On Fri, Jan 09, 2026 at 12:28:22PM -0500, Zi Yan wrote: > On 9 Jan 2026, at 6:09, Mika Penttilä wrote: > > > Hi, > > > > On 1/9/26 10:54, Francois Dugast wrote: > > > >> From: Matthew Brost <[email protected]> > >> > >> Split device-private and coherent folios into individual pages before > >> freeing so that any order folio can be formed upon the next use of the > >> pages. > >> > >> Cc: Balbir Singh <[email protected]> > >> Cc: Alistair Popple <[email protected]> > >> Cc: Zi Yan <[email protected]> > >> Cc: David Hildenbrand <[email protected]> > >> Cc: Oscar Salvador <[email protected]> > >> Cc: Andrew Morton <[email protected]> > >> Cc: [email protected] > >> Cc: [email protected] > >> Cc: [email protected] > >> Signed-off-by: Matthew Brost <[email protected]> > >> Signed-off-by: Francois Dugast <[email protected]> > >> --- > >> mm/memremap.c | 2 ++ > >> 1 file changed, 2 insertions(+) > >> > >> diff --git a/mm/memremap.c b/mm/memremap.c > >> index 63c6ab4fdf08..7289cdd6862f 100644 > >> --- a/mm/memremap.c > >> +++ b/mm/memremap.c > >> @@ -453,6 +453,8 @@ void free_zone_device_folio(struct folio *folio) > >> case MEMORY_DEVICE_COHERENT: > >> if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->folio_free)) > >> break; > >> + > >> + folio_split_unref(folio); > >> pgmap->ops->folio_free(folio); > >> percpu_ref_put_many(&folio->pgmap->ref, nr); > >> break; > > > > This breaks folio_free implementations like nouveau_dmem_folio_free > > which checks the folio order and act upon that. > > Maybe add an order parameter to folio_free or let the driver handle the > > split?
'let the driver handle the split?' - I had consisder this as an option. > > Passing an order parameter might be better to avoid exposing core MM internals > by asking drivers to undo compound pages. > It looks like Nouveau tracks free folios and free pages—something Xe’s device memory allocator (DRM Buddy) cannot do. I guess this answers my earlier question of how Nouveau avoids hitting the same bug as Xe / GPU SVM with respect to reusing folios. It appears Nouveau prefers not to split the folio, so I’m leaning toward moving this call into the driver’s folio_free function. Matt > Best Regards, > Yan, Zi
