In f828fe0d59 ("setup: add the lazytime XFS version") we added the
lazytime mount option to /var/lib/scylla, but it was quickly reverted
(8f5e80e61a) as it caused a regression on CentOS 7.
We reinstate it now with a kernel version check. This will avoid
the lazytime mount option on CentOS 7, which is unsupported anyway.
The lazytime option avoids marking the inode as dirty if it's only for the
purpose of updating mtime/ctime. This won't help much while writing sstables
(since the write also updates extent information), but may help a little
with with commitlog writes, since those are pure overwrites.
It likely won't help with the RWF_NOWAIT violations seen in [1], since
those are likely due to in-memory locking, not flushing dirty inodes
to disk.
Tested with an install to Ubuntu 24.04 LTS followed by a scylla_setup run.
The lazytime option was added the the .mount file and showed up in
the live mount.
[1] https://github.com/scylladb/seastar/issues/2974
Closes scylladb/scylladb#26436
Fixes#26002
bb02295695