Re: [RFC PATCH]: ACPI: Automatically online hot-added memory

[Prarit Bhargava <prarit@redhat.com>]

>
> Blocking does not work.
> But I have an idea, whatabout:
>   - CPU add rule which only adds a CPU if the corresponding Numa node already
>     has onlined memory
>   - Memory add rule which adds the memory and also onlines CPUs if the Numa
>     node still has offlined CPUs
>
> This has the side effect that you online a CPU which may have been offlined on
> purpose if you hotadd memory on the same node..., a rather uncommon case.
>
>   
That actually might be more of a problem than you think.  It's not 
atypical that in the evening a system's components are offlined in order 
to save power.  Maintenance also is scheduled for downtime so when 
memory is added to the system we may bring cpus into service 
erroneously.  I think the "end-user" may not be too happy with this result.

[OTOH, a little documentation could fix that issue]

> A quick try showed that it would be convenient to add the Numa node to the 
> uevent which is a bit tricky...
> Ok, I got this working, but messed up the cpu hotplugging with my patches:
> ...
> Unable to map lapic 32 to logical cpu number
> ...
> This already worked...
>
> I wanted to post something today, but I couldn't made it.
> Still I more or less could prove that above works and I hopefully can show
> some results on Monday.
>
>   

If it works then I'm all for it :)

> Comments?
>
>    Thomas
>
> BTW: I was wrong with slub. It also has bad side effects. What is strange is 
>   

FWIW, I'm testing with slab.

P.