Re: extremely slow syncing on btrfs with 2.6.39.1

[Lubos Kolouch <lubos.kolouch@gmail.com>]

Li Zefan, Tue, 12 Jul 2011 16:44:31 +0800:

>>>> I've been monitoring the lists for a while now but didn't see this
>>>> problem mentioned in particular: I've got a fairly standard desktop
>>>> system at home, 700gb WD drive, nothing special, with 2 btrfs
>>>> filesystems and some snapshots. The system runs for days, and I've
>>>> noticed unusual disk activity the other evening - turns out that it's
>>>> taking forever to sync().
>>>>
>>>> $ uname -r
>>>> 2.6.39.1
>>>> $ grep btrfs /proc/mounts
>>>> /dev/root / btrfs rw,relatime 0 0    # is /dev/sdb2 # /dev/sdb5 /home
>>>> btrfs rw,relatime 0 0 $ time sync
>>>>
>>>> real	1m5.552s
>>>> user	0m0.000s
>>>> sys	0m2.102s
>>>>
>>>> $ time sync
>>>>
>>>> real	1m16.830s
>>>> user	0m0.001s
>>>> sys	0m1.490s
>>>>
>>>> $ df -h / /home
>>>> Filesystem      Size  Used Avail Use% Mounted on /dev/root        47G
>>>> 33G  7.7G  82% / /dev/sdb5       652G  216G  421G  34% /home $ btrfs
>>>> fi df /
>>>> Data: total=35.48GB, used=29.86GB
>>>> System, DUP: total=16.00MB, used=12.00KB System: total=4.00MB,
>>>> used=0.00
>>>> Metadata, DUP: total=4.50GB, used=1.67GB
>>>>  $ btrfs fi df /home
>>>> Data: total=310.01GB, used=209.53GB
>>>> System, DUP: total=8.00MB, used=48.00KB System: total=4.00MB,
>>>> used=0.00 Metadata, DUP: total=11.00GB, used=2.98GB Metadata:
>>>> total=8.00MB, used=0.00
>>>>
>>>> I'll switch to 3.0 soon, but, given the fact that we're going to be
>>>> running MeeGo on 2.6.39 probably for a while, I was wondering if
>>>> anyone knows off the top of their heads if this issue is
>>>> known/identified. If not then I'll need to make someone do some
>>>> patching ;).
>>>>
>>>> Auke
>>>
>>> You should read the thread "Abysmal Performance" of these mailing list
>>> from last month. They had a similar problem and downgraded to a 2.6.38
>>> kernel. By the way, that works for me too for the time being.
>>>
>>> Best Regards.
>>>
>>> Jan Stilow
>> 
>> I had similar experience with two servers running on 2.6.39 - the
>> performance was terrible, after downgrade to 2.6.38 the speed is OK
>> again.
>> 
>> 
> Then you can turn to bisection to find out the culprit.

Well, I did not have chance to bisect yet, but this problem seems to be 
gone with kernel 3.0

Thank you

Lubos