On 25.02.20 15:11, Michal Hocko wrote: > On Thu 12-12-19 18:11:32, David Hildenbrand wrote: >> 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
