Stats from nd->depth usage during the venerable kernel build collected like so:
bpftrace -e 'kprobe:terminate_walk,kprobe:walk_component,kprobe:legitimize_links
{ @[probe] = lhist(((struct nameidata *)arg0)->depth, 0, 8, 1); }'

@[kprobe:legitimize_links]:
[0, 1)           6554906 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[1, 2)              3534 |                                                    |

@[kprobe:terminate_walk]:
[0, 1)          12153664 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|

@[kprobe:walk_component]:
[0, 1)          53075749 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[1, 2)            971421 |                                                    |
[2, 3)             84946 |                                                    |

Additionally a custom probe was added for depth within link_path_walk():
bpftrace -e 'kprobe:link_path_walk_probe { @[probe] = lhist(arg0, 0, 8, 1); }'
@[kprobe:link_path_walk_probe]:
[0, 1)           7528231 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[1, 2)            407905 |@@                                                  |

Given these results:
1. terminate_walk() is called towards the end of the lookup and in this
   test it never had any links to clean up.
2. legitimize_links() is also called towards the end of lookup and most
   of the time there s 0 depth. Patch consumers to avoid calling into it
   in that case.
3. walk_component() is typically called with WALK_MORE and zero depth,
   checked in that order. Check depth first and predict it is 0.
4. link_path_walk() also does not deal with a symlink most of the time
   when !*name

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

v5:
- tweak the commit message + add link_path_walk probe stats, no code
  changes

 fs/namei.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 2a112b2c0951..11295fcf877c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -785,7 +785,8 @@ static void leave_rcu(struct nameidata *nd)
 
 static void terminate_walk(struct nameidata *nd)
 {
-	drop_links(nd);
+	if (unlikely(nd->depth))
+		drop_links(nd);
 	if (!(nd->flags & LOOKUP_RCU)) {
 		int i;
 		path_put(&nd->path);
@@ -882,7 +883,7 @@ static bool try_to_unlazy(struct nameidata *nd)
 
 	BUG_ON(!(nd->flags & LOOKUP_RCU));
 
-	if (unlikely(!legitimize_links(nd)))
+	if (unlikely(nd->depth && !legitimize_links(nd)))
 		goto out1;
 	if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
 		goto out;
@@ -917,7 +918,7 @@ static bool try_to_unlazy_next(struct nameidata *nd, struct dentry *dentry)
 	int res;
 	BUG_ON(!(nd->flags & LOOKUP_RCU));
 
-	if (unlikely(!legitimize_links(nd)))
+	if (unlikely(nd->depth && !legitimize_links(nd)))
 		goto out2;
 	res = __legitimize_mnt(nd->path.mnt, nd->m_seq);
 	if (unlikely(res)) {
@@ -2179,7 +2180,7 @@ static const char *walk_component(struct nameidata *nd, int flags)
 	 * parent relationships.
 	 */
 	if (unlikely(nd->last_type != LAST_NORM)) {
-		if (!(flags & WALK_MORE) && nd->depth)
+		if (unlikely(nd->depth) && !(flags & WALK_MORE))
 			put_link(nd);
 		return handle_dots(nd, nd->last_type);
 	}
@@ -2191,7 +2192,7 @@ static const char *walk_component(struct nameidata *nd, int flags)
 		if (IS_ERR(dentry))
 			return ERR_CAST(dentry);
 	}
-	if (!(flags & WALK_MORE) && nd->depth)
+	if (unlikely(nd->depth) && !(flags & WALK_MORE))
 		put_link(nd);
 	return step_into(nd, flags, dentry);
 }
@@ -2544,7 +2545,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
 		if (unlikely(!*name)) {
 OK:
 			/* pathname or trailing symlink, done */
-			if (!depth) {
+			if (likely(!depth)) {
 				nd->dir_vfsuid = i_uid_into_vfsuid(idmap, nd->inode);
 				nd->dir_mode = nd->inode->i_mode;
 				nd->flags &= ~LOOKUP_PARENT;
-- 
2.48.1

On Wed, 19 Nov 2025 15:29:54 +0100, Mateusz Guzik wrote:
> Stats from nd->depth usage during the venerable kernel build collected like so:
> bpftrace -e 'kprobe:terminate_walk,kprobe:walk_component,kprobe:legitimize_links
> { @[probe] = lhist(((struct nameidata *)arg0)->depth, 0, 8, 1); }'
> 
> @[kprobe:legitimize_links]:
> [0, 1)           6554906 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> [1, 2)              3534 |                                                    |
> 
> [...]

Applied to the vfs-6.19.misc branch of the vfs/vfs.git tree.
Patches in the vfs-6.19.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.19.misc

[1/1] fs: add predicts based on nd->depth
      https://git.kernel.org/vfs/vfs/c/7c179096e77e