Re: [PATCH v5 03/11] thp: copy_huge_pmd(): copy huge zero page

[David Rientjes]

On Wed, 7 Nov 2012, Kirill A. Shutemov wrote:

> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index ff834ea..0d903bf 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -701,6 +701,18 @@ static inline struct page *alloc_hugepage(int defrag)
>  }
>  #endif
>  
> +static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
> +		struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd)
> +{
> +	pmd_t entry;
> +	entry = pfn_pmd(huge_zero_pfn, vma->vm_page_prot);
> +	entry = pmd_wrprotect(entry);
> +	entry = pmd_mkhuge(entry);
> +	set_pmd_at(mm, haddr, pmd, entry);
> +	pgtable_trans_huge_deposit(mm, pgtable);
> +	mm->nr_ptes++;
> +}
> +
>  int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  			       unsigned long address, pmd_t *pmd,
>  			       unsigned int flags)
> @@ -778,6 +790,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>  		pte_free(dst_mm, pgtable);
>  		goto out_unlock;
>  	}
> +	if (is_huge_zero_pmd(pmd)) {
> +		set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd);
> +		ret = 0;
> +		goto out_unlock;
> +	}

You said in the introduction message in this series that you still allow 
splitting of the pmd, so why no check for pmd_trans_splitting() before 
this?
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