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

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Message-Id: <DBCPFD7LPG5R.1J7HDRK2CQHG5@kernel.org>
Date: Tue, 15 Jul 2025 16:39:04 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Alice Ryhl" <aliceryhl@...gle.com>
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 4:35 PM CEST, Alice Ryhl wrote:
> 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.

Oh, indeed, that's fine then. :)