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    SubjectRe: msync() behaviour broken for MS_ASYNC, revert patch?
    Linus Torvalds wrote:
    >
    > On Fri, 10 Feb 2006, linux@horizon.com wrote:
    >
    >>No. MS_ASYNC says "I need the data written now.".
    >
    >
    > Says you.
    >
    > I say (and I have a decade of Linux historical behaviour to back it up)
    > that is says "I'm done, start flushing this out asynchronously like all
    > the other data I have written".
    >
    > And yes, there are performance implications. But your claim that "start IO
    > now" performs better is bogus. It _sometimes_ performs better, but
    > sometimes performs much worse.
    >
    > Take an example. You have a 200MB dirty area in a 1GB machine. You do
    > MS_ASYNC. What do you want to happen?
    >

    It quite obviously depends on the context in which one is using it,
    which will depend on what one expects it to do (unless one is an idiot).

    If linux@horizon.com's[1] database has dirtied 200MB of data and
    knows it will not dirty it again and has several hundred ms of useful
    work to do before it must call MS_SYNC, then...

    > Do you want IO to be started on all of it?

    ... yes.

    [1] Come on, linux, can you at least make up a name for me, or are
    you really called Linux? (in which case you'd better make up a
    new name anyway when arguing with Linus about Linux, for the
    sake of everyone's sanity)

    --
    SUSE Labs, Novell Inc.
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