Simple BlinkGC heap compaction.

third_party/WebKit/Source/platform/heap/Heap.h

Index: third_party/WebKit/Source/platform/heap/Heap.h
diff --git a/third_party/WebKit/Source/platform/heap/Heap.h b/third_party/WebKit/Source/platform/heap/Heap.h
index b02aa40e4b2e6110da6cbba0741dca57fb291d54..69fe2e4d4d62d4b6551702f0217d26a52fe54541 100644
--- a/third_party/WebKit/Source/platform/heap/Heap.h
+++ b/third_party/WebKit/Source/platform/heap/Heap.h
@@ -81,6 +81,7 @@ class PLATFORM_EXPORT HeapAllocHooks {
 };
 
 class CrossThreadPersistentRegion;
+class HeapCompact;
 template <typename T>
 class Member;
 template <typename T>
@@ -381,6 +382,31 @@ class PLATFORM_EXPORT ThreadHeap {
   bool weakTableRegistered(const void*);
 #endif
 
+  // Heap compaction registration methods:
+
+  // Register |slot| as containing a reference to a movable heap object.
+  //
+  // When compaction moves the object pointed to by |*slot| to |newAddress|,
+  // |*slot| must be updated to hold |newAddress| instead.
+  void registerMovingObjectReference(MovableReference*);
+
+  // Register a callback to be invoked upon moving the object starting at
+  // |reference|; see |MovingObjectCallback| documentation for details.
+  //
+  // This callback mechanism is needed to account for backing store objects
+  // containing intra-object pointers, all of which must be relocated/rebased
+  // to be done wrt the moved-to location.
+  //
+  // For Blink, |LinkedHashSet<>| is currently the only abstraction which
+  // relies on this feature.
+  void registerMovingObjectCallback(MovableReference,
+                                    MovingObjectCallback,
+                                    void* callbackData);
+
+  // Register a relocation; when |*slot| is compacted and moved,
+  // |slot| must be updated to point to |*slot|'s new location.
+  void registerRelocation(MovableReference* slot);

[haraken, 2016/11/30 06:29:52]

What's a difference between registerMovingObjectReference and
registerRelocation?

Also I cannot find any call site of registerRelocation...?

[sof, 2016/11/30 06:52:43]

Have a look at the documentation of HeapCompact::registerRelocation().

(registerRelocation() is currently not needed for Blink.)

+
   BlinkGC::GCReason lastGCReason() { return m_lastGCReason; }
   RegionTree* getRegionTree() { return m_regionTree.get(); }
 
@@ -438,6 +464,8 @@ class PLATFORM_EXPORT ThreadHeap {
   static void reportMemoryUsageHistogram();
   static void reportMemoryUsageForTracing();
 
+  HeapCompact* compaction();
+
  private:
   // Reset counters that track live and allocated-since-last-GC sizes.
   void resetHeapCounters();
@@ -463,6 +491,8 @@ class PLATFORM_EXPORT ThreadHeap {
   BlinkGC::GCReason m_lastGCReason;
   StackFrameDepth m_stackFrameDepth;
 
+  std::unique_ptr<HeapCompact> m_compaction;
+
   static ThreadHeap* s_mainThreadHeap;
 
   friend class ThreadState;