linux-kernel - Re: [PATCH 1/2] rust: alloc: specify the minimum alignment of each allocator

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Message-ID: <CAH5fLgi+6Ahh_mKrdxyfc+SBKymEhqQhgg=6MxxG7MSvpJjveg@mail.gmail.com>
Date: Tue, 15 Jul 2025 16:35:56 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, 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 1/2] rust: alloc: specify the minimum alignment of each allocator

On Tue, Jul 15, 2025 at 4:05 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> On Tue Jul 15, 2025 at 3:46 PM CEST, Alice Ryhl wrote:
> > diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
> > index a2c49e5494d334bfde67328464dafcdb31052947..c12753a5fb1c7423a4063553674b537a775c860e 100644
> > --- a/rust/kernel/alloc.rs
> > +++ b/rust/kernel/alloc.rs
> > @@ -137,6 +137,14 @@ pub mod flags {
> >  /// - 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 must be aligned to `MIN_ALIGN` even if the
> > +    /// requested layout has a smaller alignment.
>
> I'd say "is guaranteed to be aligned to" instead, "must be" reads like a
> requirement.

Yes I agree that sounds better.

> Speaking of which, I think this also needs to be expressed as a safety
> requirement of the Allocator trait itself, which the specific allocator
> implementations need to justify.

The trait safety requirements already says that the implementation
must provide the guarantee listed on each item in the trait.

Alice