Fwd: [torqueusers] Confused about vmem

Tom Rudwick tomr at intrinsity.com
Fri Oct 3 14:01:42 MDT 2008


I think you want vmem=4G, so the total
memory of all tasks will be 4GB.

I don't know if it works correctly.
In your test 2, are you sure the memtests
were simultaneous? Or could they have been
done one after the other?

Tom


Diego M. Vadell wrote:
> Anyone? Any hint will be appreciated.
> 
> TIA
>  -- Diego
> 
> 
> ----------  Forwarded Message  ----------
> 
> Subject: [torqueusers] Confused about vmem
> Date: Monday 29 September 2008
> From: "Diego M. Vadell" <dvadell at linuxclusters.com.ar>
> To: torqueusers at supercluster.org
> 
> Hi list,
> 
>    We are starting to restrict the amount of RAM with torque. We have 4 cores 
> nodes with 4Gb of RAM.
> 
>    I made some tests with setting, via qmgr, a default of pvmem = 1Gb and it 
> seemed to be what we were looking for, until we considered a particular job.
> 
>    This job uses openMP. It is one process that needs a whole node: the 4Gb 
> and the 4 cores. 
> 
>    If I ask for nodes=1:ppn=4,pvmem=1G, torque will get me a whole node, but 
> it will kill this job's only process  when it uses more than 1G. If I ask for 
> nodes=1:ppn=4,pvmem=4G, torque will look for a node with 16Gb of RAM, and I 
> don't have one of those.
> 
>    So I found vmem. As I can't make lots of test right now (I have to schedule 
> downtime to do that safely) I made some little ones (with a program called 
> memtest that just malloc's and fills memory):
> 
> 1) Got an interactive session with vmem=1Gb and ran 1 memtest: 
> qsub -I -l nodes=1:ppn=2 -l vmem=1000mb
> Commmand line: examples/memtest 
> Result: malloc failure after 993 MiB
> Expected: This is Ok as vmem is the total amount of virtual memory the whole 
> job can use.
> 
> 2) Got an interactive session with vmem=1Gb and ran 2 memtest, in parallel: 
> qsub -I -l nodes=1:ppn=2 -l vmem=1000mb
> Command line: examples/memtest & examples/memtest   
> Result: malloc failure after 993 MiB
>            malloc failure after 993 MiB
> Expected: So both can allocate almost 1Gb! I was expecting them to die at 
> 500Mb, so they would sum the max 1Gb I asked torque.
> 
> 3) Got an interactive session with pvmem=1Gb and ran 2 memtest, in parallel: 
> qsub -I -l nodes=1:ppn=2 -l pvmem=1000mb
> Command line: examples/memtest & examples/memtest   
> Result: malloc failure after 993 MiB
>            malloc failure after 993 MiB
> Expected: This is what I was expecting because both can allocate about 1Gb.
> 
> So vmem and pvmem seem to do the same. What am I missing here?
> 
> Thanks in advance,
>  -- Diego.
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> torqueusers at supercluster.org
> http://www.supercluster.org/mailman/listinfo/torqueusers
> 
> 
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