Re: [PATCH] vfs: Speed up deactivate_super for non-modular filesystems

[Mike Galbraith <efault@gmx.de>]

On Mon, 2012-05-07 at 18:07 -0700, Eric W. Biederman wrote: 
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> writes:

> What I see as the real need is the filesystem modules need to do:
> 	rcu_barrier()
> 	kmem_cache_destroy(cache);
> 
> Perhaps we can add some helpers to make it easy.  But I think
> I would be happy today with simply moving the rcu_barrier into
> every filesystems module exit path, just before the file system
> module destoryed it's inode cache.

One liner kills the reap bottleneck and 99.999% of cache bloat.  1000
backgrounded vfstpd testcases finished ~instantly and left one
persistent pid namespace vs taking ages and bloating very badly.

Hacked up hackbench still hurts with all (except user) namespaces, but
that's a different problem (modulo hackbench wonderfulness).

Previous numbers:

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


New numbers: 
marge:/usr/local/tmp/starvation # time ./hackbench
Running with 10*40 (== 400) tasks.
Time: 2.718

real    0m2.877s
user    0m0.060s
sys     0m10.057s
marge:/usr/local/tmp/starvation # time ./hackbench -namespace
Running with 10*40 (== 400) tasks.
Time: 2.689

real    0m2.878s
user    0m0.060s
sys     0m9.945s
marge:/usr/local/tmp/starvation # time ./hackbench -namespace -all
Running with 10*40 (== 400) tasks.                                                                                                                                                                                                          
Time: 2.521
                                                                                                                                                                                                                                            
real    0m27.774s
user    0m0.048s                                                                                                                                                                                                                            
sys     0m21.681s
marge:/usr/local/tmp/starvation #