[PATCH 10/12] NFS: Do not serialise O_DIRECT reads and writes

[Christoph Hellwig]

On Wed, Jun 15, 2016 at 02:52:24PM +0000, Trond Myklebust wrote:
> >But XFS allows full parallelism for direct reads and writes as long
> >as there is no more pagecache to flush.  But if you have pages in
> >the pagecache you need the exclusive lock to prevent against new
> >pagecache pages being added.
> 
> Exactly. So does this.

So let's avoid bloating the inode with another rw_semaphore, and make
everyones life easier by using the existing lock.

> We don???t use generic_file_* for O_DIRECT; we only use it for buffered I/O.

I know - this was just an answer to your reference to the generic_file_*
code.