Re: [PATCH v3 2/7] mm/hotplug: Allow memmap on memory hotplug request to fallback

[David Hildenbrand <david@xxxxxxxxxx>]

> -bool mhp_supports_memmap_on_memory(unsigned long size)
> +static bool mhp_supports_memmap_on_memory(unsigned long size)
>   {
>   	unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
>   	unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
> @@ -1339,13 +1339,12 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
>   	 * Self hosted memmap array
>   	 */
>   	if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
> -		if (!mhp_supports_memmap_on_memory(size)) {
> -			ret = -EINVAL;
> -			goto error;
> +		if (mhp_supports_memmap_on_memory(size)) {
> +			mhp_altmap.free = PHYS_PFN(size);
> +			mhp_altmap.base_pfn = PHYS_PFN(start);
> +			params.altmap = &mhp_altmap;
>   		}
> -		mhp_altmap.free = PHYS_PFN(size);
> -		mhp_altmap.base_pfn = PHYS_PFN(start);
> -		params.altmap = &mhp_altmap;
> +		/* fallback to not using altmap  */
>   	}
>   
>   	/* call arch's memory hotadd */

In general, LGTM, but please extend the documentation of the parameter 
in memory_hotplug.h, stating that this is just a hint and that the core 
can decide to no do that.

--
Cheers,

David / dhildenb