Re: [PATCH 2/2 v3] Btrfs: snapshot-aware defrag

[Liu Bo <bo.li.liu@oracle.com>]

On 10/03/2012 10:02 PM, Chris Mason wrote:
> On Tue, Sep 25, 2012 at 07:07:53PM -0600, Liu Bo wrote:
>> On 09/26/2012 01:39 AM, Mitch Harder wrote:
>>> On Mon, Sep 17, 2012 at 4:58 AM, Liu Bo <bo.li.liu@oracle.com> wrote:
>>>> This comes from one of btrfs's project ideas,
>>>> As we defragment files, we break any sharing from other snapshots.
>>>> The balancing code will preserve the sharing, and defrag needs to grow this
>>>> as well.
>>>>
>>>> Now we're able to fill the blank with this patch, in which we make full use of
>>>> backref walking stuff.
>>>>
>>>> Here is the basic idea,
>>>> o  set the writeback ranges started by defragment with flag EXTENT_DEFRAG
>>>> o  at endio, after we finish updating fs tree, we use backref walking to find
>>>>    all parents of the ranges and re-link them with the new COWed file layout by
>>>>    adding corresponding backrefs.
>>>>
>>>> Originally patch by Li Zefan <lizf@cn.fujitsu.com>
>>>> Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
>>>
>>> I'm hitting the WARN_ON in record_extent_backrefs() indicating a
>>> problem with the return value from iterate_inodes_from_logical().
> 
> Me too.  It triggers reliably with mount -o autodefrag, and then crashes
> a in the next function ;)
> 
> -chris
> 

Hi Chris, Mitch,

I'm afraid that I may need a little more time to fix all bugs in it because there seems to be
some backref walking bugs mixed in, and at least 4 different crashes make it harder to address bugs.

I use an 1G random write fio job running in background, following by creating 20 snapshots in background,
and mount -o autodefrag.

So if your crash is quite stable in one place, please let me know the steps.

thanks,
liubo