--- a/src/hotspot/share/gc/g1/g1Allocator.cpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1Allocator.cpp	Thu Dec 06 13:55:22 2018 +0100
@@ -84,8 +84,6 @@
     // we allocate to in the region sets. We'll re-add it later, when
     // it's retired again.
     _g1h->old_set_remove(retained_region);
-    bool during_im = _g1h->collector_state()->in_initial_mark_gc();
-    retained_region->note_start_of_copying(during_im);
     old->set(retained_region);
     _g1h->hr_printer()->reuse(retained_region);
     evacuation_info.set_alloc_regions_used_before(retained_region->used());

--- a/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Thu Dec 06 13:55:22 2018 +0100
@@ -4533,8 +4533,6 @@
     }
     _g1_policy->remset_tracker()->update_at_allocate(new_alloc_region);
     _hr_printer.alloc(new_alloc_region);
-    bool during_im = collector_state()->in_initial_mark_gc();
-    new_alloc_region->note_start_of_copying(during_im);
     return new_alloc_region;
   }
   return NULL;
@@ -4543,12 +4541,15 @@
 void G1CollectedHeap::retire_gc_alloc_region(HeapRegion* alloc_region,
                                              size_t allocated_bytes,
                                              InCSetState dest) {
-  bool during_im = collector_state()->in_initial_mark_gc();
-  alloc_region->note_end_of_copying(during_im);
   g1_policy()->record_bytes_copied_during_gc(allocated_bytes);
   if (dest.is_old()) {
     old_set_add(alloc_region);
   }
+
+  bool const during_im = collector_state()->in_initial_mark_gc();
+  if (during_im && allocated_bytes > 0) {
+    _cm->root_regions()->add(alloc_region);
+  }
   _hr_printer.retire(alloc_region);
 }
 

--- a/src/hotspot/share/gc/g1/g1ConcurrentMark.cpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1ConcurrentMark.cpp	Thu Dec 06 13:55:22 2018 +0100
@@ -255,21 +255,35 @@
   _free_list = NULL;
 }
 
-G1CMRootRegions::G1CMRootRegions() :
-  _survivors(NULL), _cm(NULL), _scan_in_progress(false),
-  _should_abort(false), _claimed_survivor_index(0) { }
-
-void G1CMRootRegions::init(const G1SurvivorRegions* survivors, G1ConcurrentMark* cm) {
-  _survivors = survivors;
-  _cm = cm;
+G1CMRootRegions::G1CMRootRegions(uint const max_regions) :
+  _root_regions(NEW_C_HEAP_ARRAY(HeapRegion*, max_regions, mtGC)),
+  _max_regions(max_regions),
+  _num_root_regions(0),
+  _claimed_root_regions(0),
+  _scan_in_progress(false),
+  _should_abort(false) { }
+
+G1CMRootRegions::~G1CMRootRegions() {
+  FREE_C_HEAP_ARRAY(HeapRegion*, _max_regions);
+}
+
+void G1CMRootRegions::reset() {
+  _num_root_regions = 0;
+}
+
+void G1CMRootRegions::add(HeapRegion* hr) {
+  assert_at_safepoint();
+  size_t idx = Atomic::add((size_t)1, &_num_root_regions) - 1;
+  assert(idx < _max_regions, "Trying to add more root regions than there is space " SIZE_FORMAT, _max_regions);
+  _root_regions[idx] = hr;
 }
 
 void G1CMRootRegions::prepare_for_scan() {
   assert(!scan_in_progress(), "pre-condition");
 
-  // Currently, only survivors can be root regions.
-  _claimed_survivor_index = 0;
-  _scan_in_progress = _survivors->regions()->is_nonempty();
+  _scan_in_progress = _num_root_regions > 0;
+
+  _claimed_root_regions = 0;
   _should_abort = false;
 }
 
@@ -280,18 +294,19 @@
     return NULL;
   }
 
-  // Currently, only survivors can be root regions.
-  const GrowableArray<HeapRegion*>* survivor_regions = _survivors->regions();
-
-  int claimed_index = Atomic::add(1, &_claimed_survivor_index) - 1;
-  if (claimed_index < survivor_regions->length()) {
-    return survivor_regions->at(claimed_index);
+  if (_claimed_root_regions >= _num_root_regions) {
+    return NULL;
+  }
+
+  size_t claimed_index = Atomic::add((size_t)1, &_claimed_root_regions) - 1;
+  if (claimed_index < _num_root_regions) {
+    return _root_regions[claimed_index];
   }
   return NULL;
 }
 
 uint G1CMRootRegions::num_root_regions() const {
-  return (uint)_survivors->regions()->length();
+  return (uint)_num_root_regions;
 }
 
 void G1CMRootRegions::notify_scan_done() {
@@ -307,12 +322,10 @@
 void G1CMRootRegions::scan_finished() {
   assert(scan_in_progress(), "pre-condition");
 
-  // Currently, only survivors can be root regions.
   if (!_should_abort) {
-    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());
+    assert(_claimed_root_regions >= num_root_regions(),
+           "we should have claimed all root regions, claimed " SIZE_FORMAT ", length = %u",
+           _claimed_root_regions, num_root_regions());
   }
 
   notify_scan_done();
@@ -353,7 +366,7 @@
 
   _heap(_g1h->reserved_region()),
 
-  _root_regions(),
+  _root_regions(_g1h->max_regions()),
 
   _global_mark_stack(),
 
@@ -406,8 +419,6 @@
 
   assert(CGC_lock != NULL, "CGC_lock must be initialized");
 
-  _root_regions.init(_g1h->survivor(), this);
-
   if (FLAG_IS_DEFAULT(ConcGCThreads) || ConcGCThreads == 0) {
     // Calculate the number of concurrent worker threads by scaling
     // the number of parallel GC threads.
@@ -728,6 +739,8 @@
   // For each region note start of marking.
   NoteStartOfMarkHRClosure startcl;
   _g1h->heap_region_iterate(&startcl);
+
+  _root_regions.reset();
 }
 
 
@@ -859,12 +872,12 @@
 }
 
 void G1ConcurrentMark::scan_root_region(HeapRegion* hr, uint worker_id) {
-  // Currently, only survivors can be root regions.
-  assert(hr->next_top_at_mark_start() == hr->bottom(), "invariant");
+  assert(hr->is_old() || (hr->is_survivor() && hr->next_top_at_mark_start() == hr->bottom()),
+         "Root regions must be old or survivor but region %u is %s", hr->hrm_index(), hr->get_type_str());
   G1RootRegionScanClosure cl(_g1h, this, worker_id);
 
   const uintx interval = PrefetchScanIntervalInBytes;
-  HeapWord* curr = hr->bottom();
+  HeapWord* curr = hr->next_top_at_mark_start();
   const HeapWord* end = hr->top();
   while (curr < end) {
     Prefetch::read(curr, interval);

--- a/src/hotspot/share/gc/g1/g1ConcurrentMark.hpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1ConcurrentMark.hpp	Thu Dec 06 13:55:22 2018 +0100
@@ -224,34 +224,37 @@
   template<typename Fn> void iterate(Fn fn) const PRODUCT_RETURN;
 };
 
-// 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
-// do not copy objects that are explicitly marked, what we have to do
-// for the root regions is to scan them and mark all objects reachable
-// from them. According to the SATB assumptions, we only need to visit
-// each object once during marking. So, as long as we finish this scan
-// before the next evacuation pause, we can copy the objects from the
-// root regions without having to mark them or do anything else to them.
-//
-// Currently, we only support root region scanning once (at the start
-// of the marking cycle) and the root regions are all the survivor
-// regions populated during the initial-mark pause.
+// Root Regions are regions that contain objects from nTAMS to top. These are roots
+// for marking, i.e. their referenced objects must be kept alive to maintain the
+// SATB invariant.
+// We could scan and mark them through during the initial-mark pause, but for
+// pause time reasons we move this work to the concurrent phase.
+// We need to complete this procedure before the next GC because it might determine
+// that some of these "root objects" are dead, potentially dropping some required
+// references.
+// Root regions comprise of the complete contents of survivor regions, and any
+// objects copied into old gen during GC.
 class G1CMRootRegions {
-private:
-  const G1SurvivorRegions* _survivors;
-  G1ConcurrentMark*        _cm;
+  HeapRegion** _root_regions;
+  size_t const _max_regions;
+
+  volatile size_t _num_root_regions; // Actual number of root regions.
 
-  volatile bool            _scan_in_progress;
-  volatile bool            _should_abort;
-  volatile int             _claimed_survivor_index;
+  volatile size_t _claimed_root_regions; // Number of root regions currently claimed.
+
+  volatile bool _scan_in_progress;
+  volatile bool _should_abort;
 
   void notify_scan_done();
 
 public:
-  G1CMRootRegions();
-  // We actually do most of the initialization in this method.
-  void init(const G1SurvivorRegions* survivors, G1ConcurrentMark* cm);
+  G1CMRootRegions(uint const max_regions);
+  ~G1CMRootRegions();
+
+  // Reset the data structure to allow addition of new root regions.
+  void reset();
+
+  void add(HeapRegion* hr);
 
   // Reset the claiming / scanning of the root regions.
   void prepare_for_scan();
@@ -553,7 +556,7 @@
   // them.
   void scan_root_regions();
 
-  // Scan a single root region and mark everything reachable from it.
+  // Scan a single root region from nTAMS to top and mark everything reachable from it.
   void scan_root_region(HeapRegion* hr, uint worker_id);
 
   // Do concurrent phase of marking, to a tentative transitive closure.
@@ -593,10 +596,8 @@
   void print_on_error(outputStream* st) const;
 
   // Mark the given object on the next bitmap if it is below nTAMS.
-  // If the passed obj_size is zero, it is recalculated from the given object if
-  // needed. This is to be as lazy as possible with accessing the object's size.
-  inline bool mark_in_next_bitmap(uint worker_id, HeapRegion* const hr, oop const obj, size_t const obj_size = 0);
-  inline bool mark_in_next_bitmap(uint worker_id, oop const obj, size_t const obj_size = 0);
+  inline bool mark_in_next_bitmap(uint worker_id, HeapRegion* const hr, oop const obj);
+  inline bool mark_in_next_bitmap(uint worker_id, oop const obj);
 
   inline bool is_marked_in_next_bitmap(oop p) const;
 

--- a/src/hotspot/share/gc/g1/g1ConcurrentMark.inline.hpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1ConcurrentMark.inline.hpp	Thu Dec 06 13:55:22 2018 +0100
@@ -55,12 +55,12 @@
   return _g1h->heap_region_containing(obj)->is_old_or_humongous_or_archive();
 }
 
-inline bool G1ConcurrentMark::mark_in_next_bitmap(uint const worker_id, oop const obj, size_t const obj_size) {
+inline bool G1ConcurrentMark::mark_in_next_bitmap(uint const worker_id, oop const obj) {
   HeapRegion* const hr = _g1h->heap_region_containing(obj);
-  return mark_in_next_bitmap(worker_id, hr, obj, obj_size);
+  return mark_in_next_bitmap(worker_id, hr, obj);
 }
 
-inline bool G1ConcurrentMark::mark_in_next_bitmap(uint const worker_id, HeapRegion* const hr, oop const obj, size_t const obj_size) {
+inline bool G1ConcurrentMark::mark_in_next_bitmap(uint const worker_id, HeapRegion* const hr, oop const obj) {
   assert(hr != NULL, "just checking");
   assert(hr->is_in_reserved(obj), "Attempting to mark object at " PTR_FORMAT " that is not contained in the given region %u", p2i(obj), hr->hrm_index());
 
@@ -76,7 +76,7 @@
 
   bool success = _next_mark_bitmap->par_mark(obj_addr);
   if (success) {
-    add_to_liveness(worker_id, obj, obj_size == 0 ? obj->size() : obj_size);
+    add_to_liveness(worker_id, obj, obj->size());
   }
   return success;
 }

--- a/src/hotspot/share/gc/g1/g1EvacFailure.cpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1EvacFailure.cpp	Thu Dec 06 13:55:22 2018 +0100
@@ -126,7 +126,7 @@
         // explicitly and all objects in the CSet are considered
         // (implicitly) live. So, we won't mark them explicitly and
         // we'll leave them over NTAMS.
-        _cm->mark_in_next_bitmap(_worker_id, obj);
+        _cm->mark_in_next_bitmap(_worker_id, _hr, obj);
       }
       size_t obj_size = obj->size();
 

--- a/src/hotspot/share/gc/g1/g1OopClosures.hpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1OopClosures.hpp	Thu Dec 06 13:55:22 2018 +0100
@@ -141,11 +141,6 @@
   // during the GC (i.e., non-CSet objects). It is MT-safe.
   inline void mark_object(oop obj);
 
-  // Mark the object if it's not already marked. This is used to mark
-  // objects pointed to by roots that have been forwarded during a
-  // GC. It is MT-safe.
-  inline void mark_forwarded_object(oop from_obj, oop to_obj);
-
   G1ParCopyHelper(G1CollectedHeap* g1h,  G1ParScanThreadState* par_scan_state);
   ~G1ParCopyHelper() { }
 

--- a/src/hotspot/share/gc/g1/g1OopClosures.inline.hpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1OopClosures.inline.hpp	Thu Dec 06 13:55:22 2018 +0100
@@ -208,21 +208,6 @@
   _cm->mark_in_next_bitmap(_worker_id, obj);
 }
 
-void G1ParCopyHelper::mark_forwarded_object(oop from_obj, oop to_obj) {
-  assert(from_obj->is_forwarded(), "from obj should be forwarded");
-  assert(from_obj->forwardee() == to_obj, "to obj should be the forwardee");
-  assert(from_obj != to_obj, "should not be self-forwarded");
-
-  assert(_g1h->heap_region_containing(from_obj)->in_collection_set(), "from obj should be in the CSet");
-  assert(!_g1h->heap_region_containing(to_obj)->in_collection_set(), "should not mark objects in the CSet");
-
-  // The object might be in the process of being copied by another
-  // worker so we cannot trust that its to-space image is
-  // well-formed. So we have to read its size from its from-space
-  // image which we know should not be changing.
-  _cm->mark_in_next_bitmap(_worker_id, to_obj, from_obj->size());
-}
-
 void G1ParCopyHelper::trim_queue_partially() {
   _par_scan_state->trim_queue_partially();
 }
@@ -251,11 +236,6 @@
     }
     assert(forwardee != NULL, "forwardee should not be NULL");
     RawAccess<IS_NOT_NULL>::oop_store(p, forwardee);
-    if (do_mark_object != G1MarkNone && forwardee != obj) {
-      // If the object is self-forwarded we don't need to explicitly
-      // mark it, the evacuation failure protocol will do so.
-      mark_forwarded_object(obj, forwardee);
-    }
 
     if (barrier == G1BarrierCLD) {
       do_cld_barrier(forwardee);

--- a/src/hotspot/share/gc/g1/heapRegion.hpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/heapRegion.hpp	Thu Dec 06 13:55:22 2018 +0100
@@ -526,14 +526,6 @@
   // info fields.
   inline void note_end_of_marking();
 
-  // Notify the region that it will be used as to-space during a GC
-  // and we are about to start copying objects into it.
-  inline void note_start_of_copying(bool during_initial_mark);
-
-  // Notify the region that it ceases being to-space during a GC and
-  // we will not copy objects into it any more.
-  inline void note_end_of_copying(bool during_initial_mark);
-
   // Notify the region that we are about to start processing
   // self-forwarded objects during evac failure handling.
   void note_self_forwarding_removal_start(bool during_initial_mark,

--- a/src/hotspot/share/gc/g1/heapRegion.inline.hpp	Thu Dec 06 13:55:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/heapRegion.inline.hpp	Thu Dec 06 13:55:22 2018 +0100
@@ -252,49 +252,6 @@
   _next_marked_bytes = 0;
 }
 
-inline void HeapRegion::note_start_of_copying(bool during_initial_mark) {
-  if (is_survivor()) {
-    // This is how we always allocate survivors.
-    assert(_next_top_at_mark_start == bottom(), "invariant");
-  } else {
-    if (during_initial_mark) {
-      // During initial-mark we'll explicitly mark any objects on old
-      // regions that are pointed to by roots. Given that explicit
-      // marks only make sense under NTAMS it'd be nice if we could
-      // check that condition if we wanted to. Given that we don't
-      // know where the top of this region will end up, we simply set
-      // NTAMS to the end of the region so all marks will be below
-      // NTAMS. We'll set it to the actual top when we retire this region.
-      _next_top_at_mark_start = end();
-    } else {
-      // We could have re-used this old region as to-space over a
-      // couple of GCs since the start of the concurrent marking
-      // cycle. This means that [bottom,NTAMS) will contain objects
-      // copied up to and including initial-mark and [NTAMS, top)
-      // will contain objects copied during the concurrent marking cycle.
-      assert(top() >= _next_top_at_mark_start, "invariant");
-    }
-  }
-}
-
-inline void HeapRegion::note_end_of_copying(bool during_initial_mark) {
-  if (is_survivor()) {
-    // This is how we always allocate survivors.
-    assert(_next_top_at_mark_start == bottom(), "invariant");
-  } else {
-    if (during_initial_mark) {
-      // See the comment for note_start_of_copying() for the details
-      // on this.
-      assert(_next_top_at_mark_start == end(), "pre-condition");
-      _next_top_at_mark_start = top();
-    } else {
-      // See the comment for note_start_of_copying() for the details
-      // on this.
-      assert(top() >= _next_top_at_mark_start, "invariant");
-    }
-  }
-}
-
 inline bool HeapRegion::in_collection_set() const {
   return G1CollectedHeap::heap()->is_in_cset(this);
 }