--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/memory/cardTableRS.cpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,568 @@
+/*
+ * Copyright 2001-2006 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/_cardTableRS.cpp.incl"
+
+CardTableRS::CardTableRS(MemRegion whole_heap,
+                         int max_covered_regions) :
+  GenRemSet(&_ct_bs),
+  _ct_bs(whole_heap, max_covered_regions),
+  _cur_youngergen_card_val(youngergenP1_card)
+{
+  _last_cur_val_in_gen = new jbyte[GenCollectedHeap::max_gens + 1];
+  if (_last_cur_val_in_gen == NULL) {
+    vm_exit_during_initialization("Could not last_cur_val_in_gen array.");
+  }
+  for (int i = 0; i < GenCollectedHeap::max_gens + 1; i++) {
+    _last_cur_val_in_gen[i] = clean_card_val();
+  }
+  _ct_bs.set_CTRS(this);
+}
+
+void CardTableRS::resize_covered_region(MemRegion new_region) {
+  _ct_bs.resize_covered_region(new_region);
+}
+
+jbyte CardTableRS::find_unused_youngergenP_card_value() {
+  GenCollectedHeap* gch = GenCollectedHeap::heap();
+  for (jbyte v = youngergenP1_card;
+       v < cur_youngergen_and_prev_nonclean_card;
+       v++) {
+    bool seen = false;
+    for (int g = 0; g < gch->n_gens()+1; g++) {
+      if (_last_cur_val_in_gen[g] == v) {
+        seen = true;
+        break;
+      }
+    }
+    if (!seen) return v;
+  }
+  ShouldNotReachHere();
+  return 0;
+}
+
+void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) {
+  // Parallel or sequential, we must always set the prev to equal the
+  // last one written.
+  if (parallel) {
+    // Find a parallel value to be used next.
+    jbyte next_val = find_unused_youngergenP_card_value();
+    set_cur_youngergen_card_val(next_val);
+
+  } else {
+    // In an sequential traversal we will always write youngergen, so that
+    // the inline barrier is  correct.
+    set_cur_youngergen_card_val(youngergen_card);
+  }
+}
+
+void CardTableRS::younger_refs_iterate(Generation* g,
+                                       OopsInGenClosure* blk) {
+  _last_cur_val_in_gen[g->level()+1] = cur_youngergen_card_val();
+  g->younger_refs_iterate(blk);
+}
+
+class ClearNoncleanCardWrapper: public MemRegionClosure {
+  MemRegionClosure* _dirty_card_closure;
+  CardTableRS* _ct;
+  bool _is_par;
+private:
+  // Clears the given card, return true if the corresponding card should be
+  // processed.
+  bool clear_card(jbyte* entry) {
+    if (_is_par) {
+      while (true) {
+        // In the parallel case, we may have to do this several times.
+        jbyte entry_val = *entry;
+        assert(entry_val != CardTableRS::clean_card_val(),
+               "We shouldn't be looking at clean cards, and this should "
+               "be the only place they get cleaned.");
+        if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val)
+            || _ct->is_prev_youngergen_card_val(entry_val)) {
+          jbyte res =
+            Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val);
+          if (res == entry_val) {
+            break;
+          } else {
+            assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card,
+                   "The CAS above should only fail if another thread did "
+                   "a GC write barrier.");
+          }
+        } else if (entry_val ==
+                   CardTableRS::cur_youngergen_and_prev_nonclean_card) {
+          // Parallelism shouldn't matter in this case.  Only the thread
+          // assigned to scan the card should change this value.
+          *entry = _ct->cur_youngergen_card_val();
+          break;
+        } else {
+          assert(entry_val == _ct->cur_youngergen_card_val(),
+                 "Should be the only possibility.");
+          // In this case, the card was clean before, and become
+          // cur_youngergen only because of processing of a promoted object.
+          // We don't have to look at the card.
+          return false;
+        }
+      }
+      return true;
+    } else {
+      jbyte entry_val = *entry;
+      assert(entry_val != CardTableRS::clean_card_val(),
+             "We shouldn't be looking at clean cards, and this should "
+             "be the only place they get cleaned.");
+      assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card,
+             "This should be possible in the sequential case.");
+      *entry = CardTableRS::clean_card_val();
+      return true;
+    }
+  }
+
+public:
+  ClearNoncleanCardWrapper(MemRegionClosure* dirty_card_closure,
+                           CardTableRS* ct) :
+    _dirty_card_closure(dirty_card_closure), _ct(ct) {
+    _is_par = (SharedHeap::heap()->n_par_threads() > 0);
+  }
+  void do_MemRegion(MemRegion mr) {
+    // We start at the high end of "mr", walking backwards
+    // while accumulating a contiguous dirty range of cards in
+    // [start_of_non_clean, end_of_non_clean) which we then
+    // process en masse.
+    HeapWord* end_of_non_clean = mr.end();
+    HeapWord* start_of_non_clean = end_of_non_clean;
+    jbyte*       entry = _ct->byte_for(mr.last());
+    const jbyte* first_entry = _ct->byte_for(mr.start());
+    while (entry >= first_entry) {
+      HeapWord* cur = _ct->addr_for(entry);
+      if (!clear_card(entry)) {
+        // We hit a clean card; process any non-empty
+        // dirty range accumulated so far.
+        if (start_of_non_clean < end_of_non_clean) {
+          MemRegion mr2(start_of_non_clean, end_of_non_clean);
+          _dirty_card_closure->do_MemRegion(mr2);
+        }
+        // Reset the dirty window while continuing to
+        // look for the next dirty window to process.
+        end_of_non_clean = cur;
+        start_of_non_clean = end_of_non_clean;
+      }
+      // Open the left end of the window one card to the left.
+      start_of_non_clean = cur;
+      // Note that "entry" leads "start_of_non_clean" in
+      // its leftward excursion after this point
+      // in the loop and, when we hit the left end of "mr",
+      // will point off of the left end of the card-table
+      // for "mr".
+      entry--;
+    }
+    // If the first card of "mr" was dirty, we will have
+    // been left with a dirty window, co-initial with "mr",
+    // which we now process.
+    if (start_of_non_clean < end_of_non_clean) {
+      MemRegion mr2(start_of_non_clean, end_of_non_clean);
+      _dirty_card_closure->do_MemRegion(mr2);
+    }
+  }
+};
+// clean (by dirty->clean before) ==> cur_younger_gen
+// dirty                          ==> cur_youngergen_and_prev_nonclean_card
+// precleaned                     ==> cur_youngergen_and_prev_nonclean_card
+// prev-younger-gen               ==> cur_youngergen_and_prev_nonclean_card
+// cur-younger-gen                ==> cur_younger_gen
+// cur_youngergen_and_prev_nonclean_card ==> no change.
+void CardTableRS::write_ref_field_gc_par(oop* field, oop new_val) {
+  jbyte* entry = ct_bs()->byte_for(field);
+  do {
+    jbyte entry_val = *entry;
+    // We put this first because it's probably the most common case.
+    if (entry_val == clean_card_val()) {
+      // No threat of contention with cleaning threads.
+      *entry = cur_youngergen_card_val();
+      return;
+    } else if (card_is_dirty_wrt_gen_iter(entry_val)
+               || is_prev_youngergen_card_val(entry_val)) {
+      // Mark it as both cur and prev youngergen; card cleaning thread will
+      // eventually remove the previous stuff.
+      jbyte new_val = cur_youngergen_and_prev_nonclean_card;
+      jbyte res = Atomic::cmpxchg(new_val, entry, entry_val);
+      // Did the CAS succeed?
+      if (res == entry_val) return;
+      // Otherwise, retry, to see the new value.
+      continue;
+    } else {
+      assert(entry_val == cur_youngergen_and_prev_nonclean_card
+             || entry_val == cur_youngergen_card_val(),
+             "should be only possibilities.");
+      return;
+    }
+  } while (true);
+}
+
+void CardTableRS::younger_refs_in_space_iterate(Space* sp,
+                                                OopsInGenClosure* cl) {
+  DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, _ct_bs.precision(),
+                                                   cl->gen_boundary());
+  ClearNoncleanCardWrapper clear_cl(dcto_cl, this);
+
+  _ct_bs.non_clean_card_iterate(sp, sp->used_region_at_save_marks(),
+                                dcto_cl, &clear_cl, false);
+}
+
+void CardTableRS::clear_into_younger(Generation* gen, bool clear_perm) {
+  GenCollectedHeap* gch = GenCollectedHeap::heap();
+  // Generations younger than gen have been evacuated. We can clear
+  // card table entries for gen (we know that it has no pointers
+  // to younger gens) and for those below. The card tables for
+  // the youngest gen need never be cleared, and those for perm gen
+  // will be cleared based on the parameter clear_perm.
+  // There's a bit of subtlety in the clear() and invalidate()
+  // methods that we exploit here and in invalidate_or_clear()
+  // below to avoid missing cards at the fringes. If clear() or
+  // invalidate() are changed in the future, this code should
+  // be revisited. 20040107.ysr
+  Generation* g = gen;
+  for(Generation* prev_gen = gch->prev_gen(g);
+      prev_gen != NULL;
+      g = prev_gen, prev_gen = gch->prev_gen(g)) {
+    MemRegion to_be_cleared_mr = g->prev_used_region();
+    clear(to_be_cleared_mr);
+  }
+  // Clear perm gen cards if asked to do so.
+  if (clear_perm) {
+    MemRegion to_be_cleared_mr = gch->perm_gen()->prev_used_region();
+    clear(to_be_cleared_mr);
+  }
+}
+
+void CardTableRS::invalidate_or_clear(Generation* gen, bool younger,
+                                      bool perm) {
+  GenCollectedHeap* gch = GenCollectedHeap::heap();
+  // For each generation gen (and younger and/or perm)
+  // invalidate the cards for the currently occupied part
+  // of that generation and clear the cards for the
+  // unoccupied part of the generation (if any, making use
+  // of that generation's prev_used_region to determine that
+  // region). No need to do anything for the youngest
+  // generation. Also see note#20040107.ysr above.
+  Generation* g = gen;
+  for(Generation* prev_gen = gch->prev_gen(g); prev_gen != NULL;
+      g = prev_gen, prev_gen = gch->prev_gen(g))  {
+    MemRegion used_mr = g->used_region();
+    MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);
+    if (!to_be_cleared_mr.is_empty()) {
+      clear(to_be_cleared_mr);
+    }
+    invalidate(used_mr);
+    if (!younger) break;
+  }
+  // Clear perm gen cards if asked to do so.
+  if (perm) {
+    g = gch->perm_gen();
+    MemRegion used_mr = g->used_region();
+    MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);
+    if (!to_be_cleared_mr.is_empty()) {
+      clear(to_be_cleared_mr);
+    }
+    invalidate(used_mr);
+  }
+}
+
+
+class VerifyCleanCardClosure: public OopClosure {
+  HeapWord* boundary;
+  HeapWord* begin; HeapWord* end;
+public:
+  void do_oop(oop* p) {
+    HeapWord* jp = (HeapWord*)p;
+    if (jp >= begin && jp < end) {
+      guarantee(*p == NULL || (HeapWord*)p < boundary
+                || (HeapWord*)(*p) >= boundary,
+                "pointer on clean card crosses boundary");
+    }
+  }
+  VerifyCleanCardClosure(HeapWord* b, HeapWord* _begin, HeapWord* _end) :
+    boundary(b), begin(_begin), end(_end) {}
+};
+
+class VerifyCTSpaceClosure: public SpaceClosure {
+  CardTableRS* _ct;
+  HeapWord* _boundary;
+public:
+  VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) :
+    _ct(ct), _boundary(boundary) {}
+  void do_space(Space* s) { _ct->verify_space(s, _boundary); }
+};
+
+class VerifyCTGenClosure: public GenCollectedHeap::GenClosure {
+  CardTableRS* _ct;
+public:
+  VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {}
+  void do_generation(Generation* gen) {
+    // Skip the youngest generation.
+    if (gen->level() == 0) return;
+    // Normally, we're interested in pointers to younger generations.
+    VerifyCTSpaceClosure blk(_ct, gen->reserved().start());
+    gen->space_iterate(&blk, true);
+  }
+};
+
+void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) {
+  // We don't need to do young-gen spaces.
+  if (s->end() <= gen_boundary) return;
+  MemRegion used = s->used_region();
+
+  jbyte* cur_entry = byte_for(used.start());
+  jbyte* limit = byte_after(used.last());
+  while (cur_entry < limit) {
+    if (*cur_entry == CardTableModRefBS::clean_card) {
+      jbyte* first_dirty = cur_entry+1;
+      while (first_dirty < limit &&
+             *first_dirty == CardTableModRefBS::clean_card) {
+        first_dirty++;
+      }
+      // If the first object is a regular object, and it has a
+      // young-to-old field, that would mark the previous card.
+      HeapWord* boundary = addr_for(cur_entry);
+      HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty);
+      HeapWord* boundary_block = s->block_start(boundary);
+      HeapWord* begin = boundary;             // Until proven otherwise.
+      HeapWord* start_block = boundary_block; // Until proven otherwise.
+      if (boundary_block < boundary) {
+        if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) {
+          oop boundary_obj = oop(boundary_block);
+          if (!boundary_obj->is_objArray() &&
+              !boundary_obj->is_typeArray()) {
+            guarantee(cur_entry > byte_for(used.start()),
+                      "else boundary would be boundary_block");
+            if (*byte_for(boundary_block) != CardTableModRefBS::clean_card) {
+              begin = boundary_block + s->block_size(boundary_block);
+              start_block = begin;
+            }
+          }
+        }
+      }
+      // Now traverse objects until end.
+      HeapWord* cur = start_block;
+      VerifyCleanCardClosure verify_blk(gen_boundary, begin, end);
+      while (cur < end) {
+        if (s->block_is_obj(cur) && s->obj_is_alive(cur)) {
+          oop(cur)->oop_iterate(&verify_blk);
+        }
+        cur += s->block_size(cur);
+      }
+      cur_entry = first_dirty;
+    } else {
+      // We'd normally expect that cur_youngergen_and_prev_nonclean_card
+      // is a transient value, that cannot be in the card table
+      // except during GC, and thus assert that:
+      // guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card,
+      //        "Illegal CT value");
+      // That however, need not hold, as will become clear in the
+      // following...
+
+      // We'd normally expect that if we are in the parallel case,
+      // we can't have left a prev value (which would be different
+      // from the current value) in the card table, and so we'd like to
+      // assert that:
+      // guarantee(cur_youngergen_card_val() == youngergen_card
+      //           || !is_prev_youngergen_card_val(*cur_entry),
+      //           "Illegal CT value");
+      // That, however, may not hold occasionally, because of
+      // CMS or MSC in the old gen. To wit, consider the
+      // following two simple illustrative scenarios:
+      // (a) CMS: Consider the case where a large object L
+      //     spanning several cards is allocated in the old
+      //     gen, and has a young gen reference stored in it, dirtying
+      //     some interior cards. A young collection scans the card,
+      //     finds a young ref and installs a youngergenP_n value.
+      //     L then goes dead. Now a CMS collection starts,
+      //     finds L dead and sweeps it up. Assume that L is
+      //     abutting _unallocated_blk, so _unallocated_blk is
+      //     adjusted down to (below) L. Assume further that
+      //     no young collection intervenes during this CMS cycle.
+      //     The next young gen cycle will not get to look at this
+      //     youngergenP_n card since it lies in the unoccupied
+      //     part of the space.
+      //     Some young collections later the blocks on this
+      //     card can be re-allocated either due to direct allocation
+      //     or due to absorbing promotions. At this time, the
+      //     before-gc verification will fail the above assert.
+      // (b) MSC: In this case, an object L with a young reference
+      //     is on a card that (therefore) holds a youngergen_n value.
+      //     Suppose also that L lies towards the end of the used
+      //     the used space before GC. An MSC collection
+      //     occurs that compacts to such an extent that this
+      //     card is no longer in the occupied part of the space.
+      //     Since current code in MSC does not always clear cards
+      //     in the unused part of old gen, this stale youngergen_n
+      //     value is left behind and can later be covered by
+      //     an object when promotion or direct allocation
+      //     re-allocates that part of the heap.
+      //
+      // Fortunately, the presence of such stale card values is
+      // "only" a minor annoyance in that subsequent young collections
+      // might needlessly scan such cards, but would still never corrupt
+      // the heap as a result. However, it's likely not to be a significant
+      // performance inhibitor in practice. For instance,
+      // some recent measurements with unoccupied cards eagerly cleared
+      // out to maintain this invariant, showed next to no
+      // change in young collection times; of course one can construct
+      // degenerate examples where the cost can be significant.)
+      // Note, in particular, that if the "stale" card is modified
+      // after re-allocation, it would be dirty, not "stale". Thus,
+      // we can never have a younger ref in such a card and it is
+      // safe not to scan that card in any collection. [As we see
+      // below, we do some unnecessary scanning
+      // in some cases in the current parallel scanning algorithm.]
+      //
+      // The main point below is that the parallel card scanning code
+      // deals correctly with these stale card values. There are two main
+      // cases to consider where we have a stale "younger gen" value and a
+      // "derivative" case to consider, where we have a stale
+      // "cur_younger_gen_and_prev_non_clean" value, as will become
+      // apparent in the case analysis below.
+      // o Case 1. If the stale value corresponds to a younger_gen_n
+      //   value other than the cur_younger_gen value then the code
+      //   treats this as being tantamount to a prev_younger_gen
+      //   card. This means that the card may be unnecessarily scanned.
+      //   There are two sub-cases to consider:
+      //   o Case 1a. Let us say that the card is in the occupied part
+      //     of the generation at the time the collection begins. In
+      //     that case the card will be either cleared when it is scanned
+      //     for young pointers, or will be set to cur_younger_gen as a
+      //     result of promotion. (We have elided the normal case where
+      //     the scanning thread and the promoting thread interleave
+      //     possibly resulting in a transient
+      //     cur_younger_gen_and_prev_non_clean value before settling
+      //     to cur_younger_gen. [End Case 1a.]
+      //   o Case 1b. Consider now the case when the card is in the unoccupied
+      //     part of the space which becomes occupied because of promotions
+      //     into it during the current young GC. In this case the card
+      //     will never be scanned for young references. The current
+      //     code will set the card value to either
+      //     cur_younger_gen_and_prev_non_clean or leave
+      //     it with its stale value -- because the promotions didn't
+      //     result in any younger refs on that card. Of these two
+      //     cases, the latter will be covered in Case 1a during
+      //     a subsequent scan. To deal with the former case, we need
+      //     to further consider how we deal with a stale value of
+      //     cur_younger_gen_and_prev_non_clean in our case analysis
+      //     below. This we do in Case 3 below. [End Case 1b]
+      //   [End Case 1]
+      // o Case 2. If the stale value corresponds to cur_younger_gen being
+      //   a value not necessarily written by a current promotion, the
+      //   card will not be scanned by the younger refs scanning code.
+      //   (This is OK since as we argued above such cards cannot contain
+      //   any younger refs.) The result is that this value will be
+      //   treated as a prev_younger_gen value in a subsequent collection,
+      //   which is addressed in Case 1 above. [End Case 2]
+      // o Case 3. We here consider the "derivative" case from Case 1b. above
+      //   because of which we may find a stale
+      //   cur_younger_gen_and_prev_non_clean card value in the table.
+      //   Once again, as in Case 1, we consider two subcases, depending
+      //   on whether the card lies in the occupied or unoccupied part
+      //   of the space at the start of the young collection.
+      //   o Case 3a. Let us say the card is in the occupied part of
+      //     the old gen at the start of the young collection. In that
+      //     case, the card will be scanned by the younger refs scanning
+      //     code which will set it to cur_younger_gen. In a subsequent
+      //     scan, the card will be considered again and get its final
+      //     correct value. [End Case 3a]
+      //   o Case 3b. Now consider the case where the card is in the
+      //     unoccupied part of the old gen, and is occupied as a result
+      //     of promotions during thus young gc. In that case,
+      //     the card will not be scanned for younger refs. The presence
+      //     of newly promoted objects on the card will then result in
+      //     its keeping the value cur_younger_gen_and_prev_non_clean
+      //     value, which we have dealt with in Case 3 here. [End Case 3b]
+      //   [End Case 3]
+      //
+      // (Please refer to the code in the helper class
+      // ClearNonCleanCardWrapper and in CardTableModRefBS for details.)
+      //
+      // The informal arguments above can be tightened into a formal
+      // correctness proof and it behooves us to write up such a proof,
+      // or to use model checking to prove that there are no lingering
+      // concerns.
+      //
+      // Clearly because of Case 3b one cannot bound the time for
+      // which a card will retain what we have called a "stale" value.
+      // However, one can obtain a Loose upper bound on the redundant
+      // work as a result of such stale values. Note first that any
+      // time a stale card lies in the occupied part of the space at
+      // the start of the collection, it is scanned by younger refs
+      // code and we can define a rank function on card values that
+      // declines when this is so. Note also that when a card does not
+      // lie in the occupied part of the space at the beginning of a
+      // young collection, its rank can either decline or stay unchanged.
+      // In this case, no extra work is done in terms of redundant
+      // younger refs scanning of that card.
+      // Then, the case analysis above reveals that, in the worst case,
+      // any such stale card will be scanned unnecessarily at most twice.
+      //
+      // It is nonethelss advisable to try and get rid of some of this
+      // redundant work in a subsequent (low priority) re-design of
+      // the card-scanning code, if only to simplify the underlying
+      // state machine analysis/proof. ysr 1/28/2002. XXX
+      cur_entry++;
+    }
+  }
+}
+
+void CardTableRS::verify() {
+  // At present, we only know how to verify the card table RS for
+  // generational heaps.
+  VerifyCTGenClosure blk(this);
+  CollectedHeap* ch = Universe::heap();
+  // We will do the perm-gen portion of the card table, too.
+  Generation* pg = SharedHeap::heap()->perm_gen();
+  HeapWord* pg_boundary = pg->reserved().start();
+
+  if (ch->kind() == CollectedHeap::GenCollectedHeap) {
+    GenCollectedHeap::heap()->generation_iterate(&blk, false);
+    _ct_bs.verify();
+
+    // If the old gen collections also collect perm, then we are only
+    // interested in perm-to-young pointers, not perm-to-old pointers.
+    GenCollectedHeap* gch = GenCollectedHeap::heap();
+    CollectorPolicy* cp = gch->collector_policy();
+    if (cp->is_mark_sweep_policy() || cp->is_concurrent_mark_sweep_policy()) {
+      pg_boundary = gch->get_gen(1)->reserved().start();
+    }
+  }
+  VerifyCTSpaceClosure perm_space_blk(this, pg_boundary);
+  SharedHeap::heap()->perm_gen()->space_iterate(&perm_space_blk, true);
+}
+
+
+void CardTableRS::verify_empty(MemRegion mr) {
+  if (!mr.is_empty()) {
+    jbyte* cur_entry = byte_for(mr.start());
+    jbyte* limit = byte_after(mr.last());
+    for (;cur_entry < limit; cur_entry++) {
+      guarantee(*cur_entry == CardTableModRefBS::clean_card,
+                "Unexpected dirty card found");
+    }
+  }
+}