[vm] Compute per-HeapPage usage during sweeping.

runtime/vm/pages.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef RUNTIME_VM_PAGES_H_
 #define RUNTIME_VM_PAGES_H_
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/lockers.h"
@@ skipping 19 matching lines @@
  public:
   enum PageType { kData = 0, kExecutable, kNumPageTypes };
 
   HeapPage* next() const { return next_; }
   void set_next(HeapPage* next) { next_ = next; }
 
   bool Contains(uword addr) { return memory_->Contains(addr); }
 
   uword object_start() const { return memory_->start() + ObjectStartOffset(); }
   uword object_end() const { return object_end_; }
+  uword used_in_bytes() const { return used_in_bytes_; }
+  void set_used_in_bytes(uword value) {
+    ASSERT(Utils::IsAligned(value, kObjectAlignment));
+    used_in_bytes_ = value;
+  }
 
   PageType type() const { return type_; }
 
   bool is_image_page() const { return !memory_->vm_owns_region(); }
 
   void VisitObjects(ObjectVisitor* visitor) const;
   void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
 
   RawObject* FindObject(FindObjectVisitor* visitor) const;
 
   void WriteProtect(bool read_only);
 
   static intptr_t ObjectStartOffset() {
     return Utils::RoundUp(sizeof(HeapPage), OS::kMaxPreferredCodeAlignment);
   }
 
  private:
-  void set_object_end(uword val) {
-    ASSERT((val & kObjectAlignmentMask) == kOldObjectAlignmentOffset);
-    object_end_ = val;
+  void set_object_end(uword value) {
+    ASSERT((value & kObjectAlignmentMask) == kOldObjectAlignmentOffset);
+    object_end_ = value;
   }
 
   // These return NULL on OOM.
   static HeapPage* Initialize(VirtualMemory* memory,
                               PageType type,
                               const char* name);
   static HeapPage* Allocate(intptr_t size_in_words,
                             PageType type,
                             const char* name);
 
   // Deallocate the virtual memory backing this page. The page pointer to this
   // page becomes immediately inaccessible.
   void Deallocate();
 
   VirtualMemory* memory_;
   HeapPage* next_;
   uword object_end_;
+  uword used_in_bytes_;
   PageType type_;
 
   friend class PageSpace;
 
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(HeapPage);
 };
 
 // The history holds the timing information of the last garbage collection
 // runs.
@@ skipping 342 matching lines @@
   friend class HeapIterationScope;
   friend class PageSpaceController;
   friend class SweeperTask;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_PAGES_H_