On Sat, May 17, 2014 at 03:33:05AM +0300, Kirill A. Shutemov wrote:
> Below is my attempt to play with the problem. I've took one function --
> page_referenced_one() -- which looks ugly because of different APIs for
> PTE/PMD and convert it to use vpte_t. vpte_t is union for pte_t, pmd_t
> and pud_t.
>
> Basically, the idea is instead of having different helpers to handle
> PTE/PMD/PUD, we have one, which take pair of vpte_t + pglevel.
I can't find my original attempt at this now (I am lost in a maze of
twisted git trees, all subtly different), but I called it a vpe (Virtual
Page Entry).
Rather than using a pair of vpte_t and pglevel, the vpe_t contained
enough information to discern what level it was; that's only two bits
and I think all the architectures have enough space to squeeze in two
more bits to the PTE (the PMD and PUD obviously have plenty of space).
> +static inline unsigned long vpte_size(vpte_t vptep, enum ptlevel ptlvl)
> +{
> + switch (ptlvl) {
> + case PTE:
> + return PAGE_SIZE;
> +#ifdef PMD_SIZE
> + case PMD:
> + return PMD_SIZE;
> +#endif
> +#ifdef PUD_SIZE
> + case PUD:
> + return PUD_SIZE;
> +#endif
> + default:
> + return 0; /* XXX */
As you say, XXX. This needs to be an error ... perhaps VM_BUG_ON(1)
in this case?
> @@ -676,59 +676,39 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
> spinlock_t *ptl;
> int referenced = 0;
> struct page_referenced_arg *pra = arg;
> + vpte_t *vpte;
> + enum ptlevel ptlvl = PTE;
>
> - if (unlikely(PageTransHuge(page))) {
> - pmd_t *pmd;
> + ptlvl = unlikely(PageTransHuge(page)) ? PMD : PTE;
>
> - /*
> - * rmap might return false positives; we must filter
> - * these out using page_check_address_pmd().
> - */
> - pmd = page_check_address_pmd(page, mm, address,
> - PAGE_CHECK_ADDRESS_PMD_FLAG, &ptl);
> - if (!pmd)
> - return SWAP_AGAIN;
> -
> - if (vma->vm_flags & VM_LOCKED) {
> - spin_unlock(ptl);
> - pra->vm_flags |= VM_LOCKED;
> - return SWAP_FAIL; /* To break the loop */
> - }
> + /*
> + * rmap might return false positives; we must filter these out using
> + * page_check_address_vpte().
> + */
> + vpte = page_check_address_vpte(page, mm, address, &ptl, 0);
> + if (!vpte)
> + return SWAP_AGAIN;
> +
> + if (vma->vm_flags & VM_LOCKED) {
> + vpte_unmap_unlock(vpte, ptlvl, ptl);
> + pra->vm_flags |= VM_LOCKED;
> + return SWAP_FAIL; /* To break the loop */
> + }
>
> - /* go ahead even if the pmd is pmd_trans_splitting() */
> - if (pmdp_clear_flush_young_notify(vma, address, pmd))
> - referenced++;
> - spin_unlock(ptl);
> - } else {
> - pte_t *pte;
>
> + /* go ahead even if the pmd is pmd_trans_splitting() */
> + if (vptep_clear_flush_young_notify(vma, address, vpte, ptlvl)) {
> /*
> - * rmap might return false positives; we must filter
> - * these out using page_check_address().
> + * Don't treat a reference through a sequentially read
> + * mapping as such. If the page has been used in
> + * another mapping, we will catch it; if this other
> + * mapping is already gone, the unmap path will have
> + * set PG_referenced or activated the page.
> */
> - pte = page_check_address(page, mm, address, &ptl, 0);
> - if (!pte)
> - return SWAP_AGAIN;
> -
> - if (vma->vm_flags & VM_LOCKED) {
> - pte_unmap_unlock(pte, ptl);
> - pra->vm_flags |= VM_LOCKED;
> - return SWAP_FAIL; /* To break the loop */
> - }
> -
> - if (ptep_clear_flush_young_notify(vma, address, pte)) {
> - /*
> - * Don't treat a reference through a sequentially read
> - * mapping as such. If the page has been used in
> - * another mapping, we will catch it; if this other
> - * mapping is already gone, the unmap path will have
> - * set PG_referenced or activated the page.
> - */
> - if (likely(!(vma->vm_flags & VM_SEQ_READ)))
> - referenced++;
> - }
> - pte_unmap_unlock(pte, ptl);
> + if (likely(!(vma->vm_flags & VM_SEQ_READ)))
> + referenced++;
> }
> + vpte_unmap_unlock(vpte, ptlvl, ptl);
>
> if (referenced) {
> pra->referenced++;
> --
> 2.0.0.rc2
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