On Wed, Dec 15, 2021 at 11:29:41AM -0500, Waiman Long [off-list ref] wrote:

There are additional checks for the member to partition transition which
requires that the target cpuset shouldn't have child cpuset.

Ah, I forgot the transition condition no. 4 will apply here. Clear.

So, currently full bottom up + top down walk is needed in (rare?) case
the switch from root partition to member and back.

That prevents the recovering of a invalid partition root under a
member cpuset. We could certainly remove that restriction by adding
additional code as well as additional tests to verify it works. I
haven't done that simply to avoid adding more complexity to the
current code.

I agree this restriction can be lifted later independently when the rest
settles.  (It's not so different from controllers disabling on the
unified hierarchy after all.)


Thanks,
Michal