Re: [PATCH v2 6/7] x86, mm: Support huge I/O mappings on x86

From: Toshi Kani
Date: Wed Feb 18 2015 - 16:14:12 EST

On Wed, 2015-02-18 at 21:44 +0100, Ingo Molnar wrote:
> * Toshi Kani <toshi.kani@xxxxxx> wrote:
> > This patch implements huge I/O mapping capability interfaces on x86.
> > +#ifdef CONFIG_X86_64
> > +#else
> > +#endif
> > +#endif /* CONFIG_HUGE_IOMAP */
> Hm, so why is there a Kconfig option for this? It just
> complicates things.
> For example the kernel already defaults to mapping itself
> with as large mappings as possible, without a Kconfig entry
> for it. There's no reason to make this configurable - and
> quite a bit of complexity in the patches comes from this
> configurability.

This Kconfig option was added to disable this feature in case there is
an issue. That said, since the patchset also added a new nohugeiomap
boot option for the same purpose, I agree that this Kconfig option can
be removed. So, I will remove it in the next version.

An example of such case is with multiple MTRRs described in patch 0/7.
However, I believe it is very unlikely to have such platform/use-case,
and it can also be avoided by a driver creating a separate mapping for
each MTRR range.


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