linux-ext4 - Re: Documenting MS

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Message-ID: <CAKgNAkj4EtiWpxOPFtfYn4=E1ukLjESwe7yvyNHdp04BP+kj-g@mail.gmail.com>
Date:	Fri, 20 Feb 2015 14:22:07 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Linux btrfs Developers List <linux-btrfs@...r.kernel.org>,
	XFS Developers <xfs@....sgi.com>,
	linux-man <linux-man@...r.kernel.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: Documenting MS_LAZYTIME

On 20 February 2015 at 13:32, Andreas Dilger <adilger@...ger.ca> wrote:
> On Feb 20, 2015, at 1:50 AM, Michael Kerrisk <mtk.manpages@...il.com> 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:
>>
>>              (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.
>>
>>              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.
>
> I _think_ that the lazytime mount option is generic for all filesystems.
> I believe ext4 has an extra optimization for it, but that's it.

Ah yes, looking at the code again, that makes sense. I think you're
right, and I've struck that last sentence. Thanks, Andreas.

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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