On Tue, Apr 1, 2014 at 11:18 AM, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>
> I don't think it's sufficient to avoid collisions with bits used only
> with P=0. The original value of this bit must be retained when the
> _PAGE_NUMA bit is set/cleared.
>
> Bit 7 is PAT[2] and whilst Linux currently sets up the PAT such that
> PAT[2] is a 'don't care', there has been talk up adjusting the PAT to
> include more types. So I'm not sure it's a good idea to use bit 7.
>
> What's wrong with using e.g., bit 62? And not supporting this NUMA
> rebalancing feature on 32-bit non-PAE builds?
Sounds good to me, but it's not available in 32-bit PAE. The high bits
are all reserved, afaik.
But you'd have to be insane to care about NUMA balancing on 32-bit,
even with PAE. So restricting it to x86-64 and using the high bits (I
think bits 52-62 are all available to SW) sounds fine to me.
Same goes for soft-dirty. I think it's fine if we say that you won't
have soft-dirty with a 32-bit kernel. Even with PAE.
Linus
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