linux-kernel - Re: [PATCH v4] mm: get rid of odd jump labels in find_mergeable_anon

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Message-ID: <6bc28c72-6a84-0579-da0c-59d4fd695682@redhat.com>
Date:   Mon, 18 Nov 2019 14:48:35 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linmiaohe <linmiaohe@...wei.com>, akpm@...ux-foundation.org,
        richardw.yang@...ux.intel.com, sfr@...b.auug.org.au,
        rppt@...ux.ibm.com, jannh@...gle.com, steve.capper@....com,
        catalin.marinas@....com, aarcange@...hat.com, walken@...gle.com,
        dave.hansen@...ux.intel.com, tiny.windzz@...il.com,
        jhubbard@...dia.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] mm: get rid of odd jump labels in
 find_mergeable_anon_vma()

On 18.11.19 13:24, linmiaohe wrote:
> From: Miaohe Lin <linmiaohe@...wei.com>
> 
> The jump labels try_prev and none are not really needed
> in find_mergeable_anon_vma(), eliminate them to improve
> readability.
> 
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Reviewed-by: John Hubbard <jhubbard@...dia.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
> -v2:
> 	Fix commit descriptions and further simplify the code
> 	as suggested by David Hildenbrand and John Hubbard.
> -v3:
> 	Rewrite patch version info. Don't show this in commit log.
> -v4:
> 	Get rid of var near completely as well.
> ---
>   mm/mmap.c | 36 ++++++++++++++++--------------------
>   1 file changed, 16 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 91d5e097a4ed..4d93bda30eac 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1273,26 +1273,22 @@ static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old, struct vm_
>    */
>   struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
>   {
> -	struct anon_vma *anon_vma;
> -	struct vm_area_struct *near;
> -
> -	near = vma->vm_next;
> -	if (!near)
> -		goto try_prev;
> -
> -	anon_vma = reusable_anon_vma(near, vma, near);
> -	if (anon_vma)
> -		return anon_vma;
> -try_prev:
> -	near = vma->vm_prev;
> -	if (!near)
> -		goto none;
> -
> -	anon_vma = reusable_anon_vma(near, near, vma);
> -	if (anon_vma)
> -		return anon_vma;
> -none:
> +	struct anon_vma *anon_vma = NULL;
> +
> +	/* Try next first. */
> +	if (vma->vm_next) {
> +		anon_vma = reusable_anon_vma(vma->vm_next, vma, vma->vm_next);
> +		if (anon_vma)
> +			return anon_vma;
> +	}
> +
> +	/* Try prev next. */
> +	if (vma->vm_prev)
> +		anon_vma = reusable_anon_vma(vma->vm_prev, vma->vm_prev, vma);
> +
>   	/*
> +	 * We might reach here with anon_vma == NULL if we can't find
> +	 * any reusable anon_vma.
>   	 * There's no absolute need to look only at touching neighbours:
>   	 * we could search further afield for "compatible" anon_vmas.
>   	 * But it would probably just be a waste of time searching,
> @@ -1300,7 +1296,7 @@ struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
>   	 * We're trying to allow mprotect remerging later on,
>   	 * not trying to minimize memory used for anon_vmas.
>   	 */
> -	return NULL;
> +	return anon_vma;
>   }
>   
>   /*
> 

Looks much better, thanks!

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

-- 

Thanks,

David / dhildenb