diff -r 961d832d8734 Lib/subprocess.py
--- a/Lib/subprocess.py	Wed Nov 20 12:49:05 2013 +0100
+++ b/Lib/subprocess.py	Wed Nov 20 14:58:08 2013 +0100
@@ -1555,6 +1555,10 @@ class Popen(object):
 
             self._save_input(input)
 
+            # use a memoryview to avoid memory copies
+            if input:
+                input_view = memoryview(self._input)
+
             with _PopenSelector() as selector:
                 if self.stdin and input:
                     selector.register(self.stdin, selectors.EVENT_WRITE)
@@ -1576,8 +1580,8 @@ class Popen(object):
 
                     for key, events in ready:
                         if key.fileobj is self.stdin:
-                            chunk = self._input[self._input_offset :
-                                                self._input_offset + _PIPE_BUF]
+                            chunk = input_view[self._input_offset :
+                                               self._input_offset + _PIPE_BUF]
                             try:
                                 self._input_offset += os.write(key.fd, chunk)
                             except OSError as e: