Quoting John Ettedgui at 2015-07-30-21:10:27(-0700):

On Thu, Jul 30, 2015 at 7:34 PM, Qu Wenruo [off-list ref] wrote:

quoted

Hi John,
Thanks for the trace output.

You are welcome, thank you for looking at it!

quoted

But it seems that, your root partition is also btrfs, causing a lot of btrfs
trace from your systemd journal.

Oh yes sorry about that.
I actually have 3 partition in btrfs, the problematic one being the
only big one.

quoted

Would you mind re-collecting the ftrace without such logging system caused
btrfs trace?

Sure, how would I do that?
This is my first time using ftrace.

quoted

BTW, although I'm not quite familiar with ftrace, would you please consider
collect ftrace with function_graph tracer?

Sure, how would I do that one as well?

You can use set_ftrace_pid to trace only a single process (for example,
the mount command). There is a sample script I found in the ftrace
documentation that goes something like this:

# First disable tracing, to clear the trace buffer
echo nop            > current_tracer
echo 0              > tracing_on
echo 0              > tracing_enabled

# Then re-enable it after setting the filters
echo $$             > set_ftrace_pid
echo '*btrfs*'      > set_ftrace_filter
echo function_graph > current_tracer
echo 1              > tracing_enabled
echo 1              > tracing_on

# And finally *exec* the command to trace:
exec mount ....

I tried it, but the logs were way too large, and I was still fiddling
with the trace_options to set. If someone has good advice, we can try it
again

-- 
Georgi