On 03/05/2024 01:50, Barry Song wrote:
> From: Barry Song <v-songbaohua@xxxxxxxx>
>
> There could arise a necessity to obtain the first pte_t from a swap
> pte_t located in the middle. For instance, this may occur within the
> context of do_swap_page(), where a page fault can potentially occur in
> any PTE of a large folio. To address this, the following patch introduces
> pte_move_swp_offset(), a function capable of bidirectional movement by
> a specified delta argument. Consequently, pte_increment_swp_offset()
You mean pte_next_swp_offset()?
> will directly invoke it with delta = 1.
>
> Suggested-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> ---
> mm/internal.h | 25 +++++++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index c5552d35d995..cfe4aed66a5c 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -211,18 +211,21 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
> }
>
> /**
> - * pte_next_swp_offset - Increment the swap entry offset field of a swap pte.
> + * pte_move_swp_offset - Move the swap entry offset field of a swap pte
> + * forward or backward by delta
> * @pte: The initial pte state; is_swap_pte(pte) must be true and
> * non_swap_entry() must be false.
> + * @delta: The direction and the offset we are moving; forward if delta
> + * is positive; backward if delta is negative
> *
> - * Increments the swap offset, while maintaining all other fields, including
> + * Moves the swap offset, while maintaining all other fields, including
> * swap type, and any swp pte bits. The resulting pte is returned.
> */
> -static inline pte_t pte_next_swp_offset(pte_t pte)
> +static inline pte_t pte_move_swp_offset(pte_t pte, long delta)
We have equivalent functions for pfn:
pte_next_pfn()
pte_advance_pfn()
Although the latter takes an unsigned long and only moves forward currently. I
wonder if it makes sense to have their naming and semantics match? i.e. change
pte_advance_pfn() to pte_move_pfn() and let it move backwards too.
I guess we don't have a need for that and it adds more churn.
Anyway:
Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> {
> swp_entry_t entry = pte_to_swp_entry(pte);
> pte_t new = __swp_entry_to_pte(__swp_entry(swp_type(entry),
> - (swp_offset(entry) + 1)));
> + (swp_offset(entry) + delta)));
>
> if (pte_swp_soft_dirty(pte))
> new = pte_swp_mksoft_dirty(new);
> @@ -234,6 +237,20 @@ static inline pte_t pte_next_swp_offset(pte_t pte)
> return new;
> }
>
> +
> +/**
> + * pte_next_swp_offset - Increment the swap entry offset field of a swap pte.
> + * @pte: The initial pte state; is_swap_pte(pte) must be true and
> + * non_swap_entry() must be false.
> + *
> + * Increments the swap offset, while maintaining all other fields, including
> + * swap type, and any swp pte bits. The resulting pte is returned.
> + */
> +static inline pte_t pte_next_swp_offset(pte_t pte)
> +{
> + return pte_move_swp_offset(pte, 1);
> +}
> +
> /**
> * swap_pte_batch - detect a PTE batch for a set of contiguous swap entries
> * @start_ptep: Page table pointer for the first entry.
