Re: [PATCH] mm/page_alloc: simplify page_is_buddy() for better code readability

[chenqiwu <qiwuchen55@gmail.com>]

On Mon, Mar 09, 2020 at 09:53:08AM -0700, Alexander Duyck wrote:
> On Sun, Mar 8, 2020 at 12:10 AM <qiwuchen55@gmail.com> wrote:
> >
> > From: chenqiwu <chenqiwu@xiaomi.com>
> >
> > Simplify page_is_buddy() to reduce the redundant code for better
> > code readability.
> >
> > Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
> > ---
> >  mm/page_alloc.c | 13 +++----------
> >  1 file changed, 3 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 79e950d..c6eef38 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -797,16 +797,8 @@ static inline void set_page_order(struct page *page, unsigned int order)
> >  static inline int page_is_buddy(struct page *page, struct page *buddy,
> >                                                         unsigned int order)
> >  {
> > -       if (page_is_guard(buddy) && page_order(buddy) == order) {
> > -               if (page_zone_id(page) != page_zone_id(buddy))
> > -                       return 0;
> > -
> > -               VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
> > -
> > -               return 1;
> > -       }
> > -
> > -       if (PageBuddy(buddy) && page_order(buddy) == order) {
> > +       if ((page_is_guard(buddy) || PageBuddy(buddy))
> > +            && page_order(buddy) == order) {
> >                 /*
> >                  * zone check is done late to avoid uselessly
> >                  * calculating zone/node ids for pages that could
> 
> Instead of keeping the if statement as is couldn't you flatten this
> out further by just returning 0 if !page_is_guard && !PageBuddy?
> 
> So something like:
> if (!page_is_guard(buddy) && !PageBuddy(buddy))
>         return0;
> 
> if (page_order(buddy) != order)
>         return 0;
> 
> I feel like this would be more readable than sorting out the
> parenthesis for the conditional statement. Then you can also just get
> rid of the indenting and braces for the rest of the statement. With
> that it would more closely match the description above as well as you
> are going through and checking a - d as separate tests.

I agree, for performance considering, I think the second conditional statement
should be moved up. I will resend this as proper patch v2 for review.