On Fri, Nov 10, 2017 at 10:09:09AM +1100, NeilBrown wrote: > So if an NFS server is getting lots of read/write request without opens > or other pathname lookups, it could easily have lots of disconnected > files being repeatedly accessed. Keeping the dentries on d_anon means > we don't need to keep allocating new ones for every request. > > So I'm not keen on dropping an IS_ROOT() dentry at final dput(), but > it might make sense to add the dentry to the per-fs list of IS_ROOT > dentries at that time. Watch out for dput() fast path (see fast_dput()) if you go that way. > One possible approach would be to use d_child rather than d_hash to link > together dentries that don't have a parent. > We could assign a random number to d_name.hash so it could appear to be > hashed without imposing on any one hash chain. We would still need a > spinlock in the superblock to manage the d_anon list that links the > d_child's together... > I might try to see how the code looks. Keep in mind that d_hash() includes bits of ->d_parent, aka. dentry itself. So no need for fake ->d_name.hash; you'll get spread from that part. ->d_child is... delicate. There are very interesting games around d_walk vs. dput already; I'd be very careful with that one.
