It's essentially ignored with the auto-movable policy for memory hotplugged
after boot (!MEMBLOCK_HOTPLUG). That's why only the description of
"contig-zones" below describes how it interacts with the ``movable_node``,
and we make it clear here that it's restricted to the "contig-zones" policy
as well.
<details>
Bare metal, where we care about reliably unplugging hotplugged memory
usually configures auto-onlining to "online_movable": for example, that's
the case on RHEL. auto-movable doesn't make too much sense for bare metal:
the nature of "movable_node" is to essentially online anything that might
get hotunplugged MOVABLE, especially after hotplugging memory and rebooting:
that is highly dangerous especially in virtualized environments.
"auto-movable" is valuable in virtualized environments, where we add memory
via:
* add_memory_driver_managed() like virtio-mem, whereby such memory is
never part of the firmware provided memory-map, so the policy is
always in control even after a reboot.
* Hotplugged virtual DIMMs, such as provided by x86-64/arm64, whereby we
don't include these DIMMs in the firmware-provided memory map, but
ACPI code adds them after early boot, making it behave similar to
add_memory_driver_managed() -- the policy is always in control even
after a reboot.
</details>
Do you want to put it somewhere in Documentation/ ?
It's already written anyway ;-)
I'll add to the "auto-movable" description:
"This policy ignores the ``movable_node`` kernel command line parameter
and isn't really applicable in environments that require it (e.g., bare
metal with hotunpluggable nodes) where hotplugged memory might be
exposed via the firmware-provided memory map early during boot to the
system instead of getting detected, added and onlined later during boot
(such as done by virito-mem or by some hypervisors implementing emulated
DIMMs)."
Thanks Mike!
--
Thanks,
David / dhildenb
