[Devel] NFSd threads amount policy in containers context

[bfields at fieldses.org]

On Mon, Nov 26, 2012 at 08:09:01PM +0400, Stanislav Kinsbursky wrote:
> Hello.
> I would like to discuss how to control NFSd threads amount from
> container environment (is this particular case it means start of NFS
> server in network namespace different to init_net).
> 
> So, I see three possible policies (let's assume, that there are two containers - one requested 3 NFSd threads and another one - 4 NFSd threads):
> 1) start as many threads, as requested. I.e 7 threads for specified
> case (simplest case, but probably this is to much - 100 containers
> will start ~800 threads by default).
> 2) start maximum number of requested threads. I.e. 4 threads for
> specified case (if NFSd server in container, requested 4 threads,
> will be stopped, then 3 thread will left working; will require some
> way to manage - rb tree of sorted list).
> 3) There could be some other (more flexible) policy: combine second
> one with running of one more thread for each second and further
> network namespace, started NFS server. I.e.:
> 1 net ns: 3 threads request = 3 threads started
> 2 net ns: 4 threads request = 4 + 1 (per-net thread: 1 net ns) = 5 threads started
> 3 net ns: 8 threads request = 8 + 2 (per-net threads: 2 net ns) = 10 threads started
> 
> Bruce and community, what do you think about all this?

I agree that options 2 or 3 seem more likely to be optimal.

However, looking at the problems with, for example, getting race-free
shutdown correct: I'd *strongly* prefer that we start with 1, because I
think it will be simplest to get right.

I'd rather put off figuring out how to scale to hundreds of containers
until after we demonstrate something simple and obviously correct.

--b.