Re: [PATCH v2 3/4] mm: internal: introduce FPB_LOCKLESS for folio_pte_batch_flags()

[David Hildenbrand (Arm)]

On 11/2/26 12:30, Yeoreum Yun wrote:
> From: Yuan-Hao Hsu <aa9736195201@xxxxxxxxx>
> 
> Add support for calling folio_pte_batch_flags() in GUP-fast context when we are
> not holding the PT lock. Instead of reading PTEs through ptep_get(), we have to
> use ptep_get_lockless().
> 
> Specify the new behavior through a new flag FPB_LOCKLESS. We'll make use of this
> functionality for batching PTEs in gup_fast_pte_range() next.
> 
> Signed-off-by: Yuan-Hao Hsu <aa9736195201@xxxxxxxxx>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
> ---
>  mm/internal.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index b4d0df4c35adf..c1824b0193f4d 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -373,6 +373,12 @@ typedef int __bitwise fpb_t;
>   */
>  #define FPB_MERGE_YOUNG_DIRTY		((__force fpb_t)BIT(4))
>  
> +/*
> + * Read the page table entries with ptep_get_lockless(): the caller does not
> + * hold the page table lock (e.g, GUP-fast).
> + */
> +#define FPB_LOCKLESS			((__force fpb_t)BIT(5))
> +
>  static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
>  {
>  	if (!(flags & FPB_RESPECT_DIRTY))
> @@ -442,7 +448,7 @@ static inline unsigned int folio_pte_batch_flags(struct folio *folio,
>  	ptep = ptep + nr;
>  
>  	while (nr < max_nr) {
> -		pte = ptep_get(ptep);
> +		pte = (flags & FPB_LOCKLESS) ? ptep_get_lockless(ptep) : ptep_get(ptep);
>  
>  		if (!pte_same(__pte_batch_clear_ignored(pte, flags), expected_pte))
>  			break;
> 

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David