Messages in this thread |  | | | Date | Tue, 21 Aug 2012 23:43:44 +0200 | | From | Lennart Poettering <> | | Subject | Re: [PATCH v6 3/4] cgroup: add xattr support |
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Heya,
(sorry for the late reply)
On 16.08.2012 22:00, Tejun Heo wrote: > On Thu, Aug 16, 2012 at 01:44:56PM -0400, aris@redhat.com wrote:
>>> Attaching meta information to services, in an easily discoverable >>> way. For example, in systemd we create one cgroup for each service, and >>> could then store data like the main pid of the specific service as an >>> xattr on the cgroup itself. That way we'd have almost all service state >>> in the cgroupfs, which would make it possible to terminate systemd and >>> later restart it without losing any state information. But there's more: >>> for example, some very peculiar services cannot be terminated on >>> shutdown (i.e. fakeraid DM stuff) and it would be really nice if the >>> services in question could just mark that on their cgroup, by setting an >>> xattr. On the more desktopy side of things there are other >>> possibilities: for example there are plans defining what an application >>> is along the lines of a cgroup (i.e. an app being a collection of >>> processes). With xattrs one could then attach an icon or human readable >>> program name on the cgroup. >>> >>> The key idea is that this would allow attaching runtime meta information >>> to cgroups and everything they model (services, apps, vms), that doesn't >>> need any complex userspace infrastructure, has good access control >>> (i.e. because the file system enforces that anyway, and there's the >>> "trusted." xattr namespace), notifications (inotify), and can easily be >>> shared among applications.
> > I'm not against this but unsure whether using kmem is enough for the > suggested use case. Lennart, would this suit systemd? How much > metadata are we talking about?
Just small things, like values, PIDs, i.e. a few 100 bytes or so per cgroup should be more than sufficient for our needs.
Lennart
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