linux-kernel - Re: [PATCH v3 5/7] rust: percpu: Support non-zeroable types for DynamicPerCpu

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Message-ID: <CANiq72k1oRcxKbBpp4B-uCmqm+Hd7_xPqwM1kt-BYikbcsUSVw@mail.gmail.com>
Date: Thu, 4 Sep 2025 23:57:02 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Mitchell Levy <levymitchell0@...il.com>
Cc: Yury Norov <yury.norov@...il.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Andrew Morton <akpm@...ux-foundation.org>, 
	Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>, 
	Danilo Krummrich <dakr@...nel.org>, Benno Lossin <lossin@...nel.org>, 
	Viresh Kumar <viresh.kumar@...aro.org>, Tyler Hicks <code@...icks.com>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3 5/7] rust: percpu: Support non-zeroable types for DynamicPerCpu

On Thu, Sep 4, 2025 at 11:05 PM Mitchell Levy <levymitchell0@...il.com> wrote:
>
> it *might* also be possible to use a macro and dispense with the need for
> a closure, though I'm not familiar enough with proc macros to say for
> sure. That would probably look like
>
>         for_each_possible_cpu!(cpu) {
>                 let remote_ptr = unsafe { ptr.get_remote_ptr(cpu) };
>                 // ...
>         }
>
> though personally I think the first one is better (simpler
> implementation without too much syntactic overhead, especially since
> closures are already used some within R4L).

Yeah, please avoid macros as much as possible. Sometimes macros do
have advantages, but if it is just to avoid a closure, then no, please
avoid it.

Similarly, unless there is a concrete advantage needed with the
function, please avoid it too -- the original `for` with the iterator
is the normal way of doing it and already used plenty in the kernel.

Thanks!

Cheers,
Miguel