Re: [PATCH v3 07/12] mm/gup: track FOLL_PIN pages

[Kirill A. Shutemov]

On Fri, Jan 31, 2020 at 07:40:24PM -0800, John Hubbard wrote:
> @@ -4405,7 +4392,13 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  same_page:
>  		if (pages) {
>  			pages[i] = mem_map_offset(page, pfn_offset);
> -			get_page(pages[i]);
> +			if (!try_grab_page(pages[i], flags)) {
> +				spin_unlock(ptl);
> +				remainder = 0;
> +				err = -ENOMEM;
> +				WARN_ON_ONCE(1);

The WARN_ON_ONCE deserve a comment. And I guess you can put it into 'if'
condition.

> +				break;
> +			}
>  		}
>  
>  		if (vmas)
> @@ -4965,6 +4958,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
>  	struct page *page = NULL;
>  	spinlock_t *ptl;
>  	pte_t pte;
> +
> +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> +	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
> +			 (FOLL_PIN | FOLL_GET)))
> +		return NULL;
> +
>  retry:
>  	ptl = pmd_lockptr(mm, pmd);
>  	spin_lock(ptl);
> @@ -4977,8 +4976,11 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
>  	pte = huge_ptep_get((pte_t *)pmd);
>  	if (pte_present(pte)) {
>  		page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
> -		if (flags & FOLL_GET)
> -			get_page(page);
> +		if (unlikely(!try_grab_page(page, flags))) {
> +			WARN_ON_ONCE(1);

Ditto.

> +			page = NULL;
> +			goto out;
> +		}
>  	} else {
>  		if (is_hugetlb_entry_migration(pte)) {
>  			spin_unlock(ptl);

-- 
 Kirill A. Shutemov