text: On Fri, 2012-05-04 at 00:55 -0700, Eric W. Biederman wrote: > Mike Galbraith <efault@gmx.de> writes:> > > Namespaces have something in common with cgroups. synchronize_rcu()> > makes them somewhat less than wonderful for dynamic use.> > Well unlike cgroups namespaces were not designed for heavy dynamic use.> Although it appears that vsftp puts them to that kind of use so some> of the design decisions are with revisiting.Yeah, the testcase was distilled from vsftp, so it must be beating onnamespaces pretty hard to induce a bug report.> > default flags = SIGCHLD> >> > -namespace: flag |= CLONE_NEWPID > > -all: flags |= CLONE_NEWIPC | CLONE_NEWNET | CLONE_NEWUSER> >> > marge:/usr/local/tmp/starvation # ./hackbench> > Running with 10*40 (== 400) tasks.> > Time: 2.636> > marge:/usr/local/tmp/starvation # ./hackbench -namespace> > Running with 10*40 (== 400) tasks.> > Time: 11.624> > marge:/usr/local/tmp/starvation # ./hackbench -namespace -all> > Running with 10*40 (== 400) tasks.> > Time: 51.474> > CLONE_NEWUSER? I presume you have applied my latest user namespace> patches? Otherwise you are running completely half baked code.I was testing in mainline. While fiddling with the testcase and leakagemonitor script, I decided to see what happens with all namespace flags.The others didn't cause any leakage, but did make things slow down.> hackbench? Which kernel are you running. Hackbench in some kernels is> really good at triggering cache ping-pong effects with pids, and creds.> So I'm not certain what to say there. In the latest kernels things> should be better with unix domain sockets as long as you don't actually> ask to pass your creds but hackbench is still a pretty ridiculous> benchmark. Oversharing is always going to be bad for performance.Hackbench was just to show the price of hefty namespace usage.> > You can create trash quickly, but you have to haul it away.> > Well synchronize_rcu is much better in that respect than call_rcu, which> let's the trash build up but is never carried away.> > The core design assumption with namespaces is that they will be used> much more than they will be created/destroyed, and as long as there are> progress guarantees in place I don't have a problem with that. At the> same time if there are easy things we can do to make things go faster> I am in favor of that notion.> > Still especially in the case of hackbench I think it is worth asking the> question how much of the slow down is due to cache ping-pong due to> oversharing.Dunno, and doubt I'll have time to tinker with it more. Darn bugzillathing keeps knocking on my mailbox with interesting bugs in places Iknow _diddly spit_ about.. like namespaces.-Mike