On Tue, 18 Feb 2020 11:05:32 +0100 Michal Hocko [off-list ref] wrote:

Subject: [PATCH] memory_hotplug: disable the functionality for 32b

Memory hotlug is broken for 32b systems at least since c6f03e2903c9
("mm, memory_hotplug: remove zone restrictions") which has considerably
reworked how can be memory associated with movable/kernel zones. The
same is not really trivial to achieve in 32b where only lowmem is the
kernel zone. While we can tweak this immediate problem around there are
likely other land mines hidden at other places.

It is also quite dubious that there is a real usecase for the memory
hotplug on 32b in the first place. Low memory is just too small to be
hotplugable (for hot add) and generally unusable for hotremove. Adding
more memory to highmem is also dubious because it would increase the
low mem or vmalloc space pressure for memmaps.

Restrict the functionality to 64b systems. This will help future
development to focus on usecases that have real life application.  We
can remove this restriction in future in presence of a real life usecase
of course but until then make it explicit that hotplug on 32b is broken
and requires a non trivial amount of work to fix.

(cc linux-arch)

(and linux-arm-kernel, as ARM is a major 32-bit user)

Does anyone see a problem with disabling memory hotplug on 32-bit builds?

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