Re: [PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()

[Matthew Wilcox]

On Fri, Jun 02, 2023 at 09:54:08AM +0800, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> 
> We can replace nine implict calls to compound_head() with one by using
> old_folio. However, we still need to keep old_page because we need to
> know which page in the folio we are copying.

Do we?  It's my understanding (and I am far from an expert here ...)
that the 'pte_t *' we are passed *inside hugetlbfs* is not in fact a pte
pointer at all but actually a pmd or pud pointer.  See how we do this:

        pte_t pte = huge_ptep_get(ptep);

and so the page we get back is always a head page, and we can go
directly to a folio.  ie this is different from the THP cases.