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    SubjectRe: Is sendfile all that sexy?
    On Mon, 22 Jan 2001, Helge Hafting wrote:

    > And when the next user wants the same webpage/file you read it from
    > the RAID again? Seems to me you loose the benefit of caching stuff in
    > memory with this scheme. Sure - the RAID controller might have some
    > cache, but it is usually smaller than main memory anyway.

    Hrm... good point. Using "main memory" (whose memory, on a NUMA box??) as
    a cache could be a performance boost in some circumstances. On the other
    hand, you're eating up a chunk of memory bandwidth which could be used for
    other things - even when you only cache in "spare" RAM, how do you decide
    who uses that RAM - and whether or not they should?

    There certainly comes a point at which not caching in RAM would be a net
    win, but ATM the kernel doesn't know enough to determine this.

    On a shared bus, probably the best solution would be to have the data sent
    to both devices (NIC and RAM) at once?

    > And then there are things like retransmissions...

    Hopefully handled by an intelligent NIC in most cases; if you're caching
    the file in RAM as well (by "CCing" the data there the first time) this is
    OK anyway.

    Something to think about, but probably more on-topic for linux-futures I
    suspect...


    James.

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