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

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Message-ID: <aF_eLTlirxl-1jPP@pollux>
Date: Sat, 28 Jun 2025 14:21:01 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Vitaly Wool <vitaly.wool@...sulko.se>
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 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?

> +        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?

(Btw. no need to send a new version right away, leave a few days for people to
catch up and comment on this one or the other patches before resending.)

>      ///
>      /// If the requested size is zero, `realloc` behaves equivalent to `free`.
>      ///
> @@ -191,13 +246,29 @@ fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> {
>      ///   and old size, i.e. `ret_ptr[0..min(layout.size(), old_layout.size())] ==
>      ///   p[0..min(layout.size(), old_layout.size())]`.
>      /// - when the return value is `Err(AllocError)`, then `ptr` is still valid.
> -    unsafe fn realloc(
> +    unsafe fn realloc_node(
>          ptr: Option<NonNull<u8>>,
>          layout: Layout,
>          old_layout: Layout,
>          flags: Flags,
> +        nid: NumaNode,
>      ) -> Result<NonNull<[u8]>, AllocError>;