Re: [RFC PATCH 3/5] mm, memory_hotplug: allocate memmap from the added memory range for sparse-vmemmap

[Michal Hocko]

On Wed 26-07-17 13:45:39, Heiko Carstens wrote:
[...]
> In general I do like your idea, however if I understand your patches
> correctly we might have an ordering problem on s390: it is not possible to
> access hot-added memory on s390 before it is online (MEM_GOING_ONLINE
> succeeded).

Could you point me to the code please? I cannot seem to find the
notifier which implements that.

> On MEM_GOING_ONLINE we ask the hypervisor to back the potential available
> hot-added memory region with physical pages. Accessing those ranges before
> that will result in an exception.

Can we make the range which backs the memmap range available? E.g from
s390 specific __vmemmap_populate path?
 
> However with your approach the memory is still allocated when add_memory()
> is being called, correct? That wouldn't be a change to the current
> behaviour; except for the ordering problem outlined above.

Could you be more specific please? I do not change when the memmap is
allocated.

-- 
Michal Hocko
SUSE Labs