Re: [PATCH v3 05/21] mm/hugetlb: Introduce pgtable allocation/freeing helpers

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On Sun, Nov 08, 2020 at 10:10:57PM +0800, Muchun Song wrote:
> +static inline unsigned int pgtable_pages_to_prealloc_per_hpage(struct hstate *h)
> +{
> +	unsigned long vmemmap_size = vmemmap_pages_size_per_hpage(h);
> +
> +	/*
> +	 * No need pre-allocate page tabels when there is no vmemmap pages
> +	 * to free.
 s /tabels/tables/

> +static int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
> +{
> +	int i;
> +	pgtable_t pgtable;
> +	unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
> +
> +	if (!nr)
> +		return 0;
> +
> +	vmemmap_pgtable_init(page);
> +
> +	for (i = 0; i < nr; i++) {
> +		pte_t *pte_p;
> +
> +		pte_p = pte_alloc_one_kernel(&init_mm);
> +		if (!pte_p)
> +			goto out;
> +		vmemmap_pgtable_deposit(page, virt_to_page(pte_p));
> +	}
> +
> +	return 0;
> +out:
> +	while (i-- && (pgtable = vmemmap_pgtable_withdraw(page)))
> +		pte_free_kernel(&init_mm, page_to_virt(pgtable));

	would not be enough to:

	while (pgtable = vmemmap_pgtable_withdrag(page))
		pte_free_kernel(&init_mm, page_to_virt(pgtable));

> +	return -ENOMEM;
> +}
> +
> +static void vmemmap_pgtable_free(struct hstate *h, struct page *page)
> +{
> +	pgtable_t pgtable;
> +	unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
> +
> +	if (!nr)
> +		return;

We can get rid of "nr" and its check and keep only the check below, right?
AFAICS, they go together, e.g: if page_huge_pte does not return null,
it means that we preallocated a pagetable, and viceversa.


> +
> +	pgtable = page_huge_pte(page);
> +	if (!pgtable)
> +		return;
> +
> +	while (nr-- && (pgtable = vmemmap_pgtable_withdraw(page)))
> +		pte_free_kernel(&init_mm, page_to_virt(pgtable));

	Same as above, that "nr" can go?

-- 
Oscar Salvador
SUSE L3



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