[Beowulf] Question: Who has apps that regularly swap?

Mike Davis jmdavis1 at vcu.edu
Sun Aug 29 21:09:08 PDT 2004


Since the answers to your question have thus far been somewhat less than 
relevant. I'll give it a try. We will sometimes run some large Gaussian 
calculations that run into swap. I try to get people to run these on SMP 
machines with large amounts of RAM (8-32GB) but they wind up on the 
clusters sometimes. I also have some researchers who have MC jobs that 
can run into swap on occassion as well.

Our researchers will run jobs on every processor available, even when 
its an old PIII. So the RAM varies. On my older clusters (dating to the 
time that you got your original one from Plogic as well) we only have 
512MB/node. These days I'm putting in 2GB/node and will raise that 
figure with our next machine.

Mike Davis (Who knows that Jeff is aware of swap issues and queuing but 
asked a question about swap)

Michael Will wrote:

>And then there are priority queues which allow newer high priority
>jobs to push aside lower priority jobs. They do not get canceled though
>but just SIGSTPed so that they can be resumed when the highpriority
>job is done. 
>Those would typically end up in swap until resumed, rather than reside
>in physical memory.
>On Sunday 29 August 2004 06:09 pm, Glen Gardner wrote:
>>In general, swapping is to be avoided. Typically , swapping begins when 
>>the machine runs short of memory (usually due to an application using 
>>too much memory during it's run).  A cluster with many nodes swapping is 
>>said to be "thrashing" and is operating very inefficiently. In that 
>>situation the cluster might begin to run so slowly as to be useless.  A 
>>program that causes swapping for long periods of time generally makes me 
>>worry about the life expectancy of the hard drives as well.
>>Jeffrey B. Layton wrote:
>>> I've been wanting to ask this question for some time. I'm wondering
>>>who has apps that regularly swap? Is it because the nodes don't have
>>>enough memory (i.e. haven't filled up all of the slots) or because the
>>>app just uses a lot of memory? Is it only when the app starts up, shuts
>>>down, or periodically when it is running?
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