linux-kernel - Re: [PATCH 5/6] cgroup/cpuset: optimize cpuset_mems_allowed

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Date: Tue, 14 May 2024 12:55:41 -0400
From: Waiman Long <longman@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Ben Segall <bsegall@...gle.com>,
 Daniel Bristot de Oliveira <bristot@...hat.com>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Imran Khan <imran.f.khan@...cle.com>, Ingo Molnar <mingo@...hat.com>,
 Johannes Weiner <hannes@...xchg.org>, Juri Lelli <juri.lelli@...hat.com>,
 Leonardo Bras <leobras@...hat.com>, Mel Gorman <mgorman@...e.de>,
 Peter Zijlstra <peterz@...radead.org>, Rik van Riel <riel@...riel.com>,
 Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>,
 Valentin Schneider <vschneid@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Zefan Li <lizefan.x@...edance.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH 5/6] cgroup/cpuset: optimize
 cpuset_mems_allowed_intersects()

On 5/14/24 12:50, Tejun Heo wrote:
> On Tue, May 14, 2024 at 12:47:59PM -0400, Waiman Long wrote:
>>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>>> index 4237c8748715..47ed206d4890 100644
>>> --- a/kernel/cgroup/cpuset.c
>>> +++ b/kernel/cgroup/cpuset.c
>>> @@ -5010,6 +5010,9 @@ EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);
>>>    int cpuset_mems_allowed_intersects(const struct task_struct *tsk1,
>>>    				   const struct task_struct *tsk2)
>>>    {
>>> +	if (tsk1 == tsk2)
>>> +		return 1;
>>> +
>>>    	return nodes_intersects(tsk1->mems_allowed, tsk2->mems_allowed);
>>>    }
>> Reviewed-by: Waiman Long <longman@...hat.com>
> I'm not sure this is worth the added code.

Yes, I do have a second thought afterward. The only caller of 
cpuset_mems_allowed_intersects() is oom_cpuset_eligible() in 
mm/oom_kill.c. So I believe a better fix is to avoid calling 
cpuset_mems_allowed_intersects() there if current == tsk.

Cheers,
Longman