Re: (reposting) how to get DMA'able memory within 4GB on 64-bit m achi ne

[David S. Miller]

Alan Cox writes:
 > > And when the IOMMU is "full" what happens to all the SAC only
 > > cards in the machine?  pci_map_{single,sg}() are not allowed
 > > to fail.
 > 
 > Thats something we already know has to be fixed. Its true with or without
 > an IOMMU that there may be cases where there is no free mapping space

True, but my intended point is that starving the SAC-only users then
returning DAC addresses to DAC-capable devices is just as unacceptable.

When we have one of these compute cluster cards in the box, and Jes's
suggested algorithm is used, the rest of the SAC devices in the box
would be totally screwed once the IOMMU fills up.

Later,
David S. Miller
[e-mail]