linux-kernel - Re: [PATCH] mm: remove call to find_vma in pagewalk for non-hugetlbfs

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Date:	Fri, 19 Nov 2010 17:15:58 +0900
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	David Sterba <dsterba@...e.cz>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Andy Whitcroft <apw@...onical.com>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Matt Mackall <mpm@...enic.com>, Mel Gorman <mel@....ul.ie>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH] mm: remove call to find_vma in pagewalk for non-hugetlbfs

On Fri, Nov 19, 2010 at 01:39:57AM +0100, David Sterba wrote:
> Commit d33b9f45 introduces a check if a vma is a hugetlbfs one and
> later in 5dc37642 is moved under #ifdef CONFIG_HUGETLB_PAGE but
> a needless find_vma call is left behind and it's result not used
> anywhere else in the function.
> 
> The sideefect of caching vma for @addr inside walk->mm is neither
> utilized in walk_page_range() nor in called functions.
> 
> Signed-off-by: David Sterba <dsterba@...e.cz>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Andy Whitcroft <apw@...onical.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Hugh Dickins <hugh.dickins@...cali.co.uk>
> Cc: Lee Schermerhorn <lee.schermerhorn@...com>
> Cc: Matt Mackall <mpm@...enic.com>
> Cc: Mel Gorman <mel@....ul.ie>
> Cc: Wu Fengguang <fengguang.wu@...el.com>
> ---
>  mm/pagewalk.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index 8b1a2ce..38cc58b 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -139,7 +139,6 @@ int walk_page_range(unsigned long addr, unsigned long end,
>  	pgd_t *pgd;
>  	unsigned long next;
>  	int err = 0;
> -	struct vm_area_struct *vma;
>  
>  	if (addr >= end)
>  		return err;
> @@ -149,15 +148,17 @@ int walk_page_range(unsigned long addr, unsigned long end,
>  
>  	pgd = pgd_offset(walk->mm, addr);
>  	do {
> +		struct vm_area_struct *uninitialized_var(vma);
> +
>  		next = pgd_addr_end(addr, end);
>  
> +#ifdef CONFIG_HUGETLB_PAGE
>  		/*
>  		 * handle hugetlb vma individually because pagetable walk for
>  		 * the hugetlb page is dependent on the architecture and
>  		 * we can't handled it in the same manner as non-huge pages.
>  		 */
>  		vma = find_vma(walk->mm, addr);
> -#ifdef CONFIG_HUGETLB_PAGE
>  		if (vma && is_vm_hugetlb_page(vma)) {
>  			if (vma->vm_end < next)
>  				next = vma->vm_end;

Looks good to me.

Reviewed-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

Thanks,
Naoya Horiguchi

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