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

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Message-ID: <5277de34-ecb3-831e-c697-1fd3f66b45ba@redhat.com>
Date:   Fri, 15 Nov 2019 13:58:02 +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,
        chenjianhong2@...wei.com, walken@...gle.com,
        dave.hansen@...ux.intel.com, tiny.windzz@...il.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: get rid of odd jump label in find_mergeable_anon_vma

On 15.11.19 07:36, linmiaohe wrote:
> From: Miaohe Lin <linmiaohe@...wei.com>

I'm pro removing unnecessary jump labels.

Subject: "mm: get rid of jump labels in find_mergeable_anon_vma()"

> 
> The odd jump label try_prev and none is not really need

s/odd jump label/jump labels/

s/is/are/

> in func find_mergeable_anon_vma, eliminate them to
> improve readability.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/mmap.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 4d4db76a07da..ab980d468a10 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1276,25 +1276,21 @@ 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 anon_vma *anon_vma = NULL;
>  	struct vm_area_struct *near;
>  
>  	near = vma->vm_next;
> -	if (!near)
> -		goto try_prev;
> -
> -	anon_vma = reusable_anon_vma(near, vma, near);
> +	if (near)
> +		anon_vma = reusable_anon_vma(near, vma, near);>  	if (anon_vma)
>  		return anon_vma;

Let me suggest the following instead:

/* Try next first */
near = vma->vm_next;
if (near) {
	anon_vma = reusable_anon_vma(near, vma, near);
	if (anon_vma)
		return anon_vma;
}
/* Try prev next */
near = vma->vm_prev;
if (near) {
	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);
> +	near = vma->vm_prev;
> +	if (near)
> +		anon_vma = reusable_anon_vma(near, near, vma);
>  	if (anon_vma)
>  		return anon_vma;
> -none:
> +
>  	/*
>  	 * There's no absolute need to look only at touching neighbours:
>  	 * we could search further afield for "compatible" anon_vmas.
> 


-- 

Thanks,

David / dhildenb