionEntriesBase * (region_size_log_mb + 1);

   }

   guarantee(G1RSetSparseRegionEntries > 0 && G1RSetRegionEntries > 0 , "Sanity");

 }

 bool HeapRegionRemSet::claim_iter() {

   if (_iter_state != Unclaimed) return false;

   jint res = Atomic::cmpxchg(Claimed, (jint*)(&_iter_state), Unclaimed);

   return (res == Unclaimed);

 }

 void HeapRegionRemSet::set_iter_complete() {

   _iter_state = Complete;

 }

 bool HeapRegionRemSet::iter_is_complete() {

   return _iter_state == Complete;

 }

 #ifndef PRODUCT

 void HeapRegionRemSet::print() {

   HeapRegionRemSetIterator iter(this);

   size_t card_index;

   while (iter.has_next(card_index)) {

     HeapWord* card_start =

       G1CollectedHeap::heap()->bot_shared()->address_for_index(card_index);

     gclog_or_tty->print_cr("  Card " PTR_FORMAT, card_start);

   }

   if (iter.n_yielded() != occupied()) {

     gclog_or_tty->print_cr("Yielded disagrees with occupied:");

     gclog_or_tty->print_cr("  %6d yielded (%6d coarse, %6d fine).",

                   iter.n_yielded(),

                   iter.n_yielded_coarse(), iter.n_yielded_fine());

     gclog_or_tty->print_cr("  %6d occ     (%6d coarse, %6d fine).",

                   occupied(), occ_coarse(), occ_fine());

   }

   guarantee(iter.n_yielded() == occupied(),

             "We should have yielded all the represented cards.");

 }

 #endif

 void HeapRegionRemSet::cleanup() {

   SparsePRT::cleanup_all();

 }

 void HeapRegionRemSet::clear() {

   MutexLockerEx x(&_m, Mutex::_no_safepoint_check_flag);

   clear_locked();

 }

 void HeapRegionRemSet::clear_locked() {

   _code_roots.clear();

   _other_regions.clear();

   assert(occupied_locked() == 0, "Should be clear.");

   reset_for_par_iteration();

 }

 void HeapRegionRemSet::reset_for_par_iteration() {

   _iter_state = Unclaimed;

   _iter_claimed = 0;

   // It's good to check this to make sure that the two methods are in sync.

   assert(verify_ready_for_par_iteration(), "post-condition");

 }

 void HeapRegionRemSet::scrub(CardTableModRefBS* ctbs,

                              BitMap* region_bm, BitMap* card_bm) {

   _other_regions.scrub(ctbs, region_bm, card_bm);

 }

 // Code roots support

 void HeapRegionRemSet::add_strong_code_root(nmethod* nm) {

   assert(nm != NULL, "sanity");

   _code_roots.add(nm);

 }

 void HeapRegionRemSet::remove_strong_code_root(nmethod* nm) {

   assert(nm != NULL, "sanity");

   _code_roots.remove(nm);

   // Check that there were no duplicates

   guarantee(!_code_roots.contains(nm), "duplicate entry found");

 }

 class NMethodMigrationOopClosure : public OopClosure {

   G1CollectedHeap* _g1h;

   HeapRegion* _from;

   nmethod* _nm;

   uint _num_self_forwarded;

   template <class T> void do_oop_work(T* p) {

     T heap_oop = oopDesc::load_heap_oop(p);

     if (!oopDesc::is_null(heap_oop)) {

       oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);

       if (_from->is_in(obj)) {

         // Reference still points into the source region.

         // Since roots are immediately evacuated this means that

         // we must have self forwarded the object

         assert(obj->is_forwarded(),

                err_msg("code roots should be immediately evacuated. "

                        "Ref: "PTR_FORMAT", "

                        "Obj: "PTR_FORMAT", "

                        "Region: "HR_FORMAT,

                        p, (void*) obj, HR_FORMAT_PARAMS(_from)));

         assert(obj->forwardee() == obj,

                err_msg("not self forwarded? obj = "PTR_FORMAT, (void*)obj));

         // The object has been self forwarded.

         // Note, if we're during an initial mark pause, there is

         // no need to explicitly mark object. It will be marked

         // during the regular evacuation failure handling code.

         _num_self_forwarded++;

       } else {

         // The reference points into a promotion or to-space region

         HeapRegion* to = _g1h->heap_region_containing(obj);

         to->rem_set()->add_strong_code_root(_nm);

       }

     }

   }

 public:

   NMethodMigrationOopClosure(G1CollectedHeap* g1h, HeapRegion* from, nmethod* nm):

     _g1h(g1h), _from(from), _nm(nm), _num_self_forwarded(0) {}

   void do_oop(narrowOop* p) { do_oop_work(p); }

   void do_oop(oop* p)       { do_oop_work(p); }

   uint retain() { return _num_self_forwarded > 0; }

 };

 void HeapRegionRemSet::migrate_strong_code_roots() {

   assert(hr()->in_collection_set(), "only collection set regions");

   assert(!hr()->isHumongous(),

          err_msg("humongous region "HR_FORMAT" should not have been added to the collection set",

                  HR_FORMAT_PARAMS(hr())));

   ResourceMark rm;

   // List of code blobs to retain for this region

   GrowableArray<nmethod*> to_be_retained(10);

   G1CollectedHeap* g1h = G1CollectedHeap::heap();

   while (!_code_roots.is_empty()) {

     nmethod *nm = _code_roots.pop();

     if (nm != NULL) {

       NMethodMigrationOopClosure oop_cl(g1h, hr(), nm);

       nm->oops_do(&oop_cl);

       if (oop_cl.retain()) {

         to_be_retained.push(nm);

       }

     }

   }

   // Now push any code roots we need to retain

   assert(to_be_retained.is_empty() || hr()->evacuation_failed(),

          "Retained nmethod list must be empty or "

          "evacuation of this region failed");

   while (to_be_retained.is_nonempty()) {

     nmethod* nm = to_be_retained.pop();

     assert(nm != NULL, "sanity");

     add_strong_code_root(nm);

   }

 }

 void HeapRegionRemSet::strong_code_roots_do(CodeBlobClosure* blk) const {

   _code_roots.nmethods_do(blk);

 }

 size_t HeapRegionRemSet::strong_code_roots_mem_size() {

   return _code_roots.mem_size();

 }

 //-------------------- Iteration --------------------

 HeapRegionRemSetIterator:: HeapRegionRemSetIterator(HeapRegionRemSet* hrrs) :

   _hrrs(hrrs),

   _g1h(G1CollectedHeap::heap()),

   _coarse_map(&hrrs->_other_regions._coarse_map),

   _fine_grain_regions(hrrs->_other_regions._fine_grain_regions),

   _bosa(hrrs->bosa()),

   _is(Sparse),

   // Set these values so that we increment to the first region.

   _coarse_cur_region_index(-1),

   _coarse_cur_region_cur_card(HeapRegion::CardsPerRegion-1),

   _cur_region_cur_card(0),

   _fine_array_index(-1),

   _fine_cur_prt(NULL),

   _n_yielded_coarse(0),

   _n_yielded_fine(0),

   _n_yielded_sparse(0),

   _sparse_iter(&hrrs->_other_regions._sparse_table) {}

 bool HeapRegionRemSetIterator::coarse_has_next(size_t& card_index) {

   if (_hrrs->_other_regions._n_coarse_entries == 0) return false;

   // Go to the next card.

   _coarse_cur_region_cur_card++;

   // Was the last the last card in the current region?

   if (_coarse_cur_region_cur_card == HeapRegion::CardsPerRegion) {

     // Yes: find the next region.  This may leave _coarse_cur_region_index

     // Set to the last index, in which case there are no more coarse

     // regions.

     _coarse_cur_region_index =

       (int) _coarse_map->get_next_one_offset(_coarse_cur_region_index + 1);

     if ((size_t)_coarse_cur_region_index < _coarse_map->size()) {

       _coarse_cur_region_cur_card = 0;

       HeapWord* r_bot =

         _g1h->region_at((uint) _coarse_cur_region_index)->bottom();

       _cur_region_card_offset = _bosa->index_for(r_bot);

     } else {

       return false;

     }

   }

   // If we didn't return false above, then we can yield a card.

   card_index = _cur_region_card_offset + _coarse_cur_region_cur_card;

   return true;

 }

 void HeapRegionRemSetIterator::fine_find_next_non_null_prt() {

   // Otherwise, find the next bucket list in the array.

   _fine_array_index++;

   while (_fine_array_index < (int) OtherRegionsTable::_max_fine_entries) {

     _fine_cur_prt = _fine_grain_regions[_fine_array_index];

     if (_fine_cur_prt != NULL) return;

     else _fine_array_index++;

   }

   assert(_fine_cur_prt == NULL, "Loop post");

 }

 bool HeapRegionRemSetIterator::fine_has_next(size_t& card_index) {

   if (fine_has_next()) {

     _cur_region_cur_card =

       _fine_cur_prt->_bm.get_next_one_offset(_cur_region_cur_card + 1);

   }

   while (!fine_has_next()) {

     if (_cur_region_cur_card == (size_t) HeapRegion::CardsPerRegion) {

       _cur_region_cur_card = 0;

       _fine_cur_prt = _fine_cur_prt->collision_list_next();

     }

     if (_fine_cur_prt == NULL) {

       fine_find_next_non_null_prt();

       if (_fine_cur_prt == NULL) return false;

     }

     assert(_fine_cur_prt != NULL && _cur_region_cur_card == 0,

            "inv.");

     HeapWord* r_bot =

       _fine_cur_prt->hr()->bottom();

     _cur_region_card_offset = _bosa->index_for(r_bot);

     _cur_region_cur_card = _fine_cur_prt->_bm.get_next_one_offset(0);

   }

   assert(fine_has_next(), "Or else we exited the loop via the return.");

   card_index = _cur_region_card_offset + _cur_region_cur_card;

   return true;

 }

 bool HeapRegionRemSetIterator::fine_has_next() {

   return

     _fine_cur_prt != NULL &&

     _cur_region_cur_card < HeapRegion::CardsPerRegion;

 }

 bool HeapRegionRemSetIterator::has_next(size_t& card_index) {

   switch (_is) {

   case Sparse:

     if (_sparse_iter.has_next(card_index)) {

       _n_yielded_sparse++;

       return true;

     }

     // Otherwise, deliberate fall-through

     _is = Fine;

   case Fine:

     if (fine_has_next(card_index)) {

       _n_yielded_fine++;

       return true;

     }

     // Otherwise, deliberate fall-through

     _is = Coarse;

   case Coarse:

     if (coarse_has_next(card_index)) {

       _n_yielded_coarse++;

       return true;

     }

     // Otherwise...

     break;

   }

   assert(ParallelGCThreads > 1 ||

          n_yielded() == _hrrs->occupied(),

          "Should have yielded all the cards in the rem set "

          "(in the non-par case).");

   return false;

 }

 OopOrNarrowOopStar* HeapRegionRemSet::_recorded_oops = NULL;

 HeapWord**          HeapRegionRemSet::_recorded_cards = NULL;

 HeapRegion**        HeapRegionRemSet::_recorded_regions = NULL;

 int                 HeapRegionRemSet::_n_recorded = 0;

 HeapRegionRemSet::Event* HeapRegionRemSet::_recorded_events = NULL;

 int*         HeapRegionRemSet::_recorded_event_index = NULL;

 int          HeapRegionRemSet::_n_recorded_events = 0;

 void HeapRegionRemSet::record(HeapRegion* hr, OopOrNarrowOopStar f) {

   if (_recorded_oops == NULL) {

     assert(_n_recorded == 0

            && _recorded_cards == NULL

            && _recorded_regions == NULL,

            "Inv");

     _recorded_oops    = NEW_C_HEAP_ARRAY(OopOrNarrowOopStar, MaxRecorded, mtGC);

     _recorded_cards   = NEW_C_HEAP_ARRAY(HeapWord*,          MaxRecorded, mtGC);

     _recorded_regions = NEW_C_HEAP_ARRAY(HeapRegion*,        MaxRecorded, mtGC);

   }

   if (_n_recorded == MaxRecorded) {

     gclog_or_tty->print_cr("Filled up 'recorded' (%d).", MaxRecorded);

   } else {

     _recorded_cards[_n_recorded] =

       (HeapWord*)align_size_down(uintptr_t(f),

                                  CardTableModRefBS::card_size);

     _recorded_oops[_n_recorded] = f;

     _recorded_regions[_n_recorded] = hr;

     _n_recorded++;

   }

 }

 void HeapRegionRemSet::record_event(Event evnt) {

   if (!G1RecordHRRSEvents) return;

   if (_recorded_events == NULL) {

     assert(_n_recorded_events == 0

            && _recorded_event_index == NULL,

            "Inv");

     _recorded_events = NEW_C_HEAP_ARRAY(Event, MaxRecordedEvents, mtGC);

     _recorded_event_index = NEW_C_HEAP_ARRAY(int, MaxRecordedEvents, mtGC);

   }

   if (_n_recorded_events == MaxRecordedEvents) {

     gclog_or_tty->print_cr("Filled up 'recorded_events' (%d).", MaxRecordedEvents);

   } else {

     _recorded_events[_n_recorded_events] = evnt;

     _recorded_event_index[_n_recorded_events] = _n_recorded;

     _n_recorded_events++;

   }

 }

 void HeapRegionRemSet::print_event(outputStream* str, Event evnt) {

   switch (evnt) {

   case Event_EvacStart:

     str->print("Evac Start");

     break;

   case Event_EvacEnd:

     str->print("Evac End");

     break;

   case Event_RSUpdateEnd:

     str->print("RS Update End");

     break;

   }

 }

 void HeapRegionRemSet::print_recorded() {

   int cur_evnt = 0;

   Event cur_evnt_kind;

   int cur_evnt_ind = 0;

   if (_n_recorded_events > 0) {

     cur_evnt_kind = _recorded_events[cur_evnt];

     cur_evnt_ind = _recorded_event_index[cur_evnt];

   }

   for (int i = 0; i < _n_recorded; i++) {

     while (cur_evnt < _n_recorded_events && i == cur_evnt_ind) {

       gclog_or_tty->print("Event: ");

       print_event(gclog_or_tty, cur_evnt_kind);

       gclog_or_tty->print_cr("");

       cur_evnt++;

       if (cur_evnt < MaxRecordedEvents) {

         cur_evnt_kind = _recorded_events[cur_evnt];

         cur_evnt_ind = _recorded_event_index[cur_evnt];

       }

     }

     gclog_or_tty->print("Added card " PTR_FORMAT " to region [" PTR_FORMAT "...]"

                         " for ref " PTR_FORMAT ".\n",

                         _recorded_cards[i], _recorded_regions[i]->bottom(),

                         _recorded_oops[i]);

   }

 }

 void HeapRegionRemSet::reset_for_cleanup_tasks() {

   SparsePRT::reset_for_cleanup_tasks();

 }

 void HeapRegionRemSet::do_cleanup_work(HRRSCleanupTask* hrrs_cleanup_task) {

   _other_regions.do_cleanup_work(hrrs_cleanup_task);

 }

 void

 HeapRegionRemSet::finish_cleanup_task(HRRSCleanupTask* hrrs_cleanup_task) {

   SparsePRT::finish_cleanup_task(hrrs_cleanup_task);

 }

 #ifndef PRODUCT

 void PerRegionTable::test_fl_mem_size() {

   PerRegionTable* dummy = alloc(NULL);

   free(dummy);

   guarantee(dummy->mem_size() == fl_mem_size(), "fl_mem_size() does not return the correct element size");

   // try to reset the state

   _free_list = NULL;

   delete dummy;

 }

 void HeapRegionRemSet::test_prt() {

   PerRegionTable::test_fl_mem_size();

 }

 void HeapRegionRemSet::test() {

   os::sleep(Thread::current(), (jlong)5000, false);

   G1CollectedHeap* g1h = G1CollectedHeap::heap();

   // Run with "-XX:G1LogRSetRegionEntries=2", so that 1 and 5 end up in same

   // hash bucket.

   HeapRegion* hr0 = g1h->region_at(0);

   HeapRegion* hr1 = g1h->region_at(1);

   HeapRegion* hr2 = g1h->region_at(5);

   HeapRegion* hr3 = g1h->region_at(6);

   HeapRegion* hr4 = g1h->region_at(7);

   HeapRegion* hr5 = g1h->region_at(8);

   HeapWord* hr1_start = hr1->bottom();

   HeapWord* hr1_mid = hr1_start + HeapRegion::GrainWords/2;

   HeapWord* hr1_last = hr1->end() - 1;

   HeapWord* hr2_start = hr2->bottom();

   HeapWord* hr2_mid = hr2_start + HeapRegion::GrainWords/2;

   HeapWord* hr2_last = hr2->end() - 1;

   HeapWord* hr3_start = hr3->bottom();

   HeapWord* hr3_mid = hr3_start + HeapRegion::GrainWords/2;

   HeapWord* hr3_last = hr3->end() - 1;

   HeapRegionRemSet* hrrs = hr0->rem_set();

   // Make three references from region 0x101...

   hrrs->add_reference((OopOrNarrowOopStar)hr1_start);

   hrrs->add_reference((OopOrNarrowOopStar)hr1_mid);

   hrrs->add_reference((OopOrNarrowOopStar)hr1_last);

   hrrs->add_reference((OopOrNarrowOopStar)hr2_start);

   hrrs->add_reference((OopOrNarrowOopStar)hr2_mid);

   hrrs->add_reference((OopOrNarrowOopStar)hr2_last);

   hrrs->add_reference((OopOrNarrowOopStar)hr3_start);

   hrrs->add_reference((OopOrNarrowOopStar)hr3_mid);

   hrrs->add_reference((OopOrNarrowOopStar)hr3_last);

   // Now cause a coarsening.

   hrrs->add_reference((OopOrNarrowOopStar)hr4->bottom());

   hrrs->add_reference((OopOrNarrowOopStar)hr5->bottom());

   // Now, does iteration yield these three?

   HeapRegionRemSetIterator iter(hrrs);

   size_t sum = 0;

   size_t card_index;

   while (iter.has_next(card_index)) {

     HeapWord* card_start =

       G1CollectedHeap::heap()->bot_shared()->address_for_index(card_index);

     gclog_or_tty->print_cr("  Card " PTR_FORMAT ".", card_start);

     sum++;

   }

   guarantee(sum == 11 - 3 + 2048, "Failure");

   guarantee(sum == hrrs->occupied(), "Failure");

 }

 #endif