linux-kernel - Re: [PATCHv2 1/5] mm/page_vma_mapped: Track if the page is mapped across page table boundary

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Message-ID: <7qkpt4ia3qryjp2xo2ywy7qydav6nijghasr7biwctd5ah7dat@t3epq5dzt2sd>
Date: Fri, 19 Sep 2025 13:25:36 -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 1/5] mm/page_vma_mapped: Track if the page is mapped
 across page table boundary

On Fri, Sep 19, 2025 at 01:40:32PM +0100, Kiryl Shutsemau wrote:
> From: Kiryl Shutsemau <kas@...nel.org>
> 
> Add a PVMW_PGTABLE_CROSSSED flag that page_vma_mapped_walk() will set if
> the page is mapped across page table boundary. Unlike other PVMW_*
> flags, this one is result of page_vma_mapped_walk() and not set by the
> caller.
> 
> folio_referenced_one() will use it detect if it safe to mlock the folio.
> 
> Signed-off-by: Kiryl Shutsemau <kas@...nel.org>

Reviewed-by: Shakeel Butt <shakeel.butt@...ux.dev>

> ---
>  include/linux/rmap.h | 5 +++++
>  mm/page_vma_mapped.c | 1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index 6cd020eea37a..04797cea3205 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -928,6 +928,11 @@ struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr,
>  /* Look for migration entries rather than present PTEs */
>  #define PVMW_MIGRATION		(1 << 1)
>  
> +/* Result flags */
> +
> +/* The page is mapped across page boundary */

I think you meant "page table boundary" in above comment.

> +#define PVMW_PGTABLE_CROSSSED	(1 << 16)
> +
>  struct page_vma_mapped_walk {
>  	unsigned long pfn;
>  	unsigned long nr_pages;
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index e981a1a292d2..a184b88743c3 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -309,6 +309,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>  				}
>  				pte_unmap(pvmw->pte);
>  				pvmw->pte = NULL;
> +				pvmw->flags |= PVMW_PGTABLE_CROSSSED;
>  				goto restart;
>  			}
>  			pvmw->pte++;
> -- 
> 2.50.1
>