[PATCH] powerpc/pseries: Auto online hotplugged memory

[Michael Ellerman]

On Mon, 2016-06-20 at 21:14 -0500, Nathan Fontenot wrote:
> On 06/20/2016 07:57 PM, Michael Ellerman wrote:
> > On Mon, 2016-06-20 at 08:51 -0500, Nathan Fontenot wrote:
> > 
> > > Auto online hotplugged memory
> > > 
> > > A recent update (commit id 31bc3858ea3) to the core mm hotplug code
> > > introduced the memhp_auto_online variable to allow for automatically
> > > onlining memory that is added.
> > > 
> > > This patch update the pseries memory hotplug code to enable this so that
> > > any memory DLPAR added to the system is automatically onlined. The code
> > > to add the memory block for memory added from add_memory() is removed as
> > > this is not needed, the memory_add code does this.
> > 
> > Is this a bug fix, or just a cleanup?
> 
> Hmmm.. some cleanup and some new feature. The removal of the memblock_add()
> call is a cleanup and the setting of the memhp_auto_online variable is
> taking advantage of a feature I was not previously aware of.

OK. Looking at usage of memhp_auto_online it's not clear to me that you're
supposed to be setting it in arch code.

eg. if I build my kernel with CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE=n, I will
expect it to not be onlined by default.

Similarly if I boot with memhp_default_state=offline on the kernel command line.

But this patch would then mean it is onlined by default. So that seems kind of
confusing for users.

I think instead we should be merging the bulk of this patch, but without the
forced assignment to memhp_auto_online?

cheers