Re: [PATCH 2/3] mm, slab: use an enum to define SLAB_ cache creation flags

Vlastimil Babka
2024-02-23T17:06:23Z

On 2/23/24 17:43, Vlastimil Babka wrote:
> On 2/23/24 04:12, Christoph Lameter (Ampere) wrote:
>> On Tue, 20 Feb 2024, Vlastimil Babka wrote:
>>
>>> diff --git a/mm/slub.c b/mm/slub.c
>>> index 2ef88bbf56a3..a93c5a17cbbb 100644
>>> --- a/mm/slub.c
>>> +++ b/mm/slub.c
>>> @@ -306,13 +306,13 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
>>>
>>> /* Internal SLUB flags */
>>> /* Poison object */
>>> -#define __OBJECT_POISON ((slab_flags_t __force)0x80000000U)
>>> +#define __OBJECT_POISON __SF_BIT(_SLAB_OBJECT_POISON)
>>> /* Use cmpxchg_double */
>>>
>>> #ifdef system_has_freelist_aba

Hm but we only have this in the internal mm/slab.h

>>> -#define __CMPXCHG_DOUBLE ((slab_flags_t __force)0x40000000U)
>>> +#define __CMPXCHG_DOUBLE __SF_BIT(_SLAB_CMPXCHG_DOUBLE)
>>> #else
>>> -#define __CMPXCHG_DOUBLE ((slab_flags_t __force)0U)
>>> +#define __CMPXCHG_DOUBLE 0

And keeping the 0 is desirable to make the checks compile-time false when
it's not available.

So maybe it's best if it stays here after all, or we'd pull too much of
internal details into the "public" slab.h

>>> #endif
>>
>> Maybe its good to put these internal flags together with the other flags.
>> After all there is no other slab allocator available anymore and having
>> them all together avoids confusion.
>
> Good poiint, will do. Then I can also #undef the helper macro after the last
> flag.
>
>
>