linux-kernel - Re: [PATCH RESEND v8 1/2] sched/numa: introduce per-cgroup NUMA locality info

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Message-ID: <20200221154706.GI18400@hirez.programming.kicks-ass.net>
Date:   Fri, 21 Feb 2020 16:47:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...e.de>
Cc:     ?????? <yun.wang@...ux.alibaba.com>,
        Ingo Molnar <mingo@...hat.com>,
        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>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Michal Koutn? <mkoutny@...e.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH RESEND v8 1/2] sched/numa: introduce per-cgroup NUMA
 locality info

On Fri, Feb 21, 2020 at 02:20:10PM +0000, Mel Gorman wrote:
> I fully acknowledge that this may have value for sysadmins and may be a
> good enough reason to merge it for environments that typically build and
> configure their own kernels. I doubt that general distributions would
> enable it but that's a guess.

OTOH, many sysadmins seem to 'rely' on BPF scripts and other such fancy
things these days.

 ( of course, we have the open question on what happens when we break
   one of those BPF 'important' scripts ... )

My main reservation with this patch is that it exposes, to userspace, an
ABI that is very hard to interpret and subject to implementation
details.

So while it can be disabled; people who have it enabled might suddenly
complain when we change the meaning/interpretation/whatever of these
magic numbers.

Michael; you seem to have ignored the tracepoint / BPF angle earlier in
this discussion; that is not something that could/would work for you?