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Date:	Sun, 4 Apr 2010 03:49:26 -0400
From:	Daniel Hazelton <dhazelton@...er.net>
To:	"tek-life" <teklife.kernel@...il.com>
Cc:	linux-kernel@...r.kernel.org, ebiederm@...ssion.com
Subject: Re: Fwd: Can we remove the Zone_DMA?

On Sunday 04 April 2010 01:33:09 am tek-life wrote:
> Thanks for your reply.And do you means that , If I use a modern PC,such as
> my pc (CPU:Intel dual-core 2.6GHZ; Memory 2GB; And no pci ).I can remove
> the ZONE_DMA .And make sure this system also run smoothly as before?

*MAYBE* - if you don't use parallel ports, floppy drives or similar. There 
actually are still a lot of devices that use the ISA bus in a modern PC - even 
the keyboard (well, not USB ones) is an ISA device.

Simple fact is that if it was possible to configure it out and not cause 
massive problems somebody would have already spun out a patch to allow just 
that. 

DRH

> 在 2010年4月4日 下午1:07,Daniel Hazelton <dhazelton@...er.net>写道:
> 
> 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.
> > > 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.
> > 
> > DRH
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