Is kernel oplocks = yes a good default?

[J. Bruce Fields]

On Wed, Apr 11, 2012 at 10:37:51AM -0700, Jeremy Allison wrote:
> On Wed, Apr 11, 2012 at 03:25:59PM +0200, Christian Ambach wrote:
> > I was wondering why Samba servers running on Linux are not giving
> > out Level II oplocks by default and thus cause performance
> > degradation for certain workloads.
> > 
> > Digging into that, I discovered that this due to "kernel oplocks"
> > set to yes by default and on the two platforms that have kernel
> > oplock support code for (Linux and IRIX), level 2 oplocks are not
> > supported by the kernel. (OneFS is the only platform that has
> > support for them).
> > 
> > Another bad thing is that kernel oplocks is a global parameter. So
> > if an admin is interested in getting NFS/shell interop for just a
> > certain share, (s)he cannot turn them off for the other shares to
> > get better performance from those.
> > 
> > I have worked on a patchset that converts the parameter into a share
> > option that will allow for more fine-grained configuration.
> > Please have a look at it.
> > It makes the raw.oplocks test pass when using kernel oplocks = no
> > for just the share to be tested.
> 
> Looks very good to me. Do you want to include in a 3.6.x release ?
> 
> > Additionally, I would like to question the current default value of
> > kernel oplocks: we shouldn't cut off our users from the performance
> > benefits of level II oplocks on one of our major platforms by
> > default.
> > 
> > I can update the patchset to also flip the default if this is
> > considered to be a good idea.
> 
> It probably is. The default was set to allow for out-of-the-box
> safety for Linux servers exporting the same files by both NFS
> and CIFS, but that's probably less used than I thought at the
> time, and probably can be expertly set by OEM's who know exactly
> what they're doing.
> 
> +1 from me (for this patch, and also flipping the default).

That said, ideally we'd have kernel support for level 2 oplocks and then
people wouldn't have to make this consistency/performance choice.

(What's stopping that?  There's the downgrade problem reported here:

	https://lists.samba.org/archive/samba-technical/2012-March/082376.html

which I have on my todo list.  Is there anything else you need from the
kernel?)

--b.