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

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Date:   Sat, 16 Nov 2019 08:37:25 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     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,
        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 Fri, Nov 15, 2019 at 01:58:02PM +0100, David Hildenbrand wrote:
>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;
>}
>

Can we have an array with vma->vm_next and vma->vm_prev, then iterate on the
array?

>> -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

-- 
Wei Yang
Help you, Help me