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Re: Documenting MS_LAZYTIME

To: Theodore Ts'o <tytso@xxxxxxx>
Subject: Re: Documenting MS_LAZYTIME
From: "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx>
Date: Thu, 26 Feb 2015 14:36:33 +0100
Cc: mtk.manpages@xxxxxxxxx, Eric Sandeen <sandeen@xxxxxxxxxx>, 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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On 02/26/2015 02:31 PM, Theodore Ts'o wrote:
> On Thu, Feb 26, 2015 at 09:49:39AM +0100, Michael Kerrisk (man-pages) wrote:
>>> 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"?
> 
> Sorry, no, it should be "atime".

Thanks.

>> 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.)
> 
> Yes, that's correct.  The only other thing I might add is that in the
> case of a crash, the atime (or mtime) fields on disk might be out of
> date by at most 24 hours.

So in other words, add a sentence to that last para:

    The disadvantage of MS_STRICTATIME | MS_LAZYTIME is that
    in the case of a system crash, the atime and mtime fields
    on disk might be out of date by at most 24 hours.

Right?

Cheers,

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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