Documenting MS_LAZYTIME

[Michael Kerrisk]

Hello Ted,

Based on your commit message 0ae45f63d4e, I I wrote the documentation
below for MS_LAZYTIME, to go into the mount(2) man page. Could you
please check it over and let me know if it's accurate. In particular,
I added pieces marked with "*" below that were not part of the commit
message and I'd like confirmation that they're accurate.

Thanks,

Michael

[[
       MS_LAZYTIME (since Linux 3.20)
              Only  update  filetimes (atime, mtime, ctime) on the in-
              memory version of the file  inode.   The  on-disk  time‐
              stamps are updated only when:

              (a)  the inode needs to be updated for some change unre‐
                   lated to file timestamps;

              (b)  the application  employs  fsync(2),  syncfs(2),  or
                   sync(2);

              (c)  an undeleted inode is evicted from memory; or

*             (d)  more than 24 hours have passed since the i-node was
*                  written to disk.

              This mount option significantly reduces  writes  to  the
              inode  table  for workloads that perform frequent random
              writes to preallocated files.

*             As at Linux 3.20, this option is supported only on ext4.
]]

-- 
Michael Kerrisk Linux man-pages maintainer;
http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface", http://blog.man7.org/