Hi,

On 09.02.2017 23:17 Eric Wheeler wrote:

Well, I don't know about "good enough" but I can say that the current 
bcache v1 asynchronous block IO performance is wonderful.  It seems to me 
that loopN's are confined to a single thread and incur pagecache 
duplication (maybe better with DIO loops, but that was always very slow in 
my testing).  

So, if its easy enough to get bcachefs to export blockdevs then it would 
be neat to benchmark bcachefs snapshots vs dm-thin volumes.  Compression 
is definitely a win here feature-wise.  This would make bcachefs the first 
compressed block device without loop in Linux when it gets merged!

Did you test this with kernel >=4.4 and losetup --direct-io=on ? This
makes loop use direct, async IO which is much faster and doesn't double
cache. So it might indeed be a distraction to pull this into bcachefs.

Regards,
Martin Raiber