linux-ext4 - Re: Bug#605009: serious performance regression with ext4

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Message-Id: <201011291618.25084.bernd.schubert@fastmail.fm>
Date:	Mon, 29 Nov 2010 16:18:24 +0100
From:	Bernd Schubert <bernd.schubert@...tmail.fm>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	Jonathan Nieder <jrnieder@...il.com>, linux-ext4@...r.kernel.org
Subject: Re: Bug#605009: serious performance regression with ext4

On Monday, November 29, 2010, Ted Ts'o wrote:
> By using sync_file_range() first, for all files, this forces the
> delayed allocation to be resolved, so all of the block bitmaps, inode
> data structures, etc., are updated.  Then on the first fdatasync(),
> the resulting journal commit updates all of the block bitmaps and all
> of the inode table blocks(), and we're done.  The subsequent
> fdatasync() calls become no-ops --- which the ftrace shell script will
> show.

Wouldn't it make sense to modify ext4 or even the vfs to do that on close() 
itself? Most applications expect the file to be on disk after a close anyway 
and I also don't see a good reason why one should delay a disk write-back 
after close any longer (well, there are exeption if the application is broken, 
for example such as ha-logd used by pacemaker, which did for each line of logs 
an open, seek, write, flush, close sequence..., but at least we have fixed 
that in -hg now).

Cheers,
Bernd
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