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SubjectRe: CONFIG_BIGMEM and rawio
Hi,

On Fri, 03 Sep 1999 01:25:06 +0200, Manfred Spraul
<manfreds@colorfullife.com> said:

> "Stephen C. Tweedie" wrote:
>> Exactly why it needs to be per-device. Once the high memory limit is
>> raised above 4G, this will become even more important as not all devices
>> will physically be able to support 64-bit PCI addressing.

> I doubt that bounce buffers are necessary for 4 GB:
> * most fast disk controllers use DMA
> * noone would combine a 4 GB memory computer with an old IDE disk.

There are PCI controllers which ignore the high bit of the address
line. Their limit is 2GB. Above that they need bounce buffers. Sad
but true.

> * raw-io does not set the blocksize for VFS mounts, but it ignores md
> volumes and swap partitions.
> * "mount -t ext2 /dev/swappartition" makes swapping unstable.

Yes, I know about this --- one possible answer is to require swapping to
take out a VFS registration rather than to do it at the device layer.

--Stephen

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