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

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Date:	Sun, 2 Jan 2011 23:11:57 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	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 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!

						- Ted
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