linux-kernel - Re: [PATCH 2/3] mm, slab: use an enum to define SLAB

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Message-ID: <9b6a4b83-0922-494e-9284-9214152c8e9c@suse.cz>
Date: Fri, 23 Feb 2024 18:06:20 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: "Christoph Lameter (Ampere)" <cl@...ux.com>
Cc: Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>,
 Joonsoo Kim <iamjoonsoo.kim@....com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>, Andrey Ryabinin
 <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>,
 Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>,
 Vincenzo Frascino <vincenzo.frascino@....com>,
 Zheng Yejian <zhengyejian1@...wei.com>,
 Xiongwei Song <xiongwei.song@...driver.com>,
 Chengming Zhou <chengming.zhou@...ux.dev>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH 2/3] mm, slab: use an enum to define SLAB_ cache creation
 flags

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.
> 
> 
>