Prefaulting for i/o buffers

[Konstantin Belousov]

On Fri, Feb 03, 2012 at 07:40:37PM +0000, Attilio Rao wrote:
> Do you have an ETA for reviews? When do you plan to commit this?
Obviously, I cannot have an ETA for reviews, and I am not sure that
I get any review at all (as usual). I think it is reasonable to commit
in 2-3 weeks after the first post.

> it would be valuable to get a grasp on the benchmark and refine the
> performance difference as much as possible.
The benchmark is trivial and available at 
http://people.freebsd.org/~kib/misc/bench_read.c

There is also a targeted test for uio functionality
http://people.freebsd.org/~kib/misc/uio.c
which I used together with intensive swapping workload to verify
the correctness of the patch.

Regarding the performance hit, I consider the < 10% on the worst case
a reasonable cost for finally fixing this issue. If anybody can provide
a benchmark result for e.g. postgresql tests, I will be very grateful.
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