linux-kernel - Re: [PATCHv2 3/5] mm/rmap: mlock large folios in try_to_unmap

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Message-ID: <27wxlfhnkxaat57lzyzlpo66vse3jjhp422ziswbl4oyjnamif@2jx25dwgkame>
Date: Fri, 19 Sep 2025 14:27:40 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Kiryl Shutsemau <kirill@...temov.name>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	David Hildenbrand <david@...hat.com>, Hugh Dickins <hughd@...gle.com>, 
	Matthew Wilcox <willy@...radead.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Rik van Riel <riel@...riel.com>, 
	Harry Yoo <harry.yoo@...cle.com>, Johannes Weiner <hannes@...xchg.org>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Kiryl Shutsemau <kas@...nel.org>
Subject: Re: [PATCHv2 3/5] mm/rmap: mlock large folios in try_to_unmap_one()

On Fri, Sep 19, 2025 at 01:40:34PM +0100, Kiryl Shutsemau wrote:
> From: Kiryl Shutsemau <kas@...nel.org>
> 
> 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@...nel.org>
> ---
>  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
>