Re: Help with mapping memory into kernel space?

Mark Hounschell
2004-08-18T11:17:07Z

William Lee Irwin III wrote:
>
> On Tue, Aug 17, 2004 at 10:39:38PM -0700, Brian McGrew wrote:
> > The overall problem is that the more system memory we install,
> > the fewer IBB's we can use. For instance, 256MB lets us use
> > four IBB's; 512MB lets us use three IBB's and so on. Basicly,
> > the kernel blows up trying to map memory. Each IBB has two
> > banks of 64MB of RAM on them which we try and memmap to system
> > memory for speed of addressing. So essentaily, we're sending
> > out four camera systems with only 256MB of memory which is only
> > about one quarter of what we need.
> > I can't think of any better way to explain it other than it's
> > almost like adding system memory subtracts from kernel memory.
> > Does that make any sense? We've tried building the kernel with
> > the 4GB memory model and the 64GB memory model and had no success.
>
> You appear to be trying to ioremap() vast areas. ia32 has limited
> address space, so you need to do one of two things:
> (a) subdivide into portions mapped into different address spaces
> (b) map portions on demand
>
> There is no support for (a) in Linux.
>

You might try the bigphysarea patch. We have basically the same problem
with hardware not capabile of hardware scatter/gather in DMA mode.
Bigphysarea was our solution. It does not appear to be available for the
2.6 kernel however

Mark