Bug#779628: bcache: task bcache_writebac blocked for more than 240 seconds, system load high when module used

["Ursan, Bogdan" <bogdan.ursan@phoenixmedia.ro>]

Steps to reproduce:

get the bcache-tools package... 

I used, http://debian.spnet.net/debian/pool/main/b/bcache-tools/bcache-tools_1.0.7-1_amd64.deb

Build from source if you like

make-bcache -B /dev/cciss/c0d0p2 -C /dev/cciss/c0d1p3

reboot

echo writeback > /sys/block/bcache0/bcache/cache_mode

echo 32M > /sys/block/bcache0/bcache/sequential_cutoff

mkfs.ext4 /dev/bcache0 ; mount /dev/bcache0 /mnt

wait a bit and then in dmesg or console you should see.

Aditionaly the load average is 2, for no good reason.

cat /proc/loadavg

2.21 2.06 1.97 1/127 3224

Found the same bug in Ubuntu: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1357295

This machine is a dev box, so we can try different things on it, let me know if I can help further.

Ursan Bogdan

Administrator IT
Phoenix Media