net-sched: add dynamically sized qdisc class hash helpers

Currently all qdiscs which allow to create classes uses a fixed sized hash
table with size 16 to hash the classes. This causes a large bottleneck
when using thousands of classes and unbound filters.

Add helpers for dynamically sized class hashes to fix this. The following
patches will convert the qdiscs to use them.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sch_generic.h

@@ -167,6 +167,48 @@ extern void qdisc_unlock_tree(struct net_device *dev);
 extern struct Qdisc noop_qdisc;
 extern struct Qdisc_ops noop_qdisc_ops;
 
+struct Qdisc_class_common
+{
+	u32			classid;
+	struct hlist_node	hnode;
+};
+
+struct Qdisc_class_hash
+{
+	struct hlist_head	*hash;
+	unsigned int		hashsize;
+	unsigned int		hashmask;
+	unsigned int		hashelems;
+};
+
+static inline unsigned int qdisc_class_hash(u32 id, u32 mask)
+{
+	id ^= id >> 8;
+	id ^= id >> 4;
+	return id & mask;
+}
+
+static inline struct Qdisc_class_common *
+qdisc_class_find(struct Qdisc_class_hash *hash, u32 id)
+{
+	struct Qdisc_class_common *cl;
+	struct hlist_node *n;
+	unsigned int h;
+
+	h = qdisc_class_hash(id, hash->hashmask);
+	hlist_for_each_entry(cl, n, &hash->hash[h], hnode) {
+		if (cl->classid == id)
+			return cl;
+	}
+	return NULL;
+}
+
+extern int qdisc_class_hash_init(struct Qdisc_class_hash *);
+extern void qdisc_class_hash_insert(struct Qdisc_class_hash *, struct Qdisc_class_common *);
+extern void qdisc_class_hash_remove(struct Qdisc_class_hash *, struct Qdisc_class_common *);
+extern void qdisc_class_hash_grow(struct Qdisc *, struct Qdisc_class_hash *);
+extern void qdisc_class_hash_destroy(struct Qdisc_class_hash *);
+
 extern void dev_init_scheduler(struct net_device *dev);
 extern void dev_shutdown(struct net_device *dev);
 extern void dev_activate(struct net_device *dev);

net/sched/sch_api.c

@@ -316,6 +316,110 @@ void qdisc_watchdog_cancel(struct qdisc_watchdog *wd)
 }
 EXPORT_SYMBOL(qdisc_watchdog_cancel);
 
+struct hlist_head *qdisc_class_hash_alloc(unsigned int n)
+{
+	unsigned int size = n * sizeof(struct hlist_head), i;
+	struct hlist_head *h;
+
+	if (size <= PAGE_SIZE)
+		h = kmalloc(size, GFP_KERNEL);
+	else
+		h = (struct hlist_head *)
+			__get_free_pages(GFP_KERNEL, get_order(size));
+
+	if (h != NULL) {
+		for (i = 0; i < n; i++)
+			INIT_HLIST_HEAD(&h[i]);
+	}
+	return h;
+}
+
+static void qdisc_class_hash_free(struct hlist_head *h, unsigned int n)
+{
+	unsigned int size = n * sizeof(struct hlist_head);
+
+	if (size <= PAGE_SIZE)
+		kfree(h);
+	else
+		free_pages((unsigned long)h, get_order(size));
+}
+
+void qdisc_class_hash_grow(struct Qdisc *sch, struct Qdisc_class_hash *clhash)
+{
+	struct Qdisc_class_common *cl;
+	struct hlist_node *n, *next;
+	struct hlist_head *nhash, *ohash;
+	unsigned int nsize, nmask, osize;
+	unsigned int i, h;
+
+	/* Rehash when load factor exceeds 0.75 */
+	if (clhash->hashelems * 4 <= clhash->hashsize * 3)
+		return;
+	nsize = clhash->hashsize * 2;
+	nmask = nsize - 1;
+	nhash = qdisc_class_hash_alloc(nsize);
+	if (nhash == NULL)
+		return;
+
+	ohash = clhash->hash;
+	osize = clhash->hashsize;
+
+	sch_tree_lock(sch);
+	for (i = 0; i < osize; i++) {
+		hlist_for_each_entry_safe(cl, n, next, &ohash[i], hnode) {
+			h = qdisc_class_hash(cl->classid, nmask);
+			hlist_add_head(&cl->hnode, &nhash[h]);
+		}
+	}
+	clhash->hash     = nhash;
+	clhash->hashsize = nsize;
+	clhash->hashmask = nmask;
+	sch_tree_unlock(sch);
+
+	qdisc_class_hash_free(ohash, osize);
+}
+EXPORT_SYMBOL(qdisc_class_hash_grow);
+
+int qdisc_class_hash_init(struct Qdisc_class_hash *clhash)
+{
+	unsigned int size = 4;
+
+	clhash->hash = qdisc_class_hash_alloc(size);
+	if (clhash->hash == NULL)
+		return -ENOMEM;
+	clhash->hashsize  = size;
+	clhash->hashmask  = size - 1;
+	clhash->hashelems = 0;
+	return 0;
+}
+EXPORT_SYMBOL(qdisc_class_hash_init);
+
+void qdisc_class_hash_destroy(struct Qdisc_class_hash *clhash)
+{
+	qdisc_class_hash_free(clhash->hash, clhash->hashsize);
+}
+EXPORT_SYMBOL(qdisc_class_hash_destroy);
+
+void qdisc_class_hash_insert(struct Qdisc_class_hash *clhash,
+			     struct Qdisc_class_common *cl)
+{
+	unsigned int h;
+
+	INIT_HLIST_NODE(&cl->hnode);
+	h = qdisc_class_hash(cl->classid, clhash->hashmask);
+	hlist_add_head(&cl->hnode, &clhash->hash[h]);
+	clhash->hashelems++;
+}
+EXPORT_SYMBOL(qdisc_class_hash_insert);
+
+void qdisc_class_hash_remove(struct Qdisc_class_hash *clhash,
+			     struct Qdisc_class_common *cl)
+{
+	hlist_del(&cl->hnode);
+	clhash->hashelems--;
+}
+EXPORT_SYMBOL(qdisc_class_hash_remove);
+
 /* Allocate an unique handle from space managed by kernel */
 
 static u32 qdisc_alloc_handle(struct net_device *dev)