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    SubjectRe: [PATCH]Fix broken VMI in 2.6.27-rc..
    Jeremy Fitzhardinge wrote:
    >> The Linux kernel was never a paragon of perfection - it was never
    >> meant to be. Just because a bit of cruft went unnoticed into the
    >> kernel doesn't mean we shouldn't fix it.
    > I don't really see what the issue is.
    > Fixmaps are primarily used for things that need to be mapped early
    > before we can allocate address space dynamically. They're predominantly
    > used for boot-time init, and rarely on any performance-critical path.
    > The only vaguely regular use a fixmap gets during runtime is poking at
    > apics, and that's dominated by IO time, and kmap_atomic. Statically,
    > there's only 100 references in the kernel. And it only affects 32-bit.
    > Having fixmaps at link-time fixed addresses would be nice, I suppose,
    > but hardly worth going to vast effort over.

    No, but it's hardly vast effort, either.

    >>>> Given the x86 architecture, it's inevitable that PV will want to
    >>>> reserve address space at the top of memory, and therefore the fixmap
    >>>> area needs to be moved out of that space.
    >>> OK. But there's a few places where the code uses FIXADDR_TOP to mean
    >>> "top of kernel address space", so we'd need to come up with a proper
    >>> symbol for that.
    >> I suggest KERNEL_TOP.
    > Fine by me. It would be easy to plug KERNEL_TOP/__KERNEL_TOP in now,
    > and then fix up fixmap independently.

    Yes, and we should add a symbol for the bottom of the 1:1 area as well
    (to disambiguate it from TASK_SIZE).


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      Last update: 2008-08-08 02:19    [W:0.022 / U:97.160 seconds]
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