And because there is nothing to gain, it is in addition really
trivial to fix the insane setups by simply undoing the nesting,
there is no downside for them.
I have to disagree with that. Deployment sometimes can be very
painful. In some cases, even flipping single parameter in sysfs
depending on kernel version takes considerable effort. The behavior
has been the contract that we offered userland for quite some time
now. We shouldn't be changing that underneath them without any clear
way for them to notice it.
Yes, and that's why once you deploy, you keep your updates to a minimum.
Because hell, even *perfectly legitimate bug fixes* can change your
behavior in a way you don't want. And you don't expect people to refrain
from fixing bugs because of that.
The only point where I agree with you is that it may indeed be
non-obvious to detect in case you were relying on the filesystem
hierarchy not being reflected in the controller hierarchy. But even
that depends on the usecase, whether it's a subtle performance
regression or a total failure to execute a previously supported
workload, which would be pretty damn obvious.
And imagine that happening in serveral thousand machine cluster with
fairly complicated cgroup setup and kernel update rolling out for
subset of machine types. I would be screaming bloody murder.
That is precisely why people in serious environments tend to run
-stable, distro LTSes, or anything like that. Because they don't want
any change, however minor, to potentially affect their stamped behavior.
I am not proposing this patch to -stable, btw...
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