--- old/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	2019-06-04 13:16:55.832651466 -0700
+++ new/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	2019-06-04 13:16:55.584651474 -0700
@@ -2258,7 +2258,7 @@
 }
 
 size_t G1CollectedHeap::tlab_capacity(Thread* ignored) const {
-  return (_policy->young_list_target_length() - _survivor.length()) * HeapRegion::GrainBytes;
+  return (_policy->young_list_target_length() - survivor_regions_count()) * HeapRegion::GrainBytes;
 }
 
 size_t G1CollectedHeap::tlab_used(Thread* ignored) const {
@@ -2489,7 +2489,7 @@
 G1HeapSummary G1CollectedHeap::create_g1_heap_summary() {
 
   size_t eden_used_bytes = _eden.used_bytes();
-  size_t survivor_used_bytes = _survivor.used_bytes();
+  size_t survivor_used_bytes = survivor_regions_used_bytes();
   size_t heap_used = Heap_lock->owned_by_self() ? used() : used_unlocked();
 
   size_t eden_capacity_bytes =
@@ -2877,7 +2877,7 @@
 
 void G1CollectedHeap::calculate_collection_set(G1EvacuationInfo& evacuation_info, double target_pause_time_ms) {
 
-  _collection_set.finalize_initial_collection_set(target_pause_time_ms, &_survivor);
+  _collection_set.finalize_initial_collection_set(target_pause_time_ms);
   evacuation_info.set_collectionset_regions(collection_set()->region_length() +
                                             collection_set()->optional_region_length());
 
@@ -4390,6 +4390,11 @@
   _policy->set_region_eden(hr);
 }
 
+void G1CollectedHeap::set_retained_region_short_lived_locked(HeapRegion* hr) {
+  _eden.add(hr);
+  _policy->set_region_eden_from_survivor(hr);
+}
+
 #ifdef ASSERT
 
 class NoYoungRegionsClosure: public HeapRegionClosure {
@@ -4546,6 +4551,22 @@
 }
 
 // Methods for the mutator alloc region
+void G1CollectedHeap::update_as_mutator_region(HeapRegion* alloc_region, bool is_reused) {
+  const char* msg;
+
+  if (is_reused) {
+    set_retained_region_short_lived_locked(alloc_region);
+    _hr_printer.reuse(alloc_region);
+    msg = "Mutator Region Allocation (Reuse)";
+  } else {
+    set_region_short_lived_locked(alloc_region);
+    _hr_printer.alloc(alloc_region, !policy()->should_allocate_mutator_region());
+    msg = "Mutator Region Allocation";
+  }
+
+  _verifier->check_bitmaps(msg, alloc_region);
+  _policy->remset_tracker()->update_at_allocate(alloc_region);
+}
 
 HeapRegion* G1CollectedHeap::new_mutator_alloc_region(size_t word_size,
                                                       bool force) {
@@ -4556,10 +4577,7 @@
                                               HeapRegionType::Eden,
                                               false /* do_expand */);
     if (new_alloc_region != NULL) {
-      set_region_short_lived_locked(new_alloc_region);
-      _hr_printer.alloc(new_alloc_region, !should_allocate);
-      _verifier->check_bitmaps("Mutator Region Allocation", new_alloc_region);
-      _policy->remset_tracker()->update_at_allocate(new_alloc_region);
+      update_as_mutator_region(new_alloc_region, false);
       return new_alloc_region;
     }
   }
@@ -4573,7 +4591,7 @@
 
   collection_set()->add_eden_region(alloc_region);
   increase_used(allocated_bytes);
-  _eden.add_used_bytes(allocated_bytes);
+  _eden.add_used_bytes(alloc_region, allocated_bytes);
   _hr_printer.retire(alloc_region);
 
   // We update the eden sizes here, when the region is retired,
@@ -4582,6 +4600,10 @@
   g1mm()->update_eden_size();
 }
 
+void G1CollectedHeap::reuse_retained_survivor_region(HeapRegion* alloc_region) {
+  update_as_mutator_region(alloc_region, true);
+}
+
 // Methods for the GC alloc regions
 
 bool G1CollectedHeap::has_more_regions(G1HeapRegionAttr dest) {
@@ -4640,11 +4662,17 @@
 
   bool const during_im = collector_state()->in_initial_mark_gc();
   if (during_im && allocated_bytes > 0) {
-    _cm->root_regions()->add(alloc_region);
+    _cm->root_regions()->add(alloc_region->next_top_at_mark_start(), alloc_region->top());
   }
   _hr_printer.retire(alloc_region);
 }
 
+void G1CollectedHeap::update_retained_survivor_gc_alloc_region(HeapRegion* alloc_region) {
+  _survivor.remove(alloc_region);
+  // To reuse the given region, setting EdenTag is also necessary but it will be done when
+  // the region is initialized as a mutator region.
+}
+
 HeapRegion* G1CollectedHeap::alloc_highest_free_region() {
   bool expanded = false;
   uint index = _hrm->find_highest_free(&expanded);
@@ -4771,3 +4799,23 @@
 GrowableArray<MemoryPool*> G1CollectedHeap::memory_pools() {
   return _g1mm->memory_pools();
 }
+
+uint G1CollectedHeap::eden_regions_count() const {
+  assert(_eden.length() >= _survivor.retained_length(), "Eden length (%u) should be "
+         "larger than or equal to retained region (%u).",
+         _eden.length(), _survivor.retained_length());
+  return _eden.length() - _survivor.retained_length();
+}
+
+uint G1CollectedHeap::survivor_regions_count() const {
+  return _survivor.length() + _survivor.retained_length();
+}
+
+size_t G1CollectedHeap::eden_regions_used_bytes() const {
+  return _eden.used_bytes();
+}
+
+size_t G1CollectedHeap::survivor_regions_used_bytes() const {
+  return _survivor.used_bytes() + _survivor.retained_used_bytes();
+}
+