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Date:   Wed, 14 Sep 2022 23:10:47 +0800
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Subject: Re: [External] Re: [PATCH] cgroup/cpuset: Add a new isolated
 mems.policy type.
From:   Zhongkun He <hezhongkun.hzk@bytedance.com>
To:     Michal Hocko <mhocko@suse.com>
Cc:     hannes@cmpxchg.org, roman.gushchin@linux.dev,
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        linux-mm@kvack.org, lizefan.x@bytedance.com,
        wuyun.abel@bytedance.com
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>>
>>> Back to the previous question.
>>>> The question is how to implement that with a sensible semantic.
>>>
>>> Thanks for your analysis and suggestions.It is really difficult to add
>>> policy directly to cgroup for the hierarchical enforcement. It would 
>>> be a good idea to add pidfd_set_mempolicy.
>>
>> Are you going to pursue that path?

> Hi Michal, thanks for your suggestion and reply.
> 
>  > Are you going to pursue that path?
> 
> Yes，I'll give it a try as it makes sense to modify the policy dynamically.
> 
> Thanks.

Hi Michal, i have a question about pidfd_set_mempolicy, it would be 
better if you have some suggestions.

The task_struct of processes and threads are independent. If we change 
the mempolicy of the process through pidfd_set_mempolicy, the mempolicy 
of its thread will not change. Of course users can set the mempolicy of 
all threads by iterating through /proc/tgid/task.

The question is whether we should override the thread's mempolicy when 
setting the process's mempolicy.

There are two options:
A:Change the process's mempolicy and set that mempolicy to all it's threads.
B:Only change the process's mempolicy in kernel. The mempolicy of the 
thread needs to be modified by the user through pidfd_set_mempolicy in
userspace, if necessary.

Thanks.