linux-kernel - Re: [External] Re: [RFC] proc: Add a new isolated /proc/pid/mempolicy type.

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Date:   Mon, 26 Sep 2022 16:08:43 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Zhongkun He <hezhongkun.hzk@...edance.com>
Cc:     corbet@....net, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        wuyun.abel@...edance.com
Subject: Re: [External] Re: [RFC] proc: Add a new isolated
 /proc/pid/mempolicy type.

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@...edance.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.

> 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?
-- 
Michal Hocko
SUSE Labs