--- a/hotspot/src/share/vm/gc/g1/g1EvacStats.cpp	Fri Feb 24 12:41:26 2017 -0500
+++ b/hotspot/src/share/vm/gc/g1/g1EvacStats.cpp	Thu Feb 23 12:50:49 2017 -0500
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -46,29 +46,7 @@
                       _failure_waste * HeapWordSize);
 }
 
-void G1EvacStats::adjust_desired_plab_sz() {
-  log_plab_allocation();
-
-  if (!ResizePLAB) {
-    // Clear accumulators for next round.
-    reset();
-    return;
-  }
-
-  assert(is_object_aligned(max_size()) && min_size() <= max_size(),
-         "PLAB clipping computation may be incorrect");
-
-  if (_allocated == 0) {
-    assert((_unused == 0),
-           "Inconsistency in PLAB stats: "
-           "_allocated: " SIZE_FORMAT ", "
-           "_wasted: " SIZE_FORMAT ", "
-           "_region_end_waste: " SIZE_FORMAT ", "
-           "_unused: " SIZE_FORMAT ", "
-           "_used  : " SIZE_FORMAT,
-           _allocated, _wasted, _region_end_waste, _unused, used());
-    _allocated = 1;
-  }
+size_t G1EvacStats::compute_desired_plab_sz() {
   // The size of the PLAB caps the amount of space that can be wasted at the
   // end of the collection. In the worst case the last PLAB could be completely
   // empty.
@@ -109,13 +87,7 @@
 
   size_t const total_waste_allowed = used_for_waste_calculation * TargetPLABWastePct;
   size_t const cur_plab_sz = (size_t)((double)total_waste_allowed / G1LastPLABAverageOccupancy);
-  // Take historical weighted average
-  _filter.sample(cur_plab_sz);
-  _desired_net_plab_sz = MAX2(min_size(), (size_t)_filter.average());
-
-  log_sizing(cur_plab_sz, _desired_net_plab_sz);
-  // Clear accumulators for next round.
-  reset();
+  return cur_plab_sz;
 }
 
 G1EvacStats::G1EvacStats(const char* description, size_t desired_plab_sz_, unsigned wt) :

--- a/hotspot/src/share/vm/gc/g1/g1EvacStats.hpp	Fri Feb 24 12:41:26 2017 -0500
+++ b/hotspot/src/share/vm/gc/g1/g1EvacStats.hpp	Thu Feb 23 12:50:49 2017 -0500
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -53,13 +53,13 @@
 
   virtual void log_plab_allocation();
 
+  virtual size_t compute_desired_plab_sz();
+
  public:
   G1EvacStats(const char* description, size_t desired_plab_sz_, unsigned wt);
 
   ~G1EvacStats();
 
-  virtual void adjust_desired_plab_sz();
-
   uint regions_filled() const { return _regions_filled; }
   size_t region_end_waste() const { return _region_end_waste; }
   size_t direct_allocated() const { return _direct_allocated; }

--- a/hotspot/src/share/vm/gc/shared/plab.cpp	Fri Feb 24 12:41:26 2017 -0500
+++ b/hotspot/src/share/vm/gc/shared/plab.cpp	Thu Feb 23 12:50:49 2017 -0500
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -154,30 +154,33 @@
   assert(is_object_aligned(max_size()) && min_size() <= max_size(),
          "PLAB clipping computation may be incorrect");
 
-  if (_allocated == 0) {
-    assert(_unused == 0,
-           "Inconsistency in PLAB stats: "
-           "_allocated: " SIZE_FORMAT ", "
-           "_wasted: " SIZE_FORMAT ", "
-           "_unused: " SIZE_FORMAT ", "
-           "_undo_wasted: " SIZE_FORMAT,
-           _allocated, _wasted, _unused, _undo_wasted);
+  assert(_allocated != 0 || _unused == 0,
+         "Inconsistency in PLAB stats: "
+         "_allocated: " SIZE_FORMAT ", "
+         "_wasted: " SIZE_FORMAT ", "
+         "_unused: " SIZE_FORMAT ", "
+         "_undo_wasted: " SIZE_FORMAT,
+         _allocated, _wasted, _unused, _undo_wasted);
 
-    _allocated = 1;
-  }
-  double wasted_frac    = (double)_unused / (double)_allocated;
+  size_t plab_sz = compute_desired_plab_sz();
+  // Take historical weighted average
+  _filter.sample(plab_sz);
+  _desired_net_plab_sz = MAX2(min_size(), (size_t)_filter.average());
+
+  log_sizing(plab_sz, _desired_net_plab_sz);
+  // Clear accumulators for next round
+  reset();
+}
+
+size_t PLABStats::compute_desired_plab_sz() {
+  size_t allocated      = MAX2(_allocated, size_t(1));
+  double wasted_frac    = (double)_unused / (double)allocated;
   size_t target_refills = (size_t)((wasted_frac * TargetSurvivorRatio) / TargetPLABWastePct);
   if (target_refills == 0) {
     target_refills = 1;
   }
-  size_t used = _allocated - _wasted - _unused;
+  size_t used = allocated - _wasted - _unused;
   // Assumed to have 1 gc worker thread
   size_t recent_plab_sz = used / target_refills;
-  // Take historical weighted average
-  _filter.sample(recent_plab_sz);
-  _desired_net_plab_sz = MAX2(min_size(), (size_t)_filter.average());
-
-  log_sizing(recent_plab_sz, _desired_net_plab_sz);
-
-  reset();
+  return recent_plab_sz;
 }

--- a/hotspot/src/share/vm/gc/shared/plab.hpp	Fri Feb 24 12:41:26 2017 -0500
+++ b/hotspot/src/share/vm/gc/shared/plab.hpp	Thu Feb 23 12:50:49 2017 -0500
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -165,6 +165,10 @@
 
   virtual void log_plab_allocation();
   virtual void log_sizing(size_t calculated, size_t net_desired);
+
+  // helper for adjust_desired_plab_sz().
+  virtual size_t compute_desired_plab_sz();
+
  public:
   PLABStats(const char* description, size_t desired_net_plab_sz_, unsigned wt) :
     _description(description),
@@ -197,7 +201,7 @@
 
   // Updates the current desired PLAB size. Computes the new desired PLAB size with one gc worker thread,
   // updates _desired_plab_sz and clears sensor accumulators.
-  virtual void adjust_desired_plab_sz();
+  void adjust_desired_plab_sz();
 
   inline void add_allocated(size_t v);