Re: [RFC] block layer support for DMA IOMMU bypass mode II

From: Grant Grundler (
Date: Wed Jul 02 2003 - 11:53:33 EST

On Wed, Jul 02, 2003 at 02:22:44AM +0200, Andi Kleen wrote:
> > What do you mean? You map only one 4K chunk, and this is used
> > for all the sub-1K mappings.
> How should this work when the 1K mappings are spread all over memory?

It couldn't merge in this case.

> Maybe I'm missing something but from James description it sounds like the
> block layer assumes that it can pass in a sglist with arbitary elements
> and get it back remapped to continuous DMA addresses.

In the x86-64 case, If the 1k elements are not physically contigous,
I think most of them would get their own mapping.

For x86-64, if an entry ends on a 4k alignment and the next one starts
on a 4k alignment, could those be merged into one DMA segment that uses
two adjacent mapping entries?

Anyway, using a 4k FS block size (eg ext2) would be more efficient
by allowing a 1:1 of SG elements and DMA mappings.


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