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

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Date:   Thu, 7 Oct 2021 23:39:15 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Support hugetlb charge moving at task migration

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.