[heap] Take page lock when scavenging old to new references in Scavenger.

src/heap/remembered-set.h

Index: src/heap/remembered-set.h
diff --git a/src/heap/remembered-set.h b/src/heap/remembered-set.h
index 37439bfa62d023a63a55cc6274b1f8bd90220729..b60cd451ee7166a97ded9c17682a2364b29d8c53 100644
--- a/src/heap/remembered-set.h
+++ b/src/heap/remembered-set.h
@@ -13,6 +13,8 @@
 namespace v8 {
 namespace internal {
 
+enum RememberedSetIterationMode { SYNCHRONIZED, NON_SYNCHRONIZED };
+
 // TODO(ulan): Investigate performance of de-templatizing this class.
 template <RememberedSetType type>
 class RememberedSet : public AllStatic {
@@ -98,9 +100,13 @@ class RememberedSet : public AllStatic {
   // Iterates and filters the remembered set with the given callback.
   // The callback should take (Address slot) and return SlotCallbackResult.
   template <typename Callback>
-  static void Iterate(Heap* heap, Callback callback) {
-    IterateMemoryChunks(
-        heap, [callback](MemoryChunk* chunk) { Iterate(chunk, callback); });
+  static void Iterate(Heap* heap, RememberedSetIterationMode mode,
+                      Callback callback) {
+    IterateMemoryChunks(heap, [mode, callback](MemoryChunk* chunk) {
+      if (mode == SYNCHRONIZED) chunk->mutex()->Lock();
+      Iterate(chunk, callback);
+      if (mode == SYNCHRONIZED) chunk->mutex()->Unlock();
+    });
   }
 
   // Iterates over all memory chunks that contains non-empty slot sets.
@@ -177,9 +183,12 @@ class RememberedSet : public AllStatic {
   // The callback should take (SlotType slot_type, SlotAddress slot) and return
   // SlotCallbackResult.
   template <typename Callback>
-  static void IterateTyped(Heap* heap, Callback callback) {
-    IterateMemoryChunks(heap, [callback](MemoryChunk* chunk) {
+  static void IterateTyped(Heap* heap, RememberedSetIterationMode mode,
+                           Callback callback) {
+    IterateMemoryChunks(heap, [mode, callback](MemoryChunk* chunk) {
+      if (mode == SYNCHRONIZED) chunk->mutex()->Lock();
       IterateTyped(chunk, callback);
+      if (mode == SYNCHRONIZED) chunk->mutex()->Unlock();
     });
   }