--- a/src/hotspot/share/gc/g1/g1ConcurrentMark.cpp	Wed Apr 18 10:20:09 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1ConcurrentMark.cpp	Wed Apr 18 11:36:48 2018 +0200
@@ -1012,6 +1012,8 @@
   G1CollectedHeap* _g1h;
   G1ConcurrentMark* _cm;
 
+  G1PrintRegionLivenessInfoClosure _cl;
+
   uint _num_regions_selected_for_rebuild;  // The number of regions actually selected for rebuild.
 
   void update_remset_before_rebuild(HeapRegion * hr) {
@@ -1025,12 +1027,56 @@
     _cm->update_top_at_rebuild_start(hr);
   }
 
+  void distribute_marked_bytes(HeapRegion* hr, size_t marked_words) {
+    uint const region_idx = hr->hrm_index();
+    uint num_regions_in_humongous = (uint)G1CollectedHeap::humongous_obj_size_in_regions(marked_words);
+
+    for (uint i = region_idx; i < (region_idx + num_regions_in_humongous); i++) {
+      HeapRegion* const r = _g1h->region_at(i);
+      size_t const words_to_add = MIN2(HeapRegion::GrainWords, marked_words);
+      assert(words_to_add > 0, "Out of space to distribute before end of humongous object in region %u (starts %u)", i, region_idx);
+
+      log_trace(gc, marking)("Adding " SIZE_FORMAT " words to humongous region %u (%s)",
+                             words_to_add, i, r->get_type_str());
+      r->add_to_marked_bytes(words_to_add * HeapWordSize);
+      marked_words -= words_to_add;
+    }
+    assert(marked_words == 0,
+           SIZE_FORMAT " words left after distributing space across %u regions",
+           marked_words, num_regions_in_humongous);
+  }
+
+  void update_marked_bytes(HeapRegion* hr) {
+    uint const region_idx = hr->hrm_index();
+    size_t marked_words = _cm->liveness(region_idx);
+    // The marking attributes the object's size completely to the humongous starts
+    // region. We need to distribute this value across the entire set of regions a
+    // humongous object spans.
+    if (hr->is_humongous()) {
+      assert(hr->is_starts_humongous() || marked_words == 0,
+             "Should not have marked words " SIZE_FORMAT " in non-starts humongous region %u (%s)",
+             marked_words, region_idx, hr->get_type_str());
+
+      if (marked_words > 0) {
+        distribute_marked_bytes(hr, marked_words);
+      }
+    } else {
+      log_trace(gc, marking)("Adding " SIZE_FORMAT " words to region %u (%s)", marked_words, region_idx, hr->get_type_str());
+      hr->add_to_marked_bytes(marked_words * HeapWordSize);
+    }
+  }
+
 public:
   G1UpdateRemSetTrackingBeforeRebuild(G1CollectedHeap* g1h, G1ConcurrentMark* cm) :
-    _g1h(g1h), _cm(cm), _num_regions_selected_for_rebuild(0) { }
+    _g1h(g1h), _cm(cm), _cl("Post-Marking"), _num_regions_selected_for_rebuild(0) { }
 
   virtual bool do_heap_region(HeapRegion* r) {
     update_remset_before_rebuild(r);
+    update_marked_bytes(r);
+    if (log_is_enabled(Trace, gc, liveness)) {
+      _cl.do_heap_region(r);
+    }
+    r->note_end_of_marking();
     return false;
   }
 
@@ -1087,6 +1133,8 @@
       flush_all_task_caches();
     }
 
+    // Install newly created mark bitmap as "prev".
+    swap_mark_bitmaps();
     {
       GCTraceTime(Debug, gc, phases)("Update Remembered Set Tracking Before Rebuild");
       G1UpdateRemSetTrackingBeforeRebuild cl(_g1h, this);
@@ -1095,7 +1143,7 @@
                                       _g1h->num_regions(), cl.num_selected_for_rebuild());
     }
 
-    verify_during_pause(G1HeapVerifier::G1VerifyRemark, VerifyOption_G1UseNextMarking, "Remark after");
+    verify_during_pause(G1HeapVerifier::G1VerifyRemark, VerifyOption_G1UsePrevMarking, "Remark after");
 
     assert(!restart_for_overflow(), "sanity");
     // Completely reset the marking state since marking completed
@@ -1113,7 +1161,7 @@
 
   {
     GCTraceTime(Debug, gc, phases)("Report Object Count");
-    report_object_count();
+    report_object_count(mark_finished);
   }
 
   // Statistics
@@ -1151,8 +1199,6 @@
     const uint humongous_regions_removed() { return _humongous_regions_removed; }
 
     bool do_heap_region(HeapRegion *hr) {
-      hr->note_end_of_marking();
-
       if (hr->used() > 0 && hr->max_live_bytes() == 0 && !hr->is_young() && !hr->is_archive()) {
         _freed_bytes += hr->used();
         hr->set_containing_set(NULL);
@@ -1247,7 +1293,7 @@
 
   double start = os::elapsedTime();
 
-  verify_during_pause(G1HeapVerifier::G1VerifyCleanup, VerifyOption_G1UseNextMarking, "Cleanup before");
+  verify_during_pause(G1HeapVerifier::G1VerifyCleanup, VerifyOption_G1UsePrevMarking, "Cleanup before");
 
   {
     GCTraceTime(Debug, gc, phases)("Update Remembered Set Tracking After Rebuild");
@@ -1260,8 +1306,6 @@
     _g1h->heap_region_iterate(&cl);
   }
 
-  // Install newly created mark bitmap as "prev".
-  swap_mark_bitmaps();
   {
     GCTraceTime(Debug, gc, phases)("Reclaim Empty Regions");
     reclaim_empty_regions();
@@ -1629,11 +1673,33 @@
   }
 }
 
-void G1ConcurrentMark::report_object_count() {
-  G1CMIsAliveClosure is_alive(_g1h);
-  _gc_tracer_cm->report_object_count_after_gc(&is_alive);
+// When sampling object counts, we already swapped the mark bitmaps, so we need to use
+// the prev bitmap determining liveness.
+class G1ObjectCountIsAliveClosure: public BoolObjectClosure {
+  G1CollectedHeap* _g1;
+ public:
+  G1ObjectCountIsAliveClosure(G1CollectedHeap* g1) : _g1(g1) { }
+
+  bool do_object_b(oop obj) {
+    HeapWord* addr = (HeapWord*)obj;
+    return addr != NULL &&
+           (!_g1->is_in_g1_reserved(addr) || !_g1->is_obj_dead(obj));
+  }
+};
+
+void G1ConcurrentMark::report_object_count(bool mark_completed) {
+  // Depending on the completion of the marking liveness needs to be determined
+  // using either the next or prev bitmap.
+  if (mark_completed) {
+    G1ObjectCountIsAliveClosure is_alive(_g1h);
+    _gc_tracer_cm->report_object_count_after_gc(&is_alive);
+  } else {
+    G1CMIsAliveClosure is_alive(_g1h);
+    _gc_tracer_cm->report_object_count_after_gc(&is_alive);
+  }
 }
 
+
 void G1ConcurrentMark::swap_mark_bitmaps() {
   G1CMBitMap* temp = _prev_mark_bitmap;
   _prev_mark_bitmap = _next_mark_bitmap;

--- a/src/hotspot/share/gc/g1/g1ConcurrentMark.hpp	Wed Apr 18 10:20:09 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1ConcurrentMark.hpp	Wed Apr 18 11:36:48 2018 +0200
@@ -367,7 +367,7 @@
   void weak_refs_work_parallel_part(BoolObjectClosure* is_alive, bool purged_classes);
   void weak_refs_work(bool clear_all_soft_refs);
 
-  void report_object_count();
+  void report_object_count(bool mark_completed);
 
   void swap_mark_bitmaps();
 

--- a/src/hotspot/share/gc/g1/g1RemSet.cpp	Wed Apr 18 10:20:09 2018 +0100
+++ b/src/hotspot/share/gc/g1/g1RemSet.cpp	Wed Apr 18 11:36:48 2018 +0200
@@ -844,7 +844,7 @@
           assert(hr->top() == top_at_mark_start || hr->top() == top_at_rebuild_start,
                  "More than one object in the humongous region?");
           humongous_obj->oop_iterate(&_update_cl, mr);
-          return top_at_mark_start != hr->bottom() ? mr.byte_size() : 0;
+          return top_at_mark_start != hr->bottom() ? mr.intersection(MemRegion((HeapWord*)humongous_obj, humongous_obj->size())).byte_size() : 0;
         } else {
           return 0;
         }
@@ -883,7 +883,7 @@
       size_t total_marked_bytes = 0;
       size_t const chunk_size_in_words = G1RebuildRemSetChunkSize / HeapWordSize;
 
-      HeapWord* const top_at_mark_start = hr->next_top_at_mark_start();
+      HeapWord* const top_at_mark_start = hr->prev_top_at_mark_start();
 
       HeapWord* cur = hr->bottom();
       while (cur < hr->end()) {
@@ -900,7 +900,7 @@
         }
 
         const Ticks start = Ticks::now();
-        size_t marked_bytes = rebuild_rem_set_in_region(_cm->next_mark_bitmap(),
+        size_t marked_bytes = rebuild_rem_set_in_region(_cm->prev_mark_bitmap(),
                                                         top_at_mark_start,
                                                         top_at_rebuild_start,
                                                         hr,
@@ -923,7 +923,6 @@
                                         p2i(top_at_rebuild_start));
 
         if (marked_bytes > 0) {
-          hr->add_to_marked_bytes(marked_bytes);
           total_marked_bytes += marked_bytes;
         }
         cur += chunk_size_in_words;
@@ -937,12 +936,11 @@
       // Simply filter out those regions. We can not just use region type because there
       // might have already been new allocations into these regions.
       DEBUG_ONLY(HeapWord* const top_at_rebuild_start = _cm->top_at_rebuild_start(region_idx);)
-      assert(!hr->is_old() ||
-             top_at_rebuild_start == NULL ||
-             total_marked_bytes == _cm->liveness(region_idx) * HeapWordSize,
-             "Marked bytes " SIZE_FORMAT " for region %u (%s) in [bottom, TAMS) do not match liveness during mark " SIZE_FORMAT " "
+      assert(top_at_rebuild_start == NULL ||
+             total_marked_bytes == hr->marked_bytes(),
+             "Marked bytes " SIZE_FORMAT " for region %u (%s) in [bottom, TAMS) do not match calculated marked bytes " SIZE_FORMAT " "
              "(" PTR_FORMAT " " PTR_FORMAT " " PTR_FORMAT ")",
-             total_marked_bytes, hr->hrm_index(), hr->get_type_str(), _cm->liveness(region_idx) * HeapWordSize,
+             total_marked_bytes, hr->hrm_index(), hr->get_type_str(), hr->marked_bytes(),
              p2i(hr->bottom()), p2i(top_at_mark_start), p2i(top_at_rebuild_start));
        // Abort state may have changed after the yield check.
       return _cm->has_aborted();