Re: [PATCH v2 3/9] mm/huge_memory: support huge zero folio in vmf_insert_folio_pmd()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Thu, Jul 17, 2025 at 01:52:06PM +0200, David Hildenbrand wrote:
> Just like we do for vmf_insert_page_mkwrite() -> ... ->
> insert_page_into_pte_locked() with the shared zeropage, support the
> huge zero folio in vmf_insert_folio_pmd().
>
> When (un)mapping the huge zero folio in page tables, we neither
> adjust the refcount nor the mapcount, just like for the shared zeropage.
>
> For now, the huge zero folio is not marked as special yet, although
> vm_normal_page_pmd() really wants to treat it as special. We'll change
> that next.
>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Signed-off-by: David Hildenbrand <david@redhat.com>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  mm/huge_memory.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 849feacaf8064..db08c37b87077 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1429,9 +1429,11 @@ static vm_fault_t insert_pmd(struct vm_area_struct *vma, unsigned long addr,
>  	if (fop.is_folio) {
>  		entry = folio_mk_pmd(fop.folio, vma->vm_page_prot);
>
> -		folio_get(fop.folio);
> -		folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma);
> -		add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
> +		if (!is_huge_zero_folio(fop.folio)) {
> +			folio_get(fop.folio);
> +			folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma);
> +			add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
> +		}
>  	} else {
>  		entry = pmd_mkhuge(pfn_pmd(fop.pfn, prot));
>  		entry = pmd_mkspecial(entry);
> --
> 2.50.1
>