Re: Documenting MS_LAZYTIME

On 2/20/15 2:50 AM, Michael Kerrisk wrote:

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:

"filetimes" and "file inode" seems a bit awkward.  How about:

       MS_LAZYTIME (since Linux 3.20)
	Reduce on-disk updates of inode timestamps (atime, mtime, ctime)
		by maintaining these changes only in memory, unless:

(maybe I'm bike-shedding too much, if so, sorry).

              (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.

Please don't use "i-node" - simply "inode" is much more common in the manpages
AFAICT.

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

This seems like an overly specific description of a single workload out
of many which may benefit, but what do others think?  "inode table" is also
fairly extN-specific.

-Eric
 

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

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