Re: [PATCH RFC 05/12] mm/slab: abstract slabobj_ext.objcg access

[Vlastimil Babka (SUSE)]

On 7/16/26 03:27, Suren Baghdasaryan wrote:
> On Wed, Jul 15, 2026 at 3:11 AM Vlastimil Babka (SUSE)
> <vbabka@xxxxxxxxxx> wrote:
>> --- a/mm/slab.h
>> +++ b/mm/slab.h
>> @@ -555,7 +555,7 @@ static inline bool need_kmalloc_no_objext(void)
>>   */
>>  struct slabobj_ext {
>>  #ifdef CONFIG_MEMCG
>> -       struct obj_cgroup *objcg;
>> +       struct obj_cgroup *_objcg;
>>  #endif
>>  #ifdef CONFIG_MEM_ALLOC_PROFILING
>>         union codetag_ref ref;
>> @@ -661,6 +661,13 @@ slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,
>>         return kasan_reset_tag(obj_ext);
>>  }
>>
>> +#ifdef CONFIG_MEMCG
>> +static inline struct obj_cgroup **slab_obj_ext_objcgp(struct slabobj_ext *obj_ext)
> 
> I understand why you need to return obj_cgroup** but maybe instead we
> can have a separate setter function and just return a pointer here?

Yeah I rewrote it now and it looks better. Thanks! It ended up like this due
to some previous attempt I made.

> That would also help catch cases when someone wants to set
> obj_ext._objcg that was optimized away (for that the setter would need
> an additional parameter to identify whether we allocated optimized
> objext vector).

It would need passing the slab parameter to assert
slab_obj_ext_has_codetag() in debug mode. I don't think it's worth it given
the get/set is only called from few specialized places.

> 
>> +{
>> +       return &obj_ext->_objcg;
>> +}
>> +#endif
>> +
>>  int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
>>                         gfp_t gfp, unsigned int alloc_flags);
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 5e3f53bcd0d3..48e10198a3ce 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -2523,7 +2523,7 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
>>         if (obj_exts) {
>>                 get_slab_obj_exts(obj_exts);
>>                 obj_ext = slab_obj_ext(s, slab, obj_exts, p);
>> -               if (unlikely(obj_ext->objcg)) {
>> +               if (unlikely(*slab_obj_ext_objcgp(obj_ext))) {
>>                         put_slab_obj_exts(obj_exts);
>>                         return true;
>>                 }
>>
>> --
>> 2.55.0
>>