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SubjectRe: Kernel virtual memory?
On Thu, 7 Aug 1997, Jochen Karrer wrote:
> > DMA memory could be allocated by moving allocated blocks away from the
> > lower 16MB, and other parts of kernel could be made happy by changing the
> > page tables accordingly.
> >
> > So, is this possible/feasible/too ugly to implement?
> Not possible.

Both Benjamin LaHaise and I are working on [different] schemes which
allow this.
Infact, it is possible to do (to a limited extent) with the current
Memory Managment scheme. Although, it would be very ugly.

Once there was the idea of supporting a re-locatable kernel; when memory
is greater than 16MB loading the kernel into high memory would make more
DMA pages available (for Intel with the ISA restrictions).
There was a problem with some (SCSI?) drivers which assumed the data/BSS
section has DMAable (which wouldn't be true for a high loaded kernel), but
I'm not aware of any other reason why this wasn't implemented....someone
care to comment?

Regards,

markhe

------------------------------------------------------------------
Mark Hemment, Unix/C Software Engineer (Contractor)
markhe@nextd.demon.co.uk http://www.nextd.demon.co.uk/
"Success has many fathers, failure is a B**TARD!" - anon
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