Re: [PATCH v3 00/38] vfs, nfsd: implement directory delegations

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2025-09-25 at 09:39 -0400, Chuck Lever wrote:
> On 9/24/25 11:05 AM, Jeff Layton wrote:
> > This patchset is an update to a patchset that I posted in early June
> > this year [1]. This version should be basically feature-complete, with a
> > few caveats.
> > 
> > NFSv4.1 adds a GET_DIR_DELEGATION operation, to allow clients
> > to request a delegation on a directory. If the client holds a directory
> > delegation, then it knows that nothing will change the dentries in it
> > until it has been recalled (modulo the case where the client requests
> > notifications of directory changes).
> > 
> > In 2023, Rick Macklem gave a talk at the NFS Bakeathon on his
> > implementation of directory delegations for FreeBSD [2], and showed that
> > it can greatly improve LOOKUP-heavy workloads. There is also some
> > earlier work by CITI [3] that showed similar results. The SMB protocol
> > also has a similar sort of construct, and they have also seen large
> > performance improvements on certain workloads.
> > 
> > This version also starts with support for trivial directory delegations
> > that support no notifications.  From there it adds VFS support for
> > ignoring certain break_lease() events in directories. It then adds
> > support for basic CB_NOTIFY calls (with names only). Next, support for
> > sending attributes in the notifications is added.
> > 
> > I think that this version should be getting close to merge ready. Anna
> > has graciously agreed to work on the client-side pieces for this. I've
> > mostly been testing using pynfs tests (which I will submit soon).
> > 
> > The main limitation at this point is that callback requests are
> > currently limited to a single page, so we can't send very many in a
> > single CB_NOTIFY call. This will make it easy to "get into the weeds" if
> > you're changing a directory quickly. The server will just recall the
> > delegation in that case, so it's harmless even though it's not ideal.
> > 
> > If this approach looks acceptable I'll see if we can increase that
> > limitation (it seems doable).
> > 
> > If anyone wishes to try this out, it's in the "dir-deleg" branch in my
> > tree at kernel.org [4].
> > 
> > [1]: https://lore.kernel.org/linux-nfs/20250602-dir-deleg-v2-0-a7919700de86@kernel.org/
> > [2]: https://www.youtube.com/watch?v=DdFyH3BN5pI
> > [3]: https://linux-nfs.org/wiki/index.php/CITI_Experience_with_Directory_Delegations
> > [4]: https://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux.git/
> > 
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > Changes in v3:
> > - Rework to do minimal work in fsnotify callbacks
> > - Add support for sending attributes in CB_NOTIFY calls
> > - Add support for dir attr change notifications
> > - Link to v2: https://lore.kernel.org/r/20250602-dir-deleg-v2-0-a7919700de86@kernel.org
> > 
> > Changes in v2:
> > - add support for ignoring certain break_lease() events
> > - basic support for CB_NOTIFY
> > - Link to v1: https://lore.kernel.org/r/20240315-dir-deleg-v1-0-a1d6209a3654@kernel.org
> > 
> > ---
> > Jeff Layton (38):
> >       filelock: push the S_ISREG check down to ->setlease handlers
> >       filelock: add a lm_may_setlease lease_manager callback
> >       vfs: add try_break_deleg calls for parents to vfs_{link,rename,unlink}
> >       vfs: allow mkdir to wait for delegation break on parent
> >       vfs: allow rmdir to wait for delegation break on parent
> >       vfs: break parent dir delegations in open(..., O_CREAT) codepath
> >       vfs: make vfs_create break delegations on parent directory
> >       vfs: make vfs_mknod break delegations on parent directory
> >       filelock: lift the ban on directory leases in generic_setlease
> >       nfsd: allow filecache to hold S_IFDIR files
> >       nfsd: allow DELEGRETURN on directories
> >       nfsd: check for delegation conflicts vs. the same client
> >       nfsd: wire up GET_DIR_DELEGATION handling
> >       filelock: rework the __break_lease API to use flags
> >       filelock: add struct delegated_inode
> >       filelock: add support for ignoring deleg breaks for dir change events
> >       filelock: add a tracepoint to start of break_lease()
> >       filelock: add an inode_lease_ignore_mask helper
> >       nfsd: add protocol support for CB_NOTIFY
> >       nfs_common: add new NOTIFY4_* flags proposed in RFC8881bis
> >       nfsd: allow nfsd to get a dir lease with an ignore mask
> >       vfs: add fsnotify_modify_mark_mask()
> >       nfsd: update the fsnotify mark when setting or removing a dir delegation
> >       nfsd: make nfsd4_callback_ops->prepare operation bool return
> >       nfsd: add callback encoding and decoding linkages for CB_NOTIFY
> >       nfsd: add data structures for handling CB_NOTIFY to directory delegation
> >       nfsd: add notification handlers for dir events
> >       nfsd: add tracepoint to dir_event handler
> >       nfsd: apply the notify mask to the delegation when requested
> >       nfsd: add helper to marshal a fattr4 from completed args
> >       nfsd: allow nfsd4_encode_fattr4_change() to work with no export
> >       nfsd: send basic file attributes in CB_NOTIFY
> >       nfsd: allow encoding a filehandle into fattr4 without a svc_fh
> >       nfsd: add a fi_connectable flag to struct nfs4_file
> >       nfsd: add the filehandle to returned attributes in CB_NOTIFY
> >       nfsd: properly track requested child attributes
> >       nfsd: track requested dir attributes
> >       nfsd: add support to CB_NOTIFY for dir attribute changes
> > 
> >  Documentation/sunrpc/xdr/nfs4_1.x    | 267 +++++++++++++++++-
> >  drivers/base/devtmpfs.c              |   2 +-
> >  fs/attr.c                            |   4 +-
> >  fs/cachefiles/namei.c                |   2 +-
> >  fs/ecryptfs/inode.c                  |   2 +-
> >  fs/fuse/dir.c                        |   1 +
> >  fs/init.c                            |   2 +-
> >  fs/locks.c                           | 122 ++++++--
> >  fs/namei.c                           | 253 +++++++++++------
> >  fs/nfs/nfs4file.c                    |   2 +
> >  fs/nfsd/filecache.c                  | 101 +++++--
> >  fs/nfsd/filecache.h                  |   2 +
> >  fs/nfsd/nfs4callback.c               |  60 +++-
> >  fs/nfsd/nfs4layouts.c                |   3 +-
> >  fs/nfsd/nfs4proc.c                   |  36 ++-
> >  fs/nfsd/nfs4recover.c                |   2 +-
> >  fs/nfsd/nfs4state.c                  | 531 +++++++++++++++++++++++++++++++++--
> >  fs/nfsd/nfs4xdr.c                    | 298 +++++++++++++++++---
> >  fs/nfsd/nfs4xdr_gen.c                | 506 ++++++++++++++++++++++++++++++++-
> >  fs/nfsd/nfs4xdr_gen.h                |  20 +-
> >  fs/nfsd/state.h                      |  73 ++++-
> >  fs/nfsd/trace.h                      |  21 ++
> >  fs/nfsd/vfs.c                        |   7 +-
> >  fs/nfsd/vfs.h                        |   2 +-
> >  fs/nfsd/xdr4.h                       |   3 +
> >  fs/nfsd/xdr4cb.h                     |  12 +
> >  fs/notify/mark.c                     |  29 ++
> >  fs/open.c                            |   8 +-
> >  fs/overlayfs/overlayfs.h             |   2 +-
> >  fs/posix_acl.c                       |  12 +-
> >  fs/smb/client/cifsfs.c               |   3 +
> >  fs/smb/server/vfs.c                  |   2 +-
> >  fs/utimes.c                          |   4 +-
> >  fs/xattr.c                           |  16 +-
> >  fs/xfs/scrub/orphanage.c             |   2 +-
> >  include/linux/filelock.h             | 143 +++++++---
> >  include/linux/fs.h                   |  11 +-
> >  include/linux/fsnotify_backend.h     |   1 +
> >  include/linux/nfs4.h                 | 127 ---------
> >  include/linux/sunrpc/xdrgen/nfs4_1.h | 304 +++++++++++++++++++-
> >  include/linux/xattr.h                |   4 +-
> >  include/trace/events/filelock.h      |  38 ++-
> >  include/uapi/linux/nfs4.h            |   2 -
> >  43 files changed, 2636 insertions(+), 406 deletions(-)
> > ---
> > base-commit: 36c204d169319562eed170f266c58460d5dad635
> > change-id: 20240215-dir-deleg-e212210ba9d4
> > 
> > Best regards,
> 
> Series is clean and easy to read, thanks for your hard work! I agree
> that the NFSD portions appear to be complete and ready to accept.
> 
> Because the series is cross-subsystem, we will need to discuss a merge
> plan. So I'll hold off on R-b or Acked until that is nailed down.
> 

Thanks. It's sensible to hold off for a bit. There is at least one leak
that I found earlier today, and a few cleanups that I have queued up.

We also have a bake-a-thon in another couple of weeks where I hope to
test this more extensively. After that, I'm hoping we'll be in
reasonable shape to take it into linux-next.

What I may do is reorder the vfs patches to the front of the queue and
plead to Christian and Al to take them into a branch that feeds into
linux-next. That way we can at least get some feedback and testing with
those bits in place, and a foundation on which we can merge the nfsd
bits.

-- 
Jeff Layton <jlayton@kernel.org>