Subject: Re: Can Linux live without DMA zone?
From: Arjan van de Ven <arjan@infradead.org>
To: Jun Sun <jsun@junsun.net>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <20061102021547.GA1240@srv.junsun.net>
References: <20061102021547.GA1240@srv.junsun.net>
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Organization: Intel International BV
Date: Thu, 02 Nov 2006 10:16:11 +0100
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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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