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AJvYcCU4hA9IzkicZuc8ZQegBX4MotrL0SWRQq9P1WNqMStGe5S7EGVSeJMU1IWVUJ1gfQshwk1Sj8dnIpFM6IyJ+g==@vger.kernel.org X-Gm-Message-State: AOJu0Yzx38t89AkDrNfXxN5vJekvfOT21rvYXCMb8FC8wW1dLt450kOq u7S75r7ZBd+6BL5UGkk3YbSPVqZ1UV+Ff6gIKbDoz7xFdLmytUug2NMVCwvM4gWwhHDUtwfz+eL YiTNnr127sP8BBOypNA== X-Google-Smtp-Source: AGHT+IGVFBUwaaa/F7bzovvs5bi07WRrtlErBamaJXDnsQpNl3azykN7jpk5GtfI5Ut0vaY+zfMAi1mzj4KxOn4= X-Received: from wmne21.prod.google.com ([2002:a05:600c:4395:b0:47a:98a6:7c41]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:3152:b0:479:1a0a:ebbe with SMTP id 5b1f17b1804b1-47d84b18db4mr198669435e9.14.1768209513178; Mon, 12 Jan 2026 01:18:33 -0800 (PST) Date: Mon, 12 Jan 2026 09:18:32 +0000 In-Reply-To: <20260111050558.3147975-2-fujita.tomonori@gmail.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260111050558.3147975-1-fujita.tomonori@gmail.com> <20260111050558.3147975-2-fujita.tomonori@gmail.com> Message-ID: Subject: Re: [PATCH v3 1/2] rust: sync: atomic: Add i32-backed Flag for atomic booleans From: Alice Ryhl To: FUJITA Tomonori Cc: boqun.feng@gmail.com, ojeda@kernel.org, peterz@infradead.org, will@kernel.org, a.hindborg@kernel.org, bjorn3_gh@protonmail.com, dakr@kernel.org, gary@garyguo.net, lossin@kernel.org, mark.rutland@arm.com, tmgross@umich.edu, rust-for-linux@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 for boolean flags. > > The backing integer type is an implementation detail; it is currently > i32 but may change in the future. > > Document when Atomic is generally preferable to Atomic: 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 can be > slower for RMW operations. > > Signed-off-by: FUJITA Tomonori > --- > 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(&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