linux-kernel - Re: ext2/3/4: punch support?

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Message-ID: <AANLkTimntcYVCyVo3-GRhFKd2eCbBpRan4G8+hLSRyLZ@mail.gmail.com>
Date:	Tue, 1 Mar 2011 09:27:40 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Josef Bacik <josef@...hat.com>, Theodore Tso <tytso@....edu>,
	linux-ext4@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: ext2/3/4: punch support?

On Mon, Feb 28, 2011 at 11:17 PM, Eric Sandeen <sandeen@...hat.com> wrote:
> On 2/28/11 8:29 AM, Dave Young wrote:
>> On Mon, Feb 28, 2011 at 9:11 PM, Josef Bacik <josef@...hat.com> wrote:
>>> On Mon, Feb 28, 2011 at 03:03:40PM +0800, Dave Young wrote:
>>>> Hi, josef and ext guys
>>>>
>>>> Do you have any plan with ext4 hole punching support? And the
>>>> fallocate for ext2/3?
>>>>
>>>> What's the obstacle to work on this? could someone tell the status of
>>>> this issue?
>>>
>>> There is no obstacle, just nobody has bothered to do it.  If you want to do it
>>> go for it.  Thanks,
>>
>> Yes, I want to do some kvm image space discard stuff,
>> I use ext4 as my filesystem, but currently only xfs support something
>> like trim/discard.
>
> As Lukas said, ext4 & ext3 support various forms of trim/discard already.
>
> But that's different from punch...

Lukas and Eric, thanks for pointing out, I think I means punch,
although trim/discard is
useful as well in guest side.

>
> And as for fallocate on ext3, you need somewhere to put the metadata to indicate a block is allocated but not written.  This was a lot more straightforward for ext4, since it describes a large range of blocks with a single extent structure.

As for ext3 fallocate, I found some interesting discuss:
http://www.mail-archive.com/linux-ext4@vger.kernel.org/msg02371.html

Andrew, do you know what's the status of above issue?

>
> -Eric
>
>> I know general knowledge about ext filesystem, but nearly new to ext4 code,
>> could you give some hint where to start?
>>
>> --
>> Thanks
>> dave
>> --
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>
>



-- 
Regards
dave
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