linux-kernel - [PATCH v4 0/2] rcu-based inode lookup for iget*

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Message-ID: <20240611173824.535995-1-mjguzik@gmail.com>
Date: Tue, 11 Jun 2024 19:38:21 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: brauner@...nel.org
Cc: viro@...iv.linux.org.uk,
	jack@...e.cz,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-btrfs@...r.kernel.org,
	josef@...icpanda.com,
	hch@...radead.org,
	Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH v4 0/2] rcu-based inode lookup for iget*

I revamped the commit message for patch 1, explicitly spelling out a
bunch of things and adding bpftrace output. Please read it.

There was some massaging of lines in the include/linux/fs.h header
files. If you don't like it I would appreciate if you adjusted it
however you see fit on your own.

This adjusts the state to what was suggested by Christian.

Specific results:

ext4 (needed mkfs.ext4 -N 24000000):
before:	3.77s user 890.90s system 1939% cpu 46.118 total
after:  3.24s user 397.73s system 1858% cpu 21.581 total (-53%)

btrfs (s/iget5_locked/iget5_locked_rcu in fs/btrfs/inode.c):
before: 3.54s user 892.30s system 1966% cpu 45.549 total
after:  3.28s user 738.66s system 1955% cpu 37.932 total (-16.7%)

btrfs bottlenecks itself on its own locks here.

Benchmark info in the commit message to the first patch.

fs rundown is as follows:
- ext4 patched implicitly
- xfs does not use the inode hash
- bcachefs is out of the picture as Kent decided to implement his own
  inode hashing based on rhashtable, for now private to his fs.
- btrfs handled in the patchset

I have not looked at others.

v4:
- only provide iget5_locked_rcu
- add a btrfs ack

v3:
- export new routines with _GPL
- don't use the extern keyword
- add ilookup5_rcu to follow iget5_locked scheme

v2:
- add argument lists to new routines
- assert the inode hash lock is not held as applicable
- real btrfs patch included

Mateusz Guzik (2):
  vfs: add rcu-based find_inode variants for iget ops
  btrfs: use iget5_locked_rcu

 fs/btrfs/inode.c   |   2 +-
 fs/inode.c         | 119 ++++++++++++++++++++++++++++++++++++++-------
 include/linux/fs.h |  10 +++-
 3 files changed, 112 insertions(+), 19 deletions(-)

-- 
2.43.0