linux-kernel - Re: [PATCH v2 4/4] mm/memory: convert do_read

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Date:   Wed, 5 Jul 2023 13:25:56 -0700
From:   Sidhartha Kumar <sidhartha.kumar@...cle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH v2 4/4] mm/memory: convert do_read_fault() to use folios

On 7/5/23 1:19 PM, Matthew Wilcox wrote:
> On Wed, Jul 05, 2023 at 12:43:35PM -0700, Sidhartha Kumar wrote:
>> Saves one implicit call to compound_head()
>>
>> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
> 
> Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> 
>> @@ -4543,10 +4544,12 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
>>   	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
>>   		return ret;
>>   
>> +	folio = page_folio(vmf->page);
> 
> Why not move this down to after the call to finish_fault()?  The
> compiler should be able to do a better job with that; it may have to
> spill it to the stack to preserve it over the function call.
> 

I just noticed that the page inside the vmf was being used in 
finish_fault() so it would stable enough to do the folio conversion 
before. I can move it after for compiler reasons.

>>   	ret |= finish_fault(vmf);
>> -	unlock_page(vmf->page);
>> +	folio_unlock(folio);
>>   	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
>> -		put_page(vmf->page);
>> +		folio_put(folio);
>>   	return ret;
> 
>