Re: [PATCH v2 3/3] nfsd: keep a tally of RECLAIM_COMPLETE operations when using nfsdcld

J. Bruce Fields
2018-12-19T18:36:02Z

On Tue, Dec 18, 2018 at 09:29:26AM -0500, Scott Mayhew wrote:
> When using nfsdcld for NFSv4 client tracking, track the number of
> RECLAIM_COMPLETE operations we receive from "known" clients to help in
> deciding if we can lift the grace period early (or whether we need to
> start a v4 grace period at all).
>
> Signed-off-by: Scott Mayhew <smayhew@redhat.com>
> ---
> fs/nfsd/netns.h | 3 +++
> fs/nfsd/nfs4recover.c | 5 +++++
> fs/nfsd/nfs4state.c | 52 +++++++++++++++++++++++++++++++++++++++++++
> fs/nfsd/nfsctl.c | 1 +
> 4 files changed, 61 insertions(+)
>
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index 32cb8c027483..b42aaa22fba2 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -104,6 +104,9 @@ struct nfsd_net {
> time_t nfsd4_grace;
> bool somebody_reclaimed;
>
> + bool track_reclaim_completes;
> + atomic_t nr_reclaim_complete;
> +
> bool nfsd_net_up;
> bool lockd_up;
>
> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> index 89c2a27956d0..ae74814b2397 100644
> --- a/fs/nfsd/nfs4recover.c
> +++ b/fs/nfsd/nfs4recover.c
> @@ -1251,6 +1251,7 @@ nfsd4_cld_grace_done(struct nfsd_net *nn)
> free_cld_upcall(cup);
> out_err:
> nfs4_release_reclaim(nn);
> + atomic_set(&nn->nr_reclaim_complete, 0);
> if (ret)
> printk(KERN_ERR "NFSD: Unable to end grace period: %d\n", ret);
> }
> @@ -1270,6 +1271,8 @@ nfs4_cld_state_init(struct net *net)
> for (i = 0; i < CLIENT_HASH_SIZE; i++)
> INIT_LIST_HEAD(&nn->reclaim_str_hashtbl[i]);
> nn->reclaim_str_hashtbl_size = 0;
> + nn->track_reclaim_completes = true;
> + atomic_set(&nn->nr_reclaim_complete, 0);
>
> return 0;
> }
> @@ -1279,6 +1282,7 @@ nfs4_cld_state_shutdown(struct net *net)
> {
> struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>
> + nn->track_reclaim_completes = false;
> kfree(nn->reclaim_str_hashtbl);
> }
>
> @@ -1318,6 +1322,7 @@ nfsd4_cld_tracking_exit(struct net *net)
> struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>
> nfs4_release_reclaim(nn);
> + atomic_set(&nn->nr_reclaim_complete, 0);
> nfsd4_remove_cld_pipe(net);
> nfs4_cld_state_shutdown(net);
> }
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 777fbb0d2761..5dfc3cd51d08 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -77,6 +77,7 @@ static u64 current_sessionid = 1;
> /* forward declarations */
> static bool check_for_locks(struct nfs4_file *fp, struct nfs4_lockowner *lowner);
> static void nfs4_free_ol_stateid(struct nfs4_stid *stid);
> +void nfsd4_end_grace(struct nfsd_net *nn);
>
> /* Locking: */
>
> @@ -1988,10 +1989,41 @@ destroy_client(struct nfs4_client *clp)
> __destroy_client(clp);
> }
>
> +static void inc_reclaim_complete(struct nfs4_client *clp)
> +{
> + struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
> +
> + if (!nn->track_reclaim_completes)
> + return;
> + if (!test_bit(NFSD4_CLIENT_RECLAIM_COMPLETE, &clp->cl_flags))
> + return;

Looking at the code.... This test will never fail, will it? We could
make it a WARN_ON_ONCE(!test_bit(...)) but it doesn't look like a likely
bug to me.

> + if (!nfsd4_find_reclaim_client(clp->cl_name, nn))
> + return;
> + if (atomic_inc_return(&nn->nr_reclaim_complete) ==
> + nn->reclaim_str_hashtbl_size) {
> + printk(KERN_INFO "NFSD: all clients done reclaiming, ending NFSv4 grace period (net %x)\n",
> + clp->net->ns.inum);
> + nfsd4_end_grace(nn);
> + }
> +}
> +
> +static void dec_reclaim_complete(struct nfs4_client *clp)
> +{
> + struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
> +
> + if (!nn->track_reclaim_completes)
> + return;
> + if (!test_bit(NFSD4_CLIENT_RECLAIM_COMPLETE, &clp->cl_flags))
> + return;
> + if (nfsd4_find_reclaim_client(clp->cl_name, nn))
> + atomic_dec(&nn->nr_reclaim_complete);
> +}
> +
> static void expire_client(struct nfs4_client *clp)
> {
> unhash_client(clp);
> nfsd4_client_record_remove(clp);
> + dec_reclaim_complete(clp);
> __destroy_client(clp);
> }

This doesn't look right to me. If a client reclaims and then
immediately calls DESTROY_CLIENTID or something--that should still count
as a reclaim, and that shouldn't prevent us from ending the grace period
early.

I think dec_reclaim_complete is unnecessary.

--b.

>
> @@ -3339,6 +3371,7 @@ nfsd4_reclaim_complete(struct svc_rqst *rqstp,
>
> status = nfs_ok;
> nfsd4_client_record_create(cstate->session->se_client);
> + inc_reclaim_complete(cstate->session->se_client);
> out:
> return status;
> }
> @@ -4734,6 +4767,10 @@ static bool clients_still_reclaiming(struct nfsd_net *nn)
> unsigned long double_grace_period_end = nn->boot_time +
> 2 * nn->nfsd4_lease;
>
> + if (nn->track_reclaim_completes &&
> + atomic_read(&nn->nr_reclaim_complete) ==
> + nn->reclaim_str_hashtbl_size)
> + return false;
> if (!nn->somebody_reclaimed)
> return false;
> nn->somebody_reclaimed = false;
> @@ -7253,10 +7290,25 @@ nfs4_state_start_net(struct net *net)
> return ret;
> locks_start_grace(net, &nn->nfsd4_manager);
> nfsd4_client_tracking_init(net);
> + if (nn->track_reclaim_completes && nn->reclaim_str_hashtbl_size == 0)
> + goto skip_grace;
> printk(KERN_INFO "NFSD: starting %ld-second grace period (net %x)\n",
> nn->nfsd4_grace, net->ns.inum);
> queue_delayed_work(laundry_wq, &nn->laundromat_work, nn->nfsd4_grace * HZ);
> return 0;
> +
> +skip_grace:
> + printk(KERN_INFO "NFSD: no clients to reclaim, skipping NFSv4 grace period (net %x)\n",
> + net->ns.inum);
> + queue_delayed_work(laundry_wq, &nn->laundromat_work, nn->nfsd4_lease * HZ);
> + /*
> + * we could call nfsd4_end_grace() here, but it has a dprintk()
> + * that would be confusing if debug logging is enabled
> + */
> + nn->grace_ended = true;
> + nfsd4_record_grace_done(nn);
> + locks_end_grace(&nn->nfsd4_manager);
> + return 0;
> }
>
> /* initialization to perform when the nfsd service is started: */
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index 6384c9b94898..950ac6683be9 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -1240,6 +1240,7 @@ static __net_init int nfsd_init_net(struct net *net)
> nn->nfsd4_lease = 45; /* default lease time */
> nn->nfsd4_grace = 45;
> nn->somebody_reclaimed = false;
> + nn->track_reclaim_completes = false;
> nn->clverifier_counter = prandom_u32();
> nn->clientid_counter = prandom_u32();
> nn->s2s_cp_cl_id = nn->clientid_counter++;
> --
> 2.17.1