benchmarks of O_STREAMING in 2.5

[Robert Love]

I gave the O_STREAMING in Andrew's 2.5-mm tree the treatment..

Short summary: It works.

The streaming read test in the following benchmarks is simply a read()
in 64KB byte chunks of an 800MB file.

First test.  Show the cache effects are indeed as we intend and the
overhead is negligible.  Here, mem=2G.

	O_STREAMING?	Wall time	Cache Delta
	Yes		21.827s		0
	No		21.734s		+800MB

Second test.  Same deal, but mem=8M.  There was slight swapping, so I
suspect the reduced VM pressure is why the O_STREAMING run is faster.

	O_STREAMING?	Wall time	Cache Delta
	Yes		22.303s		0
	No		28.812s		+1MB

Third and final test. Kernel compile (make -j2) with a couple streaming
reads in the background.  Again, mem=2G.  This shows that actually
saving the pagecache from the horrid waste is useful.

	O_STREAMING	Wall time to complete Kernel compile
	Yes		5m30.494s
	No		4m59.661s

So, uh, Andrew's 2.5 code works ;-)

Someone buy me a dual Xeon,

	Robert Love