linux-kernel - [PATCH] dcache: predict the name matches if parent and length also match

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Message-ID: <20251127122412.4131818-1-mjguzik@gmail.com>
Date: Thu, 27 Nov 2025 13:24:12 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: brauner@...nel.org
Cc: viro@...iv.linux.org.uk,
	jack@...e.cz,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH] dcache: predict the name matches if parent and length also match

dentry_cmp() has predicts inside, but they were not enough to convince
the compiler.

As for difference in asm, some of the code is reshuffled and there is
one less unconditional jump to get there.

Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
---

i know it's late, but given the non-semantic-modifying nature of the
change, i think it can still make it for 6.19

 fs/dcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 23d1752c29e6..bc84f89156fa 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2346,7 +2346,7 @@ struct dentry *__d_lookup_rcu(const struct dentry *parent,
 			continue;
 		if (dentry->d_name.hash_len != hashlen)
 			continue;
-		if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
+		if (unlikely(dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0))
 			continue;
 		*seqp = seq;
 		return dentry;
-- 
2.34.1