linux-kernel - Re: [PATCH v8 3/4] rust: add support for NUMA ids in allocations

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Message-Id: <61DAD282-B00A-4809-B579-3F47F4781BBC@konsulko.se>
Date: Sat, 28 Jun 2025 17:25:52 +0200
From: Vitaly Wool <vitaly.wool@...sulko.se>
To: Danilo Krummrich <dakr@...nel.org>
Cc: linux-mm@...ck.org,
 akpm@...ux-foundation.org,
 linux-kernel@...r.kernel.org,
 Uladzislau Rezki <urezki@...il.com>,
 Alice Ryhl <aliceryhl@...gle.com>,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v8 3/4] rust: add support for NUMA ids in allocations



> On Jun 28, 2025, at 2:21 PM, Danilo Krummrich <dakr@...nel.org> wrote:
> 
> On Sat, Jun 28, 2025 at 12:26:11PM +0200, Vitaly Wool wrote:
>> +/// Non Uniform Memory Access (NUMA) node identifier
>> +#[derive(Clone, Copy, PartialEq)]
>> +pub struct NumaNode(i32);
>> +
>> +impl NumaNode {
>> +    /// create a new NUMA node identifer (non-negative integer)
>> +    /// returns EINVAL if a negative id is specified
>> +    pub fn new(node: i32) -> Result<Self> {
>> +        if node < 0 {
>> +            return Err(EINVAL);
>> +        }
> 
> Should we also check for MAX_NUMNODES?

Good point, thanks.

> 
>> +        Ok(Self(node))
>> +    }
>> +}
> 
> <snip>
> 
>> +    /// Re-allocate an existing memory allocation to satisfy the requested `layout` and
>> +    /// optionally a specific NUMA node request to allocate the memory for.
> 
> It's not an Option anymore, so we may want to drop 'optionally'. Also please
> leave an empty line here.
> 
>> +    /// Systems employing a Non Uniform Memory Access (NUMA) architecture contain
>> +    /// collections of hardware resources including processors, memory, and I/O buses,
>> +    /// that comprise what is commonly known as a NUMA node.
>> +    /// `nid` stands for NUMA id, i. e. NUMA node identifier, which is a non-negative
>> +    /// integer if a node needs to be specified, or NUMA_NO_NODE if the caller doesn't care.
> 
> Please also explain what happens when the NumaNode changes between calls to
> realloc_node().
> 
> Does it have to remain the same NumaNode? Do we need a safety requirement for
> that?

Since we don’t implement that logic, we trust the C part. The current implementation will refuse to realloc for a different node, and I believe that is the right thing to do because transferring an allocation to a different node doesn’t go well with the concept of simple adjustment of the allocation size.

Do you believe it is necessary to explicitly state it here in the comments?

<snip>