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Re: Documenting MS_LAZYTIME

To: Michael Kerrisk <mtk.manpages@xxxxxxxxx>, "Theodore Ts'o" <tytso@xxxxxxx>
Subject: Re: Documenting MS_LAZYTIME
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Fri, 20 Feb 2015 09:49:34 -0600
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>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <CAHO5Pa0k7QkV_6BDjwTVxa7LV9tFyN9nGFFcSvOC6HYO08wfrw@xxxxxxxxxxxxxx>
References: <CAHO5Pa0k7QkV_6BDjwTVxa7LV9tFyN9nGFFcSvOC6HYO08wfrw@xxxxxxxxxxxxxx>
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  timeâ
>               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 unreâ
>                    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

>               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.

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

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