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SubjectRe: Cache incoherencies
On Fri, Aug 27, 1999, Rogier Wolff <R.E.Wolff@BitWizard.nl> wrote:

>I think we should take a step back, abstract the GFP mechansism to the
>point where it can satisfy a "gimmy any page" request, which
>technically turns into "preferably a page from non-DMA memory, but if
>you're out of those, give me a DMA-able page".
>
>A driver wanting to do DMA will request "a DMA-ABLE page" (with either
>the 16M ISA limit, the 1M XT limit, or the 4G PCI limit!), with "if
>you're out of those, give up".
>
>I think that GFP may need to be redesigned one time or another.
>However, once that is done, taking along things as "uncached" pages,
>should become a breeze. Yes, the current implementation makes it a
>quick hack to vmalloc.

I beleive we should not confuse DMA-able and unached. DMA can be
perfectly fine on cachable memory on a non-coherent architecture if you
do the appropriate flush when needed. Making all DMA memory non-cachable
would have a huge performance hit on some platform.

>I think that generalizing gfp is a good idea in the end.

I'll let more competent people handle this and keep my vmalloc stuff for
now ;-)

--
Perso. e-mail: <mailto:bh40@calva.net>
Work e-mail: <mailto:benh@mipsys.com>
BenH. Web : <http://calvaweb.calvacom.fr/bh40/>




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