linux-kernel - [RFC][PATCH 0/2] fsnotify: super block watch

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Date:   Tue, 20 Dec 2016 17:20:05 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Eric Paris <eparis@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC][PATCH 0/2] fsnotify: super block watch

Jan,

This 2 patch series is the 2nd part of fanotify super block watch work.

The full work is available on my github:
1. fsnotify: misc cleanups - 4 patches posted on Dec 17
https://github.com/amir73il/linux/commits/fsnotify_dentry
2. fsnotify: super block watch - 2 patches in this posting
https://github.com/amir73il/linux/commits/fsnotify_sb
3. fanotify: add support for more events - 6 patches posted on Oct 10
https://github.com/amir73il/linux/commits/fanotify_dentry
4. fanotify: add super block watch - 6 patches not posted yet
https://github.com/amir73il/linux/commits/fanotify_sb

On the Oct 10 posting you asked me about the use case and it was hard
to explain the use case with only part of the work done.

The issue, which this work sets to solve, is the poor scalability of
recursive inotify watches.

Other operating systems have a scalable way of watching changes on
a large file system. Windows has USN Journal, macOS has FSEvents
and BSD has kevents.

The only way in Linux to monitor file system namei events
(e.g. create/delete/move) is the recursive inotify watch way and
this method scales very poorly for large enough directory trees.
Beyond the exploding probability of a need for full scan, pinning
all directory inodes wastes a lot of memory.

The efforts to merge fanotify took several steps in the direction
of solving the scalability issue, but they did not go all the way
to provide the functionality required to replace inotify.

Unfortunately, the fsnotify subsystem has been suffering from
neglection for quite some time, so it hard for me to get proper
feedback on this work.

The fanotify super block watch feature is currently being tested
by my employer and by other interested parties as well.

I am planning to write some more testing tools and gather more
benchmark results before posting the patches for the last part
of this work (fanotify_sb).

Any assistance you can provide with review and with helping
to push this work forward would be very much appreciated.

Thanks!
Amir.

Amir Goldstein (2):
  fsnotify: add event mask FS_EVENT_ON_SB
  fsnotify: implement event reporting to super block's root inode

 fs/notify/fsnotify.c             | 60 ++++++++++++++++++++++++++++++++++++----
 include/linux/fsnotify_backend.h | 29 +++++++++++++++++--
 2 files changed, 81 insertions(+), 8 deletions(-)

-- 
2.7.4