Re: [PATCH] mm: Convert memory block states (MEM_*) macros to enum

[David Hildenbrand <david@redhat.com>]

On 26.10.25 17:22, Israel Batista wrote:
> The MEM_* constants indicating the state of the memory block are
> currently defined as macros, meaning their definitions will be omitted
> from the debuginfo on most kernel builds. This makes it harder for
> debuggers to correctly map the block state at runtime, which can be
> quite useful when analysing errors related to memory hot plugging and
> unplugging with tools such as drgn and eBPF.
> 
> Converting the constants to an enum will ensure the correct information
> is emitted by the compiler and available for the debugger, without needing
> to hard-code them into the debugger and track their changes.
> 
> Signed-off-by: Israel Batista <linux@israelbatista.dev.br>
> ---
>   include/linux/memory.h | 16 +++++++++-------
>   1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index ba1515160894..8feba3bfcd18 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -89,13 +89,15 @@ int arch_get_memory_phys_device(unsigned long start_pfn);
>   unsigned long memory_block_size_bytes(void);
>   int set_memory_block_size_order(unsigned int order);
>   
> -/* These states are exposed to userspace as text strings in sysfs */
> -#define	MEM_ONLINE		(1<<0) /* exposed to userspace */
> -#define	MEM_GOING_OFFLINE	(1<<1) /* exposed to userspace */
> -#define	MEM_OFFLINE		(1<<2) /* exposed to userspace */
> -#define	MEM_GOING_ONLINE	(1<<3)
> -#define	MEM_CANCEL_ONLINE	(1<<4)
> -#define	MEM_CANCEL_OFFLINE	(1<<5)
> +enum mem_states {
> +	/* These states are exposed to userspace as text strings in sysfs */
> +	MEM_ONLINE		 = (1<<0), /* exposed to userspace */
> +	MEM_GOING_OFFLINE	 = (1<<1), /* exposed to userspace */
> +	MEM_OFFLINE		 = (1<<2), /* exposed to userspace */
> +	MEM_GOING_ONLINE	 = (1<<3),
> +	MEM_CANCEL_ONLINE	 = (1<<4),
> +	MEM_CANCEL_OFFLINE	 = (1<<5),
> +};
>   
>   struct memory_notify {
>   	unsigned long start_pfn;

CCing Lorenzo, we recently had a discussion about such conversions.

The states are mutually exclusive (so no flags), so I wonder if we can 
just drop the (1<< X) setting completely. IIRC, these values are not 
exposed to user space, only the corresponding names are, see state_show().


Won't the compiler now complain that e.g., kcore_callback() does snot 
handle all cases? (no default statement)

-- 
Cheers

David / dhildenb