Messages in this thread | | | Subject | Re: Can we remove the Zone_DMA? | From | Bernd Petrovitsch <> | Date | Sun, 18 Apr 2010 13:04:30 +0200 |
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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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