linux-ext4 - Re: Question about ext4 online defrag test case

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Message-ID: <87f94c371001141304n18bcd208kd97f08646d37d1e2@mail.gmail.com>
Date:	Thu, 14 Jan 2010 16:04:01 -0500
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	Akira Fujita <a-fujita@...jp.nec.com>,
	Sandeep K Sinha <sandeepksinha@...il.com>
Cc:	Theodore Tso <tytso@....edu>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Question about ext4 online defrag test case

On Thu, Jan 14, 2010 at 5:19 AM, Akira Fujita <a-fujita@...jp.nec.com> wrote:
> Hi Ted,
>
>> E2defrag should hopefully be releasable in Karmic+1.
>> There are still a lot of bugs that are still being fixed in the defrag
>> code,
>> some of which could cause data loss. They work fine
>> if the system isn't under stress, sure, but acid test is to make sure
>> things work OK even when the system is under memory pressure and
>> swapping heavily, or when the file is being actively modified at the point
>> where the defrag takes place.
>
> I found your comment about ext4 online defrag on Ubuntu BBS by accident.
> https://bugs.launchpad.net/ubuntu/+source/e2fsprogs/+bug/321528
>
> I would like to address this problem so I ran e4defrag on the system
> which was under memory pressure. But unfortunately I could not find the bug.
> If you have already known how to reproduce this kind of problem,
> could you teach me how?
>
> Regards,
> Akira Fujita

Sandeep, I've added you and I to this thread since oshm is using the
same ext4_move_extents ioctl as E2defrag.

Also, the above highlights the need for us to test ohsm relocates with
data updates in progress.  Also with memory pressure which I had not
really thought about before.

We can discuss that on the ohsm list if needed.

Greg
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