Re: [PATCH v2 00/16] nfsd/sunrpc: add support for a workqueue-based nfsd

[Jeff Layton]

On Fri, 12 Dec 2014 03:02:06 +0000
Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:

> On Thu, Dec 11, 2014 at 06:29:37PM -0800, Linus Torvalds wrote:
> > On Thu, Dec 11, 2014 at 6:12 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > Linus, do you see any problems with the following patch (against the mainline)?
> > 
> > Not concpetually, but create_kthread() uses CLONE_FS, and I don't
> > think it's just umask that things like nfsd want to avoid sharing.
> > What about all the *other* fields?
> > 
> > Just as an example: even if all the threads actually end up all having
> > the same global root, what about contention on 'fs->lock'?
> > 
> > I have *not* looked at the details, and maybe there's some reason I'm
> > completely off, but it worries me.
> 
> Umm...  I would be very surprised if it turned out to be a problem.
> nfsd really doesn't give a fuck about its cwd and root - not in the
> thread side of things.  And (un)exporting is (a) not on a hot path
> and (b) not done from a kernel thread anyway.  fh_to_dentry and friends
> doesn't care about root/cwd, etc.
> 
> I don't see anything that could cause that kind of issues.

I like the change overall -- it would certainly make my patch series
simpler, but what about pathwalking? We do take the fs->lock in
unlazy_walk. Is it possible we'd end up with more contention there?

-- 
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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