[PATCH v3 1/2] tools/xenstore: set oom score for xenstore daemon on Linux

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Juergen Gross writes ("[PATCH v3 1/2] tools/xenstore: set oom score for 
xenstore daemon on Linux"):
> Xenstored is absolutely mandatory for a Xen host and it can't be
> restarted, so being killed by OOM-killer in case of memory shortage is
> to be avoided.
> 
> Set /proc/$pid/oom_score_adj (if available) per default to -500 (this
> translates to 50% of dom0 memory size) in order to allow xenstored to
> use large amounts of memory without being killed.
...
> +## Type: integer
> +## Default: 50
> +#
> +# Percentage of dom0 memory size the xenstore daemon can use before the
> +# OOM killer is allowed to kill it.
> +#XENSTORED_OOM_MEM_THRESHOLD=50
> +
>  ## Type: string
>  ## Default: @LIBEXEC@/boot/xenstore-stubdom.gz

Thanks for working on this.  I approve of the principle.

I have one question about detail:

>       }
> +     [ -z "$XENSTORED_OOM_MEM_THRESHOLD" ] || XENSTORED_OOM_MEM_THRESHOLD=50
> +     XS_OOM_SCORE=-$(($XENSTORED_OOM_MEM_THRESHOLD * 10))
> +
> +     rm -f @XEN_RUN_DIR@/xenstored.pid
...
> +     XS_PID=`cat @XEN_RUN_DIR@/xenstored.pid`
> +     echo $XS_OOM_SCORE >/proc/$XS_PID/oom_score_adj

The effect of all this is that the value specified in
XENSTORED_OOM_MEM_THRESHOLD is transformed before being echoed into
/proc, by being multiplied by -10.

Of course an alternative would be to ask the user to specify the
tuneable directly but given its rather more obscure semantics I think
it is reasonable to have this done by the script.

But maybe we could add something to the doc comment ?

Eg
  # (The specified value is multiplied by -10 and echoed into
  # /proc/PID/oom_score_adj.)

?

Thanks,
Ian.