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

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Date:	Thu, 2 Nov 2006 11:43:38 +0800
From:	"Conke Hu" <conke.hu@....com>
To:	"Jun Sun" <jsun@...sun.net>, <linux-kernel@...r.kernel.org>
Subject: RE: Can Linux live without DMA zone?

It seems a good idea.
Is dma zone is still necessay on most modern computers?

Best regards,
Conke @ AMD, Inc.

-----Original Message-----
From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Jun Sun
Sent: 2006年11月2日 10:16
To: linux-kernel@...r.kernel.org
Subject: Can Linux live without DMA zone?

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)?

Cheers.

Jun
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