From b59d02ed086907e2d4ea3ecf0720f0cbd54a2601 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Thu, 4 Jun 2020 16:48:51 -0700 Subject: mm/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. Robin said: "32-bit Arm doesn't support memory hotplug, and as far as I'm aware there's little likelihood of it ever wanting to. FWIW it looks like SuperH is the only pure-32-bit architecture to have hotplug support at all" Signed-off-by: Michal Hocko Signed-off-by: Andrew Morton Acked-by: David Hildenbrand Acked-by: Baoquan He Cc: Wei Yang Cc: Naoya Horiguchi Cc: Oscar Salvador Cc: Robin Murphy Cc: Vamshi K Sthambamkadi Link: http://lkml.kernel.org/r/20200218100532.GA4151@dhcp22.suse.cz Link: https://bugzilla.kernel.org/show_bug.cgi?id=206401 Signed-off-by: Linus Torvalds --- mm/Kconfig | 1 + 1 file changed, 1 insertion(+) (limited to 'mm/Kconfig') diff --git a/mm/Kconfig b/mm/Kconfig index 5b28240d2af8..cffc276fa19c 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -158,6 +158,7 @@ config MEMORY_HOTPLUG bool "Allow for memory hot-add" depends on SPARSEMEM || X86_64_ACPI_NUMA depends on ARCH_ENABLE_MEMORY_HOTPLUG + depends on 64BIT || BROKEN select NUMA_KEEP_MEMINFO if NUMA config MEMORY_HOTPLUG_SPARSE -- cgit v1.2.3