NFSv4: Further reduce the footprint of the idmapper

commit 685f50f9 upstream.

Don't allocate the legacy idmapper tables until we actually need
them.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
[bwh: Backported to 3.2: adjust context in nfs_idmap_delete()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/nfs/idmap.c

@@ -323,7 +323,7 @@ struct idmap_hashent {
 
 struct idmap_hashtable {
 	__u8			h_type;
-	struct idmap_hashent	h_entries[IDMAP_HASH_SZ];
+	struct idmap_hashent	*h_entries;
 };
 
 struct idmap {
@@ -378,20 +378,39 @@ nfs_idmap_new(struct nfs_client *clp)
 	return 0;
 }
 
+static void
+idmap_alloc_hashtable(struct idmap_hashtable *h)
+{
+	if (h->h_entries != NULL)
+		return;
+	h->h_entries = kcalloc(IDMAP_HASH_SZ,
+			sizeof(*h->h_entries),
+			GFP_KERNEL);
+}
+
+static void
+idmap_free_hashtable(struct idmap_hashtable *h)
+{
+	int i;
+
+	if (h->h_entries == NULL)
+		return;
+	for (i = 0; i < IDMAP_HASH_SZ; i++)
+		kfree(h->h_entries[i].ih_name);
+	kfree(h->h_entries);
+}
+
 void
 nfs_idmap_delete(struct nfs_client *clp)
 {
 	struct idmap *idmap = clp->cl_idmap;
-	int i;
 
 	if (!idmap)
 		return;
 	rpc_unlink(idmap->idmap_dentry);
 	clp->cl_idmap = NULL;
-	for (i = 0; i < ARRAY_SIZE(idmap->idmap_user_hash.h_entries); i++)
-		kfree(idmap->idmap_user_hash.h_entries[i].ih_name);
-	for (i = 0; i < ARRAY_SIZE(idmap->idmap_group_hash.h_entries); i++)
-		kfree(idmap->idmap_group_hash.h_entries[i].ih_name);
+	idmap_free_hashtable(&idmap->idmap_user_hash);
+	idmap_free_hashtable(&idmap->idmap_group_hash);
 	kfree(idmap);
 }
 
@@ -401,6 +420,8 @@ nfs_idmap_delete(struct nfs_client *clp)
 static inline struct idmap_hashent *
 idmap_name_hash(struct idmap_hashtable* h, const char *name, size_t len)
 {
+	if (h->h_entries == NULL)
+		return NULL;
 	return &h->h_entries[fnvhash32(name, len) % IDMAP_HASH_SZ];
 }
 
@@ -409,6 +430,8 @@ idmap_lookup_name(struct idmap_hashtable *h, const char *name, size_t len)
 {
 	struct idmap_hashent *he = idmap_name_hash(h, name, len);
 
+	if (he == NULL)
+		return NULL;
 	if (he->ih_namelen != len || memcmp(he->ih_name, name, len) != 0)
 		return NULL;
 	if (time_after(jiffies, he->ih_expires))
@@ -419,6 +442,8 @@ idmap_lookup_name(struct idmap_hashtable *h, const char *name, size_t len)
 static inline struct idmap_hashent *
 idmap_id_hash(struct idmap_hashtable* h, __u32 id)
 {
+	if (h->h_entries == NULL)
+		return NULL;
 	return &h->h_entries[fnvhash32(&id, sizeof(id)) % IDMAP_HASH_SZ];
 }
 
@@ -426,6 +451,9 @@ static struct idmap_hashent *
 idmap_lookup_id(struct idmap_hashtable *h, __u32 id)
 {
 	struct idmap_hashent *he = idmap_id_hash(h, id);
+
+	if (he == NULL)
+		return NULL;
 	if (he->ih_id != id || he->ih_namelen == 0)
 		return NULL;
 	if (time_after(jiffies, he->ih_expires))
@@ -441,12 +469,14 @@ idmap_lookup_id(struct idmap_hashtable *h, __u32 id)
 static inline struct idmap_hashent *
 idmap_alloc_name(struct idmap_hashtable *h, char *name, size_t len)
 {
+	idmap_alloc_hashtable(h);
 	return idmap_name_hash(h, name, len);
 }
 
 static inline struct idmap_hashent *
 idmap_alloc_id(struct idmap_hashtable *h, __u32 id)
 {
+	idmap_alloc_hashtable(h);
 	return idmap_id_hash(h, id);
 }