Re: [PATCH] nfs: only do COMMIT for range written with direct I/O

[Malahal Naineni <malahal@us.ibm.com>]

Jeff Layton [jlayton@redhat.com] wrote:
> When given a range to write with unstable writes, the current code
> always does a COMMIT of the entire file afterward. This is potentially
> expensive on some servers and unnecessary. Instead, just do a COMMIT for
> the offset and count that was written.
> 
> Khoa, who reported this bug, stated that this made a big difference in
> performance in their environment, which I believe involves GPFS on the
> server. He didn't pass along any hard numbers so I can't quantify the
> gain, but it stands to reason that clustered filesystems might suffer
> more contention issues when issuing a commit over the whole file.
> 
> Reported-by: Khoa Huynh <khoa@us.ibm.com>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/nfs/direct.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
> index 1940f1a..33f2be7 100644
> --- a/fs/nfs/direct.c
> +++ b/fs/nfs/direct.c
> @@ -77,6 +77,7 @@ struct nfs_direct_req {
>  	/* completion state */
>  	atomic_t		io_count;	/* i/os we're waiting for */
>  	spinlock_t		lock;		/* protect completion state */
> +	loff_t			pos;		/* offset into file */

Why not call it "offset"? Should we set this to zero in
nfs_direct_req_alloc (just like count is set to zero there)?

Thanks, Malahal.