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(cst-prg-14-82.cust.vodafone.cz. [46.135.14.82]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6416001a4a8sm6054882a12.15.2025.11.10.02.05.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Nov 2025 02:05:07 -0800 (PST) From: Mateusz Guzik To: viro@zeniv.linux.org.uk Cc: brauner@kernel.org, jack@suse.cz, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Mateusz Guzik Subject: [PATCH v2] fs: avoid calls to legitimize_links() if possible Date: Mon, 10 Nov 2025 11:05:03 +0100 Message-ID: <20251110100503.1434167-1-mjguzik@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The routine is always called towards the end of lookup. According to bpftrace on my boxen and boxen of people I asked, the depth count is almost always 0, thus the call can be avoided in the common case. one-liner: bpftrace -e 'kprobe:legitimize_links { @[((struct nameidata *)arg0)->depth]= =3D count(); }' sample results from few minutes of tracing: @[1]: 59 @[0]: 147236 @[2]: 1 @[1]: 12087 @[0]: 5926235 And of course the venerable kernel build: @[1]: 3563 @[0]: 6625425 Signed-off-by: Mateusz Guzik Reviewed-by: Jan Kara --- v2: - drop 'noinline' - spell out the check at call sites verified no change in asm fs/namei.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 2a112b2c0951..0de0344a2ab2 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -882,7 +882,7 @@ static bool try_to_unlazy(struct nameidata *nd) =20 BUG_ON(!(nd->flags & LOOKUP_RCU)); =20 - 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 +917,7 @@ static bool try_to_unlazy_next(struct nameidata *nd, st= ruct dentry *dentry) int res; BUG_ON(!(nd->flags & LOOKUP_RCU)); =20 - if (unlikely(!legitimize_links(nd))) + if (unlikely(nd->depth && !legitimize_links(nd))) goto out2; res =3D __legitimize_mnt(nd->path.mnt, nd->m_seq); if (unlikely(res)) { --=20 2.48.1