8336086: G1: Use one G1CardSet instance for all young regions

Reviewed-by: tschatzl, ayang

src/hotspot/share/gc/g1/g1CardSet.cpp

@@ -244,6 +244,10 @@ class G1CardSetHashTable : public CHeapObj<mtGCCardSet> {
   using CHTScanTask = CardSetHash::ScanTask;
 
   const static uint BucketClaimSize = 16;
+  // The claim size for group cardsets should be smaller to facilitate
+  // better work distribution. The group cardsets should be larger than
+  // the per region cardsets.
+  const static uint GroupBucketClaimSize = 4;
   // Did we insert at least one card in the table?
   bool volatile _inserted_card;
 
@@ -347,7 +351,15 @@ public:
   }
 
   void reset_table_scanner() {
-    _table_scanner.set(&_table, BucketClaimSize);
+    reset_table_scanner(BucketClaimSize);
+  }
+
+  void reset_table_scanner_for_groups() {
+    reset_table_scanner(GroupBucketClaimSize);
+  }
+
+  void reset_table_scanner(uint claim_size) {
+    _table_scanner.set(&_table, claim_size);
   }
 
   void grow() {
@@ -1042,3 +1054,7 @@ void G1CardSet::clear() {
 void G1CardSet::reset_table_scanner() {
   _table->reset_table_scanner();
 }
+
+void G1CardSet::reset_table_scanner_for_groups() {
+  _table->reset_table_scanner_for_groups();
+}

src/hotspot/share/gc/g1/g1CardSet.hpp

@@ -380,6 +380,8 @@ public:
 
   void reset_table_scanner();
 
+  void reset_table_scanner_for_groups();
+
   // Iterate over the container, calling a method on every card or card range contained
   // in the card container.
   // For every container, first calls

src/hotspot/share/gc/g1/g1CollectedHeap.cpp

@@ -1159,6 +1159,8 @@ G1CollectedHeap::G1CollectedHeap() :
   _rem_set(nullptr),
   _card_set_config(),
   _card_set_freelist_pool(G1CardSetConfiguration::num_mem_object_types()),
+  _young_regions_cardset_mm(card_set_config(), card_set_freelist_pool()),
+  _young_regions_cardset(card_set_config(), &_young_regions_cardset_mm),
   _cm(nullptr),
   _cm_thread(nullptr),
   _cr(nullptr),
@@ -2693,6 +2695,7 @@ bool G1CollectedHeap::is_old_gc_alloc_region(G1HeapRegion* hr) {
 void G1CollectedHeap::set_region_short_lived_locked(G1HeapRegion* hr) {
   _eden.add(hr);
   _policy->set_region_eden(hr);
+  hr->install_group_cardset(young_regions_cardset());
 }
 
 #ifdef ASSERT
@@ -2902,6 +2905,8 @@ G1HeapRegion* G1CollectedHeap::new_gc_alloc_region(size_t word_size, G1HeapRegio
       new_alloc_region->set_survivor();
       _survivor.add(new_alloc_region);
       register_new_survivor_region_with_region_attr(new_alloc_region);
+      // Install the group cardset.
+      new_alloc_region->install_group_cardset(young_regions_cardset());
     } else {
       new_alloc_region->set_old();
     }
@@ -3043,3 +3048,7 @@ void G1CollectedHeap::finish_codecache_marking_cycle() {
   CodeCache::on_gc_marking_cycle_finish();
   CodeCache::arm_all_nmethods();
 }
+
+void G1CollectedHeap::prepare_group_cardsets_for_scan () {
+  _young_regions_cardset.reset_table_scanner_for_groups();
+}

src/hotspot/share/gc/g1/g1CollectedHeap.hpp

@@ -779,7 +779,19 @@ private:
 
   G1MonotonicArenaFreePool _card_set_freelist_pool;
 
+  // Group cardsets
+  G1CardSetMemoryManager _young_regions_cardset_mm;
+  G1CardSet _young_regions_cardset;
+
 public:
+  G1CardSetConfiguration* card_set_config() { return &_card_set_config; }
+
+  G1CardSet* young_regions_cardset() { return &_young_regions_cardset; };
+
+  G1CardSetMemoryManager* young_regions_card_set_mm() { return &_young_regions_cardset_mm; }
+
+  void prepare_group_cardsets_for_scan();
+
   // After a collection pause, reset eden and the collection set.
   void clear_eden();
   void clear_collection_set();

src/hotspot/share/gc/g1/g1CollectionSet.cpp

@@ -297,7 +297,7 @@ double G1CollectionSet::finalize_young_part(double target_pause_time_ms, G1Survi
 
   verify_young_cset_indices();
 
-  double predicted_base_time_ms = _policy->predict_base_time_ms(pending_cards);
+  double predicted_base_time_ms = _policy->predict_base_time_ms(pending_cards, _g1h->young_regions_cardset()->occupied());
   // Base time already includes the whole remembered set related time, so do not add that here
   // again.
   double predicted_eden_time = _policy->predict_young_region_other_time_ms(eden_region_length) +

src/hotspot/share/gc/g1/g1ConcurrentMark.cpp

@@ -2980,6 +2980,7 @@ G1PrintRegionLivenessInfoClosure::G1PrintRegionLivenessInfoClosure(const char* p
   _total_capacity_bytes(0),
   _total_live_bytes(0),
   _total_remset_bytes(0),
+  _young_cardset_bytes_per_region(0),
   _total_code_roots_bytes(0)
 {
   if (!log_is_enabled(Trace, gc, liveness)) {
@@ -2990,6 +2991,13 @@ G1PrintRegionLivenessInfoClosure::G1PrintRegionLivenessInfoClosure(const char* p
   MemRegion reserved = g1h->reserved();
   double now = os::elapsedTime();
 
+  uint num_young_regions = g1h->young_regions_count();
+  size_t young_cardset_bytes = g1h->young_regions_cardset()->mem_size();
+
+  if (num_young_regions > 0) {
+    _young_cardset_bytes_per_region = young_cardset_bytes / num_young_regions;
+  }
+
   // Print the header of the output.
   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX" PHASE %s @ %1.3f", phase_name, now);
   log_trace(gc, liveness)(G1PPRL_LINE_PREFIX" HEAP"
@@ -3041,6 +3049,10 @@ bool G1PrintRegionLivenessInfoClosure::do_heap_region(G1HeapRegion* r) {
   const char* remset_type = r->rem_set()->get_short_state_str();
   FormatBuffer<16> gc_efficiency("");
 
+  if (r->is_young()) {
+    remset_bytes = _young_cardset_bytes_per_region;
+  }
+
   _total_used_bytes      += used_bytes;
   _total_capacity_bytes  += capacity_bytes;
   _total_live_bytes      += live_bytes;

src/hotspot/share/gc/g1/g1ConcurrentMark.hpp

@@ -958,6 +958,8 @@ class G1PrintRegionLivenessInfoClosure : public G1HeapRegionClosure {
   // Accumulator for the remembered set size
   size_t _total_remset_bytes;
 
+  size_t _young_cardset_bytes_per_region;
+
   // Accumulator for code roots memory size
   size_t _total_code_roots_bytes;
 

src/hotspot/share/gc/g1/g1ConcurrentRefine.cpp

@@ -254,21 +254,18 @@ uint64_t G1ConcurrentRefine::adjust_threads_wait_ms() const {
 }
 
 class G1ConcurrentRefine::RemSetSamplingClosure : public G1HeapRegionClosure {
-  size_t _sampled_card_rs_length;
   size_t _sampled_code_root_rs_length;
 
 public:
   RemSetSamplingClosure() :
-    _sampled_card_rs_length(0), _sampled_code_root_rs_length(0) {}
+    _sampled_code_root_rs_length(0) {}
 
   bool do_heap_region(G1HeapRegion* r) override {
     G1HeapRegionRemSet* rem_set = r->rem_set();
-    _sampled_card_rs_length += rem_set->occupied();
     _sampled_code_root_rs_length += rem_set->code_roots_list_length();
     return false;
   }
 
-  size_t sampled_card_rs_length() const { return _sampled_card_rs_length; }
   size_t sampled_code_root_rs_length() const { return _sampled_code_root_rs_length; }
 };
 
@@ -286,10 +283,15 @@ public:
 // gen size to keep pause time length goal.
 void G1ConcurrentRefine::adjust_young_list_target_length() {
   if (_policy->use_adaptive_young_list_length()) {
+    G1CollectedHeap* g1h = G1CollectedHeap::heap();
+    G1CollectionSet* cset = g1h->collection_set();
     RemSetSamplingClosure cl;
-    G1CollectionSet* cset = G1CollectedHeap::heap()->collection_set();
     cset->iterate(&cl);
-    _policy->revise_young_list_target_length(cl.sampled_card_rs_length(), cl.sampled_code_root_rs_length());
+
+    size_t card_rs_length = g1h->young_regions_cardset()->occupied();
+
+    size_t sampled_code_root_rs_length = cl.sampled_code_root_rs_length();
+    _policy->revise_young_list_target_length(card_rs_length, sampled_code_root_rs_length);
   }
 }
 

src/hotspot/share/gc/g1/g1FullCollector.cpp

@@ -172,6 +172,7 @@ public:
 
   bool do_heap_region(G1HeapRegion* hr) {
     hr->prepare_for_full_gc();
+    hr->uninstall_group_cardset();
     G1CollectedHeap::heap()->prepare_region_for_full_compaction(hr);
     _collector->before_marking_update_attribute_table(hr);
     return false;
@@ -247,6 +248,8 @@ void G1FullCollector::complete_collection() {
 
   _heap->resize_all_tlabs();
 
+  _heap->young_regions_cardset()->clear();
+
   _heap->policy()->record_full_collection_end();
   _heap->gc_epilogue(true);
 

src/hotspot/share/gc/g1/g1HeapRegion.cpp

@@ -119,6 +119,7 @@ void G1HeapRegion::hr_clear(bool clear_space) {
   clear_young_index_in_cset();
   clear_index_in_opt_cset();
   uninstall_surv_rate_group();
+  uninstall_group_cardset();
   set_free();
   reset_pre_dummy_top();
 
@@ -215,6 +216,9 @@ void G1HeapRegion::clear_humongous() {
 }
 
 void G1HeapRegion::prepare_remset_for_scan() {
+  if (is_young()) {
+    uninstall_group_cardset();
+  }
   _rem_set->reset_table_scanner();
 }
 

src/hotspot/share/gc/g1/g1HeapRegion.hpp

@@ -36,6 +36,7 @@
 #include "runtime/mutex.hpp"
 #include "utilities/macros.hpp"
 
+class G1CardSet;
 class G1CardSetConfiguration;
 class G1CollectedHeap;
 class G1CMBitMap;
@@ -508,6 +509,9 @@ public:
   void install_surv_rate_group(G1SurvRateGroup* surv_rate_group);
   void uninstall_surv_rate_group();
 
+  void install_group_cardset(G1CardSet* group_cardset);
+  void uninstall_group_cardset();
+
   void record_surv_words_in_group(size_t words_survived);
 
   // Determine if an address is in the parsable or the to-be-scrubbed area.

src/hotspot/share/gc/g1/g1HeapRegion.inline.hpp

@@ -511,4 +511,12 @@ inline void G1HeapRegion::add_pinned_object_count(size_t value) {
   Atomic::add(&_pinned_object_count, value, memory_order_relaxed);
 }
 
+inline void G1HeapRegion::install_group_cardset(G1CardSet* group_cardset) {
+  _rem_set->install_group_cardset(group_cardset);
+}
+
+inline void G1HeapRegion::uninstall_group_cardset() {
+  _rem_set->uninstall_group_cardset();
+}
+
 #endif // SHARE_GC_G1_G1HEAPREGION_INLINE_HPP

src/hotspot/share/gc/g1/g1HeapRegionRemSet.cpp

@@ -55,11 +55,19 @@ void G1HeapRegionRemSet::initialize(MemRegion reserved) {
   _heap_base_address = reserved.start();
 }
 
+void G1HeapRegionRemSet::uninstall_group_cardset() {
+  if (_saved_card_set != nullptr) {
+    _card_set = _saved_card_set;
+    _saved_card_set = nullptr;
+  }
+}
+
 G1HeapRegionRemSet::G1HeapRegionRemSet(G1HeapRegion* hr,
                                    G1CardSetConfiguration* config) :
   _code_roots(),
   _card_set_mm(config, G1CollectedHeap::heap()->card_set_freelist_pool()),
-  _card_set(config, &_card_set_mm),
+  _card_set(new G1CardSet(config, &_card_set_mm)),
+  _saved_card_set(nullptr),
   _hr(hr),
   _state(Untracked) { }
 
@@ -68,11 +76,12 @@ void G1HeapRegionRemSet::clear_fcc() {
 }
 
 void G1HeapRegionRemSet::clear(bool only_cardset, bool keep_tracked) {
+  assert(_saved_card_set == nullptr, "pre-condition");
   if (!only_cardset) {
     _code_roots.clear();
   }
   clear_fcc();
-  _card_set.clear();
+  _card_set->clear();
   if (!keep_tracked) {
     set_state_untracked();
   } else {
@@ -83,7 +92,7 @@ void G1HeapRegionRemSet::clear(bool only_cardset, bool keep_tracked) {
 
 void G1HeapRegionRemSet::reset_table_scanner() {
   _code_roots.reset_table_scanner();
-  _card_set.reset_table_scanner();
+  _card_set->reset_table_scanner();
 }
 
 G1MonotonicArenaMemoryStats G1HeapRegionRemSet::card_set_memory_stats() const {

src/hotspot/share/gc/g1/g1HeapRegionRemSet.hpp

@@ -47,7 +47,8 @@ class G1HeapRegionRemSet : public CHeapObj<mtGC> {
   G1CardSetMemoryManager _card_set_mm;
 
   // The set of cards in the Java heap
-  G1CardSet _card_set;
+  G1CardSet* _card_set;
+  G1CardSet* _saved_card_set;
 
   G1HeapRegion* _hr;
 
@@ -58,9 +59,24 @@ class G1HeapRegionRemSet : public CHeapObj<mtGC> {
 
 public:
   G1HeapRegionRemSet(G1HeapRegion* hr, G1CardSetConfiguration* config);
+  ~G1HeapRegionRemSet() { delete _card_set; }
 
   bool cardset_is_empty() const {
-    return _card_set.is_empty();
+    return _card_set->is_empty();
+  }
+
+  void install_group_cardset(G1CardSet* group_cardset) {
+    assert(group_cardset != nullptr, "pre-condition");
+    assert(_saved_card_set == nullptr, "pre-condition");
+
+    _saved_card_set = _card_set;
+    _card_set = group_cardset;
+  }
+
+  void uninstall_group_cardset();
+
+  bool has_group_cardset() {
+    return _saved_card_set != nullptr;
   }
 
   bool is_empty() const {
@@ -68,7 +84,7 @@ public:
   }
 
   bool occupancy_less_or_equal_than(size_t occ) const {
-    return (code_roots_list_length() == 0) && _card_set.occupancy_less_or_equal_to(occ);
+    return (code_roots_list_length() == 0) && _card_set->occupancy_less_or_equal_to(occ);
   }
 
   // Iterate the card based remembered set for merging them into the card table.
@@ -77,10 +93,15 @@ public:
   template <class CardOrRangeVisitor>
   inline void iterate_for_merge(CardOrRangeVisitor& cl);
 
+  template <class CardOrRangeVisitor>
+  inline static void iterate_for_merge(G1CardSet* card_set, CardOrRangeVisitor& cl);
+
   size_t occupied() {
-    return _card_set.occupied();
+    return _card_set->occupied();
   }
 
+  G1CardSet* card_set() { return _card_set; }
+
   static void initialize(MemRegion reserved);
 
   // Coarsening statistics since VM start.
@@ -125,13 +146,13 @@ public:
   // The actual # of bytes this hr_remset takes up. Also includes the code
   // root set.
   size_t mem_size() {
-    return _card_set.mem_size()
+    return _card_set->mem_size()
            + (sizeof(G1HeapRegionRemSet) - sizeof(G1CardSet)) // Avoid double-counting G1CardSet.
            + code_roots_mem_size();
   }
 
   size_t unused_mem_size() {
-    return _card_set.unused_mem_size();
+    return _card_set->unused_mem_size();
   }
 
   // Returns the memory occupancy of all static data structures associated

src/hotspot/share/gc/g1/g1HeapRegionRemSet.inline.hpp

@@ -108,13 +108,17 @@ public:
 
 template <class CardOrRangeVisitor>
 inline void G1HeapRegionRemSet::iterate_for_merge(CardOrRangeVisitor& cl) {
-  G1HeapRegionRemSetMergeCardClosure<CardOrRangeVisitor, G1ContainerCardsOrRanges> cl2(&_card_set,
-                                                                                       cl,
-                                                                                       _card_set.config()->log2_card_regions_per_heap_region(),
-                                                                                       _card_set.config()->log2_cards_per_card_region());
-  _card_set.iterate_containers(&cl2, true /* at_safepoint */);
+  iterate_for_merge(_card_set, cl);
 }
 
+template <class CardOrRangeVisitor>
+void G1HeapRegionRemSet::iterate_for_merge(G1CardSet* card_set, CardOrRangeVisitor& cl) {
+  G1HeapRegionRemSetMergeCardClosure<CardOrRangeVisitor, G1ContainerCardsOrRanges> cl2(card_set,
+                                                                                       cl,
+                                                                                       card_set->config()->log2_card_regions_per_heap_region(),
+                                                                                       card_set->config()->log2_cards_per_card_region());
+  card_set->iterate_containers(&cl2, true /* at_safepoint */);
+}
 
 uintptr_t G1HeapRegionRemSet::to_card(OopOrNarrowOopStar from) const {
   return pointer_delta(from, _heap_base_address, 1) >> CardTable::card_shift();
@@ -130,18 +134,18 @@ void G1HeapRegionRemSet::add_reference(OopOrNarrowOopStar from, uint tid) {
     // We can't check whether the card is in the remembered set - the card container
     // may be coarsened just now.
     //assert(contains_reference(from), "We just found " PTR_FORMAT " in the FromCardCache", p2i(from));
-   return;
+    return;
   }
 
-  _card_set.add_card(to_card(from));
+  _card_set->add_card(to_card(from));
 }
 
 bool G1HeapRegionRemSet::contains_reference(OopOrNarrowOopStar from) {
-  return _card_set.contains_card(to_card(from));
+  return _card_set->contains_card(to_card(from));
 }
 
 void G1HeapRegionRemSet::print_info(outputStream* st, OopOrNarrowOopStar from) {
-  _card_set.print_info(st, to_card(from));
+  _card_set->print_info(st, to_card(from));
 }
 
 #endif // SHARE_VM_GC_G1_G1HEAPREGIONREMSET_INLINE_HPP

src/hotspot/share/gc/g1/g1Policy.cpp

@@ -1089,6 +1089,11 @@ double G1Policy::predict_base_time_ms(size_t pending_cards,
 double G1Policy::predict_base_time_ms(size_t pending_cards) const {
   bool for_young_only_phase = collector_state()->in_young_only_phase();
   size_t card_rs_length = _analytics->predict_card_rs_length(for_young_only_phase);
+  return predict_base_time_ms(pending_cards, card_rs_length);
+}
+
+double G1Policy::predict_base_time_ms(size_t pending_cards, size_t card_rs_length) const {
+  bool for_young_only_phase = collector_state()->in_young_only_phase();
   size_t code_root_rs_length = _analytics->predict_code_root_rs_length(for_young_only_phase);
   return predict_base_time_ms(pending_cards, card_rs_length, code_root_rs_length);
 }

src/hotspot/share/gc/g1/g1Policy.hpp

@@ -138,6 +138,8 @@ public:
 
   double predict_base_time_ms(size_t pending_cards) const;
 
+  double predict_base_time_ms(size_t pending_cards, size_t card_rs_length) const;
+
 private:
   // Base time contains handling remembered sets and constant other time of the
   // whole young gen, refinement buffers, and copying survivors.

src/hotspot/share/gc/g1/g1RemSet.cpp

@@ -1379,6 +1379,10 @@ public:
         G1ClearBitmapClosure clear(g1h);
         G1CombinedClosure combined(&merge, &clear);
 
+        if (_initial_evacuation) {
+          G1HeapRegionRemSet::iterate_for_merge(g1h->young_regions_cardset(), merge);
+        }
+
         g1h->collection_set_iterate_increment_from(&combined, nullptr, worker_id);
         G1MergeCardSetStats stats = merge.stats();
 

src/hotspot/share/gc/g1/g1RemSetSummary.cpp

@@ -218,15 +218,24 @@ public:
   bool do_heap_region(G1HeapRegion* r) {
     G1HeapRegionRemSet* hrrs = r->rem_set();
 
+    size_t occupied_cards = hrrs->occupied();
     // G1HeapRegionRemSet::mem_size() includes the
     // size of the code roots
     size_t rs_unused_mem_sz = hrrs->unused_mem_size();
     size_t rs_mem_sz = hrrs->mem_size();
+
+    if (r->is_young()) {
+      uint num_young  =  G1CollectedHeap::heap()->young_regions_count();
+      occupied_cards /= num_young;
+      rs_unused_mem_sz /= num_young;
+      rs_mem_sz /= num_young;
+    }
+
     if (rs_mem_sz > _max_rs_mem_sz) {
       _max_rs_mem_sz = rs_mem_sz;
       _max_rs_mem_sz_region = r;
     }
-    size_t occupied_cards = hrrs->occupied();
+
     size_t code_root_mem_sz = hrrs->code_roots_mem_size();
     if (code_root_mem_sz > max_code_root_mem_sz()) {
       _max_code_root_mem_sz = code_root_mem_sz;

src/hotspot/share/gc/g1/g1YoungCollector.cpp

@@ -295,10 +295,9 @@ class G1PrepareEvacuationTask : public WorkerTask {
     G1MonotonicArenaMemoryStats _card_set_stats;
 
     void sample_card_set_size(G1HeapRegion* hr) {
-      // Sample card set sizes for young gen and humongous before GC: this makes
-      // the policy to give back memory to the OS keep the most recent amount of
-      // memory for these regions.
-      if (hr->is_young() || hr->is_starts_humongous()) {
+      // Sample card set sizes for humongous before GC: this makes the policy to give
+      // back memory to the OS keep the most recent amount of memory for these regions.
+      if (hr->is_starts_humongous()) {
         _card_set_stats.add(hr->rem_set()->card_set_memory_stats());
       }
     }
@@ -507,6 +506,9 @@ void G1YoungCollector::pre_evacuate_collection_set(G1EvacInfo* evacuation_info)
   {
     Ticks start = Ticks::now();
     rem_set()->prepare_for_scan_heap_roots();
+
+    _g1h->prepare_group_cardsets_for_scan();
+
     phase_times()->record_prepare_heap_roots_time_ms((Ticks::now() - start).seconds() * 1000.0);
   }
 
@@ -514,7 +516,10 @@ void G1YoungCollector::pre_evacuate_collection_set(G1EvacInfo* evacuation_info)
     G1PrepareEvacuationTask g1_prep_task(_g1h);
     Tickspan task_time = run_task_timed(&g1_prep_task);
 
-    _g1h->set_young_gen_card_set_stats(g1_prep_task.all_card_set_stats());
+    G1MonotonicArenaMemoryStats sampled_card_set_stats = g1_prep_task.all_card_set_stats();
+    sampled_card_set_stats.add(_g1h->young_regions_card_set_mm()->memory_stats());
+    _g1h->set_young_gen_card_set_stats(sampled_card_set_stats);
+
     _g1h->set_humongous_stats(g1_prep_task.humongous_total(), g1_prep_task.humongous_candidates());
 
     phase_times()->record_register_regions(task_time.seconds() * 1000.0);

src/hotspot/share/gc/g1/g1YoungGCPostEvacuateTasks.cpp

@@ -673,6 +673,10 @@ public:
 
     G1Policy *policy = g1h->policy();
     policy->old_gen_alloc_tracker()->add_allocated_bytes_since_last_gc(_bytes_allocated_in_old_since_last_gc);
+
+    // Add the cards from the group cardsets.
+    _card_rs_length += g1h->young_regions_cardset()->occupied();
+
     policy->record_card_rs_length(_card_rs_length);
     policy->cset_regions_freed();
   }
@@ -822,9 +826,10 @@ public:
     JFREventForRegion event(r, _worker_id);
     TimerForRegion timer(timer_for_region(r));
 
-    stats()->account_card_rs_length(r);
 
     if (r->is_young()) {
+      // We only use card_rs_length statistics to estimate young regions length.
+      stats()->account_card_rs_length(r);
       assert_tracks_surviving_words(r);
       r->record_surv_words_in_group(_surviving_young_words[r->young_index_in_cset()]);
     }
@@ -911,6 +916,8 @@ public:
     p->record_serial_free_cset_time_ms((Ticks::now() - serial_time).seconds() * 1000.0);
 
     _g1h->clear_collection_set();
+
+    _g1h->young_regions_cardset()->clear();
   }
 
   double worker_cost() const override { return G1CollectedHeap::heap()->collection_set()->region_length(); }