Comment 29 for bug 1349711

With btrfs-tools 4.0-2, and kernel 4.2.0-34-generic, I got a kthread pegging up 1 core at 100%, and the whole system was almost completely unusable.

this persisted for several minutes. Then it quieted down, and then the problem reappeared... even after rebooting.

I had 2GB of free space. I now freed up a bit more, and I have 30GB... let's see if it'll happen again.

While it was happening, I got some perf dump with:

sudo perf record -g --proc-map-timeout 100000 -a sleep 10

and I found that most of the time was spent in native_queued_spin_lock_slowpath (name not unexpected, since it's a spin lock), I'll attach the perf.data now (I have 3 of them)