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SubjectRe: Can we remove the Zone_DMA?
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On Son, 2010-04-04 at 01:07 -0400, Daniel Hazelton wrote:
> On Sunday 04 April 2010 12:21:54 am tek-life wrote:
> > I’m a newbie on the linux kernel. Now I am reading the source code of
> > Linux . I have a question in the following about ZONE_DMA.
> >
> > In Linux , The Memory is divided to three zone. They are ZONE_DMA
> > 、ZONE_NORMAL and ZONE_HIGHMEM. From the book of "Undstand the Linux
> > kernel ", the ZONE_DMA has the effect that the Direct Memory Access
> > (DMA) processors for old ISA buses have a strong limitation: they are
> > able to address only the first 16 MB of RAM. SO ,we must set a zone
> > for the DMA on ISA bus. And I suspect that the hardware has
> > developed so quickly .And in this days the ISA has been weeded out.

That doesn't imply that the "old" systems and hardware vanishes (even
not quickly).

> > And so ,if we not defined the ZONE_DMA, is the system be effected? And
> > why not remove ZONE_DMA from the kernel . If it cann‘t to do so,the
> > compatibility is the only reason?
>
> While ISA is gone as a true peripheral interconnect for new systems it does,
> actually, still live on in a lot of systems that Linux still supports. While
> those systems, generally, are running the same kernel and userspace they were
> a decade ago I have no doubt that somebody might find an old machine and put
> Linux on it - just because they could.
>
> And that also discounts the non-IBM PC machines that are out there that Linux
> also supports. While I don't know enough about them to say for sure, I am
> quite certain that at least some of them are still using the ISA bus.

PC-104 has an ISA bus. And it is far from dead and currently deployed
for new systems.

Bernd
--
Bernd Petrovitsch Email : bernd@petrovitsch.priv.at
LUGA : http://www.luga.at

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