Hi, After some discussion with Jason, and re-reading the code and its current state in code, I've come to the conclusion that it's in the interest of brevity to remove everything in sys/kern/ and sys/uvm/ which implement the "dynamic" part of uvm_hotplug(9).
The top two reasons for this in my mind are: 1) There are no current users of the uvm_hotplug(9) KPI - balloon(9) uses it, but the unplug is unstable (wasn't able to debug this) and is thus disabled by default. 2) In order to do unplug without a balloon(9) like mechanism (eg: on native), there's a lot more state management code needed within uvm(9) - to make sure that RAM segments being unplugged have no machine references (eg: pmap related, pointers from inactive page tables, TLB pointers, etc. etc. ) This is a lot of per-architecture work, and there doesn't seem to be much demand for this feature (at least I haven't seen any comment related to this as a usecase). I believe that the project has had three useful purposes: 1) Demonstrated NetBSD code discipline - such a core part of the kernel code was developed entirely in userspace prior to integration - and due to the cross-compilable toolchain - it was done on Windows by fox@! 2) The re-org forced better modularisation in the relevant uvm/uvm_*.[hc] - ensuring even cleaner interfaces. 3) Demonstrated how TDD can reduce the pain of software dev. See: https://www.netbsd.org/gallery/presentations/santhosh/2017_AsiaBSDCon/ABC2017-P8B-uvm_hotplug-paper.pdf If there's no specific objection to this I'll be working with Jason to help make this is as painless as possible. Many Thanks! -- MattC/(~cherry)
