On Tue, Nov 03, 2015 at 05:26:15PM +0200, Kirill A. Shutemov wrote:
...
> @@ -812,60 +812,104 @@ static int page_referenced_one(struct page *page,
> struct vm_area_struct *vma,
> spinlock_t *ptl;
> int referenced = 0;
> struct page_referenced_arg *pra = arg;
> + pgd_t *pgd;
> + pud_t *pud;
> + pmd_t *pmd;
> + pte_t *pte;
>
> - if (unlikely(PageTransHuge(page))) {
> - pmd_t *pmd;
> -
> - /*
> - * rmap might return false positives; we must filter
> - * these out using page_check_address_pmd().
> - */
> - pmd = page_check_address_pmd(page, mm, address, &ptl);
> - if (!pmd)
> + if (unlikely(PageHuge(page))) {
> + /* when pud is not present, pte will be NULL */
> + pte = huge_pte_offset(mm, address);
> + if (!pte)
> return SWAP_AGAIN;
>
> - if (vma->vm_flags & VM_LOCKED) {
> + ptl = huge_pte_lockptr(page_hstate(page), mm, pte);
> + goto check_pte;
> + }
> +
> + pgd = pgd_offset(mm, address);
> + if (!pgd_present(*pgd))
> + return SWAP_AGAIN;
> + pud = pud_offset(pgd, address);
> + if (!pud_present(*pud))
> + return SWAP_AGAIN;
> + pmd = pmd_offset(pud, address);
> +
> + if (pmd_trans_huge(*pmd)) {
> + int ret = SWAP_AGAIN;
> +
> + ptl = pmd_lock(mm, pmd);
> + if (!pmd_present(*pmd))
> + goto unlock_pmd;
> + if (unlikely(!pmd_trans_huge(*pmd))) {
> spin_unlock(ptl);
> + goto map_pte;
> + }
> +
> + if (pmd_page(*pmd) != page)
> + goto unlock_pmd;
> +
> + if (vma->vm_flags & VM_LOCKED) {
> pra->vm_flags |= VM_LOCKED;
> - return SWAP_FAIL; /* To break the loop */
> + ret = SWAP_FAIL; /* To break the loop */
> + goto unlock_pmd;
> }
>
> if (pmdp_clear_flush_young_notify(vma, address, pmd))
> referenced++;
> -
> spin_unlock(ptl);
> + goto found;
> +unlock_pmd:
> + spin_unlock(ptl);
> + return ret;
> } else {
> - pte_t *pte;
> -
> - /*
> - * rmap might return false positives; we must filter
> - * these out using page_check_address().
> - */
> - pte = page_check_address(page, mm, address, &ptl, 0);
> - if (!pte)
> + pmd_t pmde = *pmd;
> + barrier();
This is supposed to be
pmd_t pmde = READ_ONCE(*pmd);
Right?
I don't understand why we need a barrier here. Why can't we just do
} else if (!pmd_present(*pmd))
reutnr SWAP_AGAIN;
?
Thanks,
Vladimir
> + if (!pmd_present(pmde) || pmd_trans_huge(pmde))
> return SWAP_AGAIN;
> + }
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