Re: [PATCH v2 07/19] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page

[Matthew Wilcox]

On Mon, Oct 26, 2020 at 10:51:02PM +0800, Muchun Song wrote:
> +static void split_vmemmap_pmd(pmd_t *pmd, pte_t *pte_p, unsigned long addr)
> +{
> +     struct mm_struct *mm = &init_mm;
> +     struct page *page;
> +     pmd_t old_pmd, _pmd;
> +     int i;
> +
> +     old_pmd = READ_ONCE(*pmd);
> +     page = pmd_page(old_pmd);
> +     pmd_populate_kernel(mm, &_pmd, pte_p);
> +
> +     for (i = 0; i < VMEMMAP_HPAGE_NR; i++, addr += PAGE_SIZE) {
> +             pte_t entry, *pte;
> +
> +             entry = mk_pte(page + i, PAGE_KERNEL);

I'd be happier if that were:

        pgprot_t pgprot = PAGE_KERNEL;
...
        for (i = 0; i < VMEMMAP_HPAGE_NR; i++, addr += PAGE_SIZE) {
                pte_t entry, *pte;

                entry = mk_pte(page + i, pgprot);
                pgprot = PAGE_KERNEL_RO;

so that all subsequent tail pages are mapped read-only.