Re: [PATCH] SLUB: Fix __GFP_ZERO unlikely() annotation

[Pekka Enberg <penberg@cs.helsinki.fi>]

Joe Perches wrote:
> On Wed, 2009-11-25 at 20:21 +0200, Pekka Enberg wrote:
>> The unlikely() annotation in slab_alloc() covers too much of the expression.
>> It's actually very likely that the object is not NULL so use unlikely() only
>> for the __GFP_ZERO expression like SLAB does.
> []
>> +++ b/mm/slub.c
>> @@ -1735,7 +1735,7 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
>> -	if (unlikely((gfpflags & __GFP_ZERO) && object))
>> +	if (unlikely(gfpflags & __GFP_ZERO) && object)
>>  		memset(object, 0, objsize);
> 
> so why not use
> 
> 	if (unlikely(gfpflags & __GFP_ZERO) && likely(object))

Because that has no effect on the generated code.