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

[David Miller <davem@davemloft.net>]

From: Eric Dumazet <dada1@cosmosbay.com>
Date: Mon, 30 Oct 2006 22:30:39 +0100

> 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)

Sounds like a useful optimization for sure.

You can't mount sockfs on the filesystem, but they are visible
via /proc/${pid}/fd/, I wonder if the dentry hashing is required
just to make those nodes visible properly?