linux-ext4 - Re: Documenting MS

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Message-Id: <44893EA7-B11A-469A-9911-6CE2E8B26EB4@dilger.ca>
Date:	Fri, 20 Feb 2015 05:32:58 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	Michael Kerrisk <mtk.manpages@...il.com>
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@...r.kernel.org,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: Documenting MS_LAZYTIME

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.

Cheers, Andreas





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