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    SubjectRe: patch cow-swapin [was Re: Very bad swap bug -- 2.0, 2.1 at least]

    On Sat, 26 Sep 1998 19:46:53 +0200 (CEST), Andrea Arcangeli
    <> said:

    > Please Alan be _sure_ to not apply my swapin-parent patch to 2.0.36
    > because I had a problem now (it not crashed but I' ve seen some not happy
    > prink and I rebooted istanteneously with 35 because it' s production
    > machine...).

    Which printks, exactly?

    There is a problem with your patch: you effectively fault the parent
    process without taking the mm->mmap_sem lock. Currently, the only code
    which is allowed to do that is the swapout code. I'm not entirely sure
    what the consequences are of doing a swapin without that lock, but I'm
    certain I don't want to risk changing that invariant for 2.0.

    > Stephen, do you think that I am wasting time fixing the swapin-parent
    > code for 2.0? It would be better to backport the new cache code? Or
    > all you like to live with the ugly swapin but sure safe?

    I'm sure I don't want to see new mm code in 2.0. I might be willing to
    see the swap cache stuff back-ported, because on its own the swap cache
    patches are relatively self-contained, do not change performance in
    other ways, and are pretty well tested by now.

    I'd still prefer to stay on the safe side and not make any such changes
    at all to 2.0. However, this can be a major performance problem in
    certain situations, and it would be nice to have it cleared up.


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