On Thu, Mar 1, 2012 at 4:04 PM, Mike Galbraith [off-list ref] wrote:

On Thu, 2012-03-01 at 16:02 -0500, Vivek Goyal wrote:

quoted

On Thu, Mar 01, 2012 at 09:26:43PM +0100, Mike Galbraith wrote:

quoted

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Q: you say systemd requires CONFIG_CGROUPS=y.  Why is that?  It's taking
over sysvinits job afaiui, what does that have to do with cgroups?

I think they were using it to track all the children forked by a service
and cleanup all of them if need be. So they just need it for logical
grouping functionality and don't require any controllers as such.

Hm.  Controllers are perhaps not required, but cpu controller was
configured and used without consent.  I didn't receive an offer.

AFAIK it does in fact only require `name` cgroup for it's own
monitoring purposes.  i believe the systemd folks also tried (and are
trying? see TODO) to get PR_SET_ANCHOR merged upstream:

https://lkml.org/lkml/2010/2/2/165

... which is a sort of recursive/persistent parenting flag; without
that or cgroups, there is no way to reliably supervise processes under
Linux.

the other problem is there is no way for a process to enumerate the
available cgroups -- IIRC a list had to be hard-coded in systemd
sources -- and mounting the cgroupfs without specifying a specific
subsystem simply mounts everything in one whack.

you should be able to tell systemd to ignore that specific controller,
or tell it to use existing mounts.  i for one have been using it
*exclusively* on my personal machines/home servers [archlinux] and am
very pleased ... it's very flexible and gives you an unprecedented
level of control and introspection into the system (man systemd.*) ...
i can create new services in about 3-5 lines.

... obviously this thread is not about systemd, but since it makes
such extensive use of cgroup facilities it only proves to highlight
it's deficiencies.  i think the notes and practices systemd has
established should be viewed as a good reference for what's clumsy, at
the very least, and should not be attributed to systemd, but to
cgroups.

-- 

C Anthony