Creating a KLD to dump memory

[Office Manager]

Hi,
I'm trying to create a kernel module to dump the memory of a machine like
lime <https://github.com/504ensicsLabs/LiME>.
Right now I'm using memrw implementation to read the physical memory, my
problem with this method is the garbage pages that return a page filled
with 0xFF's.
How can I create a dump containing only the physical available memory?

e.g my machine has 256mb so I want a 256mb memory dump.
Thanks.