gfs-kernel: Bug 466645 - reproduceable gfs (dlm) hanger with simple stresstest
    
    GFS used to attempt to prefetch inode/iopen locks in readdir
    in the anticipation that stats will be called on the dirents
    returned. Running a simple 'find' without stat, resulted in
    wasteful prefetching and poor performance to the point that
    it seemed like find was hanging the system.
    
    This patch performs prefetch on a directory's inodes based
    on a stat-rate. i.e the rate at which stats are performed on
    the dirents returned by readdir. If there are a significant
    number of stats being performed, we enable prefetching.
    Otherwise, readdir is performed without prefetches.