you can also reserve some physical memory at the top of memory and
dma
into that.
of course, this means you have to know how much memory you need
before
booting the kernel.

I had thought about that, however can I mmap into memory that area if I hav=
e set mem=3D250M in the boot arguments?  I would plan to DMA to above 250M =
(up to 256M).  I know that would keep the kernel out of it, but will /dev/m=
em be able to "see" that memory if I had told the kernel it was not there?

Thanks for the help!

Jonathan