[slurm-users] Using free memory available when allocating a node to a job

Tue May 29 05:15:51 MDT 2018

Alexandre,  you have made a very good point here.  "Oftentimes users only
input 1G as they really have no idea of the memory requirements,"
At my last job we introduced cgroups.  (this was in PBSPro). We had to
enforce a minumum request for memory.
Users then asked us how much memory their jobs used - so that they could
request an amoutn of memory next time which would let the job run to
completion.
We were giving users information manually regarding how much memory their
jobs used.

I realise tha tthe tools are there for users to get the information on
memory usage after a job, but I really do not expec tusrs to have to figure
this out.
What do other sites do in this case?

On 29 May 2018 at 12:57, PULIDO, Alexandre <alexandre.pulido at ariane.group>
wrote:

> Hello John, this behavior is needed because the memory usage of the codes
> executed on the nodes are particularly hard to guess. Usually, when
> exceeded the ratio is between 1.1 and 1.3 more than expected. Sometimes
> much larger.
>
>
>
> A)     Indeed there is a partition running only exclusive jobs, but a
> large amounts of nodes are also needed working on an nonexclusive
> allocation. That’s why the exact amount of available memory is required in
> this configuration. Tasks are not killed if they take more than allocated.
>
> B)      Yes currently cgroup is configured and working as expected (I
> believe), but as I said tasks need to grow larger.
>
>
>
> Oftentimes users only input 1G as they really have no idea of the memory
> requirements, and with the high demand of HPC time a lower memory
> requirement is set so the job will start.
>
> So a job cannot be started on a node where another job would be filling up
> the RAM, and would start on another node.
>
>
>
> Would this behavior cause problems in the scheduling/allocation algorithms
> ? The way I see it the actual free memory would be just another consumable
> resource.
>
> But the only way I can see this working is by tweaking the plugin, correct
> ?
>
>
>
> Thank you for your inputs.
>
>
>
>
>
> *De :* slurm-users [mailto:slurm-users-bounces at lists.schedmd.com] *De la
> part de* John Hearns
> *Envoyé :* mardi 29 mai 2018 12:39
> *À :* Slurm User Community List
> *Objet :* Re: [slurm-users] Using free memory available when allocating a
> node to a job
>
>
>
> Also regarding memory, there are system tunings you can set for the
> behaviour of the OurOfMemory Killer and also the VM overcommit.
>
>
>
> I have seen the VM overcommit parameters being discussed elsewhere, and
> generally for HPC people advise to disable overcommit
>
> https://www.suse.com/support/kb/doc/?id=7002775
>
> This of course is very dependent on what your environment and applications
> are. Would you be able to say please what the problems you are having with
> memory?
>
>
>
>
>
>
>
>
>
>
>
>
>
> On 29 May 2018 at 12:26, John Hearns <hearnsj at googlemail.com> wrote:
>
> Alexandre,   it would be helpful if you could say why this behaviour is
> desirable.
>
> For instance, do you have codes which need a large amount of memory and
> your users are seeing that these codes are crashing because other codes
> running on the same nodes are using memory.
>
>
>
> I have two thoughts:
>
>
>
> A) enable job exclusive - ie run one job on one compute node. Then that
> job has all the memory.
>
> This is a very good way to run HPC in my experience.  Yes I know it is
> inefficient if there are lots of single core jobs.
>
> SO this depends on what your mix of jobs is.
>
>
>
> B) Have you considered implementing cgroups?  Then each job will be
> allocated memory and cpu cores.
>
> Jobs will not be able to grow larger than their allocated cgroup limits.
>
>
>
> I would really ask you to consider cgroups.
>
>
>
>
>
> On 29 May 2018 at 11:34, PULIDO, Alexandre <alexandre.pulido at ariane.group>
> wrote:
>
> Hi,
>
>
>
> in the cluster where I'm deploying Slurm the job allocation has to be
> based on the actual free memory available on the node, not just the
> allocated by Slurm. This is nonnegotiable and I understand that it's not
> how Slurm is designed to work, but I'm trying anyway.
>
>
>
> Among the solutions that I'm envisaging:
>
>
>
> 1) Create and update periodically a numerical node feature, with a string
> and a special character separating the wanted value (memfree_2048). This
> definitely seems like a mess to implement and too hacky, but is there an
> equivalent to PBS' numerical complexes and sensors in Slurm?
>
>
>
> 2) Modifying the select cons_res pluging to compare against the actual
> free memory instead of the allocated memory. Is it as simple as editing the
> "_add_job_to_res" (https://github.com/SchedMD/
> slurm/blob/master/src/plugins/select/cons_res/select_cons_res.c#L816)
> function and using the real left memory ? I don't want to break anything
> else so that's my main question here, if you can guide me towards the
> solution or other thoughts on its feasibility.
>
>
>
> Thanks a lot in advance!
>
>
>
> Best regards,
>
>
>
> [image: px]
>
> [image: px]
>
> *Alexandre PULIDO*
>
> [image: px]
>
> [image: arianegroup]
>
> [image: px]
>
> [image: px]
>
> [image: px]
>
>
>
>
>
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