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    SubjectRe: [PATCH] cfq-prio #2


    Jens Axboe wrote:

    >On Tue, Nov 11 2003, Nick Piggin wrote:
    >
    >>
    >>You acked the change actually :P
    >>I guess it was done in mainline when AS was merged.
    >>
    >
    >Probably missed the semantic change of may_queue.
    >

    Anyway I won't bother digging up the email, its been done now.

    >
    >>>>Maybe my version should be called elv_force_queue?
    >>>>
    >>>>
    >>>I just hate to see more of these, really. The original idea for
    >>>may_queue was just that, may this process queue io or not. We can make
    >>>it return something else, though, to indicate whether the process must
    >>>be able to queue. Is it really needed?
    >>>
    >>>
    >>Its quite important. If the queue is full, and AS is waiting for a process
    >>to submit a request, its got a long wait.
    >>
    >>Maybe a lower limit for per process nr_requests. Ie. you may queue if this
    >>queue has less than 128 requests _or_ you have less than 8 requests
    >>outstanding. This would solve my problem. It would also give you a much more
    >>appropriate scaling for server workloads, I think. Still, thats quite a
    >>change in behaviour (simple to code though).
    >>
    >
    >That basically belongs inside your may_queue for the io scheduler, imo.
    >

    You can force it to disallow the request, but you can't force it to allow
    one (depending on a successful memory allocation, of course).


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