linux-kernel - Re: [PATCH v4 7/9] rust: percpu: Support non-zeroable types for DynamicPerCpu

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Message-ID: <87ms4o3ane.fsf@t14s.mail-host-address-is-not-set>
Date: Fri, 14 Nov 2025 16:18:45 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Mitchell Levy <levymitchell0@...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>, 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>, Yury Norov <yury.norov@...il.com>, Viresh Kumar
 <viresh.kumar@...aro.org>
Cc: Tyler Hicks <code@...icks.com>, Allen Pais <apais@...ux.microsoft.com>,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 linux-mm@...ck.org, Mitchell Levy <levymitchell0@...il.com>
Subject: Re: [PATCH v4 7/9] rust: percpu: Support non-zeroable types for
 DynamicPerCpu

"Mitchell Levy" <levymitchell0@...il.com> writes:

> Add functionality to `PerCpuPtr` to compute pointers to per-CPU variable
> slots on other CPUs. Use this facility to initialize per-CPU variables
> on all possible CPUs when a dynamic per-CPU variable is created with a
> non-zeroable type. Since `RefCell` and other `Cell`-like types fall into
> this category, `impl CheckedPerCpu` on `DynamicPerCpu` for these
> `InteriorMutable` types since they can now be used. Add examples of
> these usages to `samples/rust/rust_percpu.rs`. Add a test to ensure
> dynamic per-CPU variables properly drop their contents, done here since
> non-trivially dropped types often aren't `Zeroable`.
>
> Signed-off-by: Mitchell Levy <levymitchell0@...il.com>
> ---
>  rust/kernel/percpu/dynamic.rs |  44 +++++++++++++++++
>  samples/rust/rust_percpu.rs   | 109 +++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 146 insertions(+), 7 deletions(-)
>
> diff --git a/rust/kernel/percpu/dynamic.rs b/rust/kernel/percpu/dynamic.rs
> index 1863f31a2817..a74c8841aeb2 100644
> --- a/rust/kernel/percpu/dynamic.rs
> +++ b/rust/kernel/percpu/dynamic.rs
> @@ -89,6 +89,36 @@ pub fn new_zero(flags: Flags) -> Option<Self> {
>      }
>  }
>
> +impl<T: Clone> DynamicPerCpu<T> {
> +    /// Allocates a new per-CPU variable
> +    ///
> +    /// # Arguments
> +    /// * `val` - The initial value of the per-CPU variable on all CPUs.
> +    /// * `flags` - Flags used to allocate an [`Arc`] that keeps track of the underlying
> +    ///   [`PerCpuAllocation`].
> +    pub fn new_with(val: &T, flags: Flags) -> Option<Self> {

It would be great to be able to pass a closure here that can be used to
populate the value. Then the value does not have to be `Clone`.


Best regards,
Andreas Hindborg