Tiering should now be working - testing requested
Added 2016-09-13 02:10:00 +0000 UTCTiering should finally be working with the last big batch of fixes I pushed.
Chris Halse Rogers (RAOF in the #bcache IRC channel) has been testing it. He has been seeing an intermittent deadlock while copying large amounts of data, which may or may not be tiering related: if anyone else hits it, I'd really appreciate if you could grab backtraces. Do a "echo t > /proc/sysrq-trigger" and then grab the full dmesg log - that should be enough to figure out what the deadlock is.
I haven't gotten to device add/remove yet, don't try it - you'll need to create a new filesystem:
bcache format --tier 0 <SSD> --tier 1 <HDD>
Also, if you've already been playing with tiering, I highly recommend you create a new filesystem. One of the bugs was an issue with which pointers are considered dirty - in an extent with a tier 0 pointer and a tier 1 pointer, the tier 0 pointer was being considered dirty instead of the tier 1 pointer (with predictably bad consequences; tier 0 would fill up because the tiering thread wasn't actually making anything on tier 0 clean). On a fixed kernel, as extents are migrated it'll end up fixing which pointers are considered dirty which may or may not trigger assertions as which pointers are considered dirty changes.
