How to tell when a job is swapping?

Felix Rauch rauch at
Tue Feb 19 08:16:42 PST 2002

On Tue, 19 Feb 2002, Jeff Layton wrote:
>    I usually assume that if the free swap space falls below
> the maximum and load starts climbing that the node is
> swapping. However, when I talk to the user, he states that
> the code is running fine and the timing numbers are where
> they should be. So, I'm obviously interpreting something
> incorrectly (unless the job is really swapping but for some
> reason performance is unaffected).

When you start a job with big memory requirements, then the system
will swap out pages of other processes that are currently unused. If
these other processes are really idle, then this swapping out is done
only once at the beginning and it doesn't really hurt.

>    Does someone give me a could way to check if a job
> is swapping? Maybe a URL?

I've never done this for a whole cluster, but on single machines I
usually check with the "vmstat 1" command (look under the columns "si"
and "so" - "swap in" and "swap out").

- Felix
Felix Rauch                      | Email: rauch at
Institute for Computer Systems   | Homepage:
ETH Zentrum / RZ H18             | Phone: ++41 1 632 7489
CH - 8092 Zuerich / Switzerland  | Fax:   ++41 1 632 1307

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