Re: PATCH: Further aacraid work
From: Christoph Hellwig
Date: Thu Jun 17 2004 - 08:29:22 EST
On Thu, Jun 17, 2004 at 02:07:13PM +0100, Matthew Wilcox wrote:
> It's a hard problem. Where's the right tradeoff? I have a system that
> has a memory map that puts the first 3.75GB of memory at 0, then the
> next 256MB at 64GB, then continues from 4GB. If there's only 4GB of
> RAM in that system, I'm sure you'd rather use 32-bit descriptors and
> anything in that 256MB gets bounce-buffered.
With the SGI iommu it doesn't matter how much memory you have anyway,
if you're using DAC you'll always get high bits set in your dma address.
I suspect many other iommus work the same.
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