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Subject: [PATCH RFC 00/12] Allow concurrent directory updates.
From:   NeilBrown <neilb@suse.de>
To:     Al Viro <viro@zeniv.linux.org.uk>, Daire Byrne <daire@dneg.com>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Chuck Lever <chuck.lever@oracle.com>
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
Date:   Tue, 14 Jun 2022 09:18:21 +1000
Message-ID: <165516173293.21248.14587048046993234326.stgit@noble.brown>
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VFS currently holds an exclusive lock on a directory during create,
unlink, rename.  This imposes serialisation on all filesystems though
some may not benefit from it, and some may be able to provide finer
grained locking internally, thus reducing contention.

This series allows the filesystem to request that the inode lock be
shared rather than exclusive.  In that case an exclusive lock will be
held on the dentry instead, much as is done for parallel lookup.

The NFS filesystem can easily support concurrent updates (server does
any needed serialiation) so it is converted.

This series also converts nfsd to use the new interfaces so concurrent
incoming NFS requests in the one directory can be handled concurrently.

As a net result, if an NFS mounted filesystem is reexported over NFS,
then multiple clients can create files in a single directory and all
synchronisation will be handled on the final server.  This helps hid
latency on link from client to server.

I include a few nfsd patches that aren't strictly needed for this work,
but seem to be a logical consequence of the changes that I did have to
make.

I have only tested this lightly.  In particular the rename support is
quite new and I haven't tried to break it yet.

I post this for general review, and hopefully extra testing...  Daire
Byrne has expressed interest in the NFS re-export parallelism.

NeilBrown


---

NeilBrown (12):
      VFS: support parallel updates in the one directory.
      VFS: move EEXIST and ENOENT tests into lookup_hash_update()
      VFS: move want_write checks into lookup_hash_update()
      VFS: move dput() and mnt_drop_write() into done_path_update()
      VFS: export done_path_update()
      VFS: support concurrent renames.
      NFS: support parallel updates in the one directory.
      nfsd: allow parallel creates from nfsd
      nfsd: support concurrent renames.
      nfsd: reduce locking in nfsd_lookup()
      nfsd: use (un)lock_inode instead of fh_(un)lock
      nfsd: discard fh_locked flag and fh_lock/fh_unlock


 fs/dcache.c            |  59 ++++-
 fs/namei.c             | 578 ++++++++++++++++++++++++++++++++---------
 fs/nfs/dir.c           |  29 ++-
 fs/nfs/inode.c         |   2 +
 fs/nfs/unlink.c        |   5 +-
 fs/nfsd/nfs2acl.c      |   6 +-
 fs/nfsd/nfs3acl.c      |   4 +-
 fs/nfsd/nfs3proc.c     |  37 +--
 fs/nfsd/nfs4acl.c      |   7 +-
 fs/nfsd/nfs4proc.c     |  61 ++---
 fs/nfsd/nfs4state.c    |   8 +-
 fs/nfsd/nfsfh.c        |  10 +-
 fs/nfsd/nfsfh.h        |  58 +----
 fs/nfsd/nfsproc.c      |  31 +--
 fs/nfsd/vfs.c          | 243 ++++++++---------
 fs/nfsd/vfs.h          |   8 +-
 include/linux/dcache.h |  27 ++
 include/linux/fs.h     |   1 +
 include/linux/namei.h  |  30 ++-
 19 files changed, 791 insertions(+), 413 deletions(-)

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