Re: [PATCH v1 2/4] mm/memory_hotplug: Handle unaligned start and nr_pages in online_pages_blocks()

[David Hildenbrand]

On 14.08.19 16:17, David Hildenbrand wrote:
> On 14.08.19 16:08, Michal Hocko wrote:
>> On Fri 09-08-19 14:56:59, David Hildenbrand wrote:
>>> Take care of nr_pages not being a power of two and start not being
>>> properly aligned. Essentially, what walk_system_ram_range() could provide
>>> to us. get_order() will round-up in case it's not a power of two.
>>>
>>> This should only apply to memory blocks that contain strange memory
>>> resources (especially with holes), not to ordinary DIMMs.
>>
>> I would really like to see an example of such setup before making the
>> code hard to read. Because I am not really sure something like that
>> exists at all.
> 
> I don't have a real-live example at hand (founds this while exploring
> the code), however, the linked commit changed it without stating why it
> would be safe to do so.

So, while I agree that "not a power of two" is rare, are you sure we
will only have holes that are aligned to 4MB (especially on x86)?

-- 

Thanks,

David / dhildenb