Re: [PATCH v3 3/3] rust: alloc: move `NumaNode` to the `numa` module

[Andreas Hindborg <a.hindborg@kernel.org>]

"Gary Guo" <gary@garyguo.net> writes:

> On Wed Oct 28, 2026 at 2:36 PM GMT, Andreas Hindborg wrote:
>> "Gary Guo" <gary@garyguo.net> writes:
>>
>>>> diff --git a/rust/kernel/numa.rs b/rust/kernel/numa.rs
>>>> index 164e622d325f..4a3a880308f3 100644
>>>> --- a/rust/kernel/numa.rs
>>>> +++ b/rust/kernel/numa.rs
>>>> @@ -4,12 +4,15 @@
>>>>  //!
>>>>  //! C header: [`include/linux/nodemask.h`](srctree/include/linux/nodemask.h)
>>>>  
>>>> -use crate::bindings;
>>>>  #[cfg(CONFIG_NUMA)]
>>>>  use crate::sync::atomic::{
>>>>      Atomic,
>>>>      Relaxed, //
>>>>  };
>>>> +use crate::{
>>>> +    bindings,
>>>> +    prelude::*, //
>>>> +};
>>>>  
>>>>  /// Returns the number of online NUMA nodes.
>>>>  #[inline]
>>>> @@ -27,3 +30,33 @@ pub fn num_online_nodes() -> u32 {
>>>>          bindings::nr_online_nodes
>>>>      }
>>>>  }
>>>> +
>>>> +/// Non Uniform Memory Access (NUMA) node identifier.
>>>> +#[derive(Clone, Copy, PartialEq)]
>>>> +pub struct NumaNode(i32);
>>>
>>> FWIW the C type is nodemask_t and this should have mask in the name too. It is
>>> not an identifier. That said, this is an existing issue, so shouldn't block the
>>> move.
>>
>> What makes you say this? This is not a mask, it is a numa node id, which
>> is represented as i32. `NUMA_NO_NODE` is a valid id.
>>
>> I am using this to specify domain for block mq queues. If you take a
>> look at the allocation path:
>>
>>   blk_mq_alloc_queue
>>   blk_alloc_queue
>>   slab_alloc_node
>>
>> It's an id, named `numa_node`, `node_id`, `node`. Not a mask. Unless I
>> missed something?
>
> Right, I got myself confused because NUMA_NO_NODE is defined in
> nodemask_types.h.
>
> If it's just an ID, would it make more sense to have `Option<NumaNode>` and
> `None` to represent no node preference?

I guess we could define it as `Option<i32>`. That would be nice.

I can send a follow up once this lands. FYI there is a v4 of this [1].

Best regards,
Andreas Hindborg

[1] https://lore.kernel.org/r/20261030-cpu-helpers-v4-2-a8d840d34837@kernel.org