linux-kernel - Re: [PATCH v2] mm: get rid of odd jump labels in find_mergeable_anon

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Date:   Sun, 17 Nov 2019 19:31:57 -0800
From:   John Hubbard <jhubbard@...dia.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>,
        <david@...hat.com>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm: get rid of odd jump labels in
 find_mergeable_anon_vma()

On 11/17/19 7:22 PM, 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.
> -v2:
> 	Fix commit descriptions and further simplify the code
> 	as suggested by David Hildenbrand and John Hubbard.

Admin point: the above three lines will end up in the commit log,
which is probably not what you intended. If, instead, you put them 
below the "---" line, then they will act as comments about
the patch, and won't show up in the commit log.


thanks,
-- 
John Hubbard
NVIDIA

> 
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Reviewed-by: John Hubbard <jhubbard@...dia.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/mmap.c | 27 +++++++++++++--------------
>  1 file changed, 13 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 4d4db76a07da..ff02c23fd375 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1276,26 +1276,25 @@ 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;
>  
> +	/* Try next first. */
>  	near = vma->vm_next;
> -	if (!near)
> -		goto try_prev;
> +	if (near) {
> +		anon_vma = reusable_anon_vma(near, vma, near);
> +		if (anon_vma)
> +			return anon_vma;
> +	}
>  
> -	anon_vma = reusable_anon_vma(near, vma, near);
> -	if (anon_vma)
> -		return anon_vma;
> -try_prev:
> +	/* Try prev next. */
>  	near = vma->vm_prev;
> -	if (!near)
> -		goto none;
> +	if (near)
> +		anon_vma = reusable_anon_vma(near, near, vma);
>  
> -	anon_vma = reusable_anon_vma(near, near, vma);
> -	if (anon_vma)
> -		return anon_vma;
> -none:
>  	/*
> +	 * 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,
> @@ -1303,7 +1302,7 @@ 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;
>  }
>  
>  /*
>