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Date:   Wed, 28 Sep 2022 16:39:21 -0700
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Subject: Re: [External] Re: [RFC] proc: Add a new isolated /proc/pid/mempolicy
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To:     Michal Hocko <mhocko@suse.com>,
        Zhongkun He <hezhongkun.hzk@bytedance.com>
Cc:     corbet@lwn.net, akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        wuyun.abel@bytedance.com
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 <YzGya2Q3iuWS2WdM@dhcp22.suse.cz>
From:   Randy Dunlap <rdunlap@infradead.org>
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Hi--

On 9/26/22 07:08, Michal Hocko wrote:
> On Mon 26-09-22 20:53:19, Zhongkun He wrote:
>>> [Cc linux-api - please do so for any patches making/updating
>>> kernel<->user interfaces]
>>>
>>>
>>> On Mon 26-09-22 17:10:33, hezhongkun wrote:
>>>> From: Zhongkun He <hezhongkun.hzk@bytedance.com>
>>>>
>>>> /proc/pid/mempolicy can be used to check and adjust the userspace task's
>>>> mempolicy dynamically.In many case, the application and the control plane
>>>> are two separate systems. When the application is created, it doesn't know
>>>> how to use memory, and it doesn't care. The control plane will decide the
>>>> memory usage policy based on different reasons.In that case, we can
>>>> dynamically adjust the mempolicy using /proc/pid/mempolicy interface.
>>>
>>> Is there any reason to make it procfs interface rather than pidfd one?
>>
>> Hi michal,  thanks for your reply.
>>
>> I just think that it is easy to display and adjust the mempolicy using
>> procfs. But it may not be suitable, I will send a pidfd_set_mempolicy patch
>> later.
> 
> proc interface has many usability issues. That is why pidfd has been
> introduced. So I would rather go with the pidfd interface than repeating
> old proc API mistakes.

Sorry, I'm not familiar with the pidfd interface and I can't find any
documentation on it. Is there some?

Can I 'cat' or 'grep' in the pidfd interface?

>> Btw.in order to add per-thread-group mempolicy, is it possible to add
>> mempolicy in mm_struct?
> 
> I dunno. This would make the mempolicy interface even more confusing.
> Per mm behavior makes a lot of sense but we already do have per-thread
> semantic so I would stick to it rather than introducing a new semantic.
> 
> Why is this really important?

Thanks.

-- 
~Randy