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

Kirill A. Shutemov
2020-02-03T13:40:16Z

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