Re: CONFIG_BIGMEM and rawio

Manfred Spraul (manfreds@colorfullife.com)
Thu, 02 Sep 1999 20:46:12 +0200

Andrea Arcangeli wrote:
> On Thu, 2 Sep 1999, Manfred wrote:
>
> >Im reading the BIGMEM codes, and it seems that BIGMEM and rawio are
> >incompatible.
> >Is that correct?
>
> The thing is not black and white.
> [...]
> Maybe it worth to add a per-blockdevice bitflag to allow raw-io on bigmem
> pages with devices that uses DMA (such devices won't need any internal
> change at all to work with bigmem pages, since with DMA only userspace and
> the hardware device (and not the kernel) will touch the bigmem memory).

This sounds like a good idea.

> And you can _safely_ use raw-io in a _stock_ 2.3.16 with bigmem enabled
> too; you won't risk to crash the kernel but you'll get a graceful -EIO in
> the _worst_ case.
But this means that all user mode programs which plan to use raw-io must
support fall-back to normal io. Even worse, [buggy] programs would run
on
test machines [with less memory], and fail in actual production [with
more
memory]. A bitflags would be a good idea.

--
	Manfred


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