[systemd-devel] RFC: Setting TasksMax= by default

Lennart Poettering lennart at poettering.net
Fri Nov 13 07:57:07 PST 2015

On Fri, 13.11.15 14:27, Zbigniew Jędrzejewski-Szmek (zbyszek at in.waw.pl) wrote:

> > b) I'd like to introduce DefaultTasksMax= that controls the default
> >    value of the per-unit TasksMax= by default, and would like it to
> >    set to some value such 1024 out-of-the-box. This will mean that any
> >    service or scope created will by default be limited to 1024
> >    tasks. This of course is a change from before that has the
> >    potential to break some daemons that maintain an excessive number
> >    of processes or threads. However, I think it's a much better choice
> >    to raise the limit for them, rather than stay unlimited for all
> >    services by default. I think 1024 is not particularly low, but also
> >    not particularly high. Note that the kernel by default limits the
> >    number of processes to 32K in total anyway.
> Shouldn't it be lower than 1024? For services which have many tasks,
> 1024 will not be enough, but for 99.9% of services it will be two
> orders of magnitude too many. I guess we can start with those
> settings, and the controller turned on, and then maybe readjust based
> on real-world usage.

What are you proposing? 256? 512?

(For comparison: if I read the docs right, then Apache defaults to
something between 256 and 400 max workers by default, depending on the
MPM you pick. If that's a good benchmark, then we should probably not
set our own max to anything below 512.)


Lennart Poettering, Red Hat

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