Re: [PATCH v10 7/8] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst

Waiman Long
2022-05-04T16:02:19Z

On 5/4/22 07:25, Michal Koutný wrote:
> Hello.
>
> On Tue, May 03, 2022 at 12:21:48PM -0400, Waiman Long <longman@redhat.com> wrote:
>> Documentation/admin-guide/cgroup-v2.rst | 145 +++++++++++++-----------
>> 1 file changed, 79 insertions(+), 66 deletions(-)
> A note across various lines -- it seems your new text accidentally mixes
> both spaces and tabs for indentation.

You are right. I will fix that.

>
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index 69d7a6983f78..94e1e3771830 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> [...]
>> + The value shown in "cpuset.cpus.effective" of a partition root is
>> + the CPUs that the parent partition root can dedicate to the new
>> + partition root. They are subtracted from "cpuset.cpus.effective"
>> + of the parent and may be different from "cpuset.cpus"
> I find this paragraph a bit hard to comprehend (I read it as it talks
> about three levels of cgroups (parent, child, grandparent). It is
> correct but I'd suggect following formulation (where I additionally
> simplifed it by talking about "available" cpus):
>
>> The value shown in "cpuset.cpus.effective" of a partition root is
>> the CPUs that the partition root can dedicate to a potential new child
>> partition root. The new child subtracts available CPUs from its parent
>> "cpuset.cpus.effective".

Thanks for the suggestion, will modify the text as suggested.

>
>> + For a partition root to become valid, the following conditions
>> + must be met.
>> +
>> + 1) The "cpuset.cpus" is exclusive, i.e. they are not shared by
>> + any of its siblings (exclusivity rule).
>> + 2) The parent cgroup is a valid partition root.
>> + 3) The "cpuset.cpus" is not empty and must contain at least
>> + one of the CPUs from parent's "cpuset.cpus", i.e. they overlap.
>> + 4) The "cpuset.cpus.effective" must be a subset of "cpuset.cpus"
>> + and cannot be empty unless there is no task associated with
>> + this partition.
> This sounds good to me.
>
>> + Care must be taken to change a valid partition root to "member"
>> + as all its child partitions, if present, will become invalid.
> This does not talk about recovering. Is it intentional? (I.e. to left
> implementation defined)

This new patch series does have the ability to recover now.  I am just
not emphasizing the recovery aspect of it in the doc file. I will add a
sentence about it.

>
> Except the remarks above, I find the concepts described here good. I'll
> reply to implementation separately & later.

Thanks,
Longman