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

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Date:	Mon, 29 Nov 2010 09:54:59 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Bernd Schubert <bernd.schubert@...tmail.fm>
CC:	"Ted Ts'o" <tytso@....edu>, Jonathan Nieder <jrnieder@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: Bug#605009: serious performance regression with ext4

On 11/29/10 9:18 AM, Bernd Schubert wrote:
> 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 

but those applications would be wrong.

http://www.flamingspork.com/talks/
Eat My Data: How Everybody Gets File IO Wrong

-Eric

> 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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