linux-kernel - [PATCH v2] rust: page:: optimize rust symbol generation for Page

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Message-ID: <20250321080124.484647-1-kunwu.chan@linux.dev>
Date: Fri, 21 Mar 2025 16:01:24 +0800
From: Kunwu Chan <kunwu.chan@...ux.dev>
To: ojeda@...nel.org,
	alex.gaynor@...il.com,
	boqun.feng@...il.com,
	gary@...yguo.net,
	bjorn3_gh@...tonmail.com,
	benno.lossin@...ton.me,
	a.hindborg@...nel.org,
	aliceryhl@...gle.com,
	tmgross@...ch.edu,
	dakr@...nel.org,
	nathan@...nel.org,
	nick.desaulniers+lkml@...il.com,
	morbo@...gle.com,
	justinstitt@...gle.com
Cc: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev,
	Kunwu Chan <kunwu.chan@...mail.com>,
	Grace Deng <Grace.Deng006@...il.com>
Subject: [PATCH v2] rust: page:: optimize rust symbol generation for Page

From: Kunwu Chan <kunwu.chan@...mail.com>

When build the kernel using the llvm-18.1.3-rust-1.85.0-x86_64
with ARCH=arm64, the following symbols are generated:

$nm vmlinux | grep ' _R'.*Page | rustfilt
ffff8000805b6f98 T <kernel::page::Page>::alloc_page
ffff8000805b715c T <kernel::page::Page>::fill_zero_raw
ffff8000805b720c T <kernel::page::Page>::copy_from_user_slice_raw
ffff8000805b6fb4 T <kernel::page::Page>::read_raw
ffff8000805b7088 T <kernel::page::Page>::write_raw
ffff8000805b72fc T <kernel::page::Page as core::ops::drop::Drop>::drop

These Rust symbols(alloc_page and drop) are trivial wrappers around the C
functions alloc_pages and __free_pages. It doesn't make sense to go
through a trivial wrapper for these functions, so mark them inline.

Link: https://github.com/Rust-for-Linux/linux/issues/1145
Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
Co-developed-by: Grace Deng <Grace.Deng006@...il.com>
Signed-off-by: Grace Deng <Grace.Deng006@...il.com>
Signed-off-by: Kunwu Chan <kunwu.chan@...mail.com>

---
Changes in v2:
- mark inline only for 'alloc_page' and 'drop'
- reword commit msg
---
 rust/kernel/page.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
index f6126aca33a6..7c1b17246ed5 100644
--- a/rust/kernel/page.rs
+++ b/rust/kernel/page.rs
@@ -69,6 +69,7 @@ impl Page {
     /// let page = Page::alloc_page(GFP_KERNEL | __GFP_ZERO)?;
     /// # Ok::<(), kernel::alloc::AllocError>(())
     /// ```
+    #[inline]
     pub fn alloc_page(flags: Flags) -> Result<Self, AllocError> {
         // SAFETY: Depending on the value of `gfp_flags`, this call may sleep. Other than that, it
         // is always safe to call this method.
@@ -251,6 +252,7 @@ pub unsafe fn copy_from_user_slice_raw(
 }
 
 impl Drop for Page {
+    #[inline]
     fn drop(&mut self) {
         // SAFETY: By the type invariants, we have ownership of the page and can free it.
         unsafe { bindings::__free_pages(self.page.as_ptr(), 0) };
-- 
2.43.0