We already have the lock contention detection patch: https://review.whamcloud.com/35287/

With lock contention detection, the lock server will mark the lock resource (a shared OST object) as contention in a time period (2 seconds, by default). And the client requested a extent lock will be informed the lock contention.

Under lock contention, the lock server will not expand the lock extent to avoid unnecessary lock conflict callbacks.
And the client could be switch from buffered I/O to the direct I/O if the I/O size is large enough.