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    SubjectRe: Some questions about linux kernel.
    On Mon, 20 Mar 2000, David Whysong wrote:

    >On Mon, 20 Mar 2000, Richard B. Johnson wrote:
    >>The place where all of the system information is known is in "user
    >>space". The kernel readily "knows" stuff about the current process, but
    >>retrieving information about other tasks in a page-fault handler would
    >>result in an extremely poor performing machine. A user-space daemon can
    >>acquire information about all the tasks, can detect runaway tasks, can
    >>safeguard special tasks like Web Servers that haven't gone crazy, and
    >>can watch for performance hurting rogue programs.
    >>Such a program, if properly designed, is the solution to such
    >>out-of-memory conditions.
    >No! Or perhaps it depends on what you want this user-space daemon to do.

    Probably mlockall() and then wake up periodically checking for low-memory.
    If it gets below a certain threshold, use some magic voodoo heuristics
    (loaded from a configuration file likely) and kill something.

    >Once you reach the OOM condition, this program can not reliably run. And I
    >doubt that a user-space daemon could prevent OOM from happening on a time
    >sharing system, since a malicious (or buggy) program could try to use all
    >memory during a single timeslice.

    While everything else is paging to disk, I would assume the above program
    would get lots of time since it's the only thing left that can run. I
    haven't tried it, but it would make sense.

    -George Greer

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