Hello,

I am using bcache in my laptop (RAM 32 GiB). I have been using it
perfectly for a month. ext4 + bcache.

Yesterday, system did not want do to a normal startup. Messages where
from udev out of memory (and udevadm killed?) and system was not
mounting / (/dev/bcache0).

[    6.823222] bcache-register invoked oom-killer: gfp_mask=0x82d2,
order=0, oom_score_adj=0

Build your kernel with CONFIG_COMPACTION.  I've added it to the FAQ:
http://bcache.evilpiepirate.org/~kent/bcache/FAQ/