Re: [PATCH v3 1/3] Revert "mm/ksm: convert break_ksm() from walk_page_range_vma() to folio_walk"

[David Hildenbrand <dhildenb@redhat.com>]

On 05.11.25 18:27, Pedro Demarchi Gomes wrote:
> This reverts commit e317a8d8b4f600fc7ec9725e26417030ee594f52 and changes
> function break_ksm_pmd_entry() to use folios.
> 
> This reverts break_ksm() to use walk_page_range_vma() instead of
> folio_walk_start().
> Change break_ksm_pmd_entry() to call is_ksm_zero_pte() only if we know
> the folio is present, and also rename variable ret to found.
> This will make it easier to later modify break_ksm() to perform a proper
> range walk.
> 
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
> ---
>   mm/ksm.c | 64 ++++++++++++++++++++++++++++++++++++++++++--------------
>   1 file changed, 48 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 4f672f4f2140..de10ebcf3509 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -607,6 +607,48 @@ static inline bool ksm_test_exit(struct mm_struct *mm)
>   	return atomic_read(&mm->mm_users) == 0;
>   }
>   
> +static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next,
> +			struct mm_walk *walk)
> +{
> +	struct folio *folio = NULL;
> +	spinlock_t *ptl;
> +	pte_t *pte;
> +	pte_t ptent;
> +	int found;
> +
> +	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> +	if (!pte)
> +		return 0;
> +	ptent = ptep_get(pte);
> +	if (pte_present(ptent)) {
> +		folio = vm_normal_folio(walk->vma, addr, ptent);
> +	} else if (!pte_none(ptent)) {
> +		swp_entry_t entry = pte_to_swp_entry(ptent);
> +
> +		/*
> +		 * As KSM pages remain KSM pages until freed, no need to wait
> +		 * here for migration to end.
> +		 */
> +		if (is_migration_entry(entry))
> +			folio = pfn_swap_entry_folio(entry);
> +	}
> +	/* return 1 if the page is an normal ksm page or KSM-placed zero page */
> +	found = (folio && folio_test_ksm(folio)) || (pte_present(ptent)
> +		&& is_ksm_zero_pte(ptent));

Nit:

found = (folio && folio_test_ksm(folio)) ||
	(pte_present(ptent)&& is_ksm_zero_pte(ptent));

Thanks!

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>

-- 
Cheers

David