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

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Message-ID: <20250312101723.149135-1-richard120310@gmail.com>
Date: Wed, 12 Mar 2025 18:17:23 +0800
From: I Hsin Cheng <richard120310@...il.com>
To: rostedt@...dmis.org
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	I Hsin Cheng <richard120310@...il.com>
Subject: [PATCH] rust: sync: rcu: Mark Guard methods as inline

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>
---
 rust/kernel/sync/rcu.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/rust/kernel/sync/rcu.rs b/rust/kernel/sync/rcu.rs
index b51d9150ffe2..26df2a6cb09f 100644
--- a/rust/kernel/sync/rcu.rs
+++ b/rust/kernel/sync/rcu.rs
@@ -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() };
-- 
2.43.0