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

[Zbigniew Jędrzejewski-Szmek]

On Fri, Nov 13, 2015 at 04:57:07PM +0100, Lennart Poettering wrote:
> 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?
I'm proposing to turn it on, and gather statistics ;)

> (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.)

Zbyszek