linux-ext4 - [PATCH] ext4: Refactor breaking condition for xattr_find

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Message-ID: <20250708020013.175728-1-richard120310@gmail.com>
Date: Tue,  8 Jul 2025 10:00:13 +0800
From: I Hsin Cheng <richard120310@...il.com>
To: tytso@....edu
Cc: adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linuxfoundation.org,
	I Hsin Cheng <richard120310@...il.com>
Subject: [PATCH] ext4: Refactor breaking condition for xattr_find_entry()

Refactor the condition for breaking the loop within xattr_find_entry().
Elimate the usage of "<=" and take condition shortcut when "!cmp" is
true.

Originally, the condition was "(cmp <= 0 && (sorted || cmp == 0))", which
means after it knows "cmp <= 0" is true, it has to check the value of
"sorted" and "cmp". The checking of "cmp" here would be redundant since
it has already checked it.

Observing from the logic, when "cmp == 0" the branch is going to be true,
no need to check "cmp == 0" again, so we only need to take shortcut when
"cmp == 0", on the other hand, we'll check "sorted" when "cmp < 0".

The refactor can shrink the generated code size by 44 bytes. Numerous
instructions can be saved thus should also benefit execution efficiency
as well.

$ ./scripts/bloat-o-meter vmlinux_old vmlinux_new
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-44 (-44)
Function                                     old     new   delta
xattr_find_entry                             300     256     -44
Total: Before=22989434, After=22989390, chg -0.00%

The test is done on kernel version 6.16 with x86_64 defconfig
and gcc 13.3.0.

Signed-off-by: I Hsin Cheng <richard120310@...il.com>
---
 fs/ext4/xattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 8d15acbacc20..1993622e3c74 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -338,7 +338,7 @@ xattr_find_entry(struct inode *inode, struct ext4_xattr_entry **pentry,
 			cmp = name_len - entry->e_name_len;
 		if (!cmp)
 			cmp = memcmp(name, entry->e_name, name_len);
-		if (cmp <= 0 && (sorted || cmp == 0))
+		if (!cmp || (cmp < 0 && sorted))
 			break;
 	}
 	*pentry = entry;
-- 
2.43.0