linux-kernel - Re: [External] Re: [PATCH] cgroup/cpuset: Add a new isolated mems.policy type.

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Message-ID: <120cb50d-d617-a60a-ec24-915f826318f1@bytedance.com>
Date:   Wed, 14 Sep 2022 23:10:47 +0800
From:   Zhongkun He <hezhongkun.hzk@...edance.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     hannes@...xchg.org, roman.gushchin@...ux.dev,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, lizefan.x@...edance.com,
        wuyun.abel@...edance.com
Subject: Re: [External] Re: [PATCH] cgroup/cpuset: Add a new isolated
 mems.policy type.

>>
>>> 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.