Re: [PATCH v8 05/22] Add vm_replace_mixed()

[Kirill A. Shutemov]

On Tue, Jul 22, 2014 at 03:47:53PM -0400, Matthew Wilcox wrote:
> From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
> 
> vm_insert_mixed() will fail if there is already a valid PTE at that
> location.  The DAX code would rather replace the previous value with
> the new PTE.
> 
> Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
> ---
>  include/linux/mm.h |  8 ++++++--
>  mm/memory.c        | 34 +++++++++++++++++++++-------------
>  2 files changed, 27 insertions(+), 15 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e04f531..8d1194c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1958,8 +1958,12 @@ int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
>  int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
>  int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>  			unsigned long pfn);
> -int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
> -			unsigned long pfn);
> +int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
> +			unsigned long pfn, bool replace);
> +#define vm_insert_mixed(vma, addr, pfn)	\
> +	__vm_insert_mixed(vma, addr, pfn, false)
> +#define vm_replace_mixed(vma, addr, pfn)	\
> +	__vm_insert_mixed(vma, addr, pfn, true)
>  int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len);
>  
>  
> diff --git a/mm/memory.c b/mm/memory.c
> index 42bf429..cf06c97 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1476,7 +1476,7 @@ pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
>   * pages reserved for the old functions anyway.
>   */
>  static int insert_page(struct vm_area_struct *vma, unsigned long addr,
> -			struct page *page, pgprot_t prot)
> +			struct page *page, pgprot_t prot, bool replace)
>  {
>  	struct mm_struct *mm = vma->vm_mm;
>  	int retval;
> @@ -1492,8 +1492,12 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr,
>  	if (!pte)
>  		goto out;
>  	retval = -EBUSY;
> -	if (!pte_none(*pte))
> -		goto out_unlock;
> +	if (!pte_none(*pte)) {
> +		if (!replace)
> +			goto out_unlock;
> +		VM_BUG_ON(!mutex_is_locked(&vma->vm_file->f_mapping->i_mmap_mutex));
> +		zap_page_range_single(vma, addr, PAGE_SIZE, NULL);

zap_page_range_single() takes ptl by itself in zap_pte_range(). It's not
going to work.

And zap_page_range*() is pretty heavy weapon to shoot down one pte, which
we already have pointer to. Why?

-- 
 Kirill A. Shutemov
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