Re: [PATCH] bcache: Fix writeback_thread never writing back incomplete stripes.

[Tim Small <tim@buttersideup.com>]

On 17/09/15 19:31, Kent Overstreet wrote:
> Here's an updated patch that has a fix for _that_ theory, and also a new
> BUG_ON(). Any chance you could test it?

I've applied your patch (to the Ubuntu 4.2.1 tree - since I need some of
their non-mainline apparmour changes on this box) , and it's stopped the
excessive CPU usage by the bcache_writebac thread.

I'd first experienced this CPU spinning when I tried to disable cache
usage (I'd had some lockups on the machine and I was trying to get to
debug, so I tried switching bcache cache_mode to none whilst I debugged
as part of my process of elimination).  I assume the bug was hit whilst
trying to flush the dirty cache data.

I now have:

root@magic:~# cat /sys/block/bcache0/bcache/state
clean
root@magic:~# cat /sys/block/bcache0/bcache/dirty_data
1.5M
root@magic:~# cat /sys/block/bcache0/bcache/cache_mode
writethrough writeback writearound [none]
root@magic:~# uname -a
Linux magic 4.2.1 #2 SMP Sat Sep 26 10:00:40 UTC 2015 x86_64 x86_64
x86_64 GNU/Linux

i.e. state and cache_mode are inconsistent with dirty_data.  Is this of
any concern and/or likely to cause problems if I re-enable the cache?

Cheers,

Tim.