Bug#758870: nfs-common: nfs v4: uid/gid lookup fails for some of the users

[Tero Marttila <tero.marttila@paivola.fi>]

Similar symptoms (uid/gid 4294967294) can also be caused by running 
against the root's keyring quota in the kernel, which is used to store 
all the id_resolv/id_legacy keys for each uid and gid.

The default kernel keyring quotas (200 keys!) in jessie's 3.16 kernel 
work poorly for NFSv4 setups with more than ~100 users. The 
kernel.keys.root_{maxkeys,maxbytes} sysctls should be bumped higher:

> $ sudo sysctl kernel.keys.root_maxbytes=25000000 kernel.keys.root_maxkeys=1000000

Using the new Linux 3.18 default values:
	> 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=738c5d190f6540539a04baf36ce21d46b5da04bd

Works much better with all of the 4294967294 UIDs now showing correctly.

> $ sudo head -n1 /proc/key-users
> 0: 1248 1247/1247 1243/1000000 31475/25000000

With the current kernel.keys.root_maxkeys=200 default in 3.16, this will 
quickly be saturated.

Relevant Ubuntu bug:

> https://bugs.launchpad.net/fedora/+bug/1124250

 -- Tero Marttila