Re: [patch] bootmem: use MAX_DMA_ADDRESS instead of LOW32LIMIT

From: Martin Schwidefsky
Date: Fri Jul 28 2006 - 10:56:24 EST

On Fri, 2006-07-28 at 15:13 +0200, Ingo Molnar wrote:
> > -#define LOW32LIMIT 0xffffffff
> > if ((ptr = __alloc_bootmem_core(bdata, size,
> > - align, goal, LOW32LIMIT)))
> > + align, goal, MAX_DMA_ADDRESS)))
> but this limits things to 16MB on i686. Are you sure this wont break
> anything?

That is something we should not do. MAX_DMA_ADDRESS is not the correct
value, it says something about the DMA limitations. LOW32LIMIT says
something about the cpu addressing limitations which is a completly
different thing. I think it would be best to introduce an architecture
overridable define like LOW_ADDRESS_LIMIT. The default is 4GB-1, for
s390 it is 2GB-1. The current name is misleading LOW32LIMIT indicates
that the address for alloc_bootmem_low objects has 32 bits, which isn't
true for s390.

blue skies,

Martin Schwidefsky
Linux for zSeries Development & Services
IBM Deutschland Entwicklung GmbH

"Reality continues to ruin my life." - Calvin.

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