On Mon, 20 Dec 2004, Linus Torvalds wrote:

(It may be _possible_ to avoid the warnings by just making "pud_t" and
"pmd_t" be the same type for such architectures, and just allowing
_mixing_ of three-level and four-level accesses.  I have to say that I 
consider that pretty borderline programming practice though).

Actually, I notice that this is exactly what you did, sorry for not being 
more careful about reading your defines.

Thinking some more about it, I don't much like the "mixing" of 3-level and
4-level things, but since the only downside is a lack of type-safety for
the 4-level case (ie you can get it wrong without getting any warning),
and since that type safety _does_ exist in the case where the four levels 
are actually used, I think it's ok. 

It would be bad if the architecture that supported 4level page tables was
really rare and broken (so that mistakes would happen and not get noticed
for a while), but I suspect x86-64 by now is probably the second- or
third-most used architecture, so it's not like the lack of type safety on 
other architectures where it doesn't matter would be a huge maintenance 
problem.

Color me convinced. 

Nick, can you see if such a patch is possible? I'll test ppc64 still 
working..

		Linus
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