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SubjectRe: [PATCH] x86: mtrr cleanup for converting continuous to discrete layout v5
On Mon, Apr 28, 2008 at 7:42 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Mon, 28 Apr 2008 15:05:05 -0700 Yinghai Lu <yhlu.kernel.send@gmail.com> wrote:
>
> >
> > some BIOS like to use continus MTRR layout, and may X driver can not add
> > WB entries for graphical cards when 4g or more RAM installed.
> >
> > the patch will change MTRR to discrete.
> >
> > mtrr_chunk_size= could be used to have smaller continuous block to hold holes.
> > default is 256m, could be set according to size of graphics card memory.
> >
> > v2: fix -1 for UC checking
> > v3: default to disable, and need use enable_mtrr_cleanup to enable this feature
> > skip the var state change warning.
> > remove next_basek in range_to_mtrr()
> > v4: correct warning mask.
> > v5: CONFIG_MTRR_SANITIZER
> >
> > Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
>
>
> > +#ifdef CONFIG_MTRR_SANITIZER
> > +
> > +#ifdef CONFIG_MTRR_SANITIZER_ENABLE_DEFAULT
>
> I don't think these newly-added config items should exist, sorry. But
> then, the changelog does't describe _why_ they exist (it should!) and I
> probably missed it in the discusson.
>
> Anyone who distributes a kernel will need to enable both
> CONFIG_MTRR_SANITIZER and CONFIG_MTRR_SANITIZER_ENABLE_DEFAULT, so the
> config items are only useful for saving a bit of kernel text in custom
> kernel builds.
>
>
> > +static int enable_mtrr_cleanup __initdata = 1;
> > +#else
> > +static int enable_mtrr_cleanup __initdata;
>
> The disable_mtrr_cleanup and enable_mtrr_cleanup boot options are also
> problematic. We really really want this stuff to all happen automatically.
>
> What happens with this sort of thing is that people's machines misbehave
> and I expect most of them never find out about the magic option. They
> give up on Linux or use a different computer or use a different distro
> which happened to set the option the other way, etc, etc. Some people will
> think to do a bit of googling and might stumble across the option after a
> while.
>
> It's all rather user-unfriendly and we should try really hard to just make
> things work. Is this at all possible?

Eric or Andi said it is too risky to touch mtrr.

>
>
> Anyway. I think the problem which you have identified is solveable in
> userspace, isn't it? Read the existing mtrr settings and rewrite them in a
> better form? If so, we could prepare a little program which does that and
> make the X people and distributors aware of it. This has the significant
> advantage that it will fix pre-2.6.26 kernels too.

sounds good.

YH


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