Re: [PATCH v3 1/2] NFSD: keep track of the number of courtesy clients in the system

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2022-08-30 at 12:14 -0700, Dai Ngo wrote:
> Add counter nfs4_courtesy_client_count to nfsd_net to keep track
> of the number of courtesy clients in the system.
> 
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/nfsd/netns.h     |  2 ++
>  fs/nfsd/nfs4state.c | 14 +++++++++++---
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index ffe17743cc74..2695dff1378a 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -192,6 +192,8 @@ struct nfsd_net {
>  
>  	atomic_t		nfs4_client_count;
>  	int			nfs4_max_clients;
> +
> +	atomic_t		nfsd_courtesy_client_count;
>  };
>  
>  /* Simple check to find out if a given net was properly initialized */
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index c5d199d7e6b4..9675b5d8f408 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -169,7 +169,8 @@ static __be32 get_client_locked(struct nfs4_client *clp)
>  	if (is_client_expired(clp))
>  		return nfserr_expired;
>  	atomic_inc(&clp->cl_rpc_users);
> -	clp->cl_state = NFSD4_ACTIVE;
> +	if (xchg(&clp->cl_state, NFSD4_ACTIVE) != NFSD4_ACTIVE)
> +		atomic_add_unless(&nn->nfsd_courtesy_client_count, -1, 0);

I'd prefer this:

	if (clp->cl_state != NFSD4_ACTIVE)
		atomic_add_unless(...
	clp->cl_state = NFSD4_ACTIVE;

It's more lines, but it's easier to read. It's may also be more
efficient since you're protected by a spinlock anyway.

I think it's also less deceptive when reading the code. When I see
xchg() operations being used like that, my immediate thought is that
they must be needed for synchronization purposes. It's not in this case.

>  	return nfs_ok;
>  }
>  
> @@ -190,7 +191,8 @@ renew_client_locked(struct nfs4_client *clp)
>  
>  	list_move_tail(&clp->cl_lru, &nn->client_lru);
>  	clp->cl_time = ktime_get_boottime_seconds();
> -	clp->cl_state = NFSD4_ACTIVE;
> +	if (xchg(&clp->cl_state, NFSD4_ACTIVE) != NFSD4_ACTIVE)
> +		atomic_add_unless(&nn->nfsd_courtesy_client_count, -1, 0);
>  }
>  
>  static void put_client_renew_locked(struct nfs4_client *clp)
> @@ -2233,6 +2235,8 @@ __destroy_client(struct nfs4_client *clp)
>  	if (clp->cl_cb_conn.cb_xprt)
>  		svc_xprt_put(clp->cl_cb_conn.cb_xprt);
>  	atomic_add_unless(&nn->nfs4_client_count, -1, 0);
> +	if (clp->cl_state != NFSD4_ACTIVE)
> +		atomic_add_unless(&nn->nfsd_courtesy_client_count, -1, 0);
>  	free_client(clp);
>  	wake_up_all(&expiry_wq);
>  }
> @@ -4356,6 +4360,8 @@ void nfsd4_init_leases_net(struct nfsd_net *nn)
>  	max_clients = (u64)si.totalram * si.mem_unit / (1024 * 1024 * 1024);
>  	max_clients *= NFS4_CLIENTS_PER_GB;
>  	nn->nfs4_max_clients = max_t(int, max_clients, NFS4_CLIENTS_PER_GB);
> +
> +	atomic_set(&nn->nfsd_courtesy_client_count, 0);
>  }
>  
>  static void init_nfs4_replay(struct nfs4_replay *rp)
> @@ -5879,7 +5885,9 @@ nfs4_get_client_reaplist(struct nfsd_net *nn, struct list_head *reaplist,
>  		if (!state_expired(lt, clp->cl_time))
>  			break;
>  		if (!atomic_read(&clp->cl_rpc_users))
> -			clp->cl_state = NFSD4_COURTESY;
> +			if (xchg(&clp->cl_state, NFSD4_COURTESY) ==
> +							NFSD4_ACTIVE)
> +				atomic_inc(&nn->nfsd_courtesy_client_count);
>  		if (!client_has_state(clp))
>  			goto exp_client;
>  		if (!nfs4_anylock_blockers(clp))

-- 
Jeff Layton <jlayton@kernel.org>