Re: [v2 01/11] mm/zone_device: support large zone device private folios

[David Hildenbrand <david@redhat.com>]

On 05.08.25 13:01, Balbir Singh wrote:
> On 8/5/25 20:57, David Hildenbrand wrote:
>> On 05.08.25 06:22, Balbir Singh wrote:
>>> On 7/30/25 19:50, David Hildenbrand wrote:
>>>
>>>> I think I asked that already but maybe missed the reply: Should these folios ever be added to the deferred split queue and is there any value in splitting them under memory pressure in the shrinker?
>>>>
>>>> My gut feeling is "No", because the buddy cannot make use of these folios, but maybe there is an interesting case where we want that behavior?
>>>>
>>>
>>> I realized I did not answer this
>>>
>>> deferred_split() is the default action when partial unmaps take place. Anything that does
>>> folio_rmap_remove_ptes can cause the folio to be deferred split if it gets partially
>>> unmapped.
>>
>> Right, but it's easy to exclude zone-device folios here. So the real question is: do you want to deal with deferred splits or not?
>>
>> If not, then just disable it right from the start.
>>
> 
> I agree, I was trying to avoid special casing device private folios unless needed to the extent possible

By introducing a completely separate split logic :P

Jokes aside, we have plenty of zone_device special-casing already, no 
harm in adding one more folio_is_zone_device() there.

Deferred splitting is all weird already that you can call yourself 
fortunate if you don't have to mess with that for zone-device folios.

Again, unless there is a benefit in having it.

-- 
Cheers,

David / dhildenb