Re: [patch 00/19] sched: Rewrite MM CID management

[Thomas Gleixner <tglx@linutronix.de>]

On Fri, Oct 17 2025 at 13:31, Florian Weimer wrote:
> * 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?

get_nprocs_conf(3), which reads /sys/devices/system/cpu/possible