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    SubjectRe: [PATCH] O_STREAMING - flag for optimal streaming I/O
    On Thu Oct 10, 2002 at 10:33:36AM +0200, Giuliano Pochini wrote:
    >
    > On 10-Oct-2002 Erik Andersen wrote:
    > > I don't think grep is a very good candidate for O_STREAMING. I
    > > usually want the stuff I grep to stay in cache. O_STREAMING is
    > > much better suited to applications like ogle, vlc, xine, xmovie,
    > > xmms etc since there is little reason for the OS to cache things
    > > like songs and movies you aren't likely to hear/see again any
    > > time soon.
    >
    > The kernel already have cache pruning algorithm. O_STREAMING logic
    > should not clear caches if there is no need to do that. We could

    The entire point of O_STREAMING is to let user space specify
    policy. If user space user space knows with 100% certainty that
    the data being read/written from a particular file descriptor is
    use-once-and-discard data, then it makes sense to honor that
    hint. In this case, user space knows best and can set policy on
    a per file descriptor basis.

    Note that most applications do not want to use this flag. But
    for a few applications it just just perfect. For example, if I
    am playing a DVD there is absolutely no point in the kernel
    trying to cache the content of the DVD. A DVD has way too much
    content for caching it to do any good, and since most people
    watch a DVD once through from beginning to end, there is no point
    stuffing the DVD's content into the pagecache, thereby crowding
    out other things that should remain in cache.

    -Erik

    --
    Erik B. Andersen http://codepoet-consulting.com/
    --This message was written using 73% post-consumer electrons--
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