Re: [PATCH v2 4/4] mm/memory: convert do_read_fault() to use folios

[Matthew Wilcox]

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@xxxxxxxxxx>

Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>

> @@ -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.

>  	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;