On Thu 10-09-20 15:39:00, Oscar Salvador wrote: > On Thu, Sep 10, 2020 at 02:48:47PM +0200, Michal Hocko wrote: > > > Is there any actual usecase for a configuration like this? What is the > > > point to statically define additional memory like this when the same can > > > be achieved on the same command line? > > Well, for qemu I am not sure, but if David is right, it seems you can face > the same if you reboot a vm with hotplugged memory.
OK, thanks for the clarification. I was not aware of the reboot. > Moreover, it seems that the problem we spotted with [1], it was a VM running > on > Promox (KVM). > The Hypervisor probably said at boot time "Ey, I do have these ACPI devices, > care > to enable them now"? > > As always, there are all sorts of configurations/scenarios out there in the > wild. > > > Forgot to ask one more thing. Who is going to online that memory when > > userspace is not running yet? > > Depends, if you have CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE set or you specify > memhp_default_online_type=[online,online_*], memory will get onlined right > after hot-adding stage: > > /* online pages if requested */ > if (memhp_default_online_type != MMOP_OFFLINE) > walk_memory_blocks(start, size, NULL, online_memory_block); > > If not, systemd-udev will do the magic once the system is up. Does that imply that we need udev to scan all existing devices and reprobe them? -- Michal Hocko SUSE Labs
