linux-kernel - [PATCH 0/2] two nits for path lookup

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Message-ID: <20250416221626.2710239-1-mjguzik@gmail.com>
Date: Thu, 17 Apr 2025 00:16:24 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: brauner@...nel.org
Cc: torvalds@...ux-foundation.org,
	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 0/2] two nits for path lookup

since path looku is being looked at, two extra nits from me:

1. some trivial jump avoidance in inode_permission()

2. but more importantly avoiding a memory access which is most likely a
cache miss when descending into devcgroup_inode_permission()

the file seems to have no maintainer fwiw

anyhow I'm confident the way forward is to add IOP_FAST_MAY_EXEC (or
similar) to elide inode_permission() in the common case to begin with.
There are quite a few branches which straight up don't need execute.
On top of that btrfs has a permission hook only to check for MAY_WRITE,
which in case of path lookup is not set. With the above flag the call
will be avoided.

Mateusz Guzik (2):
  fs: touch up predicts in inode_permission()
  device_cgroup: avoid access to ->i_rdev in the common case in
    devcgroup_inode_permission()

 fs/namei.c                    | 10 +++++-----
 include/linux/device_cgroup.h |  7 ++++---
 2 files changed, 9 insertions(+), 8 deletions(-)

-- 
2.48.1