linux-kernel - Re: ksm: initialize rmap values directly and make them const

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Message-ID: <a1d5bb75-3222-4863-a24a-4343b25ca6b7@kernel.org>
Date: Fri, 6 Feb 2026 09:18:49 +0100
From: "David Hildenbrand (Arm)" <david@...nel.org>
To: xu.xin16@....com.cn, akpm@...ux-foundation.org
Cc: chengming.zhou@...ux.dev, hughd@...gle.com, wang.yaxin@....com.cn,
 yang.yang29@....com.cn, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: ksm: initialize rmap values directly and make them const

On 2/6/26 08:22, xu.xin16@....com.cn wrote:
> From: xu xin <xu.xin16@....com.cn>
> 
> Considering that commit 06fbd555dea8 ("ksm: optimize rmap_walk_ksm by passing
> a suitable addressrange") seems to have already been merged, this new patch is
> proposed to address the issue raised by David at:
> 
> https://lore.kernel.org/all/ba03780a-fd65-4a03-97de-bc0905106260@kernel.org/
> 
> This initialize rmap values (addr, pgoff_start, pgoff_end) directly and
> make them const to make code more robust. Besides, since KSM folios are always
> order-0, so folio_nr_pages(KSM folio) is always 1, so the line:
> 
> 	"pgoff_end = pgoff_start + folio_nr_pages(folio) - 1;"
> 
> becomes directly:
> 
> 	"pgoff_end = pgoff_start;"
> 
> The test reproducer of rmap_walk_ksm can be found at:
> https://lore.kernel.org/all/20260206151424734QIyWL_pA-1QeJPbJlUxsO@zte.com.cn/

Thanks!

> 
> Fixes: 06fbd555dea8 ("ksm: optimize rmap_walk_ksm by passing a suitable addressrange")
> Signed-off-by: xu xin <xu.xin16@....com.cn>

The patch does not seem to be upstream / in mm-stable yet.

Can you resend the original patch with these changes included and the 
reproducer referenced in the updated patch description?

Thanks!

> ---
>   mm/ksm.c | 13 +++++--------
>   1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 031c17e4ada6..c7ca117024a4 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -3171,8 +3171,11 @@ void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc)
>   		struct anon_vma *anon_vma = rmap_item->anon_vma;
>   		struct anon_vma_chain *vmac;
>   		struct vm_area_struct *vma;
> -		unsigned long addr;
> -		pgoff_t pgoff_start, pgoff_end;
> +		/* Ignore the stable/unstable/sqnr flags */
> +		const unsigned long addr = rmap_item->address & PAGE_MASK;
> +		const pgoff_t pgoff_start = rmap_item->address >> PAGE_SHIFT;
> +		/* KSM folios are always order-0 normal pages */
> +		const pgoff_t pgoff_end = pgoff_start;

I would move them all the way up, above the "struct anon_vma *anon_vma = 
rmap_item->anon_vma;"

-- 
Cheers,

David