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

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Message-ID: <AANLkTinX9ZwGL7tj1VEHGgSm+3Hn8vw0tF0=oUSpXXOA@mail.gmail.com>
Date:	Mon, 3 Jan 2011 09:02:56 +0200
From:	Amir Goldstein <amir73il@...il.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 Mon, Jan 3, 2011 at 6:11 AM, Ted Ts'o <tytso@....edu> 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!
>

Well, there's e2image of course, but using the qcow2 format is a better
solution than fadvise in this case.

Also, I believe that if one chooses to use VM with raw image format,
it is mostly for the purpose or read performance, which implies that
the image was fallocate'd.

Am I wrong about this?

Amir.
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