Re: [PATCH] core-parking: shrink and relocate core_parking_cpunum[]

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.03.2026 15:20, Roger Pau Monné wrote:
> On Wed, Nov 12, 2025 at 04:38:13PM +0100, Jan Beulich wrote:
>> This NR_CPUS-dimensioned array is likely unused on most installations.
>> Therefore it is especially wasteful for it to consume more space than
>> really needed. Use the smallest possible type.
>>
>> Further the array having all fields set to -1 is actually useless. Nothing
>> relies on it, and core_parking_remove() doesn't restore the sentinel for
>> vacated slots. Drop the initializers, moving the array to .bss.
>>
>> Finally take the opportunity and update an adjacent variable's type, where
>> a fixed-width type was pretty clearly inappropriate to use.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> I assume there is a reason this is acting (mostly) as a LIFO. Else a
>> simple cpumask_t would suffice.
>>
>> An alternative would be to use the new BRK allocator, at least for NR_CPUS
>> above a certain threshold.
> 
> Can't we just allocate this memory using xvzalloc_array()?  If we do
> care about it being too big certainly allocating only when needed, and
> based on the number of possible CPUs on the system would be much
> better than playing games with the array type?

Hmm, yes, how did it not occur to me to dynamically allocate the array?
It can't be used ahead of core_parking_init(). (Not shrinking the array
element type will still be a little wasteful, but perhaps that's
acceptable to keep the code simple.)

Jan