Re: [RFC PATCH 1/3] mm/numa: add exclusive node pool and numa=standby boot parameter

[Mike Rapoport <rppt@kernel.org>]

Hi,

On Tue, Jun 09, 2026 at 09:45:15PM -0400, Gregory Price wrote:
> It can be at times preferential to logically split up hotplug memory
> capacity into more nodes than are described by BIOS at boot time.
> 
> However, if nodes are not described at __init time, they are not
> possible to add later on.

...
 
> 1) Can we do dynamic addition of nodes?
> 
>    Not Trivially
> 
>    Some services utilize num_possible_nodes() as a static value to
>    calculate the amount of resources to use at runtime (bpf, md/raid5).
> 
>    Example: futex_init uses num_possible_nodes() as part of its
>             hashsize calculation during __init.

AFAIU, we don't add the additional nodes for generic hotplug memory but
rather for exclusive use of by drivers/applications that are aware of these
nodes.
Wouldn't adding them to possible nodes actually skew the calculation of the
resources by the services utilizing num_possible_nodes()?

With the futex_init() example, won't be hashsize scaled down two much
because we've added these special nodes to the possible mask?

-- 
Sincerely yours,
Mike.