Re: [PATCH] mm: huge_memory: convert __do_huge_pmd_anonymous_page() to use folios

[Matthew Wilcox]

On Mon, Apr 22, 2024 at 11:12:16AM -0700, Jianfeng Wang wrote:
> Change __do_huge_pmd_anonymous_page() to take folio as input, as its
> caller has used folio. Save one unnecessary call to compound_head().

I don't like this patch.  It makes the assumption that folios will never
be larger than PMD size, and I don't think that's an assumption that's
going to last another five years.  Look where you had to
do &folio->page:

> +	clear_huge_page(&folio->page, vmf->address, HPAGE_PMD_NR);

> +		entry = mk_huge_pmd(&folio->page, vma->vm_page_prot);

For mk_huge_pmd() in particular, you need to know the precise page, and
not just use the first page of the folio.