Re: [PATCH v1 3/3] memory-hotplug.rst: document the "auto-movable" online policy

[David Hildenbrand]

> > 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