Re: [PATCH v6 04/10] mm/memory_hotplug: export mhp_get_default_online_type

[Dave Jiang]

On 6/30/26 2:18 PM, Gregory Price wrote:
> Drivers which may pass hotplug policy down to DAX need MMOP_ symbols
> and the mhp_get_default_online_type function for hotplug use cases.
> 
> Some drivers (cxl) co-mingle their hotplug and devdax use-cases into
> the same driver code, and chose the dax_kmem path as the default driver
> path - making it difficult to require hotplug as a predicate to building
> the overall driver (it may break other non-hotplug use-cases).
> 
> Export mhp_get_default_online_type function to allow these drivers to
> build when hotplug is disabled and still use the DAX use case.
> 
> In the built-out case we simply return MMOP_OFFLINE as it's
> non-destructive.  The internal function can never return -1 either,
> so we choose this to allow for defining the function with 'enum mmop'.
> 
> Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
> Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>

> ---
>  include/linux/memory_hotplug.h | 2 ++
>  mm/memory_hotplug.c            | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 5d4b628c4a1f..4d51fcb93a37 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -317,6 +317,8 @@ extern struct zone *zone_for_pfn_range(enum mmop online_type,
>  extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
>  				      struct mhp_params *params);
>  void arch_remove_linear_mapping(u64 start, u64 size);
> +#else
> +static inline enum mmop mhp_get_default_online_type(void) { return MMOP_OFFLINE; }
>  #endif /* CONFIG_MEMORY_HOTPLUG */
>  
>  #endif /* __LINUX_MEMORY_HOTPLUG_H */
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6833208cc17c..494257054095 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -239,6 +239,7 @@ enum mmop mhp_get_default_online_type(void)
>  
>  	return mhp_default_online_type;
>  }
> +EXPORT_SYMBOL_GPL(mhp_get_default_online_type);
>  
>  void mhp_set_default_online_type(enum mmop online_type)
>  {