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    SubjectRe: Linux and physical memory
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    Max <max@Linuz.sns.it> writes:
    >
    > Even if english is not my native language, I thought my question was clear:
    >
    > >> I don't understand why the kernel needs to always have all physical memory
    > >> mapped in its address space.
    >
    > I said "ALWAYS have mapped ALL physical memory" etc.
    >
    > So I obviously mean (well, lokkgin to your answer maybe it was not so obvious):
    >
    > Why can't the kernel just map in its address space the pieces of RAM it needs
    > for kernel code/data, and unmap them when done with them?
    > User code/data would always be accessible (I am not suggesting to touch user
    > processes address space) so I thought that could work and remove the 960MB
    > problem.
    >
    > Maybe that mapping/unmapping of memory in kernel address space is expensive,
    > but I don't know. So I posted the question.
    >
    > Massimiliano Ghilardi

    From my understanding of the buffer cache, a buffer can be anywhere in
    memory (excluding kernel code and data areas).

    And yes, mapping and unmapping is rather expensive because it involves
    messing with page tables.

    --
    Corey Minyard Internet: minyard@acm.org
    Work: minyard@nortel.ca UUCP: minyard@wf-rch.cirr.com

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