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Date:   Sat, 16 Nov 2019 08:37:25 +0800
From:   Wei Yang <richardw.yang@linux.intel.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     linmiaohe <linmiaohe@huawei.com>, akpm@linux-foundation.org,
        richardw.yang@linux.intel.com, sfr@canb.auug.org.au,
        rppt@linux.ibm.com, jannh@google.com, steve.capper@arm.com,
        catalin.marinas@arm.com, aarcange@redhat.com,
        chenjianhong2@huawei.com, walken@google.com,
        dave.hansen@linux.intel.com, tiny.windzz@gmail.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: get rid of odd jump label in find_mergeable_anon_vma
Message-ID: <20191116003725.GA18271@richard>
Reply-To: Wei Yang <richardw.yang@linux.intel.com>
References: <1573799768-15650-1-git-send-email-linmiaohe@huawei.com>
 <5277de34-ecb3-831e-c697-1fd3f66b45ba@redhat.com>
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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@huawei.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@huawei.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