[slurm-users] Cgroups and swap with 18.08.1?

[John Hearns]

After doing some Googling
https://jvns.ca/blog/2017/02/17/mystery-swap/  Swapping is weird and
confusing  (Amen to that!)
https://jvns.ca/blog/2016/12/03/how-much-memory-is-my-process-using-/
(interesting article)

>From the Docker documentation, below.
Bill - this is what you are seeing. Twice as much swap as real memory
usage.  So that seems to be a kernel default behaviour.
As you say the slurm logs say swap is set to 0 though.

https://docs.docker.com/config/containers/resource_constraints/#--memory-swap-details

f --memory-swap is unset, and --memory is set, the container can use twice
as much swap as the --memory setting, if the host container has swap memory
configured. For instance, if --memory="300m" and --memory-swap is not set,
the container can use 300m of memory and 600m of swap.

On Sat, 20 Oct 2018 at 03:39, Chris Samuel <chris at csamuel.org> wrote:

> On Tuesday, 16 October 2018 2:47:34 PM AEDT Bill Broadley wrote:
>
> > AllowedSwapSpace=0
> >
> > So I expect jobs to not use swap.  Turns out if I run a 3GB ram process
> with
> > sbatch --mem=1000 I just get a process that uses 1GB ram and 2GB of swap.
>
> That's intended.  The manual page says:
>
>        AllowedSwapSpace=<number>
>               Constrain  the  job cgroup swap space to this percentage of
> the
>               allocated memory.  The default value is 0, which means that
>               RAM+Swap will  be  limited  to  AllowedRAMSpace.
>
> You probably want this as well:
>
>        MemorySwappiness=<number>
>               Configure the kernel's priority for swapping out anonymous
> pages
>               (such as program data) verses file cache pages for the job
>               cgroup.  Valid  values are  between  0 and 100, inclusive. A
>               value of 0 prevents the kernel from swapping out program
> data.
>
> cheers!
> Chris
> --
>  Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC
>
>
>
>
>
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