# HG changeset patch
# User mgerdin
# Date 1462271590 -7200
# Node ID cb68e49232233125daa2c9064c5f8c24ebd81202
# Parent  73d05e56ec863a0440f14eb4a7b824c62311ddab
8150721: Don't explicitly manage G1 young regions in YoungList
Reviewed-by: ehelin, sjohanss, tschatzl

diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1CollectedHeap.cpp
--- a/hotspot/src/share/vm/gc/g1/g1CollectedHeap.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1CollectedHeap.cpp	Tue May 03 12:33:10 2016 +0200
@@ -1355,8 +1355,7 @@
 
       // At this point there should be no regions in the
       // entire heap tagged as young.
-      assert(check_young_list_empty(true /* check_heap */),
-             "young list should be empty at this point");
+      assert(check_young_list_empty(), "young list should be empty at this point");
 
       // Update the number of full collections that have been completed.
       increment_old_marking_cycles_completed(false /* concurrent */);
@@ -1717,7 +1716,6 @@
   _has_humongous_reclaim_candidates(false),
   _archive_allocator(NULL),
   _free_regions_coming(false),
-  _young_list(new YoungList(this)),
   _gc_time_stamp(0),
   _summary_bytes_used(0),
   _survivor_evac_stats("Young", YoungPLABSize, PLABWeight),
@@ -2563,11 +2561,11 @@
 }
 
 size_t G1CollectedHeap::tlab_capacity(Thread* ignored) const {
-  return (_g1_policy->young_list_target_length() - young_list()->survivor_length()) * HeapRegion::GrainBytes;
+  return (_g1_policy->young_list_target_length() - _survivor.length()) * HeapRegion::GrainBytes;
 }
 
 size_t G1CollectedHeap::tlab_used(Thread* ignored) const {
-  return young_list()->eden_used_bytes();
+  return _eden.length() * HeapRegion::GrainBytes;
 }
 
 // For G1 TLABs should not contain humongous objects, so the maximum TLAB size
@@ -2652,10 +2650,10 @@
             p2i(_hrm.reserved().end()));
   st->cr();
   st->print("  region size " SIZE_FORMAT "K, ", HeapRegion::GrainBytes / K);
-  uint young_regions = _young_list->length();
+  uint young_regions = young_regions_count();
   st->print("%u young (" SIZE_FORMAT "K), ", young_regions,
             (size_t) young_regions * HeapRegion::GrainBytes / K);
-  uint survivor_regions = _young_list->survivor_length();
+  uint survivor_regions = survivor_regions_count();
   st->print("%u survivors (" SIZE_FORMAT "K)", survivor_regions,
             (size_t) survivor_regions * HeapRegion::GrainBytes / K);
   st->cr();
@@ -2765,10 +2763,9 @@
 #endif // PRODUCT
 
 G1HeapSummary G1CollectedHeap::create_g1_heap_summary() {
-  YoungList* young_list = heap()->young_list();
-
-  size_t eden_used_bytes = young_list->eden_used_bytes();
-  size_t survivor_used_bytes = young_list->survivor_used_bytes();
+
+  size_t eden_used_bytes = heap()->eden_regions_count() * HeapRegion::GrainBytes;
+  size_t survivor_used_bytes = heap()->survivor_regions_count() * HeapRegion::GrainBytes;
   size_t heap_used = Heap_lock->owned_by_self() ? used() : used_unlocked();
 
   size_t eden_capacity_bytes =
@@ -3188,8 +3185,6 @@
     G1HeapTransition heap_transition(this);
     size_t heap_used_bytes_before_gc = used();
 
-    assert(check_young_list_well_formed(), "young list should be well formed");
-
     // Don't dynamically change the number of GC threads this early.  A value of
     // 0 is used to indicate serial work.  When parallel work is done,
     // it will be set.
@@ -3253,7 +3248,7 @@
           concurrent_mark()->checkpointRootsInitialPre();
         }
 
-        g1_policy()->finalize_collection_set(target_pause_time_ms);
+        g1_policy()->finalize_collection_set(target_pause_time_ms, &_survivor);
 
         evacuation_info.set_collectionset_regions(collection_set()->region_length());
 
@@ -3308,14 +3303,8 @@
 
         clear_cset_fast_test();
 
-        // Don't check the whole heap at this point as the
-        // GC alloc regions from this pause have been tagged
-        // as survivors and moved on to the survivor list.
-        // Survivor regions will fail the !is_young() check.
-        assert(check_young_list_empty(false /* check_heap */),
-          "young list should be empty");
-
-        _young_list->reset_auxilary_lists();
+        guarantee(_eden.length() == 0, "eden should have been cleared");
+        g1_policy()->transfer_survivors_to_cset(survivor());
 
         if (evacuation_failed()) {
           set_used(recalculate_used());
@@ -4722,10 +4711,7 @@
   double young_time_ms     = 0.0;
   double non_young_time_ms = 0.0;
 
-  // Since the collection set is a superset of the the young list,
-  // all we need to do to clear the young list is clear its
-  // head and length, and unlink any young regions in the code below
-  _young_list->clear();
+  _eden.clear();
 
   G1Policy* policy = g1_policy();
 
@@ -4772,11 +4758,6 @@
       size_t words_survived = surviving_young_words[index];
       cur->record_surv_words_in_group(words_survived);
 
-      // At this point the we have 'popped' cur from the collection set
-      // (linked via next_in_collection_set()) but it is still in the
-      // young list (linked via next_young_region()). Clear the
-      // _next_young_region field.
-      cur->set_next_young_region(NULL);
     } else {
       int index = cur->young_index_in_cset();
       assert(index == -1, "invariant");
@@ -5043,9 +5024,12 @@
 }
 
 void G1CollectedHeap::set_region_short_lived_locked(HeapRegion* hr) {
-  _young_list->push_region(hr);
+  _eden.add(hr);
+  _g1_policy->set_region_eden(hr);
 }
 
+#ifdef ASSERT
+
 class NoYoungRegionsClosure: public HeapRegionClosure {
 private:
   bool _success;
@@ -5062,18 +5046,18 @@
   bool success() { return _success; }
 };
 
-bool G1CollectedHeap::check_young_list_empty(bool check_heap) {
-  bool ret = _young_list->check_list_empty();
-
-  if (check_heap) {
-    NoYoungRegionsClosure closure;
-    heap_region_iterate(&closure);
-    ret = ret && closure.success();
-  }
+bool G1CollectedHeap::check_young_list_empty() {
+  bool ret = (young_regions_count() == 0);
+
+  NoYoungRegionsClosure closure;
+  heap_region_iterate(&closure);
+  ret = ret && closure.success();
 
   return ret;
 }
 
+#endif // ASSERT
+
 class TearDownRegionSetsClosure : public HeapRegionClosure {
 private:
   HeapRegionSet *_old_set;
@@ -5084,12 +5068,13 @@
   bool doHeapRegion(HeapRegion* r) {
     if (r->is_old()) {
       _old_set->remove(r);
+    } else if(r->is_young()) {
+      r->uninstall_surv_rate_group();
     } else {
       // We ignore free regions, we'll empty the free list afterwards.
-      // We ignore young regions, we'll empty the young list afterwards.
       // We ignore humongous regions, we're not tearing down the
       // humongous regions set.
-      assert(r->is_free() || r->is_young() || r->is_humongous(),
+      assert(r->is_free() || r->is_humongous(),
              "it cannot be another type");
     }
     return false;
@@ -5155,16 +5140,12 @@
       r->set_allocation_context(AllocationContext::system());
       _hrm->insert_into_free_list(r);
     } else if (!_free_list_only) {
-      assert(!r->is_young(), "we should not come across young regions");
 
       if (r->is_humongous()) {
         // We ignore humongous regions. We left the humongous set unchanged.
       } else {
-        // Objects that were compacted would have ended up on regions
-        // that were previously old or free.  Archive regions (which are
-        // old) will not have been touched.
-        assert(r->is_free() || r->is_old(), "invariant");
-        // We now consider them old, so register as such. Leave
+        assert(r->is_young() || r->is_free() || r->is_old(), "invariant");
+        // We now consider all regions old, so register as such. Leave
         // archive regions set that way, however, while still adding
         // them to the old set.
         if (!r->is_archive()) {
@@ -5187,7 +5168,8 @@
   assert_at_safepoint(true /* should_be_vm_thread */);
 
   if (!free_list_only) {
-    _young_list->empty_list();
+    _eden.clear();
+    _survivor.clear();
   }
 
   RebuildRegionSetsClosure cl(free_list_only, &_old_set, &_hrm);
@@ -5256,7 +5238,7 @@
   if (dest.is_old()) {
     return true;
   } else {
-    return young_list()->survivor_length() < g1_policy()->max_survivor_regions();
+    return survivor_regions_count() < g1_policy()->max_survivor_regions();
   }
 }
 
@@ -5279,7 +5261,7 @@
     new_alloc_region->record_timestamp();
     if (is_survivor) {
       new_alloc_region->set_survivor();
-      young_list()->add_survivor_region(new_alloc_region);
+      _survivor.add(new_alloc_region);
       _verifier->check_bitmaps("Survivor Region Allocation", new_alloc_region);
     } else {
       new_alloc_region->set_old();
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1CollectedHeap.hpp
--- a/hotspot/src/share/vm/gc/g1/g1CollectedHeap.hpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1CollectedHeap.hpp	Tue May 03 12:33:10 2016 +0200
@@ -364,7 +364,8 @@
 protected:
 
   // The young region list.
-  YoungList*  _young_list;
+  G1EdenRegions _eden;
+  G1SurvivorRegions _survivor;
 
   // The current policy object for the collector.
   G1Policy* _g1_policy;
@@ -1332,18 +1333,27 @@
   void set_region_short_lived_locked(HeapRegion* hr);
   // add appropriate methods for any other surv rate groups
 
-  YoungList* young_list() const { return _young_list; }
+  const G1SurvivorRegions* survivor() const { return &_survivor; }
+
+  uint survivor_regions_count() const {
+    return _survivor.length();
+  }
+
+  uint eden_regions_count() const {
+    return _eden.length();
+  }
+
+  uint young_regions_count() const {
+    return _eden.length() + _survivor.length();
+  }
 
   uint old_regions_count() const { return _old_set.length(); }
 
   uint humongous_regions_count() const { return _humongous_set.length(); }
 
-  // debugging
-  bool check_young_list_well_formed() {
-    return _young_list->check_list_well_formed();
-  }
-
-  bool check_young_list_empty(bool check_heap);
+#ifdef ASSERT
+  bool check_young_list_empty();
+#endif
 
   // *** Stuff related to concurrent marking.  It's not clear to me that so
   // many of these need to be public.
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1CollectionSet.cpp
--- a/hotspot/src/share/vm/gc/g1/g1CollectionSet.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1CollectionSet.cpp	Tue May 03 12:33:10 2016 +0200
@@ -274,10 +274,9 @@
 }
 #endif // !PRODUCT
 
-double G1CollectionSet::finalize_young_part(double target_pause_time_ms) {
+double G1CollectionSet::finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors) {
   double young_start_time_sec = os::elapsedTime();
 
-  YoungList* young_list = _g1->young_list();
   finalize_incremental_building();
 
   guarantee(target_pause_time_ms > 0.0,
@@ -297,27 +296,14 @@
   // pause are appended to the RHS of the young list, i.e.
   //   [Newly Young Regions ++ Survivors from last pause].
 
-  uint survivor_region_length = young_list->survivor_length();
-  uint eden_region_length = young_list->eden_length();
+  uint survivor_region_length = survivors->length();
+  uint eden_region_length = _g1->eden_regions_count();
   init_region_lengths(eden_region_length, survivor_region_length);
 
-  const GrowableArray<HeapRegion*>* survivor_regions = _g1->young_list()->survivor_regions();
-  for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin();
-       it != survivor_regions->end();
-       ++it) {
-    HeapRegion* hr = *it;
-    assert(hr->is_survivor(), "badly formed young list");
-    // There is a convention that all the young regions in the CSet
-    // are tagged as "eden", so we do this for the survivors here. We
-    // use the special set_eden_pre_gc() as it doesn't check that the
-    // region is free (which is not the case here).
-    hr->set_eden_pre_gc();
-  }
-
   verify_young_cset_indices();
 
   // Clear the fields that point to the survivor list - they are all young now.
-  young_list->clear_survivors();
+  survivors->convert_to_eden();
 
   _head = _inc_head;
   _bytes_used_before = _inc_bytes_used_before;
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1CollectionSet.hpp
--- a/hotspot/src/share/vm/gc/g1/g1CollectionSet.hpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1CollectionSet.hpp	Tue May 03 12:33:10 2016 +0200
@@ -34,6 +34,7 @@
 class G1CollectorState;
 class G1GCPhaseTimes;
 class G1Policy;
+class G1SurvivorRegions;
 class HeapRegion;
 
 class G1CollectionSet VALUE_OBJ_CLASS_SPEC {
@@ -175,7 +176,7 @@
   // Choose a new collection set.  Marks the chosen regions as being
   // "in_collection_set", and links them together.  The head and number of
   // the collection set are available via access methods.
-  double finalize_young_part(double target_pause_time_ms);
+  double finalize_young_part(double target_pause_time_ms, G1SurvivorRegions* survivors);
   void finalize_old_part(double time_remaining_ms);
 
   // Add old region "hr" to the CSet.
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1ConcurrentMark.cpp
--- a/hotspot/src/share/vm/gc/g1/g1ConcurrentMark.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1ConcurrentMark.cpp	Tue May 03 12:33:10 2016 +0200
@@ -261,11 +261,11 @@
 }
 
 G1CMRootRegions::G1CMRootRegions() :
-  _young_list(NULL), _cm(NULL), _scan_in_progress(false),
+  _cm(NULL), _scan_in_progress(false),
   _should_abort(false), _claimed_survivor_index(0) { }
 
-void G1CMRootRegions::init(G1CollectedHeap* g1h, G1ConcurrentMark* cm) {
-  _young_list = g1h->young_list();
+void G1CMRootRegions::init(const G1SurvivorRegions* survivors, G1ConcurrentMark* cm) {
+  _survivors = survivors;
   _cm = cm;
 }
 
@@ -286,7 +286,7 @@
   }
 
   // Currently, only survivors can be root regions.
-  const GrowableArray<HeapRegion*>* survivor_regions = _young_list->survivor_regions();
+  const GrowableArray<HeapRegion*>* survivor_regions = _survivors->regions();
 
   int claimed_index = Atomic::add(1, &_claimed_survivor_index) - 1;
   if (claimed_index < survivor_regions->length()) {
@@ -310,9 +310,10 @@
 
   // Currently, only survivors can be root regions.
   if (!_should_abort) {
-    assert(_claimed_survivor_index >= _young_list->survivor_regions()->length(),
-           "we should have claimed all survivors, claimed index = %d, length = %d",
-           _claimed_survivor_index, _young_list->survivor_regions()->length());
+    assert(_claimed_survivor_index >= 0, "otherwise comparison is invalid: %d", _claimed_survivor_index);
+    assert((uint)_claimed_survivor_index >= _survivors->length(),
+           "we should have claimed all survivors, claimed index = %u, length = %u",
+           (uint)_claimed_survivor_index, _survivors->length());
   }
 
   notify_scan_done();
@@ -394,7 +395,7 @@
   SATBMarkQueueSet& satb_qs = JavaThread::satb_mark_queue_set();
   satb_qs.set_buffer_size(G1SATBBufferSize);
 
-  _root_regions.init(_g1h, this);
+  _root_regions.init(_g1h->survivor(), this);
 
   if (ConcGCThreads > ParallelGCThreads) {
     log_warning(gc)("Can't have more ConcGCThreads (%u) than ParallelGCThreads (%u).",
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1ConcurrentMark.hpp
--- a/hotspot/src/share/vm/gc/g1/g1ConcurrentMark.hpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1ConcurrentMark.hpp	Tue May 03 12:33:10 2016 +0200
@@ -36,6 +36,7 @@
 class G1ConcurrentMark;
 class ConcurrentGCTimer;
 class G1OldTracer;
+class G1SurvivorRegions;
 typedef GenericTaskQueue<oop, mtGC>              G1CMTaskQueue;
 typedef GenericTaskQueueSet<G1CMTaskQueue, mtGC> G1CMTaskQueueSet;
 
@@ -204,8 +205,6 @@
   template<typename Fn> void iterate(Fn fn);
 };
 
-class YoungList;
-
 // Root Regions are regions that are not empty at the beginning of a
 // marking cycle and which we might collect during an evacuation pause
 // while the cycle is active. Given that, during evacuation pauses, we
@@ -221,19 +220,19 @@
 // regions populated during the initial-mark pause.
 class G1CMRootRegions VALUE_OBJ_CLASS_SPEC {
 private:
-  YoungList*           _young_list;
-  G1ConcurrentMark*    _cm;
+  const G1SurvivorRegions* _survivors;
+  G1ConcurrentMark*        _cm;
 
-  volatile bool        _scan_in_progress;
-  volatile bool        _should_abort;
-  volatile int         _claimed_survivor_index;
+  volatile bool            _scan_in_progress;
+  volatile bool            _should_abort;
+  volatile int             _claimed_survivor_index;
 
   void notify_scan_done();
 
 public:
   G1CMRootRegions();
   // We actually do most of the initialization in this method.
-  void init(G1CollectedHeap* g1h, G1ConcurrentMark* cm);
+  void init(const G1SurvivorRegions* survivors, G1ConcurrentMark* cm);
 
   // Reset the claiming / scanning of the root regions.
   void prepare_for_scan();
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1DefaultPolicy.cpp
--- a/hotspot/src/share/vm/gc/g1/g1DefaultPolicy.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1DefaultPolicy.cpp	Tue May 03 12:33:10 2016 +0200
@@ -37,7 +37,9 @@
 #include "gc/g1/g1YoungGenSizer.hpp"
 #include "gc/g1/heapRegion.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
+#include "gc/g1/youngList.hpp"
 #include "gc/shared/gcPolicyCounters.hpp"
+#include "logging/logStream.hpp"
 #include "runtime/arguments.hpp"
 #include "runtime/java.hpp"
 #include "runtime/mutexLocker.hpp"
@@ -195,11 +197,11 @@
   // Calculate the absolute and desired min bounds first.
 
   // This is how many young regions we already have (currently: the survivors).
-  const uint base_min_length = _g1->young_list()->survivor_length();
+  const uint base_min_length = _g1->survivor_regions_count();
   uint desired_min_length = calculate_young_list_desired_min_length(base_min_length);
   // This is the absolute minimum young length. Ensure that we
   // will at least have one eden region available for allocation.
-  uint absolute_min_length = base_min_length + MAX2(_g1->young_list()->eden_length(), (uint)1);
+  uint absolute_min_length = base_min_length + MAX2(_g1->eden_regions_count(), (uint)1);
   // If we shrank the young list target it should not shrink below the current size.
   desired_min_length = MAX2(desired_min_length, absolute_min_length);
   // Calculate the absolute and desired max bounds.
@@ -360,7 +362,7 @@
 
 double G1DefaultPolicy::predict_survivor_regions_evac_time() const {
   double survivor_regions_evac_time = 0.0;
-  const GrowableArray<HeapRegion*>* survivor_regions = _g1->young_list()->survivor_regions();
+  const GrowableArray<HeapRegion*>* survivor_regions = _g1->survivor()->regions();
 
   for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin();
        it != survivor_regions->end();
@@ -394,10 +396,7 @@
 
 #ifndef PRODUCT
 bool G1DefaultPolicy::verify_young_ages() {
-  HeapRegion* head = _g1->young_list()->first_region();
-  return
-    verify_young_ages(head, _short_lived_surv_rate_group);
-  // also call verify_young_ages on any additional surv rate groups
+  return verify_young_ages(_collection_set->inc_head(), _short_lived_surv_rate_group);
 }
 
 bool G1DefaultPolicy::verify_young_ages(HeapRegion* head, SurvRateGroup *surv_rate_group) {
@@ -405,11 +404,10 @@
 
   const char* name = surv_rate_group->name();
   bool ret = true;
-  int prev_age = -1;
 
   for (HeapRegion* curr = head;
        curr != NULL;
-       curr = curr->get_next_young_region()) {
+       curr = curr->next_in_collection_set()) {
     SurvRateGroup* group = curr->surv_rate_group();
     if (group == NULL && !curr->is_survivor()) {
       log_error(gc, verify)("## %s: encountered NULL surv_rate_group", name);
@@ -417,19 +415,16 @@
     }
 
     if (surv_rate_group == group) {
-      int age = curr->age_in_surv_rate_group();
-
-      if (age < 0) {
+      if (curr->age_in_surv_rate_group() < 0) {
         log_error(gc, verify)("## %s: encountered negative age", name);
         ret = false;
       }
+    }
+  }
 
-      if (age <= prev_age) {
-        log_error(gc, verify)("## %s: region ages are not strictly increasing (%d, %d)", name, age, prev_age);
-        ret = false;
-      }
-      prev_age = age;
-    }
+  if (!ret) {
+    LogStreamHandle(Error, gc, verify) log;
+    _collection_set->print(head, &log);
   }
 
   return ret;
@@ -912,13 +907,13 @@
 }
 
 bool G1DefaultPolicy::should_allocate_mutator_region() const {
-  uint young_list_length = _g1->young_list()->length();
+  uint young_list_length = _g1->young_regions_count();
   uint young_list_target_length = _young_list_target_length;
   return young_list_length < young_list_target_length;
 }
 
 bool G1DefaultPolicy::can_expand_young_list() const {
-  uint young_list_length = _g1->young_list()->length();
+  uint young_list_length = _g1->young_regions_count();
   uint young_list_max_length = _young_list_max_length;
   return young_list_length < young_list_max_length;
 }
@@ -1160,7 +1155,37 @@
   return (uint) result;
 }
 
-void G1DefaultPolicy::finalize_collection_set(double target_pause_time_ms) {
-  double time_remaining_ms = _collection_set->finalize_young_part(target_pause_time_ms);
+void G1DefaultPolicy::finalize_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor) {
+  double time_remaining_ms = _collection_set->finalize_young_part(target_pause_time_ms, survivor);
   _collection_set->finalize_old_part(time_remaining_ms);
 }
+
+void G1DefaultPolicy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) {
+
+  // Add survivor regions to SurvRateGroup.
+  note_start_adding_survivor_regions();
+  finished_recalculating_age_indexes(true /* is_survivors */);
+
+  HeapRegion* last = NULL;
+  for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin();
+       it != survivors->regions()->end();
+       ++it) {
+    HeapRegion* curr = *it;
+    set_region_survivor(curr);
+
+    // The region is a non-empty survivor so let's add it to
+    // the incremental collection set for the next evacuation
+    // pause.
+    _collection_set->add_survivor_regions(curr);
+
+    last = curr;
+  }
+  note_stop_adding_survivor_regions();
+
+  // Don't clear the survivor list handles until the start of
+  // the next evacuation pause - we need it in order to re-tag
+  // the survivor regions from this evacuation pause as 'young'
+  // at the start of the next.
+
+  finished_recalculating_age_indexes(false /* is_survivors */);
+}
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1DefaultPolicy.hpp
--- a/hotspot/src/share/vm/gc/g1/g1DefaultPolicy.hpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1DefaultPolicy.hpp	Tue May 03 12:33:10 2016 +0200
@@ -46,6 +46,7 @@
 class CollectionSetChooser;
 class G1IHOPControl;
 class G1Analytics;
+class G1SurvivorRegions;
 class G1YoungGenSizer;
 class GCPolicyCounters;
 
@@ -347,7 +348,7 @@
   bool next_gc_should_be_mixed(const char* true_action_str,
                                const char* false_action_str) const;
 
-  virtual void finalize_collection_set(double target_pause_time_ms);
+  virtual void finalize_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor);
 private:
   // Set the state to start a concurrent marking cycle and clear
   // _initiate_conc_mark_if_possible because it has now been
@@ -396,6 +397,8 @@
     return true;
   }
 
+  void transfer_survivors_to_cset(const G1SurvivorRegions* survivors);
+
 private:
   //
   // Survivor regions policy.
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1HeapTransition.cpp
--- a/hotspot/src/share/vm/gc/g1/g1HeapTransition.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1HeapTransition.cpp	Tue May 03 12:33:10 2016 +0200
@@ -30,9 +30,8 @@
 #include "memory/metaspace.hpp"
 
 G1HeapTransition::Data::Data(G1CollectedHeap* g1_heap) {
-  YoungList* young_list = g1_heap->young_list();
-  _eden_length = young_list->eden_length();
-  _survivor_length = young_list->survivor_length();
+  _eden_length = g1_heap->eden_regions_count();
+  _survivor_length = g1_heap->survivor_regions_count();
   _old_length = g1_heap->old_regions_count();
   _humongous_length = g1_heap->humongous_regions_count();
   _metaspace_used_bytes = MetaspaceAux::used_bytes();
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1HeapVerifier.cpp
--- a/hotspot/src/share/vm/gc/g1/g1HeapVerifier.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1HeapVerifier.cpp	Tue May 03 12:33:10 2016 +0200
@@ -583,13 +583,13 @@
 
 void G1HeapVerifier::verify_dirty_young_list(HeapRegion* head) {
   G1SATBCardTableModRefBS* ct_bs = _g1h->g1_barrier_set();
-  for (HeapRegion* hr = head; hr != NULL; hr = hr->get_next_young_region()) {
+  for (HeapRegion* hr = head; hr != NULL; hr = hr->next_in_collection_set()) {
     verify_dirty_region(hr);
   }
 }
 
 void G1HeapVerifier::verify_dirty_young_regions() {
-  verify_dirty_young_list(_g1h->young_list()->first_region());
+  verify_dirty_young_list(_g1h->collection_set()->inc_head());
 }
 
 bool G1HeapVerifier::verify_no_bits_over_tams(const char* bitmap_name, G1CMBitMapRO* bitmap,
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1MonitoringSupport.cpp
--- a/hotspot/src/share/vm/gc/g1/g1MonitoringSupport.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1MonitoringSupport.cpp	Tue May 03 12:33:10 2016 +0200
@@ -177,8 +177,8 @@
   // values we read here are possible (i.e., at a STW phase at the end
   // of a GC).
 
-  uint young_list_length = g1->young_list()->length();
-  uint survivor_list_length = g1->young_list()->survivor_length();
+  uint young_list_length = g1->young_regions_count();
+  uint survivor_list_length = g1->survivor_regions_count();
   assert(young_list_length >= survivor_list_length, "invariant");
   uint eden_list_length = young_list_length - survivor_list_length;
   // Max length includes any potential extensions to the young gen
@@ -237,7 +237,7 @@
   // When a new eden region is allocated, only the eden_used size is
   // affected (since we have recalculated everything else at the last GC).
 
-  uint young_region_num = g1h()->young_list()->length();
+  uint young_region_num = g1h()->young_regions_count();
   if (young_region_num > _young_region_num) {
     uint diff = young_region_num - _young_region_num;
     _eden_used += (size_t) diff * HeapRegion::GrainBytes;
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1Policy.hpp
--- a/hotspot/src/share/vm/gc/g1/g1Policy.hpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1Policy.hpp	Tue May 03 12:33:10 2016 +0200
@@ -45,6 +45,7 @@
 class CollectionSetChooser;
 class G1IHOPControl;
 class G1Analytics;
+class G1SurvivorRegions;
 class G1YoungGenSizer;
 
 class G1Policy: public CHeapObj<mtGC> {
@@ -139,7 +140,7 @@
   // The amount of space we copied during a GC.
   virtual size_t bytes_copied_during_gc() const = 0;
 
-  virtual void finalize_collection_set(double target_pause_time_ms) = 0;
+  virtual void finalize_collection_set(double target_pause_time_ms, G1SurvivorRegions* survivor) = 0;
 
   // This sets the initiate_conc_mark_if_possible() flag to start a
   // new cycle, as long as we are not already in one. It's best if it
@@ -160,6 +161,8 @@
 
   virtual void finished_recalculating_age_indexes(bool is_survivors) = 0;
 
+  virtual void transfer_survivors_to_cset(const G1SurvivorRegions* survivors) = 0;
+
   virtual size_t young_list_target_length() const = 0;
 
   virtual bool should_allocate_mutator_region() const = 0;
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/g1YoungRemSetSamplingThread.cpp
--- a/hotspot/src/share/vm/gc/g1/g1YoungRemSetSamplingThread.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/g1YoungRemSetSamplingThread.cpp	Tue May 03 12:33:10 2016 +0200
@@ -75,22 +75,18 @@
   SuspendibleThreadSetJoiner sts;
   G1CollectedHeap* g1h = G1CollectedHeap::heap();
   G1Policy* g1p = g1h->g1_policy();
+  G1CollectionSet* g1cs = g1h->collection_set();
   if (g1p->adaptive_young_list_length()) {
     int regions_visited = 0;
-    HeapRegion* hr = g1h->young_list()->first_region();
+    HeapRegion* hr = g1cs->inc_head();
     size_t sampled_rs_lengths = 0;
 
     while (hr != NULL) {
       size_t rs_length = hr->rem_set()->occupied();
       sampled_rs_lengths += rs_length;
 
-      // The current region may not yet have been added to the
-      // incremental collection set (it gets added when it is
-      // retired as the current allocation region).
-      if (hr->in_collection_set()) {
-        // Update the collection set policy information for this region
-        g1h->collection_set()->update_young_region_prediction(hr, rs_length);
-      }
+      // Update the collection set policy information for this region
+      g1cs->update_young_region_prediction(hr, rs_length);
 
       ++regions_visited;
 
@@ -99,12 +95,13 @@
         if (sts.should_yield()) {
           sts.yield();
           // A gc may have occurred and our sampling data is stale and further
-          // traversal of the young list is unsafe
+          // traversal of the collection set is unsafe
           return;
         }
         regions_visited = 0;
       }
-      hr = hr->get_next_young_region();
+      assert(hr == g1cs->inc_tail() || hr->next_in_collection_set() != NULL, "next should only be null at tail of icset");
+      hr = hr->next_in_collection_set();
     }
     g1p->revise_young_list_target_length_if_necessary(sampled_rs_lengths);
   }
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/heapRegion.cpp
--- a/hotspot/src/share/vm/gc/g1/heapRegion.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/heapRegion.cpp	Tue May 03 12:33:10 2016 +0200
@@ -287,7 +287,6 @@
     _next_in_special_set(NULL),
     _evacuation_failed(false),
     _prev_marked_bytes(0), _next_marked_bytes(0), _gc_efficiency(0.0),
-    _next_young_region(NULL),
     _next(NULL), _prev(NULL),
 #ifdef ASSERT
     _containing_set(NULL),
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/heapRegion.hpp
--- a/hotspot/src/share/vm/gc/g1/heapRegion.hpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/heapRegion.hpp	Tue May 03 12:33:10 2016 +0200
@@ -267,9 +267,6 @@
   //   The collection set.
   HeapRegion* _next_in_special_set;
 
-  // next region in the young "generation" region set
-  HeapRegion* _next_young_region;
-
   // Fields used by the HeapRegionSetBase class and subclasses.
   HeapRegion* _next;
   HeapRegion* _prev;
@@ -523,10 +520,6 @@
   // to provide a dummy version of it.
 #endif // ASSERT
 
-  HeapRegion* get_next_young_region() { return _next_young_region; }
-  void set_next_young_region(HeapRegion* hr) {
-    _next_young_region = hr;
-  }
 
   // Reset HR stuff to default values.
   void hr_clear(bool par, bool clear_space, bool locked = false);
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/youngList.cpp
--- a/hotspot/src/share/vm/gc/g1/youngList.cpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/youngList.cpp	Tue May 03 12:33:10 2016 +0200
@@ -23,156 +23,37 @@
  */
 
 #include "precompiled.hpp"
-#include "gc/g1/g1CollectedHeap.hpp"
-#include "gc/g1/g1CollectionSet.hpp"
-#include "gc/g1/g1Policy.hpp"
 #include "gc/g1/heapRegion.hpp"
-#include "gc/g1/heapRegion.inline.hpp"
-#include "gc/g1/heapRegionRemSet.hpp"
 #include "gc/g1/youngList.hpp"
-#include "logging/log.hpp"
 #include "utilities/growableArray.hpp"
-#include "utilities/ostream.hpp"
+#include "utilities/debug.hpp"
 
-YoungList::YoungList(G1CollectedHeap* g1h) :
-    _g1h(g1h),
-    _survivor_regions(new (ResourceObj::C_HEAP, mtGC) GrowableArray<HeapRegion*>(8, true, mtGC)),
-    _head(NULL),
-    _length(0) {
-  guarantee(check_list_empty(), "just making sure...");
-}
+G1SurvivorRegions::G1SurvivorRegions() : _regions(new (ResourceObj::C_HEAP, mtGC) GrowableArray<HeapRegion*>(8, true, mtGC)) {}
 
-void YoungList::push_region(HeapRegion *hr) {
-  assert(!hr->is_young(), "should not already be young");
-  assert(hr->get_next_young_region() == NULL, "cause it should!");
-
-  hr->set_next_young_region(_head);
-  _head = hr;
-
-  _g1h->g1_policy()->set_region_eden(hr);
-  ++_length;
+void G1SurvivorRegions::add(HeapRegion* hr) {
+  assert(hr->is_survivor(), "should be flagged as survivor region");
+  _regions->append(hr);
 }
 
-void YoungList::add_survivor_region(HeapRegion* hr) {
-  assert(hr->is_survivor(), "should be flagged as survivor region");
-  assert(hr->get_next_young_region() == NULL, "cause it should!");
-
-  _survivor_regions->append(hr);
-}
-
-void YoungList::empty_list(HeapRegion* list) {
-  while (list != NULL) {
-    HeapRegion* next = list->get_next_young_region();
-    list->set_next_young_region(NULL);
-    list->uninstall_surv_rate_group();
-    // This is called before a Full GC and all the non-empty /
-    // non-humongous regions at the end of the Full GC will end up as
-    // old anyway.
-    list->set_old();
-    list = next;
-  }
-}
-
-void YoungList::empty_list() {
-  assert(check_list_well_formed(), "young list should be well formed");
-
-  empty_list(_head);
-  _head = NULL;
-  _length = 0;
-
-  if (survivor_length() > 0) {
-    empty_list(_survivor_regions->last());
-  }
-  _survivor_regions->clear();
-
-  assert(check_list_empty(), "just making sure...");
-}
-
-uint YoungList::survivor_length() {
-  return _survivor_regions->length();
+uint G1SurvivorRegions::length() const {
+  return (uint)_regions->length();
 }
 
-bool YoungList::check_list_well_formed() {
-  bool ret = true;
-
-  uint length = 0;
-  HeapRegion* curr = _head;
-  HeapRegion* last = NULL;
-  while (curr != NULL) {
-    if (!curr->is_young()) {
-      log_error(gc, verify)("### YOUNG REGION " PTR_FORMAT "-" PTR_FORMAT " "
-                            "incorrectly tagged (y: %d, surv: %d)",
-                            p2i(curr->bottom()), p2i(curr->end()),
-                            curr->is_young(), curr->is_survivor());
-      ret = false;
-    }
-    ++length;
-    last = curr;
-    curr = curr->get_next_young_region();
+void G1SurvivorRegions::convert_to_eden() {
+  for (GrowableArrayIterator<HeapRegion*> it = _regions->begin();
+       it != _regions->end();
+       ++it) {
+    HeapRegion* hr = *it;
+    hr->set_eden_pre_gc();
   }
-  ret = ret && (length == _length);
-
-  if (!ret) {
-    log_error(gc, verify)("### YOUNG LIST seems not well formed!");
-    log_error(gc, verify)("###   list has %u entries, _length is %u", length, _length);
-  }
-
-  return ret;
+  clear();
 }
 
-bool YoungList::check_list_empty() {
-  bool ret = true;
-
-  if (_length != 0) {
-    log_error(gc, verify)("### YOUNG LIST should have 0 length, not %u", _length);
-    ret = false;
-  }
-  if (_head != NULL) {
-    log_error(gc, verify)("### YOUNG LIST does not have a NULL head");
-    ret = false;
-  }
-  if (!ret) {
-    log_error(gc, verify)("### YOUNG LIST does not seem empty");
-  }
-
-  return ret;
+void G1SurvivorRegions::clear() {
+  _regions->clear();
 }
 
-void
-YoungList::reset_auxilary_lists() {
-  guarantee( is_empty(), "young list should be empty" );
-  assert(check_list_well_formed(), "young list should be well formed");
-
-  // Add survivor regions to SurvRateGroup.
-  _g1h->g1_policy()->note_start_adding_survivor_regions();
-  _g1h->g1_policy()->finished_recalculating_age_indexes(true /* is_survivors */);
-
-  HeapRegion* last = NULL;
-  for (GrowableArrayIterator<HeapRegion*> it = _survivor_regions->begin();
-       it != _survivor_regions->end();
-       ++it) {
-    HeapRegion* curr = *it;
-    _g1h->g1_policy()->set_region_survivor(curr);
-
-    // The region is a non-empty survivor so let's add it to
-    // the incremental collection set for the next evacuation
-    // pause.
-    _g1h->collection_set()->add_survivor_regions(curr);
-
-    curr->set_next_young_region(last);
-    last = curr;
-  }
-  _g1h->g1_policy()->note_stop_adding_survivor_regions();
-
-  _head   = last;
-  _length = _survivor_regions->length();
-
-  // Don't clear the survivor list handles until the start of
-  // the next evacuation pause - we need it in order to re-tag
-  // the survivor regions from this evacuation pause as 'young'
-  // at the start of the next.
-
-  _g1h->g1_policy()->finished_recalculating_age_indexes(false /* is_survivors */);
-
-  assert(check_list_well_formed(), "young list should be well formed");
+void G1EdenRegions::add(HeapRegion* hr) {
+  assert(!hr->is_eden(), "should not already be set");
+  _length++;
 }
diff -r 73d05e56ec86 -r cb68e4923223 hotspot/src/share/vm/gc/g1/youngList.hpp
--- a/hotspot/src/share/vm/gc/g1/youngList.hpp	Mon May 02 19:38:15 2016 -0400
+++ b/hotspot/src/share/vm/gc/g1/youngList.hpp	Tue May 03 12:33:10 2016 +0200
@@ -31,58 +31,38 @@
 template <typename T>
 class GrowableArray;
 
-class YoungList : public CHeapObj<mtGC> {
+class G1SurvivorRegions VALUE_OBJ_CLASS_SPEC {
 private:
-  G1CollectedHeap* _g1h;
-  GrowableArray<HeapRegion*>* _survivor_regions;
-
-  HeapRegion* _head;
-
-  uint        _length;
-
-  void         empty_list(HeapRegion* list);
+  GrowableArray<HeapRegion*>* _regions;
 
 public:
-  YoungList(G1CollectedHeap* g1h);
+  G1SurvivorRegions();
 
-  void         push_region(HeapRegion* hr);
-  void         add_survivor_region(HeapRegion* hr);
+  void add(HeapRegion* hr);
 
-  void         empty_list();
-  bool         is_empty() { return _length == 0; }
-  uint         length() { return _length; }
-  uint         eden_length() { return length() - survivor_length(); }
-  uint         survivor_length();
+  void convert_to_eden();
 
-  const GrowableArray<HeapRegion*>* survivor_regions() const { return _survivor_regions; }
+  void clear();
+
+  uint length() const;
 
-  // Currently we do not keep track of the used byte sum for the
-  // young list and the survivors and it'd be quite a lot of work to
-  // do so. When we'll eventually replace the young list with
-  // instances of HeapRegionLinkedList we'll get that for free. So,
-  // we'll report the more accurate information then.
-  size_t       eden_used_bytes() {
-    assert(length() >= survivor_length(), "invariant");
-    return (size_t) eden_length() * HeapRegion::GrainBytes;
+  const GrowableArray<HeapRegion*>* regions() const {
+    return _regions;
   }
-  size_t       survivor_used_bytes() {
-    return (size_t) survivor_length() * HeapRegion::GrainBytes;
-  }
+};
+
+class G1EdenRegions VALUE_OBJ_CLASS_SPEC {
+private:
+  int _length;
 
-  // for development purposes
-  void reset_auxilary_lists();
-  void clear() { _head = NULL; _length = 0; }
+public:
+  G1EdenRegions() : _length(0) {}
 
-  void clear_survivors() {
-    _survivor_regions->clear();
-  }
+  void add(HeapRegion* hr);
 
-  HeapRegion* first_region() { return _head; }
+  void clear() { _length = 0; }
 
-  // debugging
-  bool          check_list_well_formed();
-  bool          check_list_empty();
-  void          print();
+  uint length() const { return _length; }
 };
 
 #endif // SHARE_VM_GC_G1_YOUNGLIST_HPP