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    SubjectRe: [Patch] shm bug introduced with pagecache in 2.3.11
    Alan Cox wrote:
    >
    > > That said, I don't think this can/will be fixed for a 2.4 timeframe,
    > > especially as I haven't heard of any real-life usage where it would be an
    > > issue..
    >
    > News servers like Typhoon , high performance threaded web servers (eg Zeus)
    >

    Do you know if they are using mmap?

    >
    > Fortunately these guys tend to be using pretty serious I/O subsystems not
    > M/O disks and they are fine with 2.2.
    >

    I did a second test with a faster disk (SCSI-2-narrow 4.5 GB seagate),
    and the results were nearly identical: the mmap semaphore kill's around
    33% performance if I compare 64 threads with 64 processes. (33% slower
    or 50% faster, depending on your point of view)
    Please note that the test is extremely I/O bound, ie I defeat read-ahead
    with a RNG, and I only read one byte in every page, and the file is far
    larger than available memory.

    I'll try to find a faster drive (I had somewhere an old 10kRPM wide
    SCSI drive), but I would be surprised if the performance drop would be <
    30%.

    --
    Manfred


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