linux-kernel - [PATCH v1 09/17] bit_spinlock: __always

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Message-ID: <20240829165627.2256514-10-david@redhat.com>
Date: Thu, 29 Aug 2024 18:56:12 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	x86@...nel.org,
	linux-fsdevel@...r.kernel.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Tejun Heo <tj@...nel.org>,
	Zefan Li <lizefan.x@...edance.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Andy Lutomirski <luto@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [PATCH v1 09/17] bit_spinlock: __always_inline (un)lock functions

The compiler might decide that it is a smart idea to not inline
bit_spin_lock(), primarily when a couple of functions in the same file end
up calling it. Especially when used in RMAP context, this can negatively
affect fork() performance, where each additional function call is
noticeable.

Let's simply flag all lock/unlock functions as __always_inline;
arch_test_and_set_bit_lock() and friends are already tagged like that
(but not test_and_set_bit_lock() for some reason).

If ever a problem, we could split it into a fast and a slow path, and
only force the fast path to be inlined. But there is nothing
particularly "big" here.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/linux/bit_spinlock.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
index bbc4730a6505c..c0989b5b0407f 100644
--- a/include/linux/bit_spinlock.h
+++ b/include/linux/bit_spinlock.h
@@ -13,7 +13,7 @@
  * Don't use this unless you really need to: spin_lock() and spin_unlock()
  * are significantly faster.
  */
-static inline void bit_spin_lock(int bitnum, unsigned long *addr)
+static __always_inline void bit_spin_lock(int bitnum, unsigned long *addr)
 {
 	/*
 	 * Assuming the lock is uncontended, this never enters
@@ -38,7 +38,7 @@ static inline void bit_spin_lock(int bitnum, unsigned long *addr)
 /*
  * Return true if it was acquired
  */
-static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
+static __always_inline int bit_spin_trylock(int bitnum, unsigned long *addr)
 {
 	preempt_disable();
 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
@@ -54,7 +54,7 @@ static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
 /*
  *  bit-based spin_unlock()
  */
-static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
+static __always_inline void bit_spin_unlock(int bitnum, unsigned long *addr)
 {
 #ifdef CONFIG_DEBUG_SPINLOCK
 	BUG_ON(!test_bit(bitnum, addr));
@@ -71,7 +71,7 @@ static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
  *  non-atomic version, which can be used eg. if the bit lock itself is
  *  protecting the rest of the flags in the word.
  */
-static inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
+static __always_inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
 {
 #ifdef CONFIG_DEBUG_SPINLOCK
 	BUG_ON(!test_bit(bitnum, addr));
-- 
2.46.0