linux-kernel - [PATCH 2/4] dev_printk: Add and use dev_no

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Date: Wed, 28 Feb 2024 15:00:03 +0100
From: Geert Uytterhoeven <geert+renesas@...der.be>
To: Chris Down <chris@...isdown.name>,
	Petr Mladek <pmladek@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Jessica Yu <jeyu@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jason Baron <jbaron@...mai.com>,
	Jim Cromie <jim.cromie@...il.com>,
	Ilya Dryomov <idryomov@...il.com>,
	Xiubo Li <xiubli@...hat.com>,
	Jeff Layton <jlayton@...nel.org>
Cc: linux-kernel@...r.kernel.org,
	ceph-devel@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH 2/4] dev_printk: Add and use dev_no_printk()

When printk-indexing is enabled, each dev_printk() invocation emits a
pi_entry structure.  This is even true when the dev_printk() is
protected by an always-false check, as is typically the case for debug
messages: while the actual code to print the message is optimized out by
the compiler, the pi_entry structure is still emitted.

Avoid emitting pi_entry structures for unavailable dev_printk() kernel
messages by:
  1. Introducing a dev_no_printk() helper, mimicked after the existing
     no_printk() helper, which calls _dev_printk() instead of
     dev_printk(),
  2. Replacing all "if (0) dev_printk(...)" constructs by calls to the
     new helper.

This reduces the size of an arm64 defconfig kernel with
CONFIG_PRINTK_INDEX=y by 957 KiB.

Fixes: ad7d61f159db7397 ("printk: index: Add indexing support to dev_printk")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
 include/linux/dev_printk.h | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/include/linux/dev_printk.h b/include/linux/dev_printk.h
index 6bfe70decc9fb3bc..ae80a303c216be55 100644
--- a/include/linux/dev_printk.h
+++ b/include/linux/dev_printk.h
@@ -129,6 +129,16 @@ void _dev_info(const struct device *dev, const char *fmt, ...)
 		_dev_printk(level, dev, fmt, ##__VA_ARGS__);		\
 	})
 
+/*
+ * Dummy dev_printk for disabled debugging statements to use whilst maintaining
+ * gcc's format checking.
+ */
+#define dev_no_printk(level, dev, fmt, ...)				\
+	({								\
+		if (0)							\
+			_dev_printk(level, dev, fmt, ##__VA_ARGS__);	\
+	})
+
 /*
  * #defines for all the dev_<level> macros to prefix with whatever
  * possible use of #define dev_fmt(fmt) ...
@@ -158,10 +168,7 @@ void _dev_info(const struct device *dev, const char *fmt, ...)
 	dev_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__)
 #else
 #define dev_dbg(dev, fmt, ...)						\
-({									\
-	if (0)								\
-		dev_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__); \
-})
+	dev_no_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__)
 #endif
 
 #ifdef CONFIG_PRINTK
@@ -247,20 +254,14 @@ do {									\
 } while (0)
 #else
 #define dev_dbg_ratelimited(dev, fmt, ...)				\
-do {									\
-	if (0)								\
-		dev_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__); \
-} while (0)
+	dev_no_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__)
 #endif
 
 #ifdef VERBOSE_DEBUG
 #define dev_vdbg	dev_dbg
 #else
 #define dev_vdbg(dev, fmt, ...)						\
-({									\
-	if (0)								\
-		dev_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__); \
-})
+	dev_no_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__)
 #endif
 
 /*
-- 
2.34.1