swap or not?

Daniel Kidger Daniel.Kidger at quadrics.com
Tue Feb 5 06:59:46 PST 2002

-----Original Message-----
From: Galen Arnold [mailto:arnoldg at ncsa.uiuc.edu]

>I'm looking for some opinions (based on real cluster setups would be nice 
>too).  If you've got nodes with lots of memory (>1GB) do you run with swap 
>space configured or not?

>We're seeing the occasional run that misses its memory request by a lot 
>and it hangs nodes due to excessive paging.  

I think that opinion is quite divided here.

There are still religious issues with the virtual memory subsystem in Linux.
Even with swapoff, you can get kswapd taking lots of CPU time as memory
usage gets close to the physical limit.

Because some codes will leak memory by accident, use of 'ulimits' to limit
the max. address space a user program can use will probably help more than
having swap on or off. Also some resource managers / schedulers can police
excessive memory usage.


Dr. Dan Kidger, Quadrics Ltd.      daniel.kidger at quadrics.com
One Bridewell St., Bristol, BS1 2AA, UK         0117 915 5505
----------------------- www.quadrics.com --------------------

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