On Mon, 5 Dec 2011 10:06:49 -0800 "Myklebust, Trond" <Trond.Myklebust@xxxxxxxxxx> wrote: > > -----Original Message----- > > From: Jeff Layton [mailto:jlayton@xxxxxxxxxx] > > Sent: Monday, December 05, 2011 12:11 PM > > To: Jeff Layton > > Cc: Myklebust, Trond; linux-nfs@xxxxxxxxxxxxxxx; khoa@xxxxxxxxxx > > Subject: Re: [PATCH] nfs: only do COMMIT for range written with direct > I/O > > > > On Wed, 30 Nov 2011 09:07:54 -0500 > > Jeff Layton <jlayton@xxxxxxxxxx> 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@xxxxxxxxxx> > > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > > > Khoa found that he made a mistake when testing this originally, and > any > > benefit that the patch provides seems to be negligible. I still think > it's safe > > and reasonable to only issue a commit for the range that was written, > but > > there doesn't seem to be any compelling need for this patch right now. > > > > Trond, do you have an opinion here? Should we go ahead and commit this > > patch or something like it, or leave well-enough alone? > > I'd prefer to wait until I see a tangible benefit. I know that recent > kernels do have support for a COMMIT range on the Linux kernel server > side, so maybe it is just a question of shooting up an ext4 or XFS based > server and running a few tests with a large O_DIRECT writer on one > client, and a smaller O_DIRECT writer on another... > Khoa went back and did his tests and they confirm that there was no tangible benefit in his environment. I did some minimal testing on other rigs too, but also didn't see any clear benefit. Of course, this is highly server-dependent, so there may be places where this matters more, but for now I don't know of any. At this point, I suggest we drop this patch for now. If we can note some tangible benefit later, we can resurrect it then. Thanks, -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
