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>

diff --git a/rust/kernel/sync/rcu.rs b/rust/kernel/sync/rcu.rs
index b51d9150ffe285cee3ac752ce469cb79a880fd6c..a32bef6e490b0eebdb93f2636cf10e177036a6a9 100644 (file)
--- a/rust/kernel/sync/rcu.rs
+++ b/rust/kernel/sync/rcu.rs
@@ -17,6 +17,7 @@ pub struct Guard(NotThreadSafe);
 
 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 @@ impl Guard {
     }
 
     /// 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 @@ impl Drop for Guard {
 }
 
 /// Acquires the RCU read side lock.
+#[inline]
 pub fn read_lock() -> Guard {
     Guard::new()
 }