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Documenting MS_LAZYTIME

To: "Theodore Ts'o" <tytso@xxxxxxx>
Subject: Documenting MS_LAZYTIME
From: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Date: Fri, 20 Feb 2015 09:50:50 +0100
Cc: Ext4 Developers List <linux-ext4@xxxxxxxxxxxxxxx>, Linux btrfs Developers List <linux-btrfs@xxxxxxxxxxxxxxx>, XFS Developers <xfs@xxxxxxxxxxx>, linux-man@xxxxxxxxxxxxxxx, Linux-Fsdevel <linux-fsdevel@xxxxxxxxxxxxxxx>, Linux API <linux-api@xxxxxxxxxxxxxxx>
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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.



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

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

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

              (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;
Author of "The Linux Programming Interface", http://blog.man7.org/

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