Messages in this thread | | | From | Nick Piggin <> | Subject | Re: Definition of x86 _PAGE_SPECIAL and sharing _PAGE_UNUSED1 | Date | Thu, 28 Aug 2008 10:32:30 +1000 |
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On Thursday 28 August 2008 05:02, Jeremy Fitzhardinge wrote: > _PAGE_SPECIAL is overloading _PAGE_UNUSED1. Does it really leave > _PAGE_UNUSED1 available for other uses, or does it become an exclusive > user of that flag. Under what circumstances can they be shared? > > arch/x86/mm/pageattr-test.c is now using _PAGE_UNUSED1 as the flag used > to make sure that huge pages are shattered properly (previously it used > _PAGE_GLOBAL). Is that going to clash with _PAGE_SPECIAL?
Ah... pity it was hidden away there and not put into the include file.
> In other words, should we drop _PAGE_UNUSED1 altogether, or at least > define how the its different users can coexist?
I don't feel strongly about it. But you should put your definition in pgtable.h (and possibly explain how it coexists with _SPECIAL).
> Am I right in supposing that _PAGE_SPECIAL can only be set on user pages?
Yes.
> (Also, "SPECIAL" is awfully generic. Was there really no more > descriptive name for this?)
I thought it was about on par with its counterpart, which is "normal". Either way, I don't think a casual reader would get an adequate idea of how it works in one word. normal ~= refcounted, special ~= !refcounted I guess, but it is slightly more than that and besides, normal was there first, and I think Linus coined it... if you can convince him to change it then you have my blessing to change special into whatever you want.
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