On 25.02.20 15:11, Michal Hocko wrote:

On Thu 12-12-19 18:11:32, David Hildenbrand wrote:

quoted

virtio-mem wants to offline and remove a memory block once it unplugged
all subblocks (e.g., using alloc_contig_range()). Let's provide
an interface to do that from a driver. virtio-mem already supports to
offline partially unplugged memory blocks. Offlining a fully unplugged
memory block will not require to migrate any pages. All unplugged
subblocks are PageOffline() and have a reference count of 0 - so
offlining code will simply skip them.

All we need an interface to trigger the "offlining" and the removing in a
single operation - to make sure the memory block cannot get onlined by
user space again before it gets removed.

Why does that matter? Is it really likely that the userspace would
interfere? What would be the scenario?

I guess it's not that relevant after all (I think this comment dates
back to the times where we didn't have try_remove_memory() and could
actually BUG_ON() in remove_memory() if there would have been a race).
Can drop that part.

Or is still mostly about not requiring callers to open code this general
patter?

From kernel module context, I cannot get access to the actual memory
block device (find_memory_block()) and call the device_unregister().

Especially, also the device hotplug lock is not exported. So this is a
clean helper function to be used from kernel module context. (e.g., also
hyper-v showed interest for using that)

-- 
Thanks,

David / dhildenb