[GE users] Cannot make virtual_free consumable?

Piotr Domagalski piotr.domagalski at gmail.com
Thu Nov 20 18:00:09 GMT 2008


On Thu, Nov 20, 2008 at 5:40 PM, Piotr Domagalski
<piotr.domagalski at gmail.com> wrote:
> On Thu, Nov 20, 2008 at 2:16 PM, reuti <reuti at staff.uni-marburg.de> wrote:
>> Am 20.11.2008 um 13:51 schrieb Piotr Domagalski:
>>
>>> On Thu, Nov 20, 2008 at 11:39 AM, reuti <reuti at staff.uni-
>>> marburg.de> wrote:
>>>>> I've attached this complex to my host:
>>>>>
>>>>>   szalik at photon:~$ qconf -se photon
>>>>>   complex_values        virtual_free=4G
>>>>>
>>>>>   szalik at photon:~$ qstat -F |grep virtual_free
>>>>>       hc:virtual_free=2.087G
>>>>
>>>> is there anything else running on this machine and consuming memory,
>>>> although not requested? virtual_free is a guidance for SGE and will
>>>> not be enforced.
>>>
>>> Let me explain my understanding of this consumable complex. I thought
>>> that I could set virtual_free to 4G or any other higher value just as
> Hmm, reading:
>
> http://wikis.sun.com/display/GridEngine/Configuring+Complex+Resource+Attributes
>
> There's a note saying:
>
> "virtual_free is one of the standard load parameters of the Grid
> Engine system. The additional availability of recent memory statistics
> is taken into account automatically by the system in the virtual
> memory capacity planning. If the load report for free virtual memory
> falls below the value obtained by Grid Engine software internal
> bookkeeping, the load value is used to avoid memory
> over-subscription."

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