Re: A potential refcount issue during __folio_split

[Wei Yang <richard.weiyang@gmail.com>]

On Mon, Feb 23, 2026 at 10:23:11AM +0100, David Hildenbrand (Arm) wrote:
>> BTW, in the folio world, I do not think it is possible to perform the aforementioned
>> split_huge_page_to_list_to_order() pattern any more, since you always work on folio,
>> the head. Unless there is a need of getting hold of a tail after-split folio after
>> a folio split, the pattern would be:
>> 
>> tail_page = folio_page(folio, N);
>> 
>> folio_get(folio);
>> folio_lock(folio);
>> folio_split(folio, ..., /* new parameter: lock_at = */ tail_page, ...);
>> tail_folio = page_folio(tail_page);
>> folio_unlock(tail_folio);
>> folio_put(tail_folio);
>

Missed this. Agree.

>Agreed. Maybe it would be even nicer if the split function could return the
>new folio directly.
>
>folio_get(folio);
>folio_lock(folio);
>split_folio = folio_split_XXX(folio, ..., tail_page, ...);
>if (IS_ERR_VALUE(split_folio)) {
>	...
>}
>folio_unlock(split_folio);
>folio_put(split__folio);
>

I am afraid it would be complicated?

Well, we don't have this usecase now, could decide it when we do need it.

>-- 
>Cheers,
>
>David

-- 
Wei Yang
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