linux-kernel - Re: [PATCH v10 10/69] mmap: use the VMA iterator in count_vma_pages

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Message-ID: <5d3bf51b-3bba-3bd4-db1f-1c0a3930a1e4@redhat.com>
Date:   Tue, 21 Jun 2022 23:13:31 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Liam Howlett <liam.howlett@...cle.com>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "damon @ lists . linux . dev" <damon@...ts.linux.dev>,
        SeongJae Park <sj@...nel.org>
Subject: Re: [PATCH v10 10/69] mmap: use the VMA iterator in
 count_vma_pages_range()

On 21.06.22 22:46, Liam Howlett wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> This simplifies the implementation and is faster than using the linked
> list.
> 
> Link: https://lkml.kernel.org/r/20220504010716.661115-12-Liam.Howlett@oracle.com
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: SeongJae Park <sj@...nel.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Davidlohr Bueso <dave@...olabs.net>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  mm/mmap.c | 24 +++++++-----------------
>  1 file changed, 7 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 6be7833c781b..d7e6baa2f40f 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -675,29 +675,19 @@ munmap_vma_range(struct mm_struct *mm, unsigned long start, unsigned long len,
>  
>  	return 0;
>  }
> +
>  static unsigned long count_vma_pages_range(struct mm_struct *mm,
>  		unsigned long addr, unsigned long end)
>  {
> -	unsigned long nr_pages = 0;
> +	VMA_ITERATOR(vmi, mm, addr);
>  	struct vm_area_struct *vma;
> +	unsigned long nr_pages = 0;
>  
> -	/* Find first overlapping mapping */
> -	vma = find_vma_intersection(mm, addr, end);
> -	if (!vma)
> -		return 0;
> -
> -	nr_pages = (min(end, vma->vm_end) -
> -		max(addr, vma->vm_start)) >> PAGE_SHIFT;
> -
> -	/* Iterate over the rest of the overlaps */
> -	for (vma = vma->vm_next; vma; vma = vma->vm_next) {
> -		unsigned long overlap_len;
> -
> -		if (vma->vm_start > end)
> -			break;
> +	for_each_vma_range(vmi, vma, end) {
> +		unsigned long vm_start = max(addr, vma->vm_start);
> +		unsigned long vm_end = min(end, vma->vm_end);

I thought using max_t and min_t was the latest advisory. I might be
wrong and simply kept doing it that way ;)

>  
> -		overlap_len = min(end, vma->vm_end) - vma->vm_start;
> -		nr_pages += overlap_len >> PAGE_SHIFT;
> +		nr_pages += (vm_end - vm_start) / PAGE_SIZE;

PHYS_PFN(vm_end - vm_start)

>  	}
>  
>  	return nr_pages;

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb