linux-kernel - RE: Can Linux live without DMA zone?

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Message-ID: <FFECF24D2A7F6D418B9511AF6F358602F2D5DF@shacnexch2.atitech.com>
Date:	Thu, 2 Nov 2006 18:33:07 +0800
From:	"Conke Hu" <conke.hu@....com>
To:	"Arjan van de Ven" <arjan@...radead.org>,
	"Jun Sun" <jsun@...sun.net>
Cc:	<linux-kernel@...r.kernel.org>
Subject: RE: Can Linux live without DMA zone?

Most PCs do not have ISA or floppy, so maybe we could add an option to enable DMA zone or not.

Best regards,
Conke @ AMD, Inc.

-----Original Message-----
From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Arjan van de Ven
Sent: 2006年11月2日 17:16
To: Jun Sun
Cc: linux-kernel@...r.kernel.org
Subject: Re: Can Linux live without DMA zone?

On Wed, 2006-11-01 at 18:15 -0800, Jun Sun wrote:
> I am trying to reserve a block of memory (>16MB) starting from 0 and hide it 
> from kernel.  A consequence is that DMA zone now has size 0.  That causes
> many drivers to grief (OOMs).
> 
> I see two ways out:
> 
> 1. Modify individual drivers and convince them not to alloc with GFP_DMA.
>    I have been trying to do this but do not seem to see an end of it.  :)
> 
> 2. Simply lie and increase MAX_DMA_ADDRESS to really big (like 1GB) so that
>    the whole memory region belongs to DMA zone.
> 
> #2 sounds pretty hackish.  I am sure something bad will happen
> sooner or later (like what?). But so far it appears to be working fine.
> 
> The fundamental question is: Has anybody tried to run Linux without 0 sized
> DMA zone before?  Am I doing something that nobody has done before (which is
> something really hard to believe these days with Linux :P)?

on a PC there are still devices that need memory in the lower 16Mb.....
(like floppy)

Maybe you should reserve another area of memory instead!


-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

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