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    SubjectRe: [RFC] transcendent memory for Linux
    Hi!

    This description (whole mail) needs to go into Documentation/, somewhere.

    > Normal memory is directly addressable by the kernel,
    > of a known normally-fixed size, synchronously accessible,
    > and persistent (though not across a reboot).
    ...
    > Transcendent memory, or "tmem" for short, provides a
    > well-defined API to access this unusual class of memory.
    > The basic operations are page-copy-based and use a flexible
    > object-oriented addressing mechanism. Tmem assumes

    Should this API be documented, somewhere? Is it in-kernel API or does
    userland see it?

    > "Preswap" IS persistent, but for various reasons may not always
    > be available for use, again due to factors that may not be
    > visible to the kernel (but, briefly, if the kernel is being
    > "good" and has shared its resources nicely, then it will be
    > able to use preswap, else it will not). Once a page is put,
    > a get on the page will always succeed. So when the kernel
    > finds itself in a situation where it needs to swap out a page,
    > it first attempts to use preswap. If the put works, a disk
    > write and (usually) a disk read are avoided. If it doesn't,
    > the page is written to swap as usual. Unlike precache, whether

    Ok, how much slower this gets in the worst case? Single hypercall to
    find out that preswap is unavailable? I guess that compared to disk
    access that's lost in the noise?
    Pavel

    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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