How to pin a userland page in memory(avoid copyin and copyout)

[Bharma Ji]

Hi
I am trying to explore the option avoiding copyin and copyout when mode
switches from user to kernel and vice versa. One way to achieve this, as I
understand, is to make the memory address (which contain the data to be
copied) non pageable. Then just pass the addresses to the kernel and the
data will be used directly from the userland page. Is there already some
example code / standard way to do this?

Also is there any way one can determine the amount of time / performance hit
(CPU %)that happening on a given process due to the copyin and copyout. I
want to understand how much performance gain one can gain if I am able to
remove copyin/copyout.