Re: [PATCH v3 1/2] rust: sync: atomic: Add i32-backed Flag for atomic booleans

[Alice Ryhl <aliceryhl@google.com>]

On Sun, Jan 11, 2026 at 02:05:57PM +0900, FUJITA Tomonori wrote:
> Add a new Flag enum (Clear/Set) and implement AtomicType for it, so
> users can use Atomic<Flag> for boolean flags.
> 
> The backing integer type is an implementation detail; it is currently
> i32 but may change in the future.
> 
> Document when Atomic<Flag> is generally preferable to Atomic<bool>: in
> particular, when RMW operations such as xchg()/cmpxchg() may be used
> and minimizing memory usage is not the top priority. On some
> architectures without byte-sized RMW instructions, Atomic<bool> can be
> slower for RMW operations.
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
> ---
>  rust/kernel/sync/atomic.rs | 56 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
> 
> diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
> index ca9cab77abf0..473d3c07e234 100644
> --- a/rust/kernel/sync/atomic.rs
> +++ b/rust/kernel/sync/atomic.rs
> @@ -566,3 +566,59 @@ pub fn fetch_add<Rhs, Ordering: ordering::Ordering>(&self, v: Rhs, _: Ordering)
>          unsafe { from_repr(ret) }
>      }
>  }
> +
> +/// An atomic flag type intended to be backed by a performance-optimal integer type.
> +///
> +/// The backing integer type is an implementation detail; it is currently [`i32`] but may change
> +/// in the future.

How is it, could we make it u8 on some architectures without penalty,
and have it be i32 on others? Or is i32 better always.

Alice