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Re: Documenting MS_LAZYTIME

To: Theodore Ts'o <tytso@xxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: Documenting MS_LAZYTIME
From: "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx>
Date: Thu, 26 Feb 2015 09:49:39 +0100
Cc: mtk.manpages@xxxxxxxxx, 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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Ted,

On 02/21/2015 03:56 AM, Theodore Ts'o wrote:
> On Fri, Feb 20, 2015 at 09:49:34AM -0600, Eric Sandeen wrote:
>>
>>>               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.
> 
> How about somethign like "This mount significantly reduces writes
> needed to update the inode's timestamps, especially mtime and actime.

What is "actime" in the preceding line? Should it be "ctime"?

> Examples of workloads where this could be a large win include frequent
> random writes to preallocated files, as well as cases where the
> MS_STRICTATIME mount option is enabled."?

I think some version of the following text could also usefully go 
into the page, but...

> (The advantage of MS_STRICTATIME | MS_LAZYTIME is that stat system
> calls will return the correctly updated atime, but those atime updates
> won't get flushed to disk unless the inode needs to be updated for
> file system / data consistency reasons, or when the inode is pushed
> out of memory, or when the file system is unmounted.)

I find the wording of there a little confusing. Is the following 
a correct rewrite:

    The advantage of MS_STRICTATIME | MS_LAZYTIME is that stat(2)
    will return the correctly updated atime, but the atime updates
    will be flushed to disk only when (1) the inode needs to be 
    updated for filesystem / data consistency reasons or (2) the 
    inode is pushed out of memory, or (3) the filesystem is 
    unmounted.)

?

Thanks,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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