Re: [PATCH v1 0/3] mm/memory_hotplug: Export generic_online_page()

[David Hildenbrand]

On 23.09.19 14:07, Michal Hocko wrote:
> On Mon 23-09-19 13:34:18, David Hildenbrand wrote:
>> On 23.09.19 13:15, Michal Hocko wrote:
> [...]
>>> I am wondering why those pages get onlined when they are, in fact,
>>> supposed to be offline.
>>>
>>
>> It's the current way of emulating sub-memory-block hotplug on top of the
>> memory bock device API we have. Hyper-V and XEN have been using that for
>> a long time.
> 
> Do they really have to use the existing block interface when they in
> fact do not operate on the block granularity? Zone device memory already
> acts on sub section/block boundaries.
> 

Yes, we need memory blocks, especially for user space to properly online
them (as we discussed a while back, to decide on a zone) and for udev
events, to e.g., properly reload kexec when memory blocks get
added/removed/onlined/offlined.

ZONE_DEVICE is special as it doesn't have to worry about
onlining/offlining/dumping. Also, it doesn't care about
SECTION_IS_ONLINE, but figuring out how to detect which sub
sections/blocks have a valid memmap is still something to get fixed and
is still getting discussed on MM.

-- 

Thanks,

David / dhildenb