Re: [PATCH] mm/huge_memory.c: introduce folio_split_unmapped

[Zi Yan]

On 13 Nov 2025, at 20:22, Balbir Singh wrote:

> Unmapped was added as a parameter to __folio_split() and related
> call sites to support splitting of folios already in the midst
> of a migration. This special case arose for device private folio
> migration since during migration there could be a disconnect between
> source and destination on the folio size.
>
> Introduce folio_split_unmapped() to handle this special case. Also
> refactor code and add __folio_freeze_and_split_unmapped() helper that
> is common to both __folio_split() and folio_split_unmapped().
>
> This in turn removes the special casing introduced by the unmapped
> parameter in __folio_split().
>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>
> Cc: Rakie Kim <rakie.kim@xxxxxx>
> Cc: Byungchul Park <byungchul@xxxxxx>
> Cc: Gregory Price <gourry@xxxxxxxxxx>
> Cc: Ying Huang <ying.huang@xxxxxxxxxxxxxxxxx>
> Cc: Alistair Popple <apopple@xxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Cc: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
> Cc: Nico Pache <npache@xxxxxxxxxx>
> Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
> Cc: Dev Jain <dev.jain@xxxxxxx>
> Cc: Barry Song <baohua@xxxxxxxxxx>
> Cc: Lyude Paul <lyude@xxxxxxxxxx>
> Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxxx>
> Cc: Simona Vetter <simona@xxxxxxxx>
> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Cc: Mika Penttilä <mpenttil@xxxxxxxxxx>
> Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
> Cc: Francois Dugast <francois.dugast@xxxxxxxxx>
>
> Suggested-by: Zi Yan <ziy@xxxxxxxxxx>
> Signed-off-by: Balbir Singh <balbirs@xxxxxxxxxx>
> ---
>  include/linux/huge_mm.h |   5 +-
>  mm/huge_memory.c        | 332 ++++++++++++++++++++++------------------
>  mm/migrate_device.c     |   3 +-
>  3 files changed, 191 insertions(+), 149 deletions(-)
>
LGTM. Acked-by: Zi Yan <ziy@xxxxxxxxxx>

Best Regards,
Yan, Zi