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core: don't use the unified hierarchy for the systemd cgroup yet #4628
Nov 10, 2016
Can we please not play games of toggling this all the time. Please fix this properly, add the configure switch, and leave this enabled by default.
I am pretty sure this should stay on by default, and it should be on distros to turn it off, but we should make it easy for them by providing said configure switch plus an explanation in NEWS. But playing ping-pong and turning it off and on every second version is just wrong...
@martinpitt any chance you can prep a proper fix for this that adds such a switch and turns it on again? thanks!
Just posted #4670 which puts cgroup v2 systemd hierarchy on /sys/fs/cgroup/systemd-cgroup2 (any idea for a better name?) while maintaining the "name=systemd" hierarchy on /sys/fs/cgroup/systemd in parallel. This should avoid issues with most tools. For the ones which fail to parse if there's an entry for the v2 hierarchy in /proc/$PID/cgroup, I have no idea yet.
I didn't because IMHO a configure switch is the worst way; a runtime switch is a much lower barrier for both affected users for which it breaks, and developers of lxc, docker, and friends to try out the unified hiearchy without rebuilding. Also, it's another doubling of combinatorial explosion of which we don't test the other half.
I'd actually prefer reverting the revert and let unified cgroups be always on in upstream releases, and only revert it downstream. But if you still want that even after #4670, I'll add a configure option.
A compile time switch doesn't prohibt a kernel cmdline switch. This was discussed before, there should be a compile-time default selectable via a configure switch, and then there should be a kernel cmdline switch that overrides that if set.