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

 /*

  * Copyright 2001-2007 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.

  *

  */

 #include "incls/_precompiled.incl"

 #include "incls/_heapRegionRemSet.cpp.incl"

 #define HRRS_VERBOSE 0

 #define PRT_COUNT_OCCUPIED 1

 // OtherRegionsTable

 class PerRegionTable: public CHeapObj {

   friend class OtherRegionsTable;

   friend class HeapRegionRemSetIterator;

   HeapRegion*     _hr;

   BitMap          _bm;

 #if PRT_COUNT_OCCUPIED

   jint            _occupied;

 #endif

   PerRegionTable* _next_free;

   PerRegionTable* next_free() { return _next_free; }

   void set_next_free(PerRegionTable* prt) { _next_free = prt; }

   static PerRegionTable* _free_list;

 #ifdef _MSC_VER

   // For some reason even though the classes are marked as friend they are unable

   // to access CardsPerRegion when private/protected. Only the windows c++ compiler

   // says this Sun CC and linux gcc don't have a problem with access when private

   public:

 #endif // _MSC_VER

   enum SomePrivateConstants {

     CardsPerRegion = HeapRegion::GrainBytes >> CardTableModRefBS::card_shift

   };

 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),

 #if PRT_COUNT_OCCUPIED

     _occupied(0),

 #endif

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

   {}

   static void free(PerRegionTable* prt) {

     while (true) {

       PerRegionTable* fl = _free_list;

       prt->set_next_free(fl);

       PerRegionTable* res =

         (PerRegionTable*)

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

       if (res == fl) return;

     }

     ShouldNotReachHere();

   }

   static PerRegionTable* alloc(HeapRegion* hr) {

     PerRegionTable* fl = _free_list;

     while (fl != NULL) {

       PerRegionTable* nxt = fl->next_free();

       PerRegionTable* res =

         (PerRegionTable*)

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

       if (res == fl) {

         fl->init(hr);

         return fl;

       } else {

         fl = _free_list;

       }

     }

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

     return new PerRegionTable(hr);

   }

   void add_card_work(short from_card, bool par) {

     if (!_bm.at(from_card)) {

       if (par) {

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

 #if PRT_COUNT_OCCUPIED

           Atomic::inc(&_occupied);

 #endif

         }

       } else {

         _bm.at_put(from_card, 1);

 #if PRT_COUNT_OCCUPIED

         _occupied++;

 #endif

       }

     }

   }

   void add_reference_work(oop* from, bool par) {

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

     // concurrency.

 #if HRRS_VERBOSE

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

                            from, *from);

 #endif

     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 (loc_hr->is_in_reserved(from)) {

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

       size_t from_card =

         hw_offset >>

         (CardTableModRefBS::card_shift - LogHeapWordSize);

       add_card_work((short) from_card, par);

     }

   }

 public:

   HeapRegion* hr() const { return _hr; }

 #if PRT_COUNT_OCCUPIED

   jint occupied() const {

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

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

     return _occupied;

   }

 #else

   jint occupied() const {

     return _bm.count_one_bits();

   }

 #endif

   void init(HeapRegion* hr) {

     _hr = hr;

 #if PRT_COUNT_OCCUPIED

     _occupied = 0;

 #endif

     _bm.clear();

   }

   void add_reference(oop* from) {

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

   }

   void seq_add_reference(oop* from) {

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

   }

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

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

     int hr_first_card_index = ctbs->index_for(hr_bot);

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

 #if PRT_COUNT_OCCUPIED

     recount_occupied();

 #endif

   }

   void add_card(short from_card_index) {

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

   }

   void seq_add_card(short 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;

   }

   static size_t fl_mem_size() {

     PerRegionTable* cur = _free_list;

     size_t res = 0;

     while (cur != NULL) {

       res += sizeof(PerRegionTable);

       cur = cur->next_free();

     }

     return res;

   }

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

   bool contains_reference(oop* 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);

   }

 };

 PerRegionTable* PerRegionTable::_free_list = NULL;

 #define COUNT_PAR_EXPANDS 0

 #if COUNT_PAR_EXPANDS

 static jint n_par_expands = 0;

 static jint n_par_contracts = 0;

 static jint par_expand_list_len = 0;

 static jint max_par_expand_list_len = 0;

 static void print_par_expand() {

   Atomic::inc(&n_par_expands);

   Atomic::inc(&par_expand_list_len);

   if (par_expand_list_len > max_par_expand_list_len) {

     max_par_expand_list_len = par_expand_list_len;

   }

   if ((n_par_expands % 10) == 0) {

     gclog_or_tty->print_cr("\n\n%d par expands: %d contracts, "

                   "len = %d, max_len = %d\n.",

                   n_par_expands, n_par_contracts, par_expand_list_len,

                   max_par_expand_list_len);

   }

 }

 #endif

 class PosParPRT: public PerRegionTable {

   PerRegionTable** _par_tables;

   enum SomePrivateConstants {

     ReserveParTableExpansion = 1

   };

   void par_expand() {

     int n = HeapRegionRemSet::num_par_rem_sets()-1;

     if (n <= 0) return;

     if (_par_tables == NULL) {

       PerRegionTable* res =

         (PerRegionTable*)

         Atomic::cmpxchg_ptr((PerRegionTable*)ReserveParTableExpansion,

                             &_par_tables, NULL);

       if (res != NULL) return;

       // Otherwise, we reserved the right to do the expansion.

       PerRegionTable** ptables = NEW_C_HEAP_ARRAY(PerRegionTable*, n);

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

         PerRegionTable* ptable = PerRegionTable::alloc(hr());

         ptables[i] = ptable;

       }

       // Here we do not need an atomic.

       _par_tables = ptables;

 #if COUNT_PAR_EXPANDS

       print_par_expand();

 #endif

       // We must put this table on the expanded list.

       PosParPRT* exp_head = _par_expanded_list;

       while (true) {

         set_next_par_expanded(exp_head);

         PosParPRT* res =

           (PosParPRT*)

           Atomic::cmpxchg_ptr(this, &_par_expanded_list, exp_head);

         if (res == exp_head) return;

         // Otherwise.

         exp_head = res;

       }

       ShouldNotReachHere();

     }

   }

   void par_contract() {

     assert(_par_tables != NULL, "Precondition.");

     int n = HeapRegionRemSet::num_par_rem_sets()-1;

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

       _par_tables[i]->union_bitmap_into(bm());

       PerRegionTable::free(_par_tables[i]);

       _par_tables[i] = NULL;

     }

 #if PRT_COUNT_OCCUPIED

     // We must recount the "occupied."

     recount_occupied();

 #endif

     FREE_C_HEAP_ARRAY(PerRegionTable*, _par_tables);

     _par_tables = NULL;

 #if COUNT_PAR_EXPANDS

     Atomic::inc(&n_par_contracts);

     Atomic::dec(&par_expand_list_len);

 #endif

   }

   static PerRegionTable** _par_table_fl;

   PosParPRT* _next;

   static PosParPRT* _free_list;

   PerRegionTable** par_tables() const {

     assert(uintptr_t(NULL) == 0, "Assumption.");

     if (uintptr_t(_par_tables) <= ReserveParTableExpansion)

       return NULL;

     else

       return _par_tables;

   }

   PosParPRT* _next_par_expanded;

   PosParPRT* next_par_expanded() { return _next_par_expanded; }

   void set_next_par_expanded(PosParPRT* ppprt) { _next_par_expanded = ppprt; }

   static PosParPRT* _par_expanded_list;

 public:

   PosParPRT(HeapRegion* hr) : PerRegionTable(hr), _par_tables(NULL) {}

   jint occupied() const {

     jint res = PerRegionTable::occupied();

     if (par_tables() != NULL) {

       for (int i = 0; i < HeapRegionRemSet::num_par_rem_sets()-1; i++) {

         res += par_tables()[i]->occupied();

       }

     }

     return res;

   }

   void init(HeapRegion* hr) {

     PerRegionTable::init(hr);

     _next = NULL;

     if (par_tables() != NULL) {

       for (int i = 0; i < HeapRegionRemSet::num_par_rem_sets()-1; i++) {

         par_tables()[i]->init(hr);

       }

     }

   }

   static void free(PosParPRT* prt) {

     while (true) {

       PosParPRT* fl = _free_list;

       prt->set_next(fl);

       PosParPRT* res =

         (PosParPRT*)

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

       if (res == fl) return;

     }

     ShouldNotReachHere();

   }

   static PosParPRT* alloc(HeapRegion* hr) {

     PosParPRT* fl = _free_list;

     while (fl != NULL) {

       PosParPRT* nxt = fl->next();

       PosParPRT* res =

         (PosParPRT*)

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

       if (res == fl) {

         fl->init(hr);

         return fl;

       } else {

         fl = _free_list;

       }

     }

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

     return new PosParPRT(hr);

   }

   PosParPRT* next() const { return _next; }

   void set_next(PosParPRT* nxt) { _next = nxt; }

   PosParPRT** next_addr() { return &_next; }

   void add_reference(oop* from, int tid) {

     // Expand if necessary.

     PerRegionTable** pt = par_tables();

     if (par_tables() == NULL && tid > 0 && hr()->is_gc_alloc_region()) {

       par_expand();

       pt = par_tables();

     }

     if (pt != NULL) {

       // We always have to assume that mods to table 0 are in parallel,

       // because of the claiming scheme in parallel expansion.  A thread

       // with tid != 0 that finds the table to be NULL, but doesn't succeed

       // in claiming the right of expanding it, will end up in the else

       // clause of the above if test.  That thread could be delayed, and a

       // thread 0 add reference could see the table expanded, and come

       // here.  Both threads would be adding in parallel.  But we get to

       // not use atomics for tids > 0.

       if (tid == 0) {

         PerRegionTable::add_reference(from);

       } else {

         pt[tid-1]->seq_add_reference(from);

       }

     } else {

       // Not expanded -- add to the base table.

       PerRegionTable::add_reference(from);

     }

   }

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

     assert(_par_tables == NULL, "Precondition");

     PerRegionTable::scrub(ctbs, card_bm);

   }

   size_t mem_size() const {

     size_t res =

       PerRegionTable::mem_size() + sizeof(this) - sizeof(PerRegionTable);

     if (_par_tables != NULL) {

       for (int i = 0; i < HeapRegionRemSet::num_par_rem_sets()-1; i++) {

         res += _par_tables[i]->mem_size();

       }

     }

     return res;

   }

   static size_t fl_mem_size() {

     PosParPRT* cur = _free_list;

     size_t res = 0;

     while (cur != NULL) {

       res += sizeof(PosParPRT);

       cur = cur->next();

     }

     return res;

   }

   bool contains_reference(oop* from) const {

     if (PerRegionTable::contains_reference(from)) return true;

     if (_par_tables != NULL) {

       for (int i = 0; i < HeapRegionRemSet::num_par_rem_sets()-1; i++) {

         if (_par_tables[i]->contains_reference(from)) return true;

       }

     }

     return false;

   }

   static void par_contract_all();

 };

 void PosParPRT::par_contract_all() {

   PosParPRT* hd = _par_expanded_list;

   while (hd != NULL) {

     PosParPRT* nxt = hd->next_par_expanded();

     PosParPRT* res =

       (PosParPRT*)

       Atomic::cmpxchg_ptr(nxt, &_par_expanded_list, hd);

     if (res == hd) {

       // We claimed the right to contract this table.

       hd->set_next_par_expanded(NULL);

       hd->par_contract();

       hd = _par_expanded_list;

     } else {

       hd = res;

     }

   }

 }

 PosParPRT* PosParPRT::_free_list = NULL;

 PosParPRT* PosParPRT::_par_expanded_list = NULL;

 jint OtherRegionsTable::_cache_probes = 0;

 jint OtherRegionsTable::_cache_hits = 0;

 size_t OtherRegionsTable::_max_fine_entries = 0;

 size_t OtherRegionsTable::_mod_max_fine_entries_mask = 0;

 #if SAMPLE_FOR_EVICTION

 size_t OtherRegionsTable::_fine_eviction_stride = 0;

 size_t OtherRegionsTable::_fine_eviction_sample_size = 0;

 #endif

 OtherRegionsTable::OtherRegionsTable(HeapRegion* hr) :

   _g1h(G1CollectedHeap::heap()),

   _m(Mutex::leaf, "An OtherRegionsTable lock", true),

   _hr(hr),

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

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

   _fine_grain_regions(NULL),

   _n_fine_entries(0), _n_coarse_entries(0),

 #if SAMPLE_FOR_EVICTION

   _fine_eviction_start(0),

 #endif

   _sparse_table(hr)

 {

   typedef PosParPRT* PosParPRTPtr;

   if (_max_fine_entries == 0) {

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

     _max_fine_entries = (1 << G1LogRSRegionEntries);

     _mod_max_fine_entries_mask = _max_fine_entries - 1;

 #if SAMPLE_FOR_EVICTION

     assert(_fine_eviction_sample_size == 0

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

     _fine_eviction_sample_size = MAX2((size_t)4, (size_t)G1LogRSRegionEntries);

     _fine_eviction_stride = _max_fine_entries / _fine_eviction_sample_size;

 #endif

   }

   _fine_grain_regions = new PosParPRTPtr[_max_fine_entries];

   if (_fine_grain_regions == NULL)

     vm_exit_out_of_memory(sizeof(void*)*_max_fine_entries,

                           "Failed to allocate _fine_grain_entries.");

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

     _fine_grain_regions[i] = NULL;

   }

 }

 int** OtherRegionsTable::_from_card_cache = NULL;

 size_t OtherRegionsTable::_from_card_cache_max_regions = 0;

 size_t OtherRegionsTable::_from_card_cache_mem_size = 0;

 void OtherRegionsTable::init_from_card_cache(size_t max_regions) {

   _from_card_cache_max_regions = max_regions;

   int n_par_rs = HeapRegionRemSet::num_par_rem_sets();

   _from_card_cache = NEW_C_HEAP_ARRAY(int*, n_par_rs);

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

     _from_card_cache[i] = NEW_C_HEAP_ARRAY(int, max_regions);

     for (size_t j = 0; j < max_regions; j++) {

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

     }

   }

   _from_card_cache_mem_size = n_par_rs * max_regions * sizeof(int);

 }

 void OtherRegionsTable::shrink_from_card_cache(size_t new_n_regs) {

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

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

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

     for (size_t 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(oop* from, int tid) {

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

 #if HRRS_VERBOSE

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

                                                   from, *from);

 #endif

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

 #if HRRS_VERBOSE

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

                 hr()->bottom(), from_card,

                 _from_card_cache[tid][cur_hrs_ind]);

 #endif

 #define COUNT_CACHE 0

 #if COUNT_CACHE

   jint p = Atomic::add(1, &_cache_probes);

   if ((p % 10000) == 0) {

     jint hits = _cache_hits;

     gclog_or_tty->print_cr("%d/%d = %5.2f%% RS cache hits.",

                   _cache_hits, p, 100.0* (float)hits/(float)p);

   }

 #endif

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

 #if HRRS_VERBOSE

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

 #endif

 #if COUNT_CACHE

     Atomic::inc(&_cache_hits);

 #endif

     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);

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

   // If the region is already coarsened, return.

   if (_coarse_map.at(from_hrs_ind)) {

 #if HRRS_VERBOSE

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

 #endif

     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;

   PosParPRT* 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;

       int card_index = from_card - from_hr_bot_card_index;

       assert(0 <= card_index && card_index < PosParPRT::CardsPerRegion,

              "Must be in range.");

       if (G1HRRSUseSparseTable &&

           _sparse_table.add_card((short) from_hrs_ind, card_index)) {

         if (G1RecordHRRSOops) {

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

 #if HRRS_VERBOSE

           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);

 #endif

         }

 #if HRRS_VERBOSE

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

 #endif

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

         return;

       } else {

 #if HRRS_VERBOSE

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

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

                       tid, from_hrs_ind, cur_hrs_ind);

 #endif

       }

       // Otherwise, transfer from sparse to fine-grain.

       short cards[SparsePRTEntry::CardsPerEntry];

       if (G1HRRSUseSparseTable) {

         bool res = _sparse_table.get_cards((short) from_hrs_ind, &cards[0]);

         assert(res, "There should have been an entry");

       }

       if (_n_fine_entries == _max_fine_entries) {

         prt = delete_region_table();

       } else {

         prt = PosParPRT::alloc(from_hr);

       }

       prt->init(from_hr);

       // Record the outgoing pointer in the from_region's outgoing bitmap.

       from_hr->rem_set()->add_outgoing_reference(hr());

       PosParPRT* first_prt = _fine_grain_regions[ind];

       prt->set_next(first_prt);  // XXX Maybe move to init?

       _fine_grain_regions[ind] = prt;

       _n_fine_entries++;

       // Add in the cards from the sparse table.

       if (G1HRRSUseSparseTable) {

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

           short c = cards[i];

           if (c != SparsePRTEntry::NullEntry) {

             prt->add_card(c);

           }

         }

         // Now we can delete the sparse entry.

         bool res = _sparse_table.delete_entry((short) 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, tid);

   if (G1RecordHRRSOops) {

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

 #if HRRS_VERBOSE

     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);

 #endif

   }

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

 }

 PosParPRT*

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

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

   PosParPRT* prt = _fine_grain_regions[ind];

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

     prt = prt->next();

   }

   // Loop postcondition is the method postcondition.

   return prt;

 }

 #define DRT_CENSUS 0

 #if DRT_CENSUS

 static const int HistoSize = 6;

 static int global_histo[HistoSize] = { 0, 0, 0, 0, 0, 0 };

 static int coarsenings = 0;

 static int occ_sum = 0;

 #endif

 jint OtherRegionsTable::_n_coarsenings = 0;

 PosParPRT* OtherRegionsTable::delete_region_table() {

 #if DRT_CENSUS

   int histo[HistoSize] = { 0, 0, 0, 0, 0, 0 };

   const int histo_limits[] = { 1, 4, 16, 64, 256, 2048 };

 #endif

   assert(_m.owned_by_self(), "Precondition");

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

   PosParPRT* max = NULL;

   jint max_occ = 0;

   PosParPRT** max_prev;

   size_t max_ind;

 #if SAMPLE_FOR_EVICTION

   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.");

     }

     PosParPRT** prev = &_fine_grain_regions[ii];

     PosParPRT* 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->next_addr();

       cur = cur->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;

 #else

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

     PosParPRT** prev = &_fine_grain_regions[i];

     PosParPRT* cur = *prev;

     while (cur != NULL) {

       jint cur_occ = cur->occupied();

 #if DRT_CENSUS

       for (int k = 0; k < HistoSize; k++) {

         if (cur_occ <= histo_limits[k]) {

           histo[k]++; global_histo[k]++; break;

         }

       }

 #endif

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

         max = cur;

         max_prev = prev;

         max_ind = i;

         max_occ = cur_occ;

       }

       prev = cur->next_addr();

       cur = cur->next();

     }

   }

 #endif

   // XXX

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

 #if DRT_CENSUS

   gclog_or_tty->print_cr("In a coarsening: histo of occs:");

   for (int k = 0; k < HistoSize; k++) {

     gclog_or_tty->print_cr("  <= %4d: %5d.", histo_limits[k], histo[k]);

   }

   coarsenings++;

   occ_sum += max_occ;

   if ((coarsenings % 100) == 0) {

     gclog_or_tty->print_cr("\ncoarsenings = %d; global summary:", coarsenings);

     for (int k = 0; k < HistoSize; k++) {

       gclog_or_tty->print_cr("  <= %4d: %5d.", histo_limits[k], global_histo[k]);

     }

     gclog_or_tty->print_cr("Avg occ of deleted region = %6.2f.",

                   (float)occ_sum/(float)coarsenings);

   }

 #endif

   // Set the corresponding coarse bit.

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

   if (!_coarse_map.at(max_hrs_index)) {

     _coarse_map.at_put(max_hrs_index, true);

     _n_coarse_entries++;

 #if 0

     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);

 #endif

   }

   // Unsplice.

   *max_prev = max->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 %d:", hr()->hrs_index());

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

   if (G1RSScrubVerbose)

     gclog_or_tty->print("   Coarse map: before = %d...", _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 = %d.", _n_coarse_entries);

   // Now do the fine-grained maps.

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

     PosParPRT* cur = _fine_grain_regions[i];

     PosParPRT** prev = &_fine_grain_regions[i];

     while (cur != NULL) {

       PosParPRT* nxt = cur->next();

       // If the entire region is dead, eliminate.

       if (G1RSScrubVerbose)

         gclog_or_tty->print_cr("     For other region %d:", cur->hr()->hrs_index());

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

         *prev = nxt;

         cur->set_next(NULL);

         _n_fine_entries--;

         if (G1RSScrubVerbose)

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

         PosParPRT::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_next(NULL);

           _n_fine_entries--;

           PosParPRT::free(cur);

         } else {

           prev = cur->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 {

   // Cast away const in this case.

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

   size_t sum = occ_fine();

   sum += occ_sparse();

   sum += occ_coarse();

   return sum;

 }

 size_t OtherRegionsTable::occ_fine() const {

   size_t sum = 0;

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

     PosParPRT* cur = _fine_grain_regions[i];

     while (cur != NULL) {

       sum += cur->occupied();

       cur = cur->next();

     }

   }

   return sum;

 }

 size_t OtherRegionsTable::occ_coarse() const {

   return (_n_coarse_entries * PosParPRT::CardsPerRegion);

 }

 size_t OtherRegionsTable::occ_sparse() const {

   return _sparse_table.occupied();

 }

 size_t OtherRegionsTable::mem_size() const {

   // Cast away const in this case.

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

   size_t sum = 0;

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

     PosParPRT* cur = _fine_grain_regions[i];

     while (cur != NULL) {

       sum += cur->mem_size();

       cur = cur->next();

     }

   }

   sum += (sizeof(PosParPRT*) * _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() + PosParPRT::fl_mem_size();

 }

 void OtherRegionsTable::clear_fcc() {

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

     _from_card_cache[i][hr()->hrs_index()] = -1;

   }

 }

 void OtherRegionsTable::clear() {

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

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

     PosParPRT* cur = _fine_grain_regions[i];

     while (cur != NULL) {

       PosParPRT* nxt = cur->next();

       PosParPRT::free(cur);

       cur = nxt;

     }

     _fine_grain_regions[i] = 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.

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

   for (int 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.");

   PosParPRT** prev_addr = &_fine_grain_regions[ind];

   PosParPRT* prt = *prev_addr;

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

     prev_addr = prt->next_addr();

     prt = prt->next();

   }

   if (prt != NULL) {

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

     *prev_addr = prt->next();

     PosParPRT::free(prt);

     _n_fine_entries--;

     return true;

   } else {

     return false;

   }

 }

 bool OtherRegionsTable::contains_reference(oop* 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(oop* from) const {

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

   if (hr == NULL) return false;

   size_t hr_ind = hr->hrs_index();

   // Is this region in the coarse map?

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

   PosParPRT* 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");

     int card_index = from_card - hr_bot_card_index;

     return _sparse_table.contains_card((short)hr_ind, card_index);

   }

 }

 bool HeapRegionRemSet::_par_traversal = false;

 void HeapRegionRemSet::set_par_traversal(bool b) {

   assert(_par_traversal != b, "Proper alternation...");

   _par_traversal = b;

 }

 int HeapRegionRemSet::num_par_rem_sets() {

   // We always have at least two, so that a mutator thread can claim an

   // id and add to a rem set.

   return (int) MAX2(ParallelGCThreads, (size_t)2);

 }

 HeapRegionRemSet::HeapRegionRemSet(G1BlockOffsetSharedArray* bosa,

                                    HeapRegion* hr)

     : _bosa(bosa), _other_regions(hr),

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

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

       _iter_state(Unclaimed)

 {}

 void HeapRegionRemSet::init_for_par_iteration() {

   _iter_state = Unclaimed;

 }

 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;

 }

 void HeapRegionRemSet::init_iterator(HeapRegionRemSetIterator* iter) const {

   iter->initialize(this);

 }

 #ifndef PRODUCT

 void HeapRegionRemSet::print() const {

   HeapRegionRemSetIterator iter;

   init_iterator(&iter);

   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);

   }

   // XXX

   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::par_cleanup() {

   PosParPRT::par_contract_all();

 }

 void HeapRegionRemSet::add_outgoing_reference(HeapRegion* to_hr) {

   _outgoing_region_map.par_at_put(to_hr->hrs_index(), 1);

 }

 void HeapRegionRemSet::clear() {

   clear_outgoing_entries();

   _outgoing_region_map.clear();

   _other_regions.clear();

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

 }

 void HeapRegionRemSet::clear_outgoing_entries() {

   G1CollectedHeap* g1h = G1CollectedHeap::heap();

   size_t i = _outgoing_region_map.get_next_one_offset(0);

   while (i < _outgoing_region_map.size()) {

     HeapRegion* to_region = g1h->region_at(i);

     to_region->rem_set()->clear_incoming_entry(hr());

     i = _outgoing_region_map.get_next_one_offset(i+1);

   }

 }

 void HeapRegionRemSet::scrub(CardTableModRefBS* ctbs,

                              BitMap* region_bm, BitMap* card_bm) {

   _other_regions.scrub(ctbs, region_bm, card_bm);

 }

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

 HeapRegionRemSetIterator::

 HeapRegionRemSetIterator() :

   _hrrs(NULL),

   _g1h(G1CollectedHeap::heap()),

   _bosa(NULL),

   _sparse_iter(size_t(G1CollectedHeap::heap()->reserved_region().start())

                >> CardTableModRefBS::card_shift)

 {}

 void HeapRegionRemSetIterator::initialize(const HeapRegionRemSet* hrrs) {

   _hrrs = hrrs;

   _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 = (PosParPRT::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.init(&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 == PosParPRT::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(_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 == PosParPRT::CardsPerRegion) {

       _cur_region_cur_card = 0;

       _fine_cur_prt = _fine_cur_prt->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 < PosParPRT::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;

 }

 oop**        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, oop* f) {

   if (_recorded_oops == NULL) {

     assert(_n_recorded == 0

            && _recorded_cards == NULL

            && _recorded_regions == NULL,

            "Inv");

     _recorded_oops = NEW_C_HEAP_ARRAY(oop*, MaxRecorded);

     _recorded_cards = NEW_C_HEAP_ARRAY(HeapWord*, MaxRecorded);

     _recorded_regions = NEW_C_HEAP_ARRAY(HeapRegion*, MaxRecorded);

   }

   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);

     _recorded_event_index = NEW_C_HEAP_ARRAY(int, MaxRecordedEvents);

   }

   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]);

   }

 }

 #ifndef PRODUCT

 void HeapRegionRemSet::test() {

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

   G1CollectedHeap* g1h = G1CollectedHeap::heap();

   // Run with "-XX:G1LogRSRegionEntries=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((oop*)hr1_start);

   hrrs->add_reference((oop*)hr1_mid);

   hrrs->add_reference((oop*)hr1_last);

   hrrs->add_reference((oop*)hr2_start);

   hrrs->add_reference((oop*)hr2_mid);

   hrrs->add_reference((oop*)hr2_last);

   hrrs->add_reference((oop*)hr3_start);

   hrrs->add_reference((oop*)hr3_mid);

   hrrs->add_reference((oop*)hr3_last);

   // Now cause a coarsening.

   hrrs->add_reference((oop*)hr4->bottom());

   hrrs->add_reference((oop*)hr5->bottom());

   // Now, does iteration yield these three?

   HeapRegionRemSetIterator iter;

   hrrs->init_iterator(&iter);

   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