Re: [PATCH v7 2/2] NFSD: add shrinker to reap courtesy clients on low memory condition

dai.ngo@xxxxxxxxxx · Wed, 14 Sep 2022 11:37:24 -0700

On 9/14/22 11:32 AM, Chuck Lever III wrote:

On Sep 14, 2022, at 8:54 AM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:

Add courtesy_client_reaper to react to low memory condition triggered
by the system memory shrinker.

The delayed_work for the courtesy_client_reaper is scheduled on
the shrinker's count callback using the laundry_wq.

The shrinker's scan callback is not used for expiring the courtesy
clients due to potential deadlocks.

Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
---
fs/nfsd/netns.h     |  2 ++
fs/nfsd/nfs4state.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++-----
fs/nfsd/nfsctl.c    |  6 ++--
fs/nfsd/nfsd.h      |  7 ++--
4 files changed, 97 insertions(+), 12 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 55c7006d6109..8c854ba3285b 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;
+	struct shrinker		nfsd_client_shrinker;
+	struct delayed_work	nfsd_shrinker_work;
};

/* 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 2827329704ea..62b848bb55df 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4347,7 +4347,27 @@ 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)
+{
+	int cnt;
+	struct nfsd_net *nn = container_of(shrink,
+			struct nfsd_net, nfsd_client_shrinker);
+
+	cnt = atomic_read(&nn->nfsd_courtesy_clients);
+	if (cnt > 0)
+		mod_delayed_work(laundry_wq, &nn->nfsd_shrinker_work, 0);
+	return (unsigned long)cnt;
+}
+
+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 +4388,16 @@ 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);
+	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)
@@ -5909,10 +5939,49 @@ nfs4_get_client_reaplist(struct nfsd_net *nn, struct list_head *reaplist,
	spin_unlock(&nn->client_lock);
}

+static void
+nfs4_get_courtesy_client_reaplist(struct nfsd_net *nn,
+				struct list_head *reaplist)
+{
+	unsigned int maxreap = 0, reapcnt = 0;
+	struct list_head *pos, *next;
+	struct nfs4_client *clp;
+
+	maxreap = NFSD_CLIENT_MAX_TRIM_PER_RUN;
+	INIT_LIST_HEAD(reaplist);
+
+	spin_lock(&nn->client_lock);
+	list_for_each_safe(pos, next, &nn->client_lru) {
+		clp = list_entry(pos, struct nfs4_client, cl_lru);
+		if (clp->cl_state == NFSD4_ACTIVE)
+			break;
+		if (reapcnt >= maxreap)
+			break;
+		if (!mark_client_expired_locked(clp)) {
+			list_add(&clp->cl_lru, reaplist);
+			reapcnt++;
+		}
+	}
+	spin_unlock(&nn->client_lock);
+}
+
+static void
+nfs4_process_client_reaplist(struct list_head *reaplist)
+{
+	struct list_head *pos, *next;
+	struct nfs4_client *clp;
+
+	list_for_each_safe(pos, next, reaplist) {
+		clp = list_entry(pos, struct nfs4_client, cl_lru);
+		trace_nfsd_clid_purged(&clp->cl_clientid);
+		list_del_init(&clp->cl_lru);
+		expire_client(clp);
+	}
+}
+
static time64_t
nfs4_laundromat(struct nfsd_net *nn)
{
-	struct nfs4_client *clp;
	struct nfs4_openowner *oo;
	struct nfs4_delegation *dp;
	struct nfs4_ol_stateid *stp;
@@ -5941,12 +6010,8 @@ nfs4_laundromat(struct nfsd_net *nn)
	}
	spin_unlock(&nn->s2s_cp_lock);
	nfs4_get_client_reaplist(nn, &reaplist, &lt);
-	list_for_each_safe(pos, next, &reaplist) {
-		clp = list_entry(pos, struct nfs4_client, cl_lru);
-		trace_nfsd_clid_purged(&clp->cl_clientid);
-		list_del_init(&clp->cl_lru);
-		expire_client(clp);
-	}
+	nfs4_process_client_reaplist(&reaplist);
+
	spin_lock(&state_lock);
	list_for_each_safe(pos, next, &nn->del_recall_lru) {
		dp = list_entry (pos, struct nfs4_delegation, dl_recall_lru);
@@ -6029,6 +6094,18 @@ laundromat_main(struct work_struct *laundry)
	queue_delayed_work(laundry_wq, &nn->laundromat_work, t*HZ);
}

+static void
+courtesy_client_reaper(struct work_struct *reaper)
+{
+	struct list_head reaplist;
+	struct delayed_work *dwork = to_delayed_work(reaper);
+	struct nfsd_net *nn = container_of(dwork, struct nfsd_net,
+					nfsd_shrinker_work);
+
+	nfs4_get_courtesy_client_reaplist(nn, &reaplist);
+	nfs4_process_client_reaplist(&reaplist);
+}
+
static inline __be32 nfs4_check_fh(struct svc_fh *fhp, struct nfs4_stid *stp)
{
	if (!fh_match(&fhp->fh_handle, &stp->sc_file->fi_fhandle))
@@ -7845,6 +7922,7 @@ static int nfs4_state_create_net(struct net *net)
	INIT_LIST_HEAD(&nn->blocked_locks_lru);

	INIT_DELAYED_WORK(&nn->laundromat_work, laundromat_main);
+	INIT_DELAYED_WORK(&nn->nfsd_shrinker_work, courtesy_client_reaper);
	get_net(net);

	return 0;
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..cd92f615faa3 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -343,6 +343,7 @@ void		nfsd_lockd_shutdown(void);
#define	NFSD_COURTESY_CLIENT_TIMEOUT	(24 * 60 * 60)	/* seconds */
#define	NFSD_CLIENT_MAX_TRIM_PER_RUN	128
#define	NFS4_CLIENTS_PER_GB		1024
+#define	NFSD_CLIENT_SHRINKER_MINTIMEOUT	1   /* seconds */
You don't need this definition any more. I can remove it
when I apply the patch.

Oh yes, I missed this.


Otherwise, these patches look great. I will give a few
more days for more review comments.

Thank you Chuck,

-Dai



/*
  * The following attributes are currently not supported by the NFSv4 server:
@@ -498,7 +499,8 @@ 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 +508,8 @@ 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

--
Chuck Lever









