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

From: Christophe Leroy <[email-masked]>
Date: Sat, 14 Sep 2024 08:50:46 +0200

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