[OpenAFS] cache performance

[Jim Rees]

  So, although there's code that claims to disable atimes, empirical
  evidence suggests that it's broken, and atimes are being updated
  anyway (not a big surprise for Transarc/AFS code).

The cache manager depends on atimes to initialize the cache file lru list.
This is in afs_dcache.c:afs_InitCacheFile(), "We must put this entry in the
appropriate hash tables."  So if you run your cache partition with noatime,
when you reboot you will bash your hash with trash, and thrash your cache.