Re: [PATCH RFC 09/12] mm/slab: introduce slab_obj_ext_has_codetag()

[Vlastimil Babka (SUSE)]

On 7/16/26 06:25, Suren Baghdasaryan wrote:
> On Wed, Jul 15, 2026 at 3:11 AM Vlastimil Babka (SUSE)
> <vbabka@xxxxxxxxxx> wrote:
>>
>> mem_alloc_profiling_enabled() allows evaluating (with a static key) if
>> memory profiling is currently enabled. mem_profiling_support is a
>> variable where false means it's not possible to enable it anymore,
>> because the system was booted with "never" or it was later shut down.
>> This is possible to query by mem_alloc_profiling_permanently_disabled().
>>
>> To make slabobj_ext array size handling dynamic, we need a snapshot of
>> mem_alloc_profiling_permanently_disabled() early in boot, so that's not
>> affected by a later shutdown. We also need it to be static key based for
>> performance. Neither mem_alloc_profiling_enabled() nor
>> mem_alloc_profiling_permanently_disabled() satisfy this.
>>
>> Therefore introduce slab_obj_ext_has_codetag() with an underlying static
>> key for that use case. Its state is made to reflect the result of
>> mem_alloc_profiling_permanently_disabled() during kmem_cache_init(),
>> which does happen after setup_early_mem_profiling().
>>
>> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
> 
> Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>

Thanks!

>> +/*
>> + * Make sure the static key used by slab_obj_ext_has_codetag() reflects the
>> + * value of !mem_alloc_profiling_permanently_disabled()
>> + *
>> + * Any later mem alloc profiling shutdown won't be reflected in the static key
>> + * because obj_exts with codetags might already exist.
>> + */
>> +static void __init slab_obj_ext_has_codetag_init(void)
>> +{
>> +       bool key_enabled = IS_ENABLED(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT);
> 
> nit: This seems a bit indirect. Reader needs to remember that
> slab_obj_ext_has_codetag_key is initialized based on
> CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT. Wouldn't below code be
> simpler?:
> 
> bool need_codetag = !mem_alloc_profiling_permanently_disabled();
> if (need_codetag != static_key_enabled(&slab_obj_ext_has_codetag_key)) {
>         if (need_codetag)
>                 static_branch_enable(&slab_obj_ext_has_codetag_key);
>         else
>                 static_branch_disable(&slab_obj_ext_has_codetag_key);
> }
> 
> It might be less performant but who cares, it's __init function used
> only one time.

Good idea, will do!