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    SubjectRe: [PATCH 10/11] maps3: add /proc/kpagecount and /proc/kpageflags interfaces
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    On Mon, 2007-10-15 at 19:35 -0500, Matt Mackall wrote:
    > Perhaps we need something like:
    >
    > flags = page->flags;
    > userflags =
    > FLAG_BIT(USER_REFERENCED, flags & PG_referenced) |
    > ...
    >
    > etc. for the flags we want to export. This will let us change to
    >
    > FLAG_BIT(USER_SLAB, PageSlab(page)) |
    >
    > if we make a virtual slab bit.

    Yeah, that looks like a pretty sane scheme. Do we want to be any more
    abstract about it? Perhaps instead of USER_SLAB, it should be
    USER_KERNEL_INTERNAL, or USER_KERNEL_USE. The slab itself is going away
    as we speak. :)

    > And it shows up in grep.
    >
    > Unfortunately, i386 test_bit is an asm inline and not a macro so we
    > can't hope for the compiler to fold up a bunch of identity bit
    > mappings for us.

    We could also Yeah, that looks like a pretty sane scheme. Do we want to
    be any more abstract about it? Perhaps instead of USER_SLAB, it should
    be USER_KERNEL_INTERNAL, or USER_KERNEL_USE. The slab itself is going
    away as we speak.

    For the bits that we want to export, we could also add the unoptimized
    access functions for any that don't already have them:

    #define __ClearPageReserved(page) __clear_bit(PG_reserved, &(page)->flags)

    Anybody changing bit behavior will certainly go check all of the
    callers, such as ClearPageReserved() *and* __ClearPageReserved().

    -- Dave

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