>close must be synchronous, unless you aim for NFS semantics.

to be more explicit: think of exclusive-use services, services that wait for a close to commit,
files with DMEXCL, and files opened ORCLOSE

For DMEXCL and ORCLOSE, we'd always issue synchronously.

Perhaps we could turn on async clunk for other files when the chan has CCACHE set (mount -C iirc). We already believe that the fileserver is 'decent' then...

-- vs