[GE users] Cannot make virtual_free consumable?

reuti reuti at staff.uni-marburg.de
Thu Nov 20 19:19:07 GMT 2008


Am 20.11.2008 um 19:00 schrieb Piotr Domagalski:

> <snip>
> To sum up, I did some more tests.
>
> I set virtual_free=4G but at the moment the load sensor reports 2G.
> This is just a test case but as far as I see this, it may happen that
> the actual amount of memory is lower than what GE thinks it is.
> According to the documentation, the lower value of load sensor and
> internal bookkeeping should be used (`man complex` says so). What
> seems strange to me is that:
>
> 1. When a job has -l vf=3G it is not run -- the value from load sensor
> (2G) is used.

Correct.

> 2. The system happily allows me to run 4 jobs each having -l vf=1G

Well, not really. If your job would really consume 1GB of memory,  
then the load sensor would reflect this. Hence also only two would be  
possible. For now you used just a "sleep 60" or alike in the jobscript?

> 3. The Advance Reservation doesn't consider the value from load
> sensors at all (i.e. I can have 4 ARs on this host each requiring 1G).

This is the same as above in 2. ?!?

It can't know, what the value of the load sensor will be in the  
future. Try to submit mit 5G - it will be rejected. OTOH: in this  
case the AR will be subtracted from the load sensor - but only for  
normal jobs, not jobs submitted into the AR. Submit an AR and then a  
normal job with a duration which falls into the AR and request too  
much memory, which would make the already granted AR invalid.

Therefore, it' always best if the specified virtual_free value  
renders the real installed memory.

-- Reuti


> But this I can understand, that it was chosen for simplicity.
>
> I'm so much confused as to the role of load sensors in these cases...
>
> -- 
> Piotr Domagalski
>
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