>>> When I run umount during these ops I get an device busy. Any help 
>>> would be very appreciated!
>>
>> This is normal and expected behavior.  One problem may be that your 
>> server is slow, and thus there are RPCs left outstanding for a bit on 
>> your client after your application exits.  The COMMIT calls from that 
>> trace suggest that there is dirty data the client is writing back to 
>> the server. 
> 
> It seems to me that this should not be the expected behavior unless
> the file system is mounted "nocto".  Is it?

I'm a little puzzled myself about what dirty data there might be left 
after the application quits.  However, I'll be there is an mmap() 
lurking somewhere in the background...

Data that was dirtied via a mapped file is not subject to the writeback 
part of close-to-open.