linux-kernel - Re: [PATCH 1/3] Revert "mm/ksm: convert break_ksm() from walk_page_range_vma() to folio

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Message-ID: <57b83fd3-8a6c-4d98-bd6d-1c97c71b91a3@redhat.com>
Date: Wed, 29 Oct 2025 15:34:23 +0100
From: David Hildenbrand <david@...hat.com>
To: Pedro Demarchi Gomes <pedrodemargomes@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Xu Xin <xu.xin16@....com.cn>, Chengming Zhou <chengming.zhou@...ux.dev>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Revert "mm/ksm: convert break_ksm() from
 walk_page_range_vma() to folio_walk"

On 28.10.25 14:19, Pedro Demarchi Gomes wrote:
> This reverts commit e317a8d8b4f600fc7ec9725e26417030ee594f52 and changes
> PageKsm(page) to folio_test_ksm(page_folio(page)).
> 
> This reverts break_ksm() to use walk_page_range_vma() instead of
> folio_walk_start().
> This will make it easier to later modify break_ksm() to perform a proper
> range walk.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Pedro Demarchi Gomes <pedrodemargomes@...il.com>
> ---
>   mm/ksm.c | 63 ++++++++++++++++++++++++++++++++++++++++++--------------
>   1 file changed, 47 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 4f672f4f2140..2a9a7fd4c777 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -607,6 +607,47 @@ 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 page *page = NULL;
> +	spinlock_t *ptl;
> +	pte_t *pte;
> +	pte_t ptent;
> +	int ret;
> +
> +	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> +	if (!pte)
> +		return 0;
> +	ptent = ptep_get(pte);
> +	if (pte_present(ptent)) {
> +		page = vm_normal_page(walk->vma, addr, ptent);

folio = vm_normal_folio()

> +	} 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))
> +			page = pfn_swap_entry_to_page(entry);

folio = pfn_swap_entry_folio()

> +	}
> +	/* return 1 if the page is an normal ksm page or KSM-placed zero page */
> +	ret = (page && folio_test_ksm(page_folio(page))) || is_ksm_zero_pte(ptent);


The you can directly work with folios here.

-- 
Cheers

David / dhildenb