On 8/17/26 00:45, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <[email protected]>
>
> A PTE that is none and one that maps the shared zeropage both stand for
> a page of zeroes the mapping does not own. Code that cares only about
> the contents can treat the two alike.
>
> Move khugepaged's local helper for that test to pgtable.h, below the
> is_zero_pfn() it is built on.
>
> migrate_vma_insert_page() open-codes the same test on the slot it is
> about to fill. Convert it. It still tells none from the zeropage, but
> only to decide whether there is an old mapping to flush.
>
> No functional change intended.
>
> Assisted-by: Claude-Code:claude-opus-5
> Signed-off-by: Kiryl Shutsemau (Meta) <[email protected]>
> ---
> include/linux/pgtable.h | 17 +++++++++++++++++
> mm/khugepaged.c | 7 -------
> mm/migrate_device.c | 9 ++-------
> 3 files changed, 19 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 8c093c119e5a..bbee6d31f015 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -2064,6 +2064,23 @@ static inline struct page *_zero_page(unsigned long
> addr)
>
> #ifdef CONFIG_MMU
>
> +/**
> + * pte_none_or_zero - Does this PTE map nothing, or the shared zeropage?
> + * @pte: The page table entry to test.
> + *
> + * A PTE that is none and one that maps the shared zeropage both stand for a
> + * page of zeroes the mapping does not own, so code that only cares about the
> + * contents can treat them alike.
> + *
> + * Return: %true if @pte is none or maps the shared zeropage.
> + */
> +static inline bool pte_none_or_zero(pte_t pte)
> +{
> + if (pte_none(pte))
> + return true;
> + return pte_present(pte) && is_zero_pfn(pte_pfn(pte));
> +}
(casually skimming over some patches)
That's just a horrible function. :)
If there is no pte_zero() then there also shouldn't be a pte_none_or_zero().
And in the code-base we have "pte_t pte_zero = {0}" which actually makes sense,
but is not what we care about here.
Just have an additional helper like:
pte_maps_zero_page()
pte_is_zero_page()
pte_maps_zero_folio()
pte_is_zero_folio()
pte_zero_page()
pte_zero_folio()
And let the callers still spell both cases out.
if (pte_none(pte) || pte_is_zero_page(pte))
/* Do something amazing */
(we have both is_zero_page() and is_zero_folio() I assume "zero page" is cleaner
as this thing might soon no longer be a folio)
--
Cheers,
David
