bigphysarea mmap and direct_io

bigphysarea mmap and direct_io

[Russell Johnson]

My driver is allocating memory via bigphysarea and my application mmap's the
area for performance reasons.  With linux kernels 2.6.14 and prior on i386
platforms, I have been able to issue disk reads using direct_io to fill this
bigphysarea memory and prevent multiple copies of the data.  The file system
code for direct I/O disk reads checks for VM_IO and will not allow direct io
in that case.  So to do this I had my driver clear the VM_IO flag after
calling remap_pfn_range.

With kernel 2.6.16 and newer, remap_pfn_range sets a new flag VM_PFNMAP
which direct_io also checks.  If my driver clears VM_PFNMAP then the kernel
will oops upon an munmap call because it will attempt to free the pages.

I'm looking for the proper way to do what I want which is to allow the
application to mmap and do direct io disk access to the bigphysarea memory.
I've unsuccessfully tried writing a nopage handler and I still get an oops
upon munmap.  Can someone point me in the right direction?

Please cc me as I'm not on this list.  Thanks!

rjohnson@rtlogic.com

Russell Johnson
RT Logic!