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Thread: Do Memory & Swap Utilization % mean anything?

  1. #1
    Join Date
    Mar 2002
    Mesa, Arizona

    Do Memory & Swap Utilization % mean anything?

    I'm on Redhat and Suse systems. Seems like the old HP systems didn't use swap until things got bad.

    Memory and Swap are usually about 100% used regardless of system load according to 10g Grid Control & the OS (top & swapinfo)

    How can I tell actual memory or swap usage?

    How about pages in/out over a time period?

    Is there a utility for this?

    Then there's the system load. If we're at 37 average load, we're really at 100% capacity .. aka dead, unable to accept connections. Maybe I should apply a multiplier to this load number to get actual.

    Any ideas on realistically managing memory on Linux?

    "I do not fear computers. I fear the lack of them." Isaac Asimov
    Oracle Scirpts DBA's need

  2. #2
    Join Date
    Nov 2000
    First of all, top lies. It doesn't have a very good handle on shared memory.

    Second, having swap used is not always a bad thing. Processes can get swapped out and stay out thereby freeing up memory for other processes. You run into trouble when your active processes get swapped out to disk to make room for other processes which in turn get swapped out to disk so your process can get swapped back in.

    You can tell if you are swapping based on the io statistics and vmstat.

    On RHEL, si and so are your swap activity. si is the number of swap ins, and so is the number of swap outs. On a busy system, if your swapins + swapouts > 0 then you are swapping.

    Also, look how busy your swap device is. If you are actively swapping, it will be busy all the time. (Swap devices are usually either 0% busy or 90+% busy, at which point you are swapping).
    Jeff Hunter
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