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Confused as to the point of this.

Confused as to the point of this.

Posted Jun 25, 2013 5:24 UTC (Tue) by suckfish (guest, #69919)
In reply to: Confused as to the point of this. by mezcalero
Parent article: Changes coming for systemd and control groups

Ugghh. cgroups are a powerful tool for general administration and integration purposes. That's normally done by things like shell scripting, and the hierarchical model exposed & manipulated via the file-system is pretty convenient to access via shell scripting.

I wonder, if cgroups had been single-writer when systemd was conceived, would systemd have been written as the one-and-only single writer or would it have found a way to cooperate more democratically with other users?


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Confused as to the point of this.

Posted Jun 25, 2013 5:52 UTC (Tue) by dlang (subscriber, #313) [Link]

single hierarchy != single writer

There's no reason to force a single writer just because they are eliminating the confusion of contradictory hierarchies.

Confused as to the point of this.

Posted Jul 6, 2013 22:22 UTC (Sat) by eternaleye (subscriber, #67051) [Link]

No. Tejun Heo, the cgroups maintainer, *explicity* wants single-writer - because as he's said, "Cgroup doesn't and will not support delegation of subtrees to different security domains."[1]

[1] http://permalink.gmane.org/gmane.linux.kernel.cgroups/6899

Confused as to the point of this.

Posted Jul 6, 2013 22:25 UTC (Sat) by eternaleye (subscriber, #67051) [Link]

He links to http://thread.gmane.org/gmane.linux.kernel.cgroups/6638 which has some further info. This may be the most damning for what you would like to do, dlang:

* The configurations aren't independent. e.g. for weight-based
controllers, your weight is only meaningful in relation to other
weights at that level. Distributing configuration to whatever
entities which may write to cgroupfs simply cannot work. It's
fundamentally flawed.

That means that anyone could set a stupidly high weight, and starve their peers. You could do double-nesting hacks to isolate that, sure, but that gets painful and stupid very quickly.

Confused as to the point of this.

Posted Jul 6, 2013 22:27 UTC (Sat) by eternaleye (subscriber, #67051) [Link]

Even worse: You only have that subtree mounted, so you can't see your peers' weights. So you are *actually incapable* of knowing what weights even *would* be 'stupidly high' and starve your peers (or stupidly *low* and starve yourself)


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