Re: [PATCH] mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC

[Qian Cai]

On Tue, 2019-02-26 at 20:40 +0100, Michal Hocko wrote:
> It seems you have missed the point of my question. It simply doesn't
> make much sense to have offline memory mapped. That memory is not
> accessible in general. So mapping it at the offline time is dubious at
> best. 

Well, kernel_map_pages() is like other debug features which could look
"unusual".

> Also you do not get through the offlining phase on a newly
> hotplugged (and not yet onlined) memory. So the patch doesn't look
> correct to me and it all smells like the bug you are seeing is a wrong
> reporting.
> 

That (physical memory hotadd) is a special case like during the boot. The patch
is strictly to deal with offline/online memory, i.e., logical/soft memory
hotplug.