[PATCH v2 2/8] mm/huge_memory: add a comment to the open-coded swap entry

[Zi Yan]

On Tue Sep 8, 2026 at 11:16 AM EDT, Tal Zussman wrote:
> The swap entry of each new folio in __split_folio_to_order() is
> computed by hand from folio->swap rather than with folio_swap_entry(),
> because the folio's page count is not valid while it is being split.
> Add a comment explaining this.
>
> Signed-off-by: Tal Zussman <tz2294 at columbia.edu>
> ---
>  mm/huge_memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d1ce061601bc..1fabdcbd8c8f 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3763,6 +3763,10 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
>  		 */
>  		VM_WARN_ON_ONCE_PAGE(new_folio->private, new_head);
>  
> +		/*
> +		 * Not all folio fields are valid during a split, so open-code
> +		 * the swap entry rather than using folio_swap_entry().
> +		 */
>  		if (folio_test_swapcache(folio))
>  			new_folio->swap.val = folio->swap.val + i;
>  

LGTM.

Reviewed-by: Zi Yan <ziy at nvidia.com>



-- 
Best Regards,
Yan, Zi