linux-kernel - Re: [PATCH 2/2] x86/mm: replace a goto by merging two if clause

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Message-ID: <20191001114700.wqcglmbrajqkmc22@master>
Date:   Tue, 1 Oct 2019 11:47:00 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        dave.hansen@...ux.intel.com, luto@...nel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/mm: replace a goto by merging two if clause

On Mon, Sep 23, 2019 at 11:22:31AM +0200, Peter Zijlstra wrote:
>On Thu, Sep 19, 2019 at 10:08:44AM +0800, Wei Yang wrote:
>> There is only one place to use good_area jump, which could be reduced by
>> merging the following two if clause.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
>> ---
>>  arch/x86/mm/fault.c | 11 +++++------
>>  1 file changed, 5 insertions(+), 6 deletions(-)
>> 
>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
>> index 9d18b73b5f77..72ce6c69e195 100644
>> --- a/arch/x86/mm/fault.c
>> +++ b/arch/x86/mm/fault.c
>> @@ -1390,18 +1390,17 @@ void do_user_addr_fault(struct pt_regs *regs,
>>  	vma = find_vma(mm, address);
>>  	if (unlikely(!vma))
>>  		goto bad_area;
>> -	if (likely(vma->vm_start <= address))
>> -		goto good_area;
>> -	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
>> -		goto bad_area;
>> -	if (unlikely(expand_stack(vma, address)))
>> +	if (likely(vma->vm_start <= address)) {
>> +		/* good area, do nothing */
>> +	} else if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)) ||
>> +		   unlikely(expand_stack(vma, address))) {
>>  		goto bad_area;
>> +	}
>>  
>>  	/*
>>  	 * Ok, we have a good vm_area for this memory access, so
>>  	 * we can handle it..
>>  	 */
>> -good_area:
>>  	if (unlikely(access_error(hw_error_code, vma))) {
>>  		bad_area_access_error(regs, hw_error_code, address, vma);
>>  		return;
>
>I find the old code far easier to read... is there any actual reason to
>do this?

Hi, Peter,

Do you have some comment for the Patch 1?

-- 
Wei Yang
Help you, Help me