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

[Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>]

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@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.

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;