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

Wei Yang
2025-07-25T08:07:48Z

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>
>---
> 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);
>+ }

I think this is reasonable.

Reviewed-by: Wei Yang <richard.weiyang@gmail.com>

> } else {
> entry = pmd_mkhuge(pfn_pmd(fop.pfn, prot));
> entry = pmd_mkspecial(entry);
>--
>2.50.1
>

--
Wei Yang
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