On Sat, Sep 14, 2024 at 08:50:46AM +0200, Christophe Leroy wrote: > 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. On x86, for example, it is perfectly valid to load a 64-bit value from an offset of 0x2f relative to a pointer. So there's no need to make it even.