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

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Message-ID: <YzLVTxGHgYp3Es4t@dhcp22.suse.cz>
Date:   Tue, 27 Sep 2022 12:49:51 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Abel Wu <wuyun.abel@...edance.com>
Cc:     Zhongkun He <hezhongkun.hzk@...edance.com>, corbet@....net,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [RFC] proc: Add a new isolated /proc/pid/mempolicy type.

On Tue 27-09-22 11:20:54, Abel Wu wrote:
[...]
> > > 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?
> 
> We want soft control on memory footprint of background jobs by applying
> NUMA preferences when necessary, so the impact on different NUMA nodes
> can be managed to some extent. These NUMA preferences are given by the
> control panel, and it might not be suitable to overwrite the tasks with
> specific memory policies already (or vice versa).

Maybe the answer is somehow implicit but I do not really see any
argument for the per thread-group semantic here. In other words why a
new interface has to cover more than the local [sg]et_mempolicy?
I can see convenience as one potential argument. Also if there is a
requirement to change the policy in atomic way then this would require a
single syscall.
-- 
Michal Hocko
SUSE Labs