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Date:   Mon, 26 Oct 2020 16:01:42 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de,
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Subject: Re: [PATCH v2 07/19] mm/hugetlb: Free the vmemmap pages associated
 with each hugetlb page
Message-ID: <20201026160142.GT20115@casper.infradead.org>
References: <20201026145114.59424-1-songmuchun@bytedance.com>
 <20201026145114.59424-8-songmuchun@bytedance.com>
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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.