Re: [PATCH RFC 11/13] mm/huge_memory: clean up after-split folio freeing in __folio_split

[Zi Yan]

On Fri Aug 7, 2026 at 5:17 PM EDT, Kairui Song via B4 Relay wrote:
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> Replace free_folio_and_swap_cache() with an explicit folio_free_swap()
> and folio_put() in the after-split loop.  free_folio_and_swap_cache()
> unlocks the folio, then free_swap_cache() must trylock it again and
> re-check folio_mapped() before freeing the swap cache entries; if the
> trylock loses a race, the entries are left behind even though the folio
> reference is dropped.  The sub folios are still locked and unmapped
> here, so just directly call folio_free_swap() directly under the lock,
> unlock and drop the reference.  This makes the swap cache freeing
> deterministic and the reference drop explicit.
>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> ---
>  mm/huge_memory.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index b80d0db63225..39c91c8e5bc8 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -4304,14 +4304,16 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  		if (new_folio == page_folio(lock_at))
>  			continue;
>  
> -		folio_unlock(new_folio);
>  		/*
>  		 * Subpages whose mapping has been zapped may be freed
>  		 * earlier, but freeing them requires taking the
>  		 * lru_lock, so we defer put_page() on tail pages until
>  		 * after the split completes.

this comment needs some love.

>  		 */
> -		free_folio_and_swap_cache(new_folio);
> +		if (is_swapcache)
> +			folio_free_swap(new_folio);
> +		folio_unlock(new_folio);
> +		folio_put(new_folio);
>  	}
>  
>  out:

folio_split_unmaped()'s comment still refers to
free_folio_and_swap_cache().

Otherwise, LGTM.

Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>



-- 
Best Regards,
Yan, Zi