Re: [PATCH 07/12] mm: Remove redundant pXd_devmap calls

Jonathan Cameron
2025-05-29T11:54:40Z

On Thu, 29 May 2025 16:32:08 +1000
Alistair Popple <apopple@nvidia.com> wrote:

> DAX was the only thing that created pmd_devmap and pud_devmap entries
> however it no longer does as DAX pages are now refcounted normally and
> pXd_trans_huge() returns true for those. Therefore checking both pXd_devmap
> and pXd_trans_huge() is redundant and the former can be removed without
> changing behaviour as it will always be false.
>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>

> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8d9d706..31b4110 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1398,10 +1398,7 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> }
>
> entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
> - if (pfn_t_devmap(pfn))

Didn't this go away in patch 5? I didn't check but this looks like a bisectability issue.

> - entry = pmd_mkdevmap(entry);
> - else
> - entry = pmd_mkspecial(entry);
> + entry = pmd_mkspecial(entry);
> if (write) {
> entry = pmd_mkyoung(pmd_mkdirty(entry));
> entry = maybe_pmd_mkwrite(entry, vma);