- Use the unused top of old-space pages when allocating.

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 VM_PAGES_H_
 #define VM_PAGES_H_
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/virtual_memory.h"
@@ skipping 24 matching lines @@
   uword first_object_start() const {
     return (reinterpret_cast<uword>(this) + sizeof(HeapPage));
   }
 
   void set_used(uword used) { used_ = used; }
   uword used() const { return used_; }
   void AddUsed(uword size) {
     used_ += size;
   }
 
+  uword TryBumpAllocate(intptr_t size) {
+    uword result = top();
+    intptr_t remaining_space = end() - result;
+    if (remaining_space < size) {
+      return 0;
+    }
+    set_top(result + size);
+    return result;
+  }
+
   void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
 
   RawObject* FindObject(FindObjectVisitor* visitor) const;
 
  private:
   static HeapPage* Initialize(VirtualMemory* memory, bool is_executable);
   static HeapPage* Allocate(intptr_t size, bool is_executable);
 
   // Deallocate the virtual memory backing this page. The page pointer to this
   // page becomes immediately inaccessible.
@@ skipping 60 matching lines @@
   uword TryBumpAllocate(intptr_t size);
 
   FreeList freelist_;
 
   Heap* heap_;
 
   HeapPage* pages_;
   HeapPage* pages_tail_;
   HeapPage* large_pages_;
 
+  // Page being used for bump allocation.
+  // The value has different meanings:
+  // NULL: Still bump allocating from last allocated fresh page.
+  // !NULL: Last page that had enough room to bump allocate, when we reach the
+  // tail page, we give up bump allocating.
+  HeapPage* bump_page_;
+
   // Various sizes being tracked for this generation.
   intptr_t max_capacity_;
   intptr_t capacity_;
   intptr_t in_use_;
 
   // Old-gen GC cycle count.
   int count_;
 
   bool is_executable_;
 
   // Keep track whether a MarkSweep is currently running.
   bool sweeping_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // VM_PAGES_H_