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

[David Hildenbrand]

On 23.09.19 14:30, Michal Hocko wrote:
> On Mon 23-09-19 14:20:05, David Hildenbrand wrote:
>> 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.
> 
> Just to make sure I really follow. We need a user interface to control
> where the memory gets onlined but it is the driver which determines
> which part of the block really gets onlined, right?
> 

Yes, it's the drivers job to decide which part of the memory block can
actually get used, and when.

It's a little bit like the driver immediately allocates unbacked memory
again, to free that memory to the buddy once requested. (similar to how
ballooning works).

-- 

Thanks,

David / dhildenb