Initially unmap one of the semispaces to reduce memory use at boot time.

src/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1816 matching lines @@
   // Constructor.
   SemiSpace(Heap* heap, SemiSpaceId semispace)
     : Space(heap, NEW_SPACE, NOT_EXECUTABLE),
       start_(NULL),
       age_mark_(NULL),
       id_(semispace),
       anchor_(this),
       current_page_(NULL) { }
 
   // Sets up the semispace using the given chunk.
-  bool SetUp(Address start, int initial_capacity, int maximum_capacity);
+  void SetUp(Address start, int initial_capacity, int maximum_capacity);
 
   // Tear down the space.  Heap memory was not allocated by the space, so it
   // is not deallocated here.
   void TearDown();
 
   // True if the space has been set up but not torn down.
   bool HasBeenSetUp() { return start_ != NULL; }
 
   // Grow the semispace to the new capacity.  The new capacity
   // requested must be larger than the current capacity and less than
@@ skipping 808 matching lines @@
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_