linux-kernel - [PATCH] fs/namei: Remove redundant DCACHE_MANAGED_DENTRY check in __follow_mount

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Message-Id: <20260105-dcache-v1-1-f0d904b4a7c2@debian.org>
Date: Mon, 05 Jan 2026 07:10:27 -0800
From: Breno Leitao <leitao@...ian.org>
To: Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
 jlayton@...nel.org, rostedt@...dmis.org, kernel-team@...a.com, 
 Breno Leitao <leitao@...ian.org>
Subject: [PATCH] fs/namei: Remove redundant DCACHE_MANAGED_DENTRY check in
 __follow_mount_rcu

The check for DCACHE_MANAGED_DENTRY at the start of __follow_mount_rcu()
is redundant because the only caller (handle_mounts) already verifies
d_managed(dentry) before calling this function, so, dentry in
__follow_mount_rcu() has always DCACHE_MANAGED_DENTRY set.

This early-out optimization never fires in practice - but it is marking
as likely().

This was detected with branch profiling, which shows 100% misprediction
in this likely.

Remove the whole if clause instead of removing the likely, given we
know for sure that dentry is not DCACHE_MANAGED_DENTRY.

Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 fs/namei.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index bf0f66f0e9b9..774a2f5b0a10 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1623,9 +1623,6 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path)
 	struct dentry *dentry = path->dentry;
 	unsigned int flags = dentry->d_flags;

-	if (likely(!(flags & DCACHE_MANAGED_DENTRY)))
-		return true;
-
 	if (unlikely(nd->flags & LOOKUP_NO_XDEV))
 		return false;

---
base-commit: 3609fa95fb0f2c1b099e69e56634edb8fc03f87c
change-id: 20260105-dcache-01aa5d1c9b32

Best regards,
--  
Breno Leitao <leitao@...ian.org>