[RFC] Any strong reason why socket dentries are hashed in global d_hash table ?

[Eric Dumazet <dada1@cosmosbay.com>]

In sock_attach_fd(), we are currently using

d_add(file->f_dentry, SOCK_INODE(sock));

This has the effect to insert the dentry into the dentry_hashtable.

I was wondering if it is really necessary : On a machine with many sockets, 
the dentry_hashtable lookups may be slowed down for no good reason. (sockets 
are not accessable by other means than socket() syscall, and not subject to 
'unuse and LRU freeable syndrom').

If we replace d_add(file->f_dentry, SOCK_INODE(sock)) call by
d_instantiate(file->f_dentry, SOCK_INODE(sock)), we also avoid using rcu 
callback when socket is closed. (We would have to not provide a d_op->d_delete 
() method in sockfs_dentry_operations)

Maybe I just provide a patch instead of just talking ? :)

Eric