linux-kernel - Re: ext4 bug? last write time precedes last mount time on a writable volume!

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Date:	Fri, 2 Mar 2012 15:45:21 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Neil Clarkson <neilaclarkson@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: ext4 bug? last write time precedes last mount time on a
 writable volume!

On Fri, Mar 02, 2012 at 12:39:57PM +0000, Neil Clarkson wrote:
> Isn't the s_wtime field of the ext4 superblock supposed to show the
> time, in seconds since the epoch, of the last write? It isn't
> happening!

It shows the last time the superblock has been modified, and one of
the things that we've been doing lately has been to optimize ext4 so
that it writes to the superblock *much* less often.  It was a
performance bottleneck to be constantly updating the number of free
blocks in the superblock each time we write to a new block, for
example --- or update the superblock to update the number of free
inodes each time we allocate a new inode.

Is there a reason why you particularly care about s_wtime being
updated?

					- Ted
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