linux-kernel - Re: [PATCH] sched/numa: Fix NULL pointer access to mm

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Message-ID: <20250704082635.GD2001818@noisy.programming.kicks-ass.net>
Date: Fri, 4 Jul 2025 10:26:35 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Libo Chen <libo.chen@...cle.com>
Cc: "Chen, Yu C" <yu.c.chen@...el.com>, Michal Hocko <mhocko@...e.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>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tim Chen <tim.c.chen@...el.com>, linux-kernel@...r.kernel.org,
	Jirka Hladky <jhladky@...hat.com>,
	Srikanth Aithal <Srikanth.Aithal@....com>,
	Suneeth D <Suneeth.D@....com>
Subject: Re: [PATCH] sched/numa: Fix NULL pointer access to mm_struct durng
 task swap

On Thu, Jul 03, 2025 at 04:35:42PM -0700, Libo Chen wrote:

> Probably not as bad as you may think. Systems with one NUMA node or NUMA
> balancing disabled (which will be most of the machines) won't be affected
> by this at all , task_numa_migrate() is also ratelimited so it doesn't get
> touched nearly as often as most of other scheduler events.
> 
> If this is on a really hot and critical path that most of us have to take,
> such as wakeup, I won't argue with you at all. I don't want to be too
> persistent here, it's fine to use eBPF with the existing tracepoints. I
> just think this is convenient and doesn't really hurt those who don't care
> about these numbers. 

Its not about this one path per-se, more a general rant on the 'merit'
of endlessly adding statistics and accounting to code.