Re: [PATCH 4/4] mm: prepare page_referenced() and page_idle to new THP refcounting

[Vladimir Davydov]

On Tue, Nov 03, 2015 at 05:26:15PM +0200, Kirill A. Shutemov wrote:
...
> @@ -56,23 +56,69 @@ static int page_idle_clear_pte_refs_one(struct page *page,
>  {
>  	struct mm_struct *mm = vma->vm_mm;
>  	spinlock_t *ptl;
> +	pgd_t *pgd;
> +	pud_t *pud;
>  	pmd_t *pmd;
>  	pte_t *pte;
>  	bool referenced = false;
>  
> -	if (unlikely(PageTransHuge(page))) {
> -		pmd = page_check_address_pmd(page, mm, addr, &ptl);
> -		if (pmd) {
> -			referenced = pmdp_clear_young_notify(vma, addr, pmd);
> +	pgd = pgd_offset(mm, addr);
> +	if (!pgd_present(*pgd))
> +		return SWAP_AGAIN;
> +	pud = pud_offset(pgd, addr);
> +	if (!pud_present(*pud))
> +		return SWAP_AGAIN;
> +	pmd = pmd_offset(pud, addr);
> +
> +	if (pmd_trans_huge(*pmd)) {
> +		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;
> +
> +		referenced = pmdp_clear_young_notify(vma, addr, pmd);
> +		spin_unlock(ptl);
> +		goto found;
> +unlock_pmd:
> +		spin_unlock(ptl);
> +		return SWAP_AGAIN;
>  	} else {
> -		pte = page_check_address(page, mm, addr, &ptl, 0);
> -		if (pte) {
> -			referenced = ptep_clear_young_notify(vma, addr, pte);
> -			pte_unmap_unlock(pte, ptl);
> -		}
> +		pmd_t pmde = *pmd;
> +		barrier();
> +		if (!pmd_present(pmde) || pmd_trans_huge(pmde))
> +			return SWAP_AGAIN;
> +
> +	}
> +map_pte:
> +	pte = pte_offset_map(pmd, addr);
> +	if (!pte_present(*pte)) {
> +		pte_unmap(pte);
> +		return SWAP_AGAIN;
>  	}
> +
> +	ptl = pte_lockptr(mm, pmd);
> +	spin_lock(ptl);
> +
> +	if (!pte_present(*pte)) {
> +		pte_unmap_unlock(pte, ptl);
> +		return SWAP_AGAIN;
> +	}
> +
> +	/* THP can be referenced by any subpage */
> +	if (pte_pfn(*pte) - page_to_pfn(page) >= hpage_nr_pages(page)) {
> +		pte_unmap_unlock(pte, ptl);
> +		return SWAP_AGAIN;
> +	}
> +
> +	referenced = ptep_clear_young_notify(vma, addr, pte);
> +	pte_unmap_unlock(pte, ptl);
> +found:

Can't we hide this stuff in a helper function, which would be used by
both page_referenced_one and page_idle_clear_pte_refs_one, instead of
duplicating page_referenced_one code here?

Thanks,
Vladimir
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