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Re: [PATCH 1/5] fallocate() implementation in i86, x86_64 and powerpc

To: "Amit K. Arora" <aarora@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 1/5] fallocate() implementation in i86, x86_64 and powerpc
From: Mingming Cao <cmm@xxxxxxxxxx>
Date: Wed, 09 May 2007 10:07:25 -0700
Cc: torvalds@xxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, suparna@xxxxxxxxxx
In-reply-to: <20070509160102.GA30745@xxxxxxxxxxxxxxxxxxxx>
Organization: IBM LTC
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On Wed, 2007-05-09 at 21:31 +0530, Amit K. Arora wrote:
> I have the updated patches ready which take care of Andrew's comments.
> Will run some tests and post them soon.
> 
> But, before submitting these patches, I think it will be better to finalize
> on certain things which might be worth some discussion here:
> 
> 1) Should the file size change when preallocation is done beyond EOF ?
>    - Andreas and Chris Wedgwood are in favor of not changing the
>      file size in this case. I also tend to agree with them. Does anyone
>      has an argument in favor of changing the filesize ?
>      If not, I will remove the code which changes the filesize, before I
>      resubmit the concerned ext4 patch.
> 

If we chose not to update the file size beyong EOF, then for filesystem
without fallocate() support (ext2,3 currently), posix_fallocate() will
follow the hard way(zero-out) to do preallocation. Then we will get
different behavior on filesystems w/o fallocate() support. It make sense
to be consistent, IMO.

My point of view, preallocation is just a efficient way to allocating
blocks for files without zero-out, other than this, the new behavior
should be consistent with the old way: file size update,mtime/ctime,
ENOSPC etc.

Mingming



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