linux-kernel - Re: [PATCH] rust: sync: rcu: Mark Guard methods as inline

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Message-ID: <D8E9IKGUUUJZ.2797G3WP1GVA3@proton.me>
Date: Wed, 12 Mar 2025 11:48:30 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: I Hsin Cheng <richard120310@...il.com>, rostedt@...dmis.org
Cc: paulmck@...nel.org, frederic@...nel.org, neeraj.upadhyay@...nel.org, joel@...lfernandes.org, josh@...htriplett.org, boqun.feng@...il.com, urezki@...il.com, mathieu.desnoyers@...icios.com, jiangshanlai@...il.com, qiang.zhang1211@...il.com, ojeda@...nel.org, alex.gaynor@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu, dakr@...nel.org, rcu@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, skhan@...uxfoundation.org, jserv@...s.ncku.edu.tw
Subject: Re: [PATCH] rust: sync: rcu: Mark Guard methods as inline

On Wed Mar 12, 2025 at 11:17 AM CET, I Hsin Cheng wrote:
> Currenyly the implementation of "Guard" methods are basically wrappers
> around rcu's function within kernel. Building the kernel with llvm
> 18.1.8 on x86_64 machine will generate the following symbols:
>
> $ nm vmlinux | grep ' _R'.*Guard | rustfilt
> ffffffff817b6c90 T <kernel::sync::rcu::Guard>::new
> ffffffff817b6cb0 T <kernel::sync::rcu::Guard>::unlock
> ffffffff817b6cd0 T <kernel::sync::rcu::Guard as core::ops::drop::Drop>::drop
> ffffffff817b6c90 T <kernel::sync::rcu::Guard as core::default::Default>::default
>
> These Rust symbols are basically wrappers around functions
> "rcu_read_lock" and "rcu_read_unlock". Marking them as inline can
> reduce the generation of these symbols, and saves the size of code
> generation for 100 bytes.
>
> $ ./scripts/bloat-o-meter vmlinux_old vmlinux_new
> add/remove: 0/8 grow/shrink: 0/0 up/down: 0/-100 (-100)
> Function                                     old     new   delta
> _RNvXs_NtNtCsaYBeKL739Xz_6kernel4sync3rcuNtB4_5GuardNtNtCsdaXADs8PRFB_4core7default7Default7default       9       -      -9
> _RNvXs0_NtNtCsaYBeKL739Xz_6kernel4sync3rcuNtB5_5GuardNtNtNtCsdaXADs8PRFB_4core3ops4drop4Drop4drop       9       -      -9
> _RNvMNtNtCsaYBeKL739Xz_6kernel4sync3rcuNtB2_5Guard6unlock       9       -      -9
> _RNvMNtNtCsaYBeKL739Xz_6kernel4sync3rcuNtB2_5Guard3new       9       -      -9
> __pfx__RNvXs_NtNtCsaYBeKL739Xz_6kernel4sync3rcuNtB4_5GuardNtNtCsdaXADs8PRFB_4core7default7Default7default      16       -     -16
> __pfx__RNvXs0_NtNtCsaYBeKL739Xz_6kernel4sync3rcuNtB5_5GuardNtNtNtCsdaXADs8PRFB_4core3ops4drop4Drop4drop      16       -     -16
> __pfx__RNvMNtNtCsaYBeKL739Xz_6kernel4sync3rcuNtB2_5Guard6unlock      16       -     -16
> __pfx__RNvMNtNtCsaYBeKL739Xz_6kernel4sync3rcuNtB2_5Guard3new      16       -     -16
> Total: Before=23385830, After=23385730, chg -0.00%
>
> Link: https://github.com/Rust-for-Linux/linux/issues/1145
> Signed-off-by: I Hsin Cheng <richard120310@...il.com>

Reviewed-by: Benno Lossin <benno.lossin@...ton.me>

---
Cheers,
Benno