On (30/05/08 17:58), Andy Whitcroft didst pronounce:
quoted text
> 
> Create some new accessors for vma private data to cut down on and contain
> the casts.  Encapsulates the huge and small page offset calculations.  Also
> adds a couple of VM_BUG_ONs for consistency.
> 

Things are a bit more readable with the helpers for sure. Thanks for catching
the missing VM_BUG_ONs as well.

quoted text
> Signed-off-by: Andy Whitcroft <apw@shadowen.org>

Acked-by: Mel Gorman <mel@csn.ul.ie>

quoted text
> ---
>  mm/hugetlb.c |   56 +++++++++++++++++++++++++++++++++++++++++++-------------
>  1 files changed, 43 insertions(+), 13 deletions(-)
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 729a830..7a5ac81 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -40,6 +40,26 @@ static int hugetlb_next_nid;
>   */
>  static DEFINE_SPINLOCK(hugetlb_lock);
>  
> +/*
> + * Convert the address within this vma to the page offset within
> + * the mapping, in base page units.
> + */
> +pgoff_t vma_page_offset(struct vm_area_struct *vma, unsigned long address)
> +{
> +	return ((address - vma->vm_start) >> PAGE_SHIFT) +
> +					(vma->vm_pgoff >> PAGE_SHIFT);
> +}
> +
> +/*
> + * Convert the address within this vma to the page offset within
> + * the mapping, in pagecache page units; huge pages here.
> + */
> +pgoff_t vma_pagecache_offset(struct vm_area_struct *vma, unsigned long address)
> +{
> +	return ((address - vma->vm_start) >> HPAGE_SHIFT) +
> +			(vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
> +}
> +
>  #define HPAGE_RESV_OWNER    (1UL << (BITS_PER_LONG - 1))
>  #define HPAGE_RESV_UNMAPPED (1UL << (BITS_PER_LONG - 2))
>  #define HPAGE_RESV_MASK (HPAGE_RESV_OWNER | HPAGE_RESV_UNMAPPED)
> @@ -53,36 +73,48 @@ static DEFINE_SPINLOCK(hugetlb_lock);
>   * to reset the VMA at fork() time as it is not in use yet and there is no
>   * chance of the global counters getting corrupted as a result of the values.
>   */
> +static unsigned long get_vma_private_data(struct vm_area_struct *vma)
> +{
> +	return (unsigned long)vma->vm_private_data;
> +}
> +
> +static void set_vma_private_data(struct vm_area_struct *vma,
> +							unsigned long value)
> +{
> +	vma->vm_private_data = (void *)value;
> +}
> +
>  static unsigned long vma_resv_huge_pages(struct vm_area_struct *vma)
>  {
>  	VM_BUG_ON(!is_vm_hugetlb_page(vma));
>  	if (!(vma->vm_flags & VM_SHARED))
> -		return (unsigned long)vma->vm_private_data & ~HPAGE_RESV_MASK;
> +		return get_vma_private_data(vma) & ~HPAGE_RESV_MASK;
>  	return 0;
>  }
>  
>  static void set_vma_resv_huge_pages(struct vm_area_struct *vma,
>  							unsigned long reserve)
>  {
> -	unsigned long flags;
>  	VM_BUG_ON(!is_vm_hugetlb_page(vma));
>  	VM_BUG_ON(vma->vm_flags & VM_SHARED);
>  
> -	flags = (unsigned long)vma->vm_private_data & HPAGE_RESV_MASK;
> -	vma->vm_private_data = (void *)(reserve | flags);
> +	set_vma_private_data(vma,
> +		(get_vma_private_data(vma) & HPAGE_RESV_MASK) | reserve);
>  }
>  
>  static void set_vma_resv_flags(struct vm_area_struct *vma, unsigned long flags)
>  {
> -	unsigned long reserveflags = (unsigned long)vma->vm_private_data;
>  	VM_BUG_ON(!is_vm_hugetlb_page(vma));
> -	vma->vm_private_data = (void *)(reserveflags | flags);
> +	VM_BUG_ON(vma->vm_flags & VM_SHARED);
> +
> +	set_vma_private_data(vma, get_vma_private_data(vma) | flags);
>  }
>  
>  static int is_vma_resv_set(struct vm_area_struct *vma, unsigned long flag)
>  {
>  	VM_BUG_ON(!is_vm_hugetlb_page(vma));
> -	return ((unsigned long)vma->vm_private_data & flag) != 0;
> +
> +	return (get_vma_private_data(vma) & flag) != 0;
>  }
>  
>  /* Decrement the reserved pages in the hugepage pool by one */
> @@ -1150,11 +1182,10 @@ static struct page *hugetlbfs_pagecache_page(struct vm_area_struct *vma,
>  			unsigned long address)
>  {
>  	struct address_space *mapping;
> -	unsigned long idx;
> +	pgoff_t idx;
>  
>  	mapping = vma->vm_file->f_mapping;
> -	idx = ((address - vma->vm_start) >> HPAGE_SHIFT)
> -		+ (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
> +	idx = vma_pagecache_offset(vma, address);
>  
>  	return find_lock_page(mapping, idx);
>  }
> @@ -1163,7 +1194,7 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  			unsigned long address, pte_t *ptep, int write_access)
>  {
>  	int ret = VM_FAULT_SIGBUS;
> -	unsigned long idx;
> +	pgoff_t idx;
>  	unsigned long size;
>  	struct page *page;
>  	struct address_space *mapping;
> @@ -1182,8 +1213,7 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  	}
>  
>  	mapping = vma->vm_file->f_mapping;
> -	idx = ((address - vma->vm_start) >> HPAGE_SHIFT)
> -		+ (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
> +	idx = vma_pagecache_offset(vma, address);
>  
>  	/*
>  	 * Use page lock to guard against racing truncation
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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