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    SubjectRe: Frontswap [PATCH 0/4] (was Transcendent Memory): overview
    On 04/28/2010 08:55 AM, Pavel Machek wrote:
    >
    >> That's a reasonable analogy. Frontswap serves nicely as an
    >> emergency safety valve when a guest has given up (too) much of
    >> its memory via ballooning but unexpectedly has an urgent need
    >> that can't be serviced quickly enough by the balloon driver.
    >>
    > wtf? So lets fix the ballooning driver instead?
    >

    You can't have a negative balloon size. The two models are not equivalent.

    Balloon allows you to give up a page for which you have a struct page.
    Frontswap (and swap) allows you to gain a page for which you don't have
    a struct page, but you can't access it directly. The similarity is that
    in both cases the host may want the guest to give up a page, but cannot
    force it.

    > There's no reason it could not be as fast as frontswap, right?
    > Actually I'd expect it to be faster -- it can deal with big chunks.
    >

    There's no reason for swapping and ballooning to behave differently when
    swap backing storage is RAM (they probably do now since swap was tuned
    for disks, not flash, but that's a bug if it's true).

    --
    I have a truly marvellous patch that fixes the bug which this
    signature is too narrow to contain.



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