Re: [v6 04/15] mm/huge_memory: implement device-private THP splitting

[David Hildenbrand]

On 16.09.25 14:21, Balbir Singh wrote:
> Add support for splitting device-private THP folios, enabling fallback
> to smaller page sizes when large page allocation or migration fails.
>
> Key changes:
> - split_huge_pmd(): Handle device-private PMD entries during splitting
> - Preserve RMAP_EXCLUSIVE semantics for anonymous exclusive folios
> - Skip RMP_USE_SHARED_ZEROPAGE for device-private entries as they
>    don't support shared zero page semantics
>
> Signed-off-by: Balbir Singh <balbirs@xxxxxxxxxx>
> 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>
> ---
>   mm/huge_memory.c | 138 +++++++++++++++++++++++++++++++++--------------
>   1 file changed, 98 insertions(+), 40 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 78166db72f4d..5291ee155a02 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2872,16 +2872,18 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>   	struct page *page;
>   	pgtable_t pgtable;
>   	pmd_t old_pmd, _pmd;
> -	bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
> -	bool anon_exclusive = false, dirty = false;
> +	bool soft_dirty, uffd_wp = false, young = false, write = false;
> +	bool anon_exclusive = false, dirty = false, present = false;
>   	unsigned long addr;
>   	pte_t *pte;
>   	int i;
> +	swp_entry_t swp_entry;

Not renaming this variable avoids a lot of churn below. So please keep 
it called "entry" in this patch.

--
Cheers

David / dhildenb