Re: [v5 2/3] mm/hotplug: make remove_memory() interface useable

[Dave Hansen <dave.hansen@intel.com>]

> -static inline void remove_memory(int nid, u64 start, u64 size) {}
> +static inline bool remove_memory(int nid, u64 start, u64 size)
> +{
> +	return -EBUSY;
> +}

This seems like an appropriate place for a WARN_ONCE(), if someone
manages to call remove_memory() with hotplug disabled.

BTW, I looked and can't think of a better errno, but -EBUSY probably
isn't the best error code, right?

> -void remove_memory(int nid, u64 start, u64 size)
> +/**
> + * remove_memory
> + * @nid: the node ID
> + * @start: physical address of the region to remove
> + * @size: size of the region to remove
> + *
> + * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> + * and online/offline operations before this call, as required by
> + * try_offline_node().
> + */
> +void __remove_memory(int nid, u64 start, u64 size)
>  {
> +
> +	/*
> +	 * trigger BUG() is some memory is not offlined prior to calling this
> +	 * function
> +	 */
> +	if (try_remove_memory(nid, start, size))
> +		BUG();
> +}

Could we call this remove_offline_memory()?  That way, it makes _some_
sense why we would BUG() if the memory isn't offline.