[Beowulf] Question: Who has apps that regularly swap?
Jeffrey B. Layton
laytonjb at charter.net
Mon Aug 30 18:50:56 EDT 2004
Think of this question as kind of a poll. I'm just looking for how
many people or how many apps swap.
> 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,
>>>> down, or periodically when it is running?
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