swap or not?

[Alan Scheinine]

Galen Arnold wrote:
 > 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 recommend having swap space, perhaps half a gigabyte.  At the same time,
if a job uses alot of page, it must be killed without remorse.  To be
notified of the problem, I suppose (I have not tried it) you can
modify a script of Big Brother.  My point is, these days, when even
main memory is considered slow relative to level one cache, a job that
pages to disk will take a very, very long time to finish in comparison
to the same job with a smaller dataset that does not use swap.  On the
other hand, there may be jobs that need the extra space for a limited
amount of time, in which case the swap space would be useful.
Alan