Commit 9520371e authored Mar 19, 2025 by I Hsin Cheng Committed by Joel Fernandes May 16, 2025

rust: sync: rcu: Mark Guard methods as inline

Currently 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 132 bytes.

$ ./scripts/bloat-o-meter vmlinux_old vmlinux_new
(Output is demangled for readability)

add/remove: 0/10 grow/shrink: 0/1 up/down: 0/-132 (-132)
Function                                     old     new   delta
rust_driver_pci::SampleDriver::probe        1041    1034      -7
kernel::sync::rcu::Guard::default             9       -      -9
kernel::sync::rcu::Guard::drop                9       -      -9
kernel::sync::rcu::read_lock                  9       -      -9
kernel::sync::rcu::Guard::unlock              9       -      -9
kernel::sync::rcu::Guard::new                 9       -      -9
__pfx__kernel::sync::rcu::Guard::default     16       -     -16
__pfx__kernel::sync::rcu::Guard::drop        16       -     -16
__pfx__kernel::sync::rcu::read_lock          16       -     -16
__pfx__kernel::sync::rcu::Guard::unlock      16       -     -16
__pfx__kernel::sync::rcu::Guard::new         16       -     -16
Total: Before=23365955, After=23365823, chg -0.00%

Link: https://github.com/Rust-for-Linux/linux/issues/1145


Signed-off-by: I Hsin Cheng <richard120310@gmail.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Charalampos Mitrodimas <charmitro@posteo.net>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>

parent da6b8559

rust/kernel/sync/rcu.rs

+5 −0

Original line number	Diff line number	Diff line
		@@ -17,6 +17,7 @@

		impl Guard {
		/// Acquires the RCU read side lock and returns a guard.
		#[inline]
		pub fn new() -> Self {
		// SAFETY: An FFI call with no additional requirements.
		unsafe { bindings::rcu_read_lock() };
		@@ -25,16 +26,19 @@ pub fn new() -> Self {
		}

		/// Explicitly releases the RCU read side lock.
		#[inline]
		pub fn unlock(self) {}
		}

		impl Default for Guard {
		#[inline]
		fn default() -> Self {
		Self::new()
		}
		}

		impl Drop for Guard {
		#[inline]
		fn drop(&mut self) {
		// SAFETY: By the type invariants, the RCU read side is locked, so it is ok to unlock it.
		unsafe { bindings::rcu_read_unlock() };
		@@ -42,6 +46,7 @@ fn drop(&mut self) {
		}

		/// Acquires the RCU read side lock.
		#[inline]
		pub fn read_lock() -> Guard {
		Guard::new()
		}