Re: [PATCHv2 3/5] mm/rmap: mlock large folios in try_to_unmap_one()

[Shakeel Butt]

On Fri, Sep 19, 2025 at 01:40:34PM +0100, Kiryl Shutsemau wrote:
> From: Kiryl Shutsemau <kas@xxxxxxxxxx>
> 
> Currently, try_to_unmap_once() only tries to mlock small folios.
> 
> Use logic similar to folio_referenced_one() to mlock large folios:
> only do this for fully mapped folios and under page table lock that
> protects all page table entries.
> 
> Signed-off-by: Kiryl Shutsemau <kas@xxxxxxxxxx>
> ---
>  mm/rmap.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 3d0235f332de..482e6504fa88 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1870,6 +1870,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>  	unsigned long nr_pages = 1, end_addr;
>  	unsigned long pfn;
>  	unsigned long hsz = 0;
> +	int ptes = 0;
>  
>  	/*
>  	 * When racing against e.g. zap_pte_range() on another cpu,
> @@ -1910,10 +1911,26 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>  		 */
>  		if (!(flags & TTU_IGNORE_MLOCK) &&
>  		    (vma->vm_flags & VM_LOCKED)) {
> +			ptes++;
> +			ret = false;
> +
> +			/* Only mlock fully mapped pages */
> +			if (pvmw.pte && ptes != pvmw.nr_pages)
> +				continue;
> +
> +			/*
> +			 * All PTEs must be protected by page table lock in
> +			 * order to mlock the page.
> +			 *
> +			 * If page table boundary has been cross, current ptl
> +			 * only protect part of ptes.
> +			 */
> +			if (pvmw.flags & PVMW_PGTABLE_CROSSSED)
> +				goto walk_done;

Should it be goto walk_abort?

> +
>  			/* Restore the mlock which got missed */
> -			if (!folio_test_large(folio))
> -				mlock_vma_folio(folio, vma);
> -			goto walk_abort;
> +			mlock_vma_folio(folio, vma);
> +			goto walk_done;

Here too?

>  		}
>  
>  		if (!pvmw.pte) {
> -- 
> 2.50.1
>