On Thu, 12 Nov 2020 14:38:13 +0100 David Hildenbrand [off-list ref] wrote:

virtio-mem soon wants to use offline_and_remove_memory() memory that
exceeds a single Linux memory block (memory_block_size_bytes()). Let's
remove that restriction.

Let's remember the old state and try to restore that if anything goes
wrong. While re-onlining can, in general, fail, it's highly unlikely to
happen (usually only when a notifier fails to allocate memory, and these
are rather rare).

This will be used by virtio-mem to offline+remove memory ranges that are
bigger than a single memory block - for example, with a device block
size of 1 GiB (e.g., gigantic pages in the hypervisor) and a Linux memory
block size of 128MB.

While we could compress the state into 2 bit, using 8 bit is much
easier.

This handling is similar, but different to acpi_scan_try_to_offline():

a) We don't try to offline twice. I am not sure if this CONFIG_MEMCG
optimization is still relevant - it should only apply to ZONE_NORMAL
(where we have no guarantees). If relevant, we can always add it.

b) acpi_scan_try_to_offline() simply onlines all memory in case
something goes wrong. It doesn't restore previous online type. Let's do
that, so we won't overwrite what e.g., user space configured.

...

uint8_t is a bit of a mouthful.  u8 is less typing ;)  Doesn't matter.

Acked-by: Andrew Morton <akpm@linux-foundation.org>
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