linux-kernel - Re: [PATCH] mm/mlock: stop counting mlocked pages when none vma is found

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Message-ID: <2e3ff8fb-8d8f-b906-2187-3b558e56adfa@redhat.com>
Date:   Fri, 5 Feb 2021 09:14:44 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mlock: stop counting mlocked pages when none vma is
 found

On 04.02.21 12:07, Miaohe Lin wrote:
> There will be no vma satisfies addr < vm_end when find_vma() returns NULL.
> Thus it's meaningless to traverse the vma list below because we can't find
> any vma to count mlocked pages. Stop counting mlocked pages in this case to
> save some vma list traversal cycles.

I think this is correct. We will have addr >= vm_end for any VMA, so 
there are no applicable VMAs.

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

> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>   mm/mlock.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 73960bb3464d..f8f8cc32d03d 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -622,7 +622,7 @@ static unsigned long count_mm_mlocked_page_nr(struct mm_struct *mm,
>   
>   	vma = find_vma(mm, start);
>   	if (vma == NULL)
> -		vma = mm->mmap;
> +		return 0;
>   
>   	for (; vma ; vma = vma->vm_next) {
>   		if (start >= vma->vm_end)
> 


-- 
Thanks,

David / dhildenb