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From:   =?UTF-8?B?5p2O5riv?= <ligang.bdlg@bytedance.com>
Date:   Tue, 9 Nov 2021 16:28:28 +0800
Message-ID: <CAMx52ARF1fVH9=YLQMjE=8ckKJ=q3X2-ovtKuQcoTyo564mQnQ@mail.gmail.com>
Subject: Re: Re: Re: [PATCH v1] sched/numa: add per-process numa_balancing
To:     Mel Gorman <mgorman@suse.de>
Cc:     Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        linux-api@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org
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Hi, sorry for the late reply.

On Fri, Oct 29, 2021 at 4:37 PM Mel Gorman <mgorman@suse.de> wrote:
>
> My point is that as it stands,
> prctl(PR_NUMA_BALANCING,PR_SET_NUMA_BALANCING,1) either does nothing or
> fails. If per-process numa balancing is to be introduced, it should have
> meaning with the global tuning affecting default behaviour and the prctl
> affecting specific behaviour.
>

If the global tuning affects default behaviour and the prctl
affects specific behaviour.  Then when prctl specifies
numa_balancing for a process, there is no way for the
global tuning to affect that process. In other words, global tuning
become a default value, not a switch for global numa_balancing.

My idea is that the global numa_balancning still has absolute control, and prctl
can only optionally turn off numa_balancing for process when the global is on.
After all, It is more common to enable global numa_balancing and disable it in
several processes than to disable global numa_balancing and enable it in
several processes.

This is my personal opinion, what do you think.
:-)

Do we need the global to be a switch, or a default value?