HUGE contiguous mem space with 2.4

[Christophe Beaumont]

Hi...

I am facing an odd problem here. I have an application here
that requires a HUGE physically contiguous memory area to 
be locked (yes, I have hardware DMA'ing in and out of that
area, over the PCI bus). HUGE being like one Gig (could be
more if needed...)
I am trying to use the mem=1024M option at boot time (yes,
the box has 2 Gigs of RAM) and then ioremap() from within 
my module. There I have a couple of issues:
 - if I use high_memory as is, I cannot remap any area 
(high_memory=f800:0000 ???)
 - if I use high_memory thru virt_to_phys, I can then remap...
up to 64 Megs (maybe a little more, but for sure less than
128 Megs) (virt_to_phys(high_mem)=3800:0000)

I tried with other values (like mem=250M 512M 1536M) and could
NOT remap anything close to the whole amount of "reserved" memory
(best case being with mem=256M I can remap 512M out of 1.75Gigs)

I guess I am missing a point somewhere.... or have totally 
been "ignoring" some doc somewhere (alessandro could be the man
for this one thing *-) )

[system is a dual P3 with 2 gigs of RAM, a 2.4.3 kernel with SMP
turned on... and the nice option for 4Gigs of RAM... would the
64Gig option help me??? just wondering there...]

Any pointer, advise, help, hint... laugh at the stupid thing I 
have forgotten is more than welcome..

tia

Chris.