--- old/src/hotspot/share/gc/g1/g1ParScanThreadState.inline.hpp	2018-04-11 13:44:10.223627371 +0200
+++ new/src/hotspot/share/gc/g1/g1ParScanThreadState.inline.hpp	2018-04-11 13:44:09.955619141 +0200
@@ -29,6 +29,7 @@
 #include "gc/g1/g1RemSet.hpp"
 #include "oops/access.inline.hpp"
 #include "oops/oop.inline.hpp"
+#include "utilities/ticks.inline.hpp"
 
 template <class T> void G1ParScanThreadState::do_oop_evac(T* p) {
   // Reference should not be NULL here as such are never pushed to the task queue.
@@ -151,4 +152,42 @@
   }
 }
 
+inline bool G1ParScanThreadState::should_start_trim_queue_partially() const {
+  return !_refs->overflow_empty() || _refs->size() > _stack_drain_upper_threshold;
+}
+
+inline bool G1ParScanThreadState::should_end_trim_queue_partially() const {
+  return _refs->overflow_empty() && _refs->size() <= _stack_drain_lower_threshold;
+}
+
+inline void G1ParScanThreadState::trim_queue_partially_internal() {
+  StarTask ref;
+  do {
+    // Drain the overflow stack first, so other threads can potentially steal.
+    while (_refs->pop_overflow(ref)) {
+      if (!_refs->try_push_to_taskqueue(ref)) {
+        dispatch_reference(ref);
+      }
+    }
+
+    while (_refs->pop_local(ref, _stack_drain_lower_threshold)) {
+      dispatch_reference(ref);
+    }
+  } while (!should_end_trim_queue_partially());
+}
+
+inline void G1ParScanThreadState::trim_queue_partially() {
+  if (should_start_trim_queue_partially()) {
+    const Ticks start = Ticks::now();
+    trim_queue_partially_internal();
+    _trim_ticks += Ticks::now() - start;
+  }
+}
+
+inline Tickspan G1ParScanThreadState::trim_ticks_and_reset() {
+  Tickspan result = _trim_ticks;
+  _trim_ticks = Tickspan();
+  return result;
+}
+
 #endif // SHARE_VM_GC_G1_G1PARSCANTHREADSTATE_INLINE_HPP