[PATCH-v2 0/5] add support for a lazytime mount option

[Theodore Ts'o]

This is an updated version of what had originally been an
ext4-specific patch which significantly improves performance by lazily
writing timestamp updates (and in particular, mtime updates) to disk.
The in-memory timestamps are always correct, but they are only written
to disk when required for correctness.

This provides a huge performance boost for ext4 due to how it handles
journalling, but it's valuable for all file systems running on flash
storage or drive-managed SMR disks by reducing the metadata write
load.  So upon request, I've moved the functionality to the VFS layer.
Once the /sbin/mount program adds support for MS_LAZYTIME, all file
systems should be able to benefit from this optimization.

There is still an ext4-specific optimization, which may be applicable
for other file systems which store more than one inode in a block, but
it will require file system specific code.  It is purely optional,
however.

Please note the changes to update_time() and the new write_time() inode
operations functions, which impact btrfs and xfs.  The changes are
fairly simple, but I would appreciate confirmation from the btrfs and
xfs teams that I got things right.   Thanks!!

Any objections to my carrying these patches in the ext4 git tree?

Changes since -v1:
   - Added explanatory comments in update_time() regarding i_ts_dirty_days
   - Fix type used for days_since_boot
   - Improve SMP scalability in update_time and ext4_update_other_inodes_time
   - Added tracepoints to help test and characterize how often and under
         what circumstances inodes have their timestamps lazily updated

Theodore Ts'o (5):
  fs: split update_time() into update_time() and write_time()
  vfs: add support for a lazytime mount option
  vfs: don't let the dirty time inodes get more than a day stale
  vfs: add lazytime tracepoints for better debugging
  ext4: add support for a lazytime mount option

 fs/btrfs/inode.c            |  10 +++++
 fs/ext4/inode.c             |  48 ++++++++++++++++++--
 fs/ext4/super.c             |   9 ++++
 fs/fs-writeback.c           |  42 +++++++++++++++++-
 fs/inode.c                  | 104 +++++++++++++++++++++++++++++++++++++++-----
 fs/proc_namespace.c         |   1 +
 fs/sync.c                   |   7 +++
 fs/xfs/xfs_iops.c           |  39 +++++++----------
 include/linux/fs.h          |   5 +++
 include/trace/events/ext4.h |  29 ++++++++++++
 include/trace/events/fs.h   |  56 ++++++++++++++++++++++++
 include/uapi/linux/fs.h     |   1 +
 12 files changed, 313 insertions(+), 38 deletions(-)
 create mode 100644 include/trace/events/fs.h

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2.1.0