Re: [PATCH part5 0/7] Arrange hotpluggable memory as ZONE_MOVABLE.

[KOSAKI Motohiro]

(8/12/13 1:23 PM), H. Peter Anvin wrote:
> On 08/12/2013 10:01 AM, Tang Chen wrote:
> > > > I'm just thinking of a more extreme case. For example, if a machine
> > > > has only one node hotpluggable, and the kernel resides in that node.
> > > > Then the system has no hotpluggable node.
> > >
> > > Yeah, sure, then there's no way that node can be hotpluggable and the
> > > right thing to do is booting up the machine and informing the userland
> > > that memory is not hotpluggable.
> > >
> > > > If we can prevent the kernel from using hotpluggable memory, in such
> > > > a machine, users can still do memory hotplug.
> > > >
> > > > I wanted to do it as generic as possible. But yes, finding out the
> > > > nodes the kernel resides in and make it unhotpluggable can work.
> > >
> > > Short of being able to remap memory under the kernel, I don't think
> > > this can be very generic and as a compromise trying to keep as many
> > > hotpluggable nodes as possible doesn't sound too bad.
> >
> > I think making one of the node hotpluggable is better. But OK, it is
> > no big deal. There won't be such machine in reality, I think. :)
>
> The user may very well have configured a system with mirrored memory for
> the kernel node as that will be non-hotpluggable, but not for the
> others.  One can wonder how much that actually buys in real life, but
> still...

Note. Such system is much cheaper than full memory mirroring system. That's
one of reason why server vendors are interesting in hot plugging.

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