Messages in this thread | | | Subject | Re: [PATCH 0/2] Support hugetlb charge moving at task migration | From | Baolin Wang <> | Date | Fri, 8 Oct 2021 17:17:12 +0800 |
| |
On 2021/10/8 15:12, Michal Hocko wrote: > On Thu 07-10-21 23:39:15, Baolin Wang wrote: >> 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. > > Could you be more specific please? What do you mean by cgroup usage is > incorrect? Ideally could you describe your usecase?
Sorry for confusing, what I mean is, when tasks from one hugetlb cgroup are migrated to a new hugetlb cgroup, the new hugetlb cgroup's hugetlb page usage is not increased accordingly. The issue I found is just from my testing for the hugetlb cgroup, and I think this is not resonable if we've already set a hugetlb limitation for a cgroup, but we always ignore it when tasks migration 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. > > The operation is quite expensive. Synchronization with charging is not > trivial. I do not have the full list handy but you can search the > mm mailing list archives for more information.
Sure, thanks.
> >>> 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? > > It would be good to describe those use cases and why they really need > this. Because as things stand now, the charge migration is not supported > in cgroup v2 for memory cgroup controller and there are no plans to add > the support so it would be quite unexpected that hugetlb controller > would behave differently. And cgroup v1 is considered legacy and new > features are ususally not added as there is a hope to move users to v2.
OK, understood. Seems you have a strong opinion that it is unnecessary to introduce this feature for cgroup v1 now, then I will drop this patch set. Thanks for your input.
| |