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From: Florian Weimer <fweimer@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	 Peter Zijlstra <peterz@infradead.org>,
	 Gabriele Monaco <gmonaco@redhat.com>,
	 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	 Michael Jeanson <mjeanson@efficios.com>,
	 Jens Axboe <axboe@kernel.dk>,
	 "Paul E. McKenney" <paulmck@kernel.org>,
	 "Gautham R. Shenoy" <gautham.shenoy@amd.com>,
	 Tim Chen <tim.c.chen@intel.com>,
	 TCMalloc Team <tcmalloc-eng@google.com>
Subject: Re: [patch 00/19] sched: Rewrite MM CID management
Date: Fri, 17 Oct 2025 13:31:39 +0200	[thread overview]
Message-ID: <lhuzf9plq78.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20251015164952.694882104@linutronix.de> (Thomas Gleixner's message of "Wed, 15 Oct 2025 19:29:23 +0200 (CEST)")

* Thomas Gleixner:

> The CID space compaction itself is not a functional correctness
> requirement, it is only a useful optimization mechanism to reduce the
> memory foot print in unused user space pools.
>
> The optimal CID space is:
>
>     min(nr_tasks, nr_cpus_allowed);
>
> Where @nr_tasks is the number of actual user space threads associated to
> the mm.
>
> @nr_cpus_allowed is the superset of all task affinities. It is growth
> only as it would be insane to take a racy snapshot of all task
> affinities when the affinity of one task changes just do redo it 2
> milliseconds later when the next task changes its affinity.

How can userspace obtain the maximum possible nr_cpus_allowed value?

Thanks,
Florian


  parent reply	other threads:[~2025-10-17 11:31 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-10-15 17:29 [patch 00/19] sched: Rewrite MM CID management Thomas Gleixner
2025-10-15 17:29 ` [patch 01/19] sched/mmcid: Revert the complex " Thomas Gleixner
2025-10-15 17:29 ` [patch 02/19] sched/mmcid: Use proper data structures Thomas Gleixner
2025-10-15 17:29 ` [patch 03/19] sched/mmcid: Cacheline align MM CID storage Thomas Gleixner
2025-10-15 17:29 ` [patch 04/19] sched: Fixup whitespace damage Thomas Gleixner
2025-10-15 17:29 ` [patch 05/19] sched/mmcid: Move scheduler code out of global header Thomas Gleixner
2025-10-15 17:29 ` [patch 06/19] sched/mmcid: Prevent pointless work in mm_update_cpus_allowed() Thomas Gleixner
2025-10-17 11:12   ` Peter Zijlstra
2025-10-17 12:49     ` Thomas Gleixner
2025-10-17 17:58       ` Peter Zijlstra
2025-10-17 18:19         ` Peter Zijlstra
2025-10-19 20:32           ` Thomas Gleixner
2025-10-20  8:22             ` Peter Zijlstra
2025-10-21 18:25               ` Thomas Gleixner
2025-10-15 17:29 ` [patch 07/19] cpumask: Introduce cpumask_or_weight() Thomas Gleixner
2025-10-15 17:41   ` Yury Norov
2025-10-15 18:06     ` Yury Norov
2025-10-21 20:21       ` Thomas Gleixner
2025-10-21 19:34     ` Thomas Gleixner
2025-10-15 17:29 ` [patch 08/19] sched/mmcid: Use cpumask_or_weight() Thomas Gleixner
2025-10-15 17:29 ` [patch 09/19] sched/mmcid: Convert mm CID mask to a bitmap Thomas Gleixner
2025-10-15 17:29 ` [patch 10/19] signal: Move MMCID exit out of sighand lock Thomas Gleixner
2025-10-15 17:29 ` [patch 11/19] sched/mmcid: Move initialization out of line Thomas Gleixner
2025-10-15 17:29 ` [patch 12/19] sched/mmcid: Provide precomputed maximal value Thomas Gleixner
2025-10-15 17:29 ` [patch 13/19] sched/mmcid: Serialize sched_mm_cid_fork()/exit() with a mutex Thomas Gleixner
2025-10-15 17:29 ` [patch 14/19] sched/mmcid: Introduce per task/CPU ownership infrastrcuture Thomas Gleixner
2025-10-15 17:29 ` [patch 15/19] sched/mmcid: Provide new scheduler CID mechanism Thomas Gleixner
2025-10-15 17:29 ` [patch 16/19] sched/mmcid: Provide CID ownership mode fixup functions Thomas Gleixner
2025-10-20  6:34   ` Thomas Gleixner
2025-10-20  9:13   ` Peter Zijlstra
2025-10-20  9:16   ` Peter Zijlstra
2025-10-20  9:27   ` Peter Zijlstra
2025-10-21 18:27     ` Thomas Gleixner
2025-10-15 17:29 ` [patch 17/19] irqwork: Move data struct to a types header Thomas Gleixner
2025-10-15 17:29 ` [patch 18/19] sched/mmcid: Implement deferred mode change Thomas Gleixner
2025-10-15 17:30 ` [patch 19/19] sched/mmcid: Switch over to the new mechanism Thomas Gleixner
2025-10-17  7:09 ` [patch 00/19] sched: Rewrite MM CID management Thomas Gleixner
2025-10-17 11:31 ` Florian Weimer [this message]
2025-10-17 12:56   ` Thomas Gleixner

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