linux-kernel - Re: [PATCH] x86: make mm/gup.c more virtualization friendly

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Date:	Tue, 23 Sep 2008 06:42:57 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: make mm/gup.c more virtualization friendly

No objections from me.

On Wed, Sep 17, 2008 at 04:48:17PM +0100, Jan Beulich wrote:
> Since pte_flags() is much cheaper than pte_val() in some virtualized
> environments (namely, Xen), use the former whereever possible.
> 
> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
> Cc: Nick Piggin <npiggin@...e.de>
> 
> ---
>  arch/x86/mm/gup.c         |   10 +++++-----
>  include/asm-x86/pgtable.h |    2 +-
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> --- linux-2.6.27-rc6/arch/x86/mm/gup.c	2008-08-21 14:37:29.000000000 +0200
> +++ 2.6.27-rc6-x86-gup-virt/arch/x86/mm/gup.c	2008-09-02 13:33:42.000000000 +0200
> @@ -82,7 +82,7 @@ static noinline int gup_pte_range(pmd_t 
>  		pte_t pte = gup_get_pte(ptep);
>  		struct page *page;
>  
> -		if ((pte_val(pte) & (mask | _PAGE_SPECIAL)) != mask) {
> +		if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
>  			pte_unmap(ptep);
>  			return 0;
>  		}
> @@ -116,10 +116,10 @@ static noinline int gup_huge_pmd(pmd_t p
>  	mask = _PAGE_PRESENT|_PAGE_USER;
>  	if (write)
>  		mask |= _PAGE_RW;
> -	if ((pte_val(pte) & mask) != mask)
> +	if ((pte_flags(pte) & mask) != mask)
>  		return 0;
>  	/* hugepages are never "special" */
> -	VM_BUG_ON(pte_val(pte) & _PAGE_SPECIAL);
> +	VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
>  	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
>  
>  	refs = 0;
> @@ -173,10 +173,10 @@ static noinline int gup_huge_pud(pud_t p
>  	mask = _PAGE_PRESENT|_PAGE_USER;
>  	if (write)
>  		mask |= _PAGE_RW;
> -	if ((pte_val(pte) & mask) != mask)
> +	if ((pte_flags(pte) & mask) != mask)
>  		return 0;
>  	/* hugepages are never "special" */
> -	VM_BUG_ON(pte_val(pte) & _PAGE_SPECIAL);
> +	VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
>  	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
>  
>  	refs = 0;
> --- linux-2.6.27-rc6/include/asm-x86/pgtable.h	2008-08-21 14:37:34.000000000 +0200
> +++ 2.6.27-rc6-x86-gup-virt/include/asm-x86/pgtable.h	2008-09-02 13:31:50.000000000 +0200
> @@ -183,7 +183,7 @@ static inline int pte_exec(pte_t pte)
>  
>  static inline int pte_special(pte_t pte)
>  {
> -	return pte_val(pte) & _PAGE_SPECIAL;
> +	return pte_flags(pte) & _PAGE_SPECIAL;
>  }
>  
>  static inline int pmd_large(pmd_t pte)
> 
> 
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