Re: Can Linux live without DMA zone?

[Phillip Susi]

Shouldn't only ancient ISA drivers be using GFP_DMA?  You know, ones 
that actually require it?  PCI drivers should not have this limit.

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)?
>
> Cheers.
>
> Jun

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