[Linux-cachefs] Does fs-cache work in conjunction with NFS4 + Kerberos?

[Hans Meine]

Hi,

I suffer from a very slow NFS4 setup here at our university.  The exact cause 
is not known (might be related to our complex Kerberos/Active Directory/... 
setup), but I thought I'd give FS-Cache a try in case that helps.

However, /proc/fs/fscache/histogram stays empty and I only see zeros in 
/proc/fs/fscache/stats (except Cookies: idx=2 of course).

My main question now is whether I can use fs-cache at all, when I am using 
krb5 to make sure that not even root is able to access the files in my home 
directory?  I thought that /could/ be a problem, although OTOH the data does 
pass through the kernel, so expecting the kernel to be able to cache it is not 
totally out of the question either, is it?

Since our setup is  fairly unusual, I figured it could be possible that the 
existing HowTos [1] do  not contain an "in case you're using idmapd/gssd, 
caching is not possible" yet even if that's be the case.

A few details on the state of things: I am using Gentoo's 2.6.31-gentoo-r6-
default linux sources, with everything fscache-related (except the _DEBUG 
options) enabled, cachefilesd version 0.10.1 is running, and I do see nice 
messages in the syslog:

...
Sep  8 15:48:22 kogspc46 cachefilesd[4848]: About to bind cache 
Sep  8 15:48:22 kogspc46 cachefilesd[4848]: Bound cache 
Sep  8 15:48:22 kogspc46 cachefilesd[5140]: Daemon Started 
Sep  8 15:48:22 kogspc46 klogd: [   30.735580] FS-Cache: Cache "mycache" added 
(type cachefiles)
Sep  8 15:48:22 kogspc46 klogd: [   30.735584] CacheFiles: File cache on sda2 
registered
Sep  8 15:48:22 kogspc46 cachefilesd[5140]: Scan complete 
Sep  8 15:48:28 kogspc46 Service nfsmount starting
...

Also, I have mounted the NFS partition with the 'fsc' option as one can see in 
the output of 'mount':

rzfilesrv1:/informatik on /informatik type nfs4 \ 
(rw,sec=krb5,fsc,clientaddr=...,addr=...)

However, I don't see content in /proc/fs/fscache/ appearing, and the cache 
directory does not seem to be populated (is there a good way to check, since 
there seem to be 177Mb used on that partition according to df, maybe xattrs?).

BTW: I have dedicated a whole partition to the cache, so AFAICS I should 
eventually try using cachefs instead of cachefilesd, but I wanted to follow 
documented procedures first.

Have a nice day,
  Hans

[1] I was looking http://en.gentoo-wiki.com/wiki/CacheFS, for example.