[PATCH] user_ns: Improve the user_ns on-the-slab packaging

[Serge E. Hallyn]

Quoting Pavel Emelyanov (xemul at parallels.com):
> On 12/07/2010 05:27 PM, Serge E. Hallyn wrote:
> > Quoting Pavel Emelyanov (xemul at parallels.com):
> >> Currently on 64-bit arch the user_namespace is 2096 and when
> >> being kmalloc-ed it resides on a 4k slab wasting 2003 bytes.
> >>
> >> If we allocate a separate cache for it and reduce the hash size
> >> from 128 to 64 chains the packaging becomes *much* better - the
> > 
> > Hey Pavel,
> > 
> > I trust you've done some performance tests and found no
> > regressions with a few hundred users?
> 
> How many hundreds are you interested in? :) 128 users didn't
> reveal any regressions.

I have no good guess, would have said 500, 128 sounds good :)  So
long as actual benchmarks showed no regression within a 95%
confidence interval.

Thanks for the patch, the memory savings are impressive.

Acked-by: Serge E. Hallyn <serge at hallyn.com>

-serge

PS - I'm hoping to send out a version of the targeted capabilities
(based on userns) patchset later this week.