> On Aug 30, 2022, at 3:40 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
>> ---
>> 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.
Agree: generally speaking, primitives like xchg() are used only when
hardware-assisted synchronization is needed. These are expensive
operations, to be used sparingly.
Let's replace these with plain vanilla "=", as Jeff suggested.
Likewise, I'm not totally convinced that nfsd_courtesy_client_count
has to be an atomic.
>> 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@xxxxxxxxxx>
--
Chuck Lever
