Re: [PATCH 2/3] mm/gup: small refactoring: simplify try_grab_page()

[John Hubbard]

On 8/8/21 11:38 PM, Christoph Hellwig wrote:
> On Sun, Aug 08, 2021 at 04:50:17PM -0700, John Hubbard wrote:
> > try_grab_page() does the same thing as try_grab_compound_head(...,
> > refs=1, ...), just with a different API. So there is a lot of code
> > duplication there.
> >
> > Change try_grab_page() to call try_grab_compound_head(), while keeping
> > the API contract identical for callers.
> >
> > Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> > ---
> >   mm/gup.c | 29 ++---------------------------
> >   1 file changed, 2 insertions(+), 27 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 5cb18b62921c..4be6f060fa0b 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -203,33 +203,8 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
> >    */
> >   bool __must_check try_grab_page(struct page *page, unsigned int flags)
> >   {
> > +	if (flags & (FOLL_GET | FOLL_PIN))
> > +		return try_grab_compound_head(page, 1, flags) != NULL;
> >   
> >   	return true;
>
> Nit: something like:
>
> 	if (!(flags & (FOLL_GET | FOLL_PIN)))
> 		return true;
> 	return try_grab_compound_head(page, 1, flags) != NULL;
>
> would be a little easier to read.

Really? Well I'll be darned, that's what I wrote in my first draft. And then
I looked at the diffs and thought, "positive logic is clearer, and the diffs
are smaller too", and went with the current version. Which now is apparently
a little worse. oops.

Well, "50-50/90", as we used to say in an earlier job: 50% chance of either
outcome, and due to The Way Things Go, a 90% chance of picking the wrong one!

I can no longer tell which one is easier to read now, so I'll be glad to change
it. :)

thanks,
--
John Hubbard
NVIDIA