btrfs: track odirect bytes in flight

When diagnosing a slowdown of generic/224 I noticed we were wasting a
lot of time in shrink_delalloc() despite all writes being O_DIRECT
writes.  O_DIRECT writes still have outstanding extents, but obviously
cannot be directly flushed, instead we need to wait on their
corresponding ordered extent.  Track the outstanding odirect write bytes
and if this amount is higher than the delalloc bytes in the system go
ahead and force us to wait on the ordered extents.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
4 files changed