[ovs-discuss] ovs-vswitchd mlockall and stack size

[Ben Pfaff]

On Tue, Jul 08, 2014 at 05:08:43PM +0100, Anoob Soman wrote:
> Since openvswitch has moved to multi-threaded model, RSS usage of
> ovs-vswitchd has increased quite significantly compared to the last
> release we used (ovs-1.4.x). Part of the problem is using mlockall
> (with MCL_CURRENT|MCL_FUTURE) on ovs-vswitchd, which causes every
> pthreads stack's and heap's virtual address to locked to RAM.
> ovs-vswitch (2.1.x) running on a 8 vCPU dom0 (10 pthreads) uses
> around 89M of RSS (80MB just for stack), without any VMs running on
> the host. One way to reduce RSS would be to reduce the number of
> "n-handler-threads" and "n-revalidator-threads", but I am not sure
> about the performance impact of having these thread numbers reduced.
> I am wondering if the stack size of the pthreads can be reduce
> (using pthread_attr_setstack). By default pthreads max stack size is
> 8MB and mlockall locks all of this 8MB into RAM. What could be
> optimal stack size that can be used.

I think it would be very reasonable to reduce the stack sizes, but I
don't know the "correct" size off-hand.  Since you're looking at the
problem already, perhaps you should consider some experiments.