On Fri, Apr 3, 2020 at 6:55 AM Leonardo Bras <leona...@linux.ibm.com> wrote: > > While providing guests, it's desirable to resize it's memory on demand. > > By now, it's possible to do so by creating a guest with a small base > memory, hot-plugging all the rest, and using 'movable_node' kernel > command-line parameter, which puts all hot-plugged memory in > ZONE_MOVABLE, allowing it to be removed whenever needed. > > But there is an issue regarding guest reboot: > If memory is hot-plugged, and then the guest is rebooted, all hot-plugged > memory goes to ZONE_NORMAL, which offers no guaranteed hot-removal. > It usually prevents this memory to be hot-removed from the guest. > > It's possible to use device-tree information to fix that behavior, as > it stores flags for LMB ranges on ibm,dynamic-memory-vN. > It involves marking each memblock with the correct flags as hotpluggable > memory, which mm/memblock.c puts in ZONE_MOVABLE during boot if > 'movable_node' is passed.
I don't really understand why the flag is needed at all. According to PAPR any memory provided by dynamic reconfiguration can be hot-removed so why aren't we treating all DR memory as hot removable? The only memory guaranteed to be there 100% of the time is what's in the /memory@0 node since that's supposed to cover the real mode area.