Re: [PATCH 0/2] Support hugetlb charge moving at task migration

[Baolin Wang]

Hi Michal,

(Sorry for late reply due to my holidays)
On 2021/9/30 18:46, Michal Hocko wrote:
> On Wed 29-09-21 18:19:26, Baolin Wang wrote:
> > Hi,
> >
> > Now in the hugetlb cgroup, charges associated with a task aren't moved
> > to the new hugetlb cgroup at task migration, which is odd for hugetlb
> > cgroup usage.
>
> Could you elaborate some more about the usecase and/or problems you see
> with the existing semantic?

The problems is that, it did not check if the tasks can move to the new 
hugetlb cgroup if the new hugetlb cgroup has a limitation, and the 
hugetlb cgroup usage is incorrect when moving tasks among hugetlb cgroups.

> > This patch set adds hugetlb cgroup charge moving when
> > migrate tasks among cgroups, which are based on the memcg charge moving.
>
> Memcg charge moving has shown some problems over time and hence this is
> not part of cgroup v2 interface anymore. Even for cgroup v1 this has

Sorry, I missed this part, could you elaborate on the issues? I can have 
a close look about the problems of memcg charge moving.

> been an opt-in. I do not see anything like that in this patch series.
> Why should all existing workloads follow a different semantic during
> task migration now?

But I think it is reasonable for some cases moving the old charging to 
the new cgroup when task migration. Maybe I can add a new hugetlb cgroup 
file to control if need this or not?

Thanks for your comments.