[heap] Use the thread-safe free modes also for RemoveRange in SlotSet.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index d1f46a45ac6e7be05e9e92749105be5ff6767c33..7bb8ad870f11e25a141e02be43dc6d87720c247e 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -5963,8 +5963,10 @@ void Heap::ClearRecordedSlotRange(Address start, Address end) {
   if (!page->InNewSpace()) {
     store_buffer()->MoveEntriesToRememberedSet();
     DCHECK_EQ(page->owner()->identity(), OLD_SPACE);
-    RememberedSet<OLD_TO_NEW>::RemoveRange(page, start, end);
-    RememberedSet<OLD_TO_OLD>::RemoveRange(page, start, end);
+    RememberedSet<OLD_TO_NEW>::RemoveRange(page, start, end,
+                                           SlotSet::PREFREE_EMPTY_BUCKETS);
+    RememberedSet<OLD_TO_OLD>::RemoveRange(page, start, end,

[Hannes Payer (out of office), 2016/10/07 07:50:57]

I added an additional mode here because old to old will never have concurrent
access and can be freed directly. However, it may be beneficial to never
deallocate on the main thread an push the work to concurrent tasks. Any
thoughts?

[Michael Lippautz, 2016/10/07 09:11:06]

Even if there's not concurrent access, I would in the end try to free them at
the same place, i.e., I would deallocate them in the sweeper.

+                                           SlotSet::FREE_EMPTY_BUCKETS);
   }
 }