Re: [PATCH net-next v1] mm: fix build on powerpc with GCC 14

[Christophe Leroy]

Hi,

Le 13/09/2024 à 21:22, Matthew Wilcox a écrit :
> On Fri, Sep 13, 2024 at 07:20:36PM +0000, Mina Almasry wrote:
> > +++ b/include/linux/page-flags.h
> > @@ -239,8 +239,8 @@ static inline unsigned long _compound_head(const struct page *page)
> >   {
> >   	unsigned long head = READ_ONCE(page->compound_head);
> >   
> > -	if (unlikely(head & 1))
> > -		return head - 1;
> > +	if (unlikely(head & 1UL))
> > +		return head & ~1UL;
> >   	return (unsigned long)page_fixed_fake_head(page);
>
> NAK, that pessimises compound_head().

Can you please give more details on what the difference is ?

I can't see what it pessimises. In both cases, you test if the value is 
odd, when it is odd you make it even.

Christophe