linux-kernel - Re: [PATCH v3 07/10] thp: implement splitting pmd for huge zero page

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Date:	Fri, 12 Oct 2012 11:23:37 +0800
From:	Ni zhan Chen <nizhan.chen@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v3 07/10] thp: implement splitting pmd for huge zero page

On 10/02/2012 11:19 PM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>
> We can't split huge zero page itself, but we can split the pmd which
> points to it.
>
> On splitting the pmd we create a table with all ptes set to normal zero
> page.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reviewed-by: Andrea Arcangeli <aarcange@...hat.com>
> ---
>   mm/huge_memory.c |   32 ++++++++++++++++++++++++++++++++
>   1 files changed, 32 insertions(+), 0 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 95032d3..3f1c59c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1600,6 +1600,7 @@ int split_huge_page(struct page *page)
>   	struct anon_vma *anon_vma;
>   	int ret = 1;
>   
> +	BUG_ON(is_huge_zero_pfn(page_to_pfn(page)));
>   	BUG_ON(!PageAnon(page));
>   	anon_vma = page_lock_anon_vma(page);
>   	if (!anon_vma)
> @@ -2503,6 +2504,32 @@ static int khugepaged(void *none)
>   	return 0;
>   }
>   
> +static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
> +		unsigned long haddr, pmd_t *pmd)
> +{
> +	pgtable_t pgtable;
> +	pmd_t _pmd;
> +	int i;
> +
> +	pmdp_clear_flush_notify(vma, haddr, pmd);

why I can't find function pmdp_clear_flush_notify in kernel source code? 
Do you mean pmdp_clear_flush_young_notify or something like that?

> +	/* leave pmd empty until pte is filled */
> +
> +	pgtable = get_pmd_huge_pte(vma->vm_mm);
> +	pmd_populate(vma->vm_mm, &_pmd, pgtable);
> +
> +	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
> +		pte_t *pte, entry;
> +		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
> +		entry = pte_mkspecial(entry);
> +		pte = pte_offset_map(&_pmd, haddr);
> +		VM_BUG_ON(!pte_none(*pte));
> +		set_pte_at(vma->vm_mm, haddr, pte, entry);
> +		pte_unmap(pte);
> +	}
> +	smp_wmb(); /* make pte visible before pmd */
> +	pmd_populate(vma->vm_mm, pmd, pgtable);
> +}
> +
>   void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
>   		pmd_t *pmd)
>   {
> @@ -2516,6 +2543,11 @@ void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
>   		spin_unlock(&vma->vm_mm->page_table_lock);
>   		return;
>   	}
> +	if (is_huge_zero_pmd(*pmd)) {
> +		__split_huge_zero_page_pmd(vma, haddr, pmd);
> +		spin_unlock(&vma->vm_mm->page_table_lock);
> +		return;
> +	}
>   	page = pmd_page(*pmd);
>   	VM_BUG_ON(!page_count(page));
>   	get_page(page);

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