Re: [PATCH v2 27/29] mm/memory_hotplug: extend offline_and_remove_memory() to handle more than one memory block

David Hildenbrand
2020-11-18T09:00:21Z

On 18.11.20 05:53, Andrew Morton wrote:
> On Thu, 12 Nov 2020 14:38:13 +0100 David Hildenbrand <david@redhat.com> 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.

In case I have to resend, I'll change it :)

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

Thanks!

--
Thanks,

David / dhildenb