Avoid scanning huge freelists for large enough free blocks.

runtime/vm/freelist.h

 // Copyright (c) 2012, 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_FREELIST_H_
 #define RUNTIME_VM_FREELIST_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bit_set.h"
@@ skipping 80 matching lines @@
   // Returns a large element, at least 'minimum_size', or NULL if none exists.
   FreeListElement* TryAllocateLarge(intptr_t minimum_size);
   FreeListElement* TryAllocateLargeLocked(intptr_t minimum_size);
 
   // Allocates locked and unprotected memory, but only from small elements
   // (i.e., fixed size lists).
   uword TryAllocateSmallLocked(intptr_t size);
 
  private:
   static const int kNumLists = 128;
+  static const intptr_t kInitialFreeListSearchBudget = 1000;
 
   static intptr_t IndexForSize(intptr_t size);
 
   intptr_t LengthLocked(int index) const;
 
   void EnqueueElement(FreeListElement* element, intptr_t index);
   FreeListElement* DequeueElement(intptr_t index);
 
   void SplitElementAfterAndEnqueue(FreeListElement* element,
                                    intptr_t size,
                                    bool is_protected);
 
   void PrintSmall() const;
   void PrintLarge() const;
 
   // Lock protecting the free list data structures.
   Mutex* mutex_;
 
   BitSet<kNumLists> free_map_;
 
   FreeListElement* free_lists_[kNumLists + 1];
 
+  intptr_t freelist_search_budget_;
+
   // The largest available small size in bytes, or negative if there is none.
   intptr_t last_free_small_size_;
 
   DISALLOW_COPY_AND_ASSIGN(FreeList);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_FREELIST_H_