Re: ksm: initialize rmap values directly and make them const

[David Hildenbrand (Arm)]

On 2/6/26 08:22, xu.xin16@xxxxxxxxxx wrote:
> From: xu xin <xu.xin16@xxxxxxxxxx>
>
> 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@xxxxxxxxxx/
>
> 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@xxxxxxxxxx/

Thanks!

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

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