Re: CONFIG_BIGMEM and rawio

Alan Cox (alan@lxorguk.ukuu.org.uk)
Fri, 3 Sep 1999 14:06:50 +0100 (BST)

> On Fri, 3 Sep 1999, Alan Cox wrote:
>
> >Raw I/O from PCI/ISA space to PCI/ISA space needs bounce buffers on plenty
> >of chipsets too
>
> If the bounce buffer means to pass through an additional piece of
> regular-memory, then let the bounce buffer to be the page-cache and don't
> use raw-io in first place.

But the user doesn't know which pages are currently bouncable or not. Not
using raw I/O has two problems
1. If 99% of your pages could be directly written you lost all
the speed
2. You still need the direct I/O uncached properties for some
applications like failover across shared disk

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