In article <20070503103425.GE6220@schatzie.adilger.int> you write:

quoted text
>On May 02, 2007  18:23 +0530, Amit K. Arora wrote:

>> On Sun, Apr 29, 2007 at 10:25:59PM -0700, Chris Wedgwood wrote:

>> > On Mon, Apr 30, 2007 at 10:47:02AM +1000, David Chinner wrote:

>> >

>> > > For FA_ALLOCATE, it's supposed to change the file size if we

>> > > allocate past EOF, right?

>> >

>> > I would argue no.  Use truncate for that.

>>

>> The patch I posted for ext4 *does* change the filesize after

>> preallocation, if required (i.e. when preallocation is after EOF).

>> I may have to change that, if we decide on not doing this.

>

>I think I'd agree - it may be useful to allow preallocation beyond EOF

>for some kinds of applications (e.g. PVR preallocating live TV in 10

>minute segments or something, but not knowing in advance how long the

>show will actually be recorded or the final encoded size).

I have an application (diablo dreader) where the header-info database

basically consists of ~40.000 files, one for each group (it's more

complicated that that, but never mind that now).
If you grow those files randomly by a few hundred bytes every update,

the filesystem gets hopelessly fragmented.
I'm using XFS with preallocation turned on, and biosize=18 (which

makes it preallocate in blocks of 256KB), and a homebrew patch that

leaves the preallocated space on disk preallocated even if the

file is closed .. and it helps enormously.
Mike.

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