Re: [PATCH v12 9/9] cpuset: Support forced turning off of partition flag

From: Tejun Heo
Date: Mon Aug 27 2018 - 12:40:11 EST

Hello, Waiman.

On Mon, Aug 27, 2018 at 10:41:24AM -0400, Waiman Long wrote:
> Cpuset allows arbitrary modification of cpu list in "cpuset.cpus"
> even if the requested CPUs won't be granted in "cpuset.cpus.effective"
> as restricted by its parent. However, the validate_change() function
> will inhibit removal of CPUs that have been used in child cpusets.
> Being a partition root, however, limits the kind of cpu list
> modification that is allowed. Adding CPUs is not allowed if the new
> CPUs are not in the parent's effective cpu list that can be put into
> "cpuset.cpus.reserved". In addition, a child partition cannot exhaust
> all the parent's effective CPUs.
> Because of the implicit cpu exclusive nature of the partition root,
> cpu changes that break that cpu exclusivity will not be allowed. Other
> changes that break the conditions of being a partition root is generally
> allowed. However, the partition flag of the cpuset as well those of
> the descendant partitions will be forcefully turned off.

First of all, thanks a lot for your persistence. I'm not necessarily
against the flag being forced off but wonder whether the same
config/effective approach can be used as in .cpus and .mems. Can you
elaborate a bit on the choice here?

Thank you.