On Wed 15-01-14 16:11:40, Victor Porton wrote:
> 15.01.2014, 15:59, "Michal Hocko" <mhocko@xxxxxxx>:
> > [CCing cgroups mailing list]
> > On Wed 15-01-14 06:12:45, Victor Porton wrote:
> >
> >> I want to write software which needs to receive a signal when the cgroup
> >> created by it becomes empty. (After this the empty cgroup should be deleted
> >> just not to clutter the memory.)
> >>
> >> If the kernel does not support such notifications, it should be improved.
> >> This functionality is crucial for some kinds of software.
> >>
> >> There is /sys/fs/cgroup/systemd/release_agent but I don't understand how to
> >> use it. I don't understand why we would need it at all.
> >
> > "1.4 What does notify_on_release do ?" in
> > Documentation/cgroups/cgroups.txt the kernel source doesn't help?
>
> I've read it. I understand what it does. I don't understand how to use
> it in practice nor
You want to clean up your memcg without any tasks so the script might do
something like:
---
#!/bin/sh
CGROUP="$1"
CGROUP_MNT=`mount | grep cgroup | awk '{print $3}'`
rmdir "$CGROUP_MNT/$CGROUP"
---
> why it is done this way.
I find the interface rather awkward as well but that is a question for
those who have implement it.
The interface will change in the future (sorry I do not have any link to
discussion about the change handy).
> >> Starting a binary on emptying a cgroup with the purpose to notify an other
> >> binary looks like a big overkill.
> >
> > the binary can do rmdir which is what you want, no?
>
> I suppose a base package should do that, not my specific software. Do
> I understand right?
Yes. The notifier works on the root of the cgroup hierarchy so it is a
matter of the admin to set it.
> >> Also my program should work in userspace without the need to use
> >> release_agent which can be accessed only by root.
> >
> > The release_agent is global for all groups so the program doesn't have
> > to care.
>
> Again: What MY program should do?
Nothing. (assuming the only thing you are interested in is removing the
empty group).
[...]
--
Michal Hocko
SUSE Labs
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