Re: [2/8,v3] NUMA Hotplug Emulator: infrastructure of NUMA hotplug emulation

David Rientjes
2010-11-18T21:25:00Z

On Thu, 18 Nov 2010, Shaohui Zheng wrote:

> in our draft patch, we re-setup nr_node_ids when CONFIG_ARCH_MEMORY_PROBE enabled
> and mem=XXX was specified in grub. we set nr_node_ids as MAX_NUMNODES + 1, because
> we do not know how many nodes will be hot-added through memory/probe interface.
> it might be a little wasting of memory.
>

nr_node_ids need not be set to anything different at boot, the
MEM_GOING_ONLINE callback should be used for anything (like the slab
allocators) where a new node is introduced and needs to be dealt with
accordingly; this is how regular memory hotplug works, we need no
additional code in this regard because it's emulated. If a subsystem
needs to change in response to a new node going online and doesn't as a
result of using your emulator, that's a bug and either needs to be fixed
or prohibited from use with CONFIG_MEMORY_HOTPLUG.

(See the MEM_GOING_ONLINE callback in mm/slub.c, for instance, which deals
only with the case of node hotplug.)