From: Dipankar Sarma <dipankar@in.ibm.com>


fget() shows up on profiles, especially on SMP.  Dipankar's patch
special-cases the situation wherein there are no sharers of current->files.

In this situation we know that no other process can close this file, so it
is not necessary to increment the file's refcount.

It's ugly as sin, but makes a substantial difference.

The test is

	dd if=/dev/zero of=foo bs=1 count=1M

On 4CPU P3 xeon with 1MB L2 cache and 512MB ram:

	kernel           sys time     std-dev
	------------     --------     -------

	UP - vanilla     2.104        0.028
	UP - file        1.867        0.019

	SMP - vanilla    2.976        0.023
	SMP - file       2.719        0.026