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SubjectRe: fork: out of memory
On Wed, 26 Nov 1997, Jan Echternach wrote:

> On 26 November 1997, Mike Jagdis <mike@roan.co.uk> wrote:
> > Paging *is* on in the kernel. It isn't so much a case of the kernel
> > seeing contiguous memory as of devices seeing *physically*
> > contiguous memory. There are a few case where we know nothing
> > will want to do DMA to a multi-page region and in such cases we
> > could use vmalloc (which already exists) but that has a relatively
> > heavy set up / tear down penalty so better solutions that don't
> > use vmalloc are prefered. Vmalloc doesn't help the problem that
> > much anyway - most of the big page requests are for things like
> > floppy buffers and sound buffers which have to be physically
> > contiguous for DMA.
>
> But if we need a DMA buffer that is physically contiguous can't we
> just move non-DMA pages around and adjust the page tables such that
> logical addresses stay the same?

Memory is getting so inexpensive in some environments, wouldn't it make
sense to have an option to reserve DMA-able memory at init time? With 16
megs going for $60, it is worth setting aside 4megs or 8 megs which would
have to be specially requested.

john alvord


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