Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Dai Ngo <dai.ngo@oracle.com>
To:     chuck.lever@oracle.com, jlayton@kernel.org
Cc:     linux-nfs@vger.kernel.org
Subject: [PATCH v5 2/2] NFSD: add shrinker to reap courtesy clients on low memory condition
Date:   Sun,  4 Sep 2022 10:27:52 -0700
Message-Id: <1662312472-23981-3-git-send-email-dai.ngo@oracle.com>
In-Reply-To: <1662312472-23981-1-git-send-email-dai.ngo@oracle.com>
References: <1662312472-23981-1-git-send-email-dai.ngo@oracle.com>
Precedence: bulk

Add the courtesy client shrinker to react to low memory condition
triggered by the memory shrinker.

Currently the laundromat starts reaping courtesy clients only when
the maximum number of clients is reached. This patch adds another
trigger condition for the laundromat to reap courtesy clients.

The low memory trigger is created and the laundromat is kick started
by the shrinker's count callback. The shrinker's scan callback is
not used for expiring the courtesy clients due to potential deadlocks.

The laundromat reschedules itself to run sooner if it detects low
memory condition persists and there are more coutersy clients to reap.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 fs/nfsd/netns.h     |  2 ++
 fs/nfsd/nfs4state.c | 43 +++++++++++++++++++++++++++++++++++++++----
 fs/nfsd/nfsctl.c    |  6 ++++--
 fs/nfsd/nfsd.h      |  6 ++++--
 4 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 55c7006d6109..85e351f08e57 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -194,6 +194,8 @@ struct nfsd_net {
 	int			nfs4_max_clients;
 
 	atomic_t		nfsd_courtesy_clients;
+	atomic_t		nfsd_client_shrinker_cb_count;
+	struct shrinker		nfsd_client_shrinker;
 };
 
 /* 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 3af4fc5241b2..a27553b42e72 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4347,7 +4347,25 @@ nfsd4_init_slabs(void)
 	return -ENOMEM;
 }
 
-void nfsd4_init_leases_net(struct nfsd_net *nn)
+static unsigned long
+nfsd_courtesy_client_count(struct shrinker *shrink, struct shrink_control *sc)
+{
+	struct nfsd_net *nn = container_of(shrink,
+			struct nfsd_net, nfsd_client_shrinker);
+
+	atomic_inc(&nn->nfsd_client_shrinker_cb_count);
+	mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
+	return (unsigned long)atomic_read(&nn->nfsd_courtesy_clients);
+}
+
+static unsigned long
+nfsd_courtesy_client_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+	return SHRINK_STOP;
+}
+
+int
+nfsd4_init_leases_net(struct nfsd_net *nn)
 {
 	struct sysinfo si;
 	u64 max_clients;
@@ -4368,6 +4386,17 @@ void nfsd4_init_leases_net(struct nfsd_net *nn)
 	nn->nfs4_max_clients = max_t(int, max_clients, NFS4_CLIENTS_PER_GB);
 
 	atomic_set(&nn->nfsd_courtesy_clients, 0);
+	atomic_set(&nn->nfsd_client_shrinker_cb_count, 0);
+	nn->nfsd_client_shrinker.scan_objects = nfsd_courtesy_client_scan;
+	nn->nfsd_client_shrinker.count_objects = nfsd_courtesy_client_count;
+	nn->nfsd_client_shrinker.seeks = DEFAULT_SEEKS;
+	return register_shrinker(&nn->nfsd_client_shrinker, "nfsd-client");
+}
+
+void
+nfsd4_leases_net_shutdown(struct nfsd_net *nn)
+{
+	unregister_shrinker(&nn->nfsd_client_shrinker);
 }
 
 static void init_nfs4_replay(struct nfs4_replay *rp)
@@ -5876,12 +5905,15 @@ static void
 nfs4_get_client_reaplist(struct nfsd_net *nn, struct list_head *reaplist,
 				struct laundry_time *lt)
 {
-	unsigned int maxreap, reapcnt = 0;
+	unsigned int maxreap = 0, reapcnt = 0;
 	struct list_head *pos, *next;
 	struct nfs4_client *clp;
 
-	maxreap = (atomic_read(&nn->nfs4_client_count) >= nn->nfs4_max_clients) ?
-			NFSD_CLIENT_MAX_TRIM_PER_RUN : 0;
+	if (atomic_read(&nn->nfs4_client_count) >= nn->nfs4_max_clients ||
+			atomic_read(&nn->nfsd_client_shrinker_cb_count) > 0) {
+		maxreap = NFSD_CLIENT_MAX_TRIM_PER_RUN;
+		atomic_set(&nn->nfsd_client_shrinker_cb_count, 0);
+	}
 	INIT_LIST_HEAD(reaplist);
 	spin_lock(&nn->client_lock);
 	list_for_each_safe(pos, next, &nn->client_lru) {
@@ -5947,6 +5979,9 @@ nfs4_laundromat(struct nfsd_net *nn)
 		list_del_init(&clp->cl_lru);
 		expire_client(clp);
 	}
+	if (atomic_read(&nn->nfsd_client_shrinker_cb_count) > 0 &&
+			atomic_read(&nn->nfsd_courtesy_clients) > 0)
+		lt.new_timeo = NFSD_LAUNDROMAT_MINTIMEOUT;
 	spin_lock(&state_lock);
 	list_for_each_safe(pos, next, &nn->del_recall_lru) {
 		dp = list_entry (pos, struct nfs4_delegation, dl_recall_lru);
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 917fa1892fd2..597a26ad4183 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1481,11 +1481,12 @@ static __net_init int nfsd_init_net(struct net *net)
 		goto out_idmap_error;
 	nn->nfsd_versions = NULL;
 	nn->nfsd4_minorversions = NULL;
+	retval = nfsd4_init_leases_net(nn);
+	if (retval)
+		goto out_drc_error;
 	retval = nfsd_reply_cache_init(nn);
 	if (retval)
 		goto out_drc_error;
-	nfsd4_init_leases_net(nn);
-
 	get_random_bytes(&nn->siphash_key, sizeof(nn->siphash_key));
 	seqlock_init(&nn->writeverf_lock);
 
@@ -1507,6 +1508,7 @@ static __net_exit void nfsd_exit_net(struct net *net)
 	nfsd_idmap_shutdown(net);
 	nfsd_export_shutdown(net);
 	nfsd_netns_free_versions(net_generic(net, nfsd_net_id));
+	nfsd4_leases_net_shutdown(nn);
 }
 
 static struct pernet_operations nfsd_net_ops = {
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 57a468ed85c3..d87a465aa950 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -498,7 +498,8 @@ extern void unregister_cld_notifier(void);
 extern void nfsd4_ssc_init_umount_work(struct nfsd_net *nn);
 #endif
 
-extern void nfsd4_init_leases_net(struct nfsd_net *nn);
+extern int nfsd4_init_leases_net(struct nfsd_net *nn);
+extern void nfsd4_leases_net_shutdown(struct nfsd_net *nn);
 
 #else /* CONFIG_NFSD_V4 */
 static inline int nfsd4_is_junction(struct dentry *dentry)
@@ -506,7 +507,8 @@ static inline int nfsd4_is_junction(struct dentry *dentry)
 	return 0;
 }
 
-static inline void nfsd4_init_leases_net(struct nfsd_net *nn) {};
+static inline int nfsd4_init_leases_net(struct nfsd_net *nn) { return 0; };
+static inline void nfsd4_leases_net_shutdown(struct nfsd_net *nn) {};
 
 #define register_cld_notifier() 0
 #define unregister_cld_notifier() do { } while(0)
-- 
2.9.5