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

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Aug 05, 2025 at 02:58:42PM +0200, David Hildenbrand wrote:
> 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.

+1 on no deferred split for device folios.

Matt

> 
> -- 
> Cheers,
> 
> David / dhildenb
>