Re: [PATCH 5/5] mm/alloc_tag: add the CONFIG_ARCH_NEEDS_WEAK_PER_CPU macro when statically defining the percpu variable _shared_alloc_tag

[Mike Rapoport <rppt@kernel.org>]

On Thu, Jun 12, 2025 at 04:27:30PM +0800, Hao Ge wrote:
> From: Hao Ge <gehao@kylinos.cn>
> 
> Recently discovered this entry while checking kallsyms on ARM64:
> ffff800083e509c0 D _shared_alloc_tag
> 
> If CONFIG_ARCH_NEEDS_WEAK_PER_CPU is not defined(it is only defined for
> s390 and alpha architectures),there's no need to statically define
> the percpu variable _shared_alloc_tag. As the number of CPUs
> increases,the wasted memory will grow correspondingly.
> 
> Enclose the definition of _shared_alloc_tag within the
> CONFIG_ARCH_NEEDS_WEAK_PER_CPU condition.
> 
> Suggested-by: Suren Baghdasaryan <surenb@google.com>
> Signed-off-by: Hao Ge <gehao@kylinos.cn>
> ---
>  lib/alloc_tag.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> index c7f602fa7b23..14fd66f26e42 100644
> --- a/lib/alloc_tag.c
> +++ b/lib/alloc_tag.c
> @@ -24,8 +24,10 @@ static bool mem_profiling_support;
>  
>  static struct codetag_type *alloc_tag_cttype;
>  
> +#ifdef CONFIG_ARCH_NEEDS_WEAK_PER_CPU

It should be enough to add #ifdef ARCH_NEEDS_WEAK_PER_CPU here instead of
all the churn.

>  DEFINE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);
>  EXPORT_SYMBOL(_shared_alloc_tag);
> +#endif
>  
>  DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
>  			mem_alloc_profiling_key);
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.