linux-kernel - Re: [v4 PATCH 3/7] mm: khugepaged: better comments for anon vma check in hugepage_vma

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Date:   Wed, 15 Jun 2022 16:57:40 -0700
From:   Zach O'Keefe <zokeefe@...gle.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     vbabka@...e.cz, kirill.shutemov@...ux.intel.com,
        willy@...radead.org, linmiaohe@...wei.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v4 PATCH 3/7] mm: khugepaged: better comments for anon vma
 check in hugepage_vma_revalidate

On 15 Jun 10:29, Yang Shi wrote:
> The hugepage_vma_revalidate() needs to check if the vma is still
> anonymous vma or not since the address may be unmapped then remapped to
> file before khugepaged reaquired the mmap_lock.
> 
> The old comment is not quite helpful, elaborate this with better
> comment.
> 
> Signed-off-by: Yang Shi <shy828301@...il.com>
> ---
>  mm/khugepaged.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index db0b334a7d1f..5baa394e34c8 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -960,7 +960,13 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
>  		return SCAN_ADDRESS_RANGE;
>  	if (!hugepage_vma_check(vma, vma->vm_flags))
>  		return SCAN_VMA_CHECK;
> -	/* Anon VMA expected */
> +	/*
> +	 * Anon VMA expected, the address may be unmapped then
> +	 * remapped to file after khugepaged reaquired the mmap_lock.
> +	 *
> +	 * hugepage_vma_check may return true for qualified file
> +	 * vmas.
> +	 */
>  	if (!vma->anon_vma || !vma_is_anonymous(vma))
>  		return SCAN_VMA_CHECK;
>  	return 0;
> -- 
> 2.26.3
> 

Reviewed-by: Zach O'Keefe <zokeefe@...gle.com>