How to allocate large blocks of contiguous physical RAM?

[Alan Cudmore <embeddedpenguin@yahoo.com>]

Hi,
I'm trying to figure out how to allocate a large block
of contiguous physical memory under linux 2.4.x. I
have 4GB of RAM and have turned on the CONFIG_HIGMEM4G
option. 
Previously I was using the "bigphysarea" patch, but
that seems to have a limit of around 900MB. ( is that
because it is being allocated from the 1Gig kernel
physical memory ? )
Also, I have considered changing the PAGE_OFFSET
define to 0x80000000 to give me a little under 2GB.

Ideally I would like to do the following:
1. Pre-Allocate 2 or 3 gigs of contiguous memory
2. A custom PCI 64/66Mhz card will be DMAing data
directly into this memory at very high rates ( up to
500MBytes per second, thus the need for a few gigs ) 
3. Then I would like to be able to DMA data back out
to SCSI without picking the data up ( using SCSI
generic with Direct I/O ).

I really am a linux-MM newbie, so I would appreciate
advice on how I could accomplish such a feat, it it
can be done at all. Any suggestions would be welcome.

Thanks,
Alan C.


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