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

Glen Beane beaneg at gandalf.umcs.maine.edu
Mon Aug 30 21:19:46 EDT 2004


We don't let our apps swap (we run diskless nodes with no swap)

Jeffrey B. Layton wrote:
> 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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> 
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