linux-kernel - Re: [PATCH v2 0/2] Take ARCH_KMALLOC_MINALIGN into account for build-time XArray check

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Message-ID: <CANiq72k0FSBTB2yOjiAy9PnAuyM=-PHxL3uQQ_Cv+zwswnr_bA@mail.gmail.com>
Date: Sun, 24 Aug 2025 13:38:34 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Matthew Wilcox <willy@...radead.org>, Tamir Duberstein <tamird@...il.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <lossin@...nel.org>, Trevor Gross <tmgross@...ch.edu>, linux-mm@...ck.org, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Take ARCH_KMALLOC_MINALIGN into account for
 build-time XArray check

On Fri, Aug 15, 2025 at 9:12 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> diff --cc rust/kernel/alloc.rs
> index b39c279236f5,907301334d8c..000000000000
> --- a/rust/kernel/alloc.rs
> +++ b/rust/kernel/alloc.rs
> @@@ -164,7 -137,15 +164,15 @@@ impl NumaNode
>   /// - Implementers must ensure that all trait functions abide by the guarantees documented in the
>   ///   `# Guarantees` sections.
>   pub unsafe trait Allocator {
> +     /// The minimum alignment satisfied by all allocations from this allocator.
> +     ///
> +     /// # Guarantees
> +     ///
> +     /// Any pointer allocated by this allocator is guaranteed to be aligned to `MIN_ALIGN` even if
> +     /// the requested layout has a smaller alignment.
> +     const MIN_ALIGN: usize;
> +
>  -    /// Allocate memory based on `layout` and `flags`.
>  +    /// Allocate memory based on `layout`, `flags` and `nid`.
>       ///
>       /// On success, returns a buffer represented as `NonNull<[u8]>` that satisfies the layout
>       /// constraints (i.e. minimum size and alignment as specified by `layout`).

`MIN_ALIGN` is missing in `Cmalloc` -- from `rusttest`:

     error[E0046]: not all trait items implemented, missing: `MIN_ALIGN`
       --> rust/kernel/alloc/allocator_test.rs:48:1
        |
    48  | unsafe impl Allocator for Cmalloc {
        | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `MIN_ALIGN` in
implementation
        |
       ::: rust/kernel/alloc.rs:173:5
        |
    173 |     const MIN_ALIGN: usize;
        |     ---------------------- `MIN_ALIGN` from trait

i.e. similar to the other one.

Cheers,
Miguel