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

[Omar Sandoval <osandov@osandov.com>]

On Sun, Oct 26, 2025 at 04:22:05PM +0000, 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)

What kernel version is this patch based on? It doesn't apply on mainline
because it is missing a couple of definitions added in 6.9 by commit
c5f1e2d18909 ("mm/memory_hotplug: introduce
MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers").

> +enum mem_states {

mem_state is very vague. enum memory_block_state might be a more
appropriate name.

Thanks for sending this!

Omar

> +	/* 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;
> -- 
> 2.51.0
> 
>