Re: btrfs mount takes too long time

[Anand Jain <anand.jain@oracle.com>]

open_ctree() took 228254398 us. And 98% of it that is 225418272 us
was taken by btrfs_read_block_groups().

-------------------
  1) $ 225418272 us | } /* btrfs_read_block_groups [btrfs] */
  1) * 16934.96 us | btrfs_check_rw_degradable [btrfs]();
  0) 0.967 us | btrfs_apply_pending_changes [btrfs]();
  0) 0.239 us | btrfs_read_qgroup_config [btrfs]();
  0) * 21017.34 us | btrfs_get_root_ref [btrfs]();
  0) + 15.717 us | btrfs_start_pre_rw_mount [btrfs]();
  0) 0.865 us | btrfs_discard_resume [btrfs]();
  0) $ 228254398 us | } /* open_ctree [btrfs] */
-------------------

Now we need to run the same thing on btrfs_read_block_groups(),
could you please run.. [1] (no need of the time).

[1]
   $ umount /btrfs;
   $./ftracegraph btrfs_read_block_groups 3 "*:mod:btrfs" "mount 
/dev/vg/scratch0 /btrfs"

Thanks, Anand


On 30/08/2021 14:44, Jingyun He wrote:
> Hi, Anand,
> I have attached the new result.
> Kindly check.
> 
> Thank you.
> 
> On Mon, Aug 30, 2021 at 9:27 AM Anand Jain <anand.jain@oracle.com> wrote:
>>
>>
>> Our open_ctree() took around ~223secs (~3.7mins)
>>
>>    1) $ 223375750 us |  } /* open_ctree [btrfs] */
>>
>> Unfortunately, the default trace buffer per CPU (4K) wasn't sufficient
>> and, the trace-buffer rolled over.
>> So we still don't know how long we spent in btrfs_read_block_groups().
>> Sorry for my mistake we should go 1 step at a time and, we have to do
>> this until we narrow it down to a specific function.
>>
>> Could you please run with the depth = 2 (instead of 3) and use the time
>> command prefix. Also, pull a new ftracegraph as I have updated it to
>> display a proper time output.
>>
>> $ ftracegraph open_ctree 2 "*:mod:btrfs" "time mount /dev/vg/scratch0
>> /btrfs"
>>
>> Thanks, Anand
>>
>> On 29/08/2021 17:42, Jingyun He wrote:
>>> Hi, Anand
>>>
>>> I have attached the file.
>>> Could you kindly check this?
>>>
>>> Thank you.
>>>
>>> On Sun, Aug 29, 2021 at 7:47 AM Anand Jain <anand.jain@oracle.com> wrote:
>>>>
>>>> On 28/08/2021 19:58, Jingyun He wrote:
>>>>> Hello, all
>>>>> I'm new to btrfs, I have a HM-SMR 14TB disk, I have formatted it to
>>>>> btrfs to store the files.
>>>>>
>>>>> When the device is almost full, it needs about 5 mins to mount the device.
>>>>>
>>>>> Is it normal? is there any mount option that I can use to reduce the mount time?
>>>>>
>>>>
>>>>
>>>>     We need to figure out the function taking a longer time (maybe it is
>>>>     read-block-groups). I have similar reports on the non zoned device
>>>>     as well (with a few TB full of data). But there is no good data yet
>>>>     to analyse.
>>>>
>>>>     Could you please collect the trace data from the ftracegraph
>>>>     from here [1] (It needs trace-cmd).
>>>>
>>>>     [1] https://github.com/asj/btrfstrace.git
>>>>
>>>>     Run it as in the example below:
>>>>
>>>>     umount /btrfs;
>>>>
>>>>     ./ftracegraph open_ctree 3 "*:mod:btrfs" "mount /dev/vg/scratch0 /btrfs"
>>>>
>>>>     cat /tmp/ftracegraph.out
>>>>
>>>>
>>>> Thanks, Anand
>>>>
>>>>
>>>>
>>>>> Thank you.
>>>>>
>>>>