[systemd-devel] [ANNOUNCE] systemd v238

[Lennart Poettering]

On Fr, 09.03.18 07:57, Umut Tezduyar Lindskog (umut at tezduyar.com) wrote:

> Hello Zbigniew,
> 
> On Mon, Mar 5, 2018 at 11:37 PM, Zbigniew Jędrzejewski-Szmek
> <zbyszek at in.waw.pl> wrote:
> > Hi,
> >
> > systemd-238 has been tagged.
> >
> > https://github.com/systemd/systemd/archive/v238/systemd-238.tar.gz
> >
> > CHANGES WITH 238:
> >
> >         * The MemoryAccounting= unit property now defaults to on. After
> >           discussions with the upstream control group maintainers we learnt
> >           that the negative impact of cgroup memory accounting on current
> >           kernels is finally relatively minimal, so that it should be safe to
> >           enable this by default without affecting system performance. Besides
> >           memory accounting only task accounting is turned on by default, all
> >           other forms of resource accounting (CPU, IO, IP) remain off for now,
> >           because it's not clear yet that their impact is small enough to move
> >           from opt-in to opt-out. We recommend downstreams to leave memory
> >           accounting on by default if kernel 4.14 or higher is are primarily
> >           used. On very resource constrained systems or when support for old
> >           kernels is a necessity, -Dmemory-accounting-default=false can be used
> >           to revert this change.
> 
> Are these optimisations for v1 or v2? Do you have more resource you
> can reference?

We made this change after discussing directly and personally with
Tejun, the upstream kernel cgroups go-to guy, who suggested it was OK
to turn it on now. Facebook has turned it on across its fleet now with
good results, and hence we came to the conclussion we can do the same
by default now.

Given that cgroups v1/v2 is primarily just a question of API (and not
controller implementation) I figure it should be fine on both, but
maybe ping Tejun directly.

Of course, I figure fb's fleet is very different from let#s say an
embedded device. If you play around with this on such devices from the
other end of the spectrum, please report issues if you do experience
major problems with this change of default after all...

Thanks,

Lennart

-- 
Lennart Poettering, Red Hat