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

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Message-ID: <b96a326c-7ca7-4cfe-96e2-28c1dad5c9dc@intel.com>
Date: Thu, 3 Jul 2025 21:38:08 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: 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>, Libo Chen
	<libo.chen@...cle.com>
Subject: Re: [PATCH] sched/numa: Fix NULL pointer access to mm_struct durng
 task swap

Hi Peter,

On 7/3/2025 8:36 PM, Peter Zijlstra wrote:
> On Thu, Jul 03, 2025 at 05:20:47AM -0700, Libo Chen wrote:
> 
>> I agree. The other parts, schedstat and vmstat, are still quite helpful.
>> Also tracepoints are more expensive than counters once enabled, I think
>> that's too much for just counting numbers.
> 
> I'm not generally a fan of eBPF, but supposedly it is really good for
> stuff like this.
> 
> Attaching to a tracepoint and distributing into cgroup buckets seems
> like it should be a trivial script.

Yes, it is feasible to use eBPF. On the other hand, if some
existing monitoring programs rely on /proc/{pid}/sched to observe
the NUMA balancing metrics of processes, it might be helpful to
include the NUMA migration/swap information in /proc/{pid}/sched.
This approach can minimize the modifications needed for these
monitoring programs, eliminating the need to add a new BPF script
to obtain NUMA balancing statistics from different sources IMHO.


thanks,
Chenyu