linux-kernel - Re: [PATCH v4 08/66] mmap: Use the VMA iterator in count_vma_pages

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Message-ID: <ffbb5843-4c5a-99c1-12a6-2ff3ae818e3c@suse.cz>
Date:   Thu, 9 Dec 2021 16:54:23 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
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>
Cc:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 08/66] mmap: Use the VMA iterator in
 count_vma_pages_range()

On 12/1/21 15:29, Liam Howlett wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> This simplifies the implementation and is faster than using the linked
> list.

You mean faster because more cache friendly?
OTOH you do max(addr, vma->vm_start) which wasn't the case.

I doubt it matters though and yeah it's much simpler...

> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Acked-by: Vlastimil Babka <vbabka@...e.cz>

Btw, no signed-off-by Liam?

I now also notice some other patches (e.g. patch 4) have From: and s-o-b by
Liam followed by Matthew, despite it's Liam sending them. I guess that's
less of an issue than the missing one.

Anyway something for you to check and make consistent in the whole series, I
won't point it out individually.

> ---
>  mm/mmap.c | 24 +++++++-----------------
>  1 file changed, 7 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 9fee6e6b276f..de78fc0ce809 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -669,29 +669,19 @@ 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);
>  
> -		overlap_len = min(end, vma->vm_end) - vma->vm_start;
> -		nr_pages += overlap_len >> PAGE_SHIFT;
> +		nr_pages += (vm_end - vm_start) / PAGE_SIZE;
>  	}
>  
>  	return nr_pages;