Re: mount btrfs takes 30 minutes, btrfs check runs out of memory

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

At 07/21/2016 04:13 PM, John Ettedgui wrote:
> On Thu, Jul 21, 2016 at 1:10 AM Qu Wenruo <quwenruo@cn.fujitsu.com
> <mailto:quwenruo@cn.fujitsu.com>> wrote:
>
>     Thanks for the info, pretty helpful.
>
>     After a simple analysis, the defrag did do a pretty good job.
>
>     -----------------------------------------------------------------------
>                 | Avg Extent size | Median Extent size | Data Extents      |
>     -----------------------------------------------------------------------
>     Predefrag  | 2.6M            | 512K               | 1043589           |
>     Postdefrag | 7.4M            | 80K                | 359823            |
>
>     Defrag reduced the number of extents to 34%!
>
>     Quite awesome.
>
>     While I still see quite a lot small extents (In fact, small extents are
>     more after defrag), so I assume there can be more improvement.
>
>     But considering the mount time is only affected by number of extents
>     (data and meta, but amount of meta is not affect by defrag), so the
>     improvement is already quite obvious now.
>
>     Much more obvious than my expectation.
>
>     Thanks,
>     Qu
>
> I'm glad to be of help.
> Is there anything else you'd like me to try?
> I don't have any non-defragmented partitions anymore, but you already
> got that information so that should be ok.
>
> Thank you,
> John

No more.

The dump is already good enough for me to dig for some time.

We don't usually get such large extent tree dump from a real world use case.

It would help us in several ways, from determine how fragmented a block 
group is to determine if a defrag will help.

Thanks,
Qu