Re: [PATCH 2/2] mm/memory-failure: improve large block size folio handling.

[Matthew Wilcox <willy@infradead.org>]

On Sat, Oct 11, 2025 at 12:12:12PM +0800, Miaohe Lin wrote:
> >  		folio_set_has_hwpoisoned(folio);
> > -		if (try_to_split_thp_page(p, false) < 0) {
> > +		/*
> > +		 * If the folio cannot be split to order-0, kill the process,
> > +		 * but split the folio anyway to minimize the amount of unusable
> > +		 * pages.
> > +		 */
> > +		if (try_to_split_thp_page(p, new_order, false) || new_order) {
> > +			/* get folio again in case the original one is split */
> > +			folio = page_folio(p);
> 
> If original folio A is split and the after-split new folio is B (A != B), will the
> refcnt of folio A held above be missing? I.e. get_hwpoison_page() held the extra refcnt
> of folio A, but we put the refcnt of folio B below. Is this a problem or am I miss
> something?

That's how split works.

Zi Yan, the kernel-doc for folio_split() could use some attention.
First, it's not kernel-doc; the comment opens with /* instead of /**.
Second, it says:

 * After split, folio is left locked for caller.

which isn't actually true, right?  The folio which contains
@split_at will be locked.  Also, it will contain the additional
reference which was taken on @folio by the caller.