linux-ext4 - Re: ext4: Fix 32bit overflow in ext4_ext_find

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Date:	Mon, 03 Jan 2011 11:25:58 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>
CC:	Andreas Dilger <adilger@...ger.ca>,
	Kazuya Mio <k-mio@...jp.nec.com>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: ext4: Fix 32bit overflow in ext4_ext_find_goal()

On 01/02/2011 10:11 PM, Ted Ts'o wrote:
> On Sun, Jan 02, 2011 at 08:35:39PM -0700, Andreas Dilger wrote:
>> It was written that way because HPC applications writing to a shared
>> file normally write to an offset of task_num * task_data_size so
>> they do not overlap, and end up with a dense file. Similarly,
>> bittorrent and parallel FTP clients will write dense files after
>> seeking randomly around the file, and database files often end up
>> dense as well.
>>
>> I'd rather fix the relatively few applications that expect
>> permanently sparse files to use fadvise() to notify the kernel of
>> this.
> 
> Agreed, and I'm not sure there are enough applications that expect
> permanently sparse files that's worth adding a new fadvise().  But if
> we do add a new fadvise(), the default should clearly be the current
> behavior.
> 
> If someone knows of use cases where permanently sparse files are
> common, please let us know!

RPM database files stay sparse (Berkeley DB)

$ pwd
/var/lib/rpm
$ ls -lh Basenames; du -h Basenames
-rw-r--r-- 1 rpm rpm 11M Dec  8 12:55 Basenames
9.1M	Basenames

etc.

-Eric
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