On 26.07.19 09:57, Michal Hocko wrote: > On Thu 25-07-19 22:49:36, David Hildenbrand wrote: >> On 25.07.19 21:19, Michal Hocko wrote: > [...] >>> We need to rationalize the locking here, not to add more hacks. >> >> No, sorry. The real hack is calling a function that is *documented* to >> be called under lock without it. That is an optimization for a special >> case. That is the black magic in the code. > > OK, let me ask differently. What does the device_hotplug_lock actually > protects from in the add_memory path? (Which data structures) > > This function is meant to be used when struct pages and node/zone data > structures should be updated. Why should we even care about some device > concept here? This should all be handled a layer up. Not all memory will > have user space API to control online/offline state. Via add_memory()/__add_memory() we create memory block devices for all memory. So all memory we create via this function (IOW, hotplug) will have user space APIs. Sorry, I can't follow what you are saying here - are you confusing the function we are talking about with arch_add_memory() ? (where I pulled out the creation of memory block devices) -- Thanks, David / dhildenb
