Re: [PATCH v3 1/3] driver/base: Optimize memory block registration to reduce boot time

[David Hildenbrand <david@redhat.com>]

On 05.05.25 09:28, Oscar Salvador wrote:
> On Mon, May 05, 2025 at 09:16:48AM +0200, David Hildenbrand wrote:
>> memory hotplug code never calls register_one_node(), unless I am missing
>> something.
>>
>> During add_memory_resource(), we call __try_online_node(nid, false), meaning
>> we skip register_one_node().
>>
>> The only caller of __try_online_node(nid, true) is try_online_node(), called
>> from CPU hotplug code, and I *guess* that is not required.
> 
> Well, I guess this is because we need to link the cpus to the node.
> register_one_node() has two jobs: 1) register cpus belonging to the node
> and 2) register memory-blocks belonging to the node (if any).

Ah, via __register_one_node() ...

I would assume that an offline node

(1) has no memory
(2) has no CPUs

When we *hotplug* either memory or CPUs, and we first online the node, 
there is nothing to register. Because if there would be something, the 
node would already be online.

In particular, try_offline_node() will only offline a node if

(A) No present pages: No pages are spanned anymore. This includes
     offline memory blocks.
(B) No present CPUs.

But maybe there is some case that I am missing ...

-- 
Cheers,

David / dhildenb