linux-kernel - Re: Re: Re: Re: Re: Re: [PATCH v1] sched/numa: add per-process numa

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Message-ID: <20211117082952.GA3301@suse.de>
Date:   Wed, 17 Nov 2021 08:29:52 +0000
From:   Mel Gorman <mgorman@...e.de>
To:     Gang Li <ligang.bdlg@...edance.com>
Cc:     Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-api@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: Re: Re: Re: Re: Re: [PATCH v1] sched/numa: add per-process
 numa_balancing

On Wed, Nov 17, 2021 at 03:07:43PM +0800, Gang Li wrote:
> On 11/10/21 12:26 AM, Mel Gorman wrote:
> > 
> > Of those two, I agree with the second one, it would be tricky to implement
> > but the first one is less clear. This is based on an assumption. If prctl
> > exists to enable/disable NUMA baalancing, it's possible that someone
> > else would want to control NUMA balancing on a cgroup basis instead of
> > globally which would run into the same type of concerns -- different
> > semantics depending on the global tunable.
> > 
> 
> Hi!
> 
> You talk about the "semantics" of NUMA balancing between global, cgroup and
> process. While I read the kernel doc "NUMA Memory Policy", it occur to me
> that we may have a "NUMA Balancing Policy".
> 
> Since you are the reviewer of CONFIG_NUMA_BALANCING. I would like to discuss
> the need for introducing "NUMA Balancing Policy" with you. Is this worth
> doing?
> 

It's a bit vague but if you wanted to put together the outline, I'd read
over it. Note that this was all in the context of trying to introduce an
API like

Disable/enable per-process numa balancing:
        prctl(PR_NUMA_BALANCING, PR_SET_NUMA_BALANCING, 0/1);

i.e. one that controlled both enabling and disabling. You also have
the option of introducing the NUMAB equivalent of PR_SET_THP_DISABLE --
an API that is explicitly about disabling *only*.

-- 
Mel Gorman
SUSE Labs