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

Jeffrey B. Layton laytonjb at charter.net
Mon Aug 30 18:50:56 EDT 2004


Thanks Mike!

Think of this question as kind of a poll. I'm just looking for how
many people or how many apps swap.

Thanks!

Jeff

> Jeff,
>
> 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.
>>
>> Michael
>> 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.
>>>
>>> Glen
>>>
>>>
>>> Jeffrey B. Layton wrote:
>>>
>>>   
>>>
>>>> Hello,
>>>>
>>>> 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?
>>>>
>>>> Thanks!
>>>>
>>>> Jeff
>>>>
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>>>>     
>>>
>>
>>  
>>
>
>
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