Re: remap allocator for per-CPU memory

["Jan Beulich" <JBeulich@novell.com>]

>>> Tejun Heo <teheo@novell.com> 13.05.09 15:29 >>>
>> (b) teach the pageattr code to handle the per-CPU virtual area similarly to
>> the kernel space for x86-64 (though it's going to be a little more complicated
>> since there's no pre-determined relation between the virtual and physical
>> addresses - the necessary lookup might become expensive on systems with
>> very many [possible] CPUs).
>
>Can you elaborate this a bit?  Let's sya there's quick way to match
>whether the page is part of the remapped large page, what can pageattr
>do differently then?  Applying the same attribute to both mappings?
>Failing or filtering set_memory_*()?

It would have to split the page. Perhaps there wouldn't be a need to apply the
new attribute to the page(s) that is(are) in the process of getting its(their)
attribute(s) changed; instead, just don't re-establish a 4k mapping for those
pages that aren't part of the per-CPU space.

And of course, the request should fail when it targets one of the pages that
are actually part of the per-CPU space -- but would be a BUG() anyway.

Jan