Re: [PATCH 4/4] NFS: use a hash table for delegation lookup

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2025-07-15 at 10:58 +0200, Christoph Hellwig wrote:
> On Mon, Jul 14, 2025 at 09:14:27AM -0400, Jeff Layton wrote:
> > > +	delegation_buckets = roundup_pow_of_two(nfs_delegation_watermark / 16);
> > > +	server->delegation_hash_mask = delegation_buckets - 1;
> > > +	server->delegation_hash_table = kmalloc_array(delegation_buckets,
> > > +			sizeof(*server->delegation_hash_table), GFP_KERNEL);
> > > +	if (!server->delegation_hash_table)
> > > +		goto out_free_server;
> > > +	for (i = 0; i < delegation_buckets; i++)
> > > +		INIT_HLIST_HEAD(&server->delegation_hash_table[i]);
> > > +
> > 
> > This is going to get created for any mount, even v3 ones. It might be
> > better to only bother with this for v4 mounts. Maybe do this in
> > nfs4_server_common_setup() instead?
> 
> I tried that, but it crashes because the usual mount process goes
> through nfs_clone_server, which then doesn't set up the hash table.
> 
> I think the best idea is to pass the version to nfs_allocate_server
> and just make this code conditional, but I'm open to other suggestions.

The other thing you could do is move the allocation and setup into a
helper function, and have nfs_clone_server() call that if the source
server has a hashtable present.

-- 
Jeff Layton <jlayton@kernel.org>