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[46.135.14.82]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b72bfa0f1bbsm15430466b.65.2025.11.06.10.01.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Nov 2025 10:01:09 -0800 (PST) From: Mateusz Guzik To: brauner@kernel.org Cc: viro@zeniv.linux.org.uk, jack@suse.cz, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, tytso@mit.edu, torvalds@linux-foundation.org, josef@toxicpanda.com, linux-btrfs@vger.kernel.org, Mateusz Guzik Subject: [PATCH v2 0/4] permission check avoidance during lookup Date: Thu, 6 Nov 2025 19:00:58 +0100 Message-ID: <20251106180103.923856-1-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" To quote from patch 1: Vast majority of real-world lookups happen on directories which are traversable by anyone. Figuring out that this holds for a given inode can be done when instantiating it or changing permissions, avoiding the overhead during lookup. Stats below. A simple microbench of stating /usr/include/linux/fs.h on ext4 in a loop on Sapphire Rapids (ops/s): before: 3640352 after: 3797258 (+4%) During a kernel build about 90% of all lookups managed to skip permission checks in my setup, see the commit message for a breakdown. WARNING: more testing is needed for correctness, but I'm largely happy with the state as is. WARNING: I'm assuming the following bit is applied: diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 78ea864fa8cd..eaf776cd4175 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -5518,6 +5518,10 @@ struct inode *__ext4_iget(struct super_block *sb, un= signed long ino, goto bad_inode; brelse(iloc.bh); =20 + /* Initialize the "no ACL's" state for the simple cases */ + if (!ext4_test_inode_state(inode, EXT4_STATE_XATTR) && !ei->i_file_= acl) + cache_no_acl(inode); + unlock_new_inode(inode); return inode; Lack of the patch does not affect correctness, but it does make the patch ineffective for ext4. I did not include it in the posting as other people promised to sort it out. Discussion is here with an ack from Jan: https://lore.kernel.org/linux-fsdevel/kn44smk4dgaj5rqmtcfr7ruecixzrik6omur2= l2opitn7lbvfm@rm4y24fcfzbz/T/#m30d6cea6be48e95c0d824e98a328fb90c7a5766d and full thread: https://lore.kernel.org/linux-fsdevel/kn44smk4dgaj5rqmtcfr7ruecixzrik6omur2= l2opitn7lbvfm@rm4y24fcfzbz/T/#t v2: - productize - btrfs and tmpfs support Mateusz Guzik (4): fs: speed up path lookup with cheaper MAY_EXEC checks ext4: opt-in for IOP_MAY_FAST_EXEC btrfs: opt-in for IOP_MAY_FAST_EXEC tmpfs: opt-in for IOP_MAY_FAST_EXEC fs/attr.c | 1 + fs/btrfs/inode.c | 12 +++++- fs/ext4/inode.c | 2 + fs/ext4/namei.c | 1 + fs/namei.c | 95 +++++++++++++++++++++++++++++++++++++++++++++- fs/posix_acl.c | 1 + fs/xattr.c | 1 + include/linux/fs.h | 21 +++++++--- mm/shmem.c | 9 +++++ 9 files changed, 134 insertions(+), 9 deletions(-) --=20 2.48.1