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

Theodore Ts'o
2014-11-22T16:54:39Z

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