Re: [PATCH mm-new v2 3/3] mm/khugepaged: merge PTE scanning logic into a new helper

[Dev Jain <dev.jain@arm.com>]

On 06/10/25 8:13 pm, Lance Yang wrote:
> +static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
> +		unsigned long addr, struct collapse_control *cc,
> +		struct folio **foliop, int *none_or_zero, int *unmapped,
> +		int *shared, int *scan_result)

Nit: Will prefer the cc parameter to go at the last.

> +{
> +	struct folio *folio = NULL;
> +	struct page *page = NULL;
> +
> +	if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
> +		(*none_or_zero)++;
> +		if (!userfaultfd_armed(vma) &&
> +		    (!cc->is_khugepaged ||
> +		     *none_or_zero <= khugepaged_max_ptes_none)) {
> +			return PTE_CHECK_CONTINUE;
> +		} else {
> +			*scan_result = SCAN_EXCEED_NONE_PTE;
> +			count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> +			return PTE_CHECK_FAIL;
> +		}
> +	} else if (!pte_present(pte)) {
> +		if (!unmapped) {
> +			*scan_result = SCAN_PTE_NON_PRESENT;
> +			return PTE_CHECK_FAIL;
> +		}
> +
> +		if (non_swap_entry(pte_to_swp_entry(pte))) {
> +			*scan_result = SCAN_PTE_NON_PRESENT;
> +			return PTE_CHECK_FAIL;
> +		}
> +
> +		(*unmapped)++;
> +		if (!cc->is_khugepaged ||
> +		    *unmapped <= khugepaged_max_ptes_swap) {
> +			/*
> +			 * Always be strict with uffd-wp enabled swap
> +			 * entries. Please see comment below for
> +			 * pte_uffd_wp().
> +			 */
> +			if (pte_swp_uffd_wp(pte)) {
> +				*scan_result = SCAN_PTE_UFFD_WP;
> +				return PTE_CHECK_FAIL;
> +			}
> +			return PTE_CHECK_CONTINUE;
> +		} else {
> +			*scan_result = SCAN_EXCEED_SWAP_PTE;
> +			count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> +			return PTE_CHECK_FAIL;
> +		}
> +	} else if (pte_uffd_wp(pte)) {
> +		/*
> +		 * Don't collapse the page if any of the small PTEs are
> +		 * armed with uffd write protection. Here we can also mark
> +		 * the new huge pmd as write protected if any of the small
> +		 * ones is marked but that could bring unknown userfault
> +		 * messages that falls outside of the registered range.
> +		 * So, just be simple.
> +		 */
> +		*scan_result = SCAN_PTE_UFFD_WP;
> +		return PTE_CHECK_FAIL;
> +	}
> +
> +	page = vm_normal_page(vma, addr, pte);

You should use vm_normal_folio here and drop struct page altogether - this was also
noted during the review of the mTHP collapse patchset.