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    SubjectRe: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?]
    On Fri, May 03, 2002 at 12:30:09PM +0200, Andrea Arcangeli wrote:
    > Putting the mem_map in highmem would be the first step, after that you
    > should be just at at the 90% of work done to make it general purpose,
    > you should wrap most actions on the page struct with wrappers and it
    > will be quite an invasive change (much more invasive than pte-highmem),
    > but it could be done. For this one (unlike pte-highmem) you definitely
    > need a config option to select it, most people doesn't need this feature
    > enabled because they've less than 8G of ram and also considering it will
    > have a significant runtime cost.

    Invasive or not, if running is impossible without it, it must be done.

    This is a probable first order of business given that it is the single
    largest consumer of KVA with only really enough mitigation for
    bootability provided by my prior efforts at reducing the size of struct
    page. A clean, perhaps even mergeable design for this would be a great
    boon to all users of larger highmem systems. IIRC buffer_heads were the
    specific reported problem, and though they themselves consume excessive
    KVA only under some circumstances, they present a much greater danger
    in combination with the excessively large boot-time KVA allocation.

    Martin, can you take over? I've got plenty of ideas about what to code
    up, but you've actually got your hands on the machine and are knee-deep
    in the issues. I'm getting hit up for specifics I can't answer.

    Andrea, it might also be helpful to hear your input during the LSE
    conference call tomorrow. The topic is KVA exhaustion scenarios, which
    seem to be of interest to you as well.

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