linux-kernel - Definition of x86 _PAGE_SPECIAL and sharing _PAGE

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Date:	Wed, 27 Aug 2008 12:02:08 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Ingo Molnar <mingo@...e.hu>, Hugh Dickens <hugh@...itas.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Definition of x86 _PAGE_SPECIAL and sharing _PAGE_UNUSED1

_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?

In other words, should we drop _PAGE_UNUSED1 altogether, or at least
define how the its different users can coexist?

Am I right in supposing that _PAGE_SPECIAL can only be set on user pages?

(Also, "SPECIAL" is awfully generic.  Was there really no more
descriptive name for this?)

    J
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