Date: Tue, 16 Sep 2003 17:20:57 +0200
From: Stephan von Krawczynski <skraw@ithnet.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: marcelo.tosatti@cyclades.com.br, neilb@cse.unsw.edu.au,
       linux-kernel@vger.kernel.org
Subject: Re: experiences beyond 4 GB RAM with 2.4.22
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On Tue, 16 Sep 2003 15:36:14 +0100
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> On Maw, 2003-09-16 at 14:36, Stephan von Krawczynski wrote:
> > Well, I do understand the bounce buffer problem, but honestly the current
> > way of handling the situation seems questionable at least. If you ever
> > tried such a system you notice it is a lot worse than just dumping the
> > additional ram above 4GB. You can really watch your network connections go
> > bogus which is just unacceptable. Is there any thinkable way to ommit the
> > bounce buffers and still do something useful with the beyond-4GB ram parts?
> 
> The 2.6 tree is somewhat better about this but at the end of the day if
> your I/O subsystem can't do the job your box will not perform ideally.

Hm, "not ideally" is a real friendly word for describing the mess ;-)
Isn't there a possibility to flag this part of the memory as nonDMA-able, kind
of "do whatever you want with it, but don't expect any dma-driven i/o"...
I know this gets a problem when swap jumps in, though.
But really it is far better for the box to flag it more or less unusable
compared to a DoS done by user-space "find" ...
I know this is a real corner case of life. It looks more like taking a
different decision than current to improve the situation and not so much a real
development topic. Probably a note in kernel docs reading "DON'T DO THIS" is
either sufficient...


Regards,
Stephan

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