[v4,0/9] fs: implement multigrain timestamps

v4:
- add request_mask argument to generic_fillattr
- Drop current_ctime helper and just code functionality into current_time
- rework i_ctime accessor functions

A few weeks ago, during one of the discussions around i_version, Dave
Chinner wrote this:

"You've missed the part where I suggested lifting the "nfsd sampled
i_version" state into an inode state flag rather than hiding it in
the i_version field. At that point, we could optimise away the
secondary ctime updates just like you are proposing we do with the
i_version updates.  Further, we could also use that state it to
decide whether we need to use high resolution timestamps when
recording ctime updates - if the nfsd has not sampled the
ctime/i_version, we don't need high res timestamps to be recorded
for ctime...."

While I don't think we can practically optimize away ctime updates
like we do with i_version, I do like the idea of using this scheme to
indicate when we need to use a high-res timestamp.

The basic idea here is to use an unused bit in the timespec64.tv_nsec
field to act as a flag to indicate that the value was queried since
the last time we updated it. If that flag is set when we go to update
the timestamp, we'll clear it and grab a fine-grained ktime value for
the update.

The first couple of patches add the necessary infrastructure, and the
last several patches update various filesystems to use it. For now, I'm
focusing on widely-used, exportable filesystems, but this scheme is
probably suitable for most filesystems in the kernel.

Note that this does cause at least one test failure with LTP's statx06
test. I have submitted a patch to fix the issue (by changing how it
fetches the "after" timestamp in that test).

Jeff Layton (9):
  fs: pass the request_mask to generic_fillattr
  fs: add infrastructure for multigrain inode i_m/ctime
  overlayfs: allow it to handle multigrain timestamps
  nfsd: ensure we use ctime_peek to grab the inode->i_ctime
  ksmbd: use ctime_peek to grab the ctime out of the inode
  tmpfs: add support for multigrain timestamps
  xfs: switch to multigrain timestamps
  ext4: convert to multigrain timestamps
  btrfs: convert to multigrain timestamps

 fs/9p/vfs_inode.c             |  4 +--
 fs/9p/vfs_inode_dotl.c        |  4 +--
 fs/afs/inode.c                |  2 +-
 fs/btrfs/delayed-inode.c      |  2 +-
 fs/btrfs/inode.c              |  4 +--
 fs/btrfs/super.c              |  5 +--
 fs/btrfs/tree-log.c           |  2 +-
 fs/ceph/inode.c               |  2 +-
 fs/cifs/inode.c               |  2 +-
 fs/coda/inode.c               |  3 +-
 fs/ecryptfs/inode.c           |  5 +--
 fs/erofs/inode.c              |  2 +-
 fs/exfat/file.c               |  2 +-
 fs/ext2/inode.c               |  2 +-
 fs/ext4/inode.c               | 19 ++++++++--
 fs/ext4/super.c               |  2 +-
 fs/f2fs/file.c                |  2 +-
 fs/fat/file.c                 |  2 +-
 fs/fuse/dir.c                 |  2 +-
 fs/gfs2/inode.c               |  2 +-
 fs/hfsplus/inode.c            |  2 +-
 fs/inode.c                    | 48 +++++++++++++++++++++----
 fs/kernfs/inode.c             |  2 +-
 fs/ksmbd/smb2pdu.c            | 28 +++++++--------
 fs/ksmbd/vfs.c                |  3 +-
 fs/libfs.c                    |  4 +--
 fs/minix/inode.c              |  2 +-
 fs/nfs/inode.c                |  2 +-
 fs/nfs/namespace.c            |  3 +-
 fs/nfsd/nfsfh.c               | 11 ++++--
 fs/ntfs3/file.c               |  2 +-
 fs/ocfs2/file.c               |  2 +-
 fs/orangefs/inode.c           |  2 +-
 fs/overlayfs/file.c           |  7 ++--
 fs/overlayfs/util.c           |  2 +-
 fs/proc/base.c                |  4 +--
 fs/proc/fd.c                  |  2 +-
 fs/proc/generic.c             |  2 +-
 fs/proc/proc_net.c            |  2 +-
 fs/proc/proc_sysctl.c         |  2 +-
 fs/proc/root.c                |  3 +-
 fs/stat.c                     | 59 ++++++++++++++++++++++++------
 fs/sysv/itree.c               |  3 +-
 fs/ubifs/dir.c                |  2 +-
 fs/udf/symlink.c              |  2 +-
 fs/vboxsf/utils.c             |  2 +-
 fs/xfs/libxfs/xfs_inode_buf.c |  2 +-
 fs/xfs/xfs_inode_item.c       |  2 +-
 fs/xfs/xfs_iops.c             |  4 +--
 fs/xfs/xfs_super.c            |  2 +-
 include/linux/fs.h            | 68 +++++++++++++++++++++++++++++++++--
 mm/shmem.c                    |  4 +--
 52 files changed, 260 insertions(+), 95 deletions(-)

On Thu, 18 May 2023 07:47:33 -0400, Jeff Layton wrote:
> v4:
> - add request_mask argument to generic_fillattr
> - Drop current_ctime helper and just code functionality into current_time
> - rework i_ctime accessor functions
> 
> A few weeks ago, during one of the discussions around i_version, Dave
> Chinner wrote this:
> 
> [...]

Let's get this into -next so we can see whether this leads to any
performance or other regressions. It's moved to a vfs.unstable.* branch
for now. If nothing bad happens it'll be upgraded to a vfs.* branch.
Filesystems that prefer to carry their fs specific patch themselves can
request a stable tag for the generic changes.

---

Applied to the vfs.unstable.ctime branch of the vfs/vfs.git tree.
Patches in the vfs.unstable.ctime branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.unstable.ctime

[1/9] fs: pass the request_mask to generic_fillattr
      https://git.kernel.org/vfs/vfs/c/ec1239bab5fd
[2/9] fs: add infrastructure for multigrain inode i_m/ctime
      https://git.kernel.org/vfs/vfs/c/97e9fbb03240
[3/9] overlayfs: allow it to handle multigrain timestamps
      https://git.kernel.org/vfs/vfs/c/ada0fe43f748
[4/9] nfsd: ensure we use ctime_peek to grab the inode->i_ctime
      https://git.kernel.org/vfs/vfs/c/39493918b700
[5/9] ksmbd: use ctime_peek to grab the ctime out of the inode
      https://git.kernel.org/vfs/vfs/c/35527cdc7840
[6/9] tmpfs: add support for multigrain timestamps
      https://git.kernel.org/vfs/vfs/c/ce1dc211dbde
[7/9] xfs: switch to multigrain timestamps
      https://git.kernel.org/vfs/vfs/c/78bbdfd2fb74
[8/9] ext4: convert to multigrain timestamps
      https://git.kernel.org/vfs/vfs/c/d2100ca52e14
[9/9] btrfs: convert to multigrain timestamps
      https://git.kernel.org/vfs/vfs/c/c725b40cfbd5