rhashtable: Allow hash/comparison functions to be inlined

This patch deals with the complaint that we make indirect function
calls on the fast paths unnecessarily in rhashtable.  We resolve
it by moving the fast paths into inline functions that take struct
rhashtable_param (which obviously must be the same set of parameters
supplied to rhashtable_init) as an argument.

The only remaining indirect call is to obj_hashfn (or key_hashfn it
obj_hashfn is unset) on the rehash as well as the insert-during-
rehash slow path.

This patch also extends the support of vairable-length keys to
include those where the key is fixed but scattered in the object.
For example, in netlink we want to key off the namespace and the
portid but they're not next to each other.

This patch does this by directly using the object hash function
as the indicator of whether the key is accessible or not.  It
also adds a new function obj_cmpfn to compare a key against an
object.  This means that the caller no longer needs to supply
explicit compare functions.

All this is done in a backwards compatible manner so no existing
users are affected until they convert to the new interface.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/rhashtable.c

 /*
  * Resizable, Scalable, Concurrent Hash Table
  *
+ * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
  * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
  * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
  *
- * Based on the following paper:
- * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
- *
  * Code partially derived from nft_hash
+ * Rewritten with rehash code from br_multicast plus single list
+ * pointer as suggested by Josh Triplett
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -30,53 +30,11 @@
 #define HASH_MIN_SIZE		4U
 #define BUCKET_LOCKS_PER_CPU   128UL
 
-/* Base bits plus 1 bit for nulls marker */
-#define HASH_RESERVED_SPACE	(RHT_BASE_BITS + 1)
-
-/* The bucket lock is selected based on the hash and protects mutations
- * on a group of hash buckets.
- *
- * A maximum of tbl->size/2 bucket locks is allocated. This ensures that
- * a single lock always covers both buckets which may both contains
- * entries which link to the same bucket of the old table during resizing.
- * This allows to simplify the locking as locking the bucket in both
- * tables during resize always guarantee protection.
- *
- * IMPORTANT: When holding the bucket lock of both the old and new table
- * during expansions and shrinking, the old bucket lock must always be
- * acquired first.
- */
-static spinlock_t *bucket_lock(const struct bucket_table *tbl, u32 hash)
-{
-	return &tbl->locks[hash & tbl->locks_mask];
-}
-
-static void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he)
-{
-	return (void *) he - ht->p.head_offset;
-}
-
-static u32 rht_bucket_index(const struct bucket_table *tbl, u32 hash)
-{
-	return (hash >> HASH_RESERVED_SPACE) & (tbl->size - 1);
-}
-
-static u32 key_hashfn(struct rhashtable *ht, const struct bucket_table *tbl,
-		      const void *key)
-{
-	return rht_bucket_index(tbl, ht->p.hashfn(key, ht->p.key_len,
-						  tbl->hash_rnd));
-}
-
 static u32 head_hashfn(struct rhashtable *ht,
 		       const struct bucket_table *tbl,
 		       const struct rhash_head *he)
 {
-	const char *ptr = rht_obj(ht, he);
-
-	return likely(ht->p.key_len) ?
-	       key_hashfn(ht, tbl, ptr + ht->p.key_offset) :
-	       rht_bucket_index(tbl, ht->p.obj_hashfn(ptr, tbl->hash_rnd));
+	return rht_head_hashfn(ht, tbl, he, ht->p);
 }
 
 #ifdef CONFIG_PROVE_LOCKING
@@ -90,7 +48,7 @@ EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
 
 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
 {
-	spinlock_t *lock = bucket_lock(tbl, hash);
+	spinlock_t *lock = rht_bucket_lock(tbl, hash);
 
 	return (debug_locks) ? lockdep_is_held(lock) : 1;
 }
@@ -178,32 +136,6 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 	return tbl;
 }
 
-/**
- * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
- * @ht:		hash table
- * @tbl:	current table
- */
-static bool rht_grow_above_75(const struct rhashtable *ht,
-			      const struct bucket_table *tbl)
-{
-	/* Expand table when exceeding 75% load */
-	return atomic_read(&ht->nelems) > (tbl->size / 4 * 3) &&
-	       (!ht->p.max_size || tbl->size < ht->p.max_size);
-}
-
-/**
- * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
- * @ht:		hash table
- * @tbl:	current table
- */
-static bool rht_shrink_below_30(const struct rhashtable *ht,
-				const struct bucket_table *tbl)
-{
-	/* Shrink table beneath 30% load */
-	return atomic_read(&ht->nelems) < (tbl->size * 3 / 10) &&
-	       tbl->size > ht->p.min_size;
-}
-
 static int rhashtable_rehash_one(struct rhashtable *ht, unsigned old_hash)
 {
 	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
@@ -230,7 +162,7 @@ static int rhashtable_rehash_one(struct rhashtable *ht, unsigned old_hash)
 
 	new_hash = head_hashfn(ht, new_tbl, entry);
 
-	new_bucket_lock = bucket_lock(new_tbl, new_hash);
+	new_bucket_lock = rht_bucket_lock(new_tbl, new_hash);
 
 	spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);
 	head = rht_dereference_bucket(new_tbl->buckets[new_hash],
@@ -255,7 +187,7 @@ static void rhashtable_rehash_chain(struct rhashtable *ht, unsigned old_hash)
 	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 	spinlock_t *old_bucket_lock;
 
-	old_bucket_lock = bucket_lock(old_tbl, old_hash);
+	old_bucket_lock = rht_bucket_lock(old_tbl, old_hash);
 
 	spin_lock_bh(old_bucket_lock);
 	while (!rhashtable_rehash_one(ht, old_hash))
@@ -376,6 +308,37 @@ static void rht_deferred_worker(struct work_struct *work)
 	mutex_unlock(&ht->mutex);
 }
 
+int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
+			   struct rhash_head *obj,
+			   struct bucket_table *tbl)
+{
+	struct rhash_head *head;
+	unsigned hash;
+	int err = -EEXIST;
+
+	hash = head_hashfn(ht, tbl, obj);
+	spin_lock_nested(rht_bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
+
+	if (key && rhashtable_lookup_fast(ht, key, ht->p))
+		goto exit;
+
+	err = 0;
+
+	head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
+
+	RCU_INIT_POINTER(obj->next, head);
+
+	rcu_assign_pointer(tbl->buckets[hash], obj);
+
+	atomic_inc(&ht->nelems);
+
+exit:
+	spin_unlock(rht_bucket_lock(tbl, hash));
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(rhashtable_insert_slow);
+
 static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
 				bool (*compare)(void *, void *), void *arg)
 {
@@ -390,7 +353,7 @@ static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
 
 	old_tbl = rht_dereference_rcu(ht->tbl, ht);
 	hash = head_hashfn(ht, old_tbl, obj);
-	old_lock = bucket_lock(old_tbl, hash);
+	old_lock = rht_bucket_lock(old_tbl, hash);
 
 	spin_lock_bh(old_lock);
 
@@ -403,7 +366,8 @@ static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
 	tbl = rht_dereference_rcu(old_tbl->future_tbl, ht) ?: old_tbl;
 	if (tbl != old_tbl) {
 		hash = head_hashfn(ht, tbl, obj);
-		spin_lock_nested(bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
+		spin_lock_nested(rht_bucket_lock(tbl, hash),
+				 SINGLE_DEPTH_NESTING);
 	}
 
 	if (compare &&
@@ -430,7 +394,7 @@ static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
 
 exit:
 	if (tbl != old_tbl)
-		spin_unlock(bucket_lock(tbl, hash));
+		spin_unlock(rht_bucket_lock(tbl, hash));
 
 	spin_unlock_bh(old_lock);
 
@@ -471,7 +435,7 @@ static bool __rhashtable_remove(struct rhashtable *ht,
 	bool ret = false;
 
 	hash = head_hashfn(ht, tbl, obj);
-	lock = bucket_lock(tbl, hash);
+	lock = rht_bucket_lock(tbl, hash);
 
 	spin_lock_bh(lock);
 
@@ -537,19 +501,6 @@ bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj)
 }
 EXPORT_SYMBOL_GPL(rhashtable_remove);
 
-struct rhashtable_compare_arg {
-	struct rhashtable *ht;
-	const void *key;
-};
-
-static bool rhashtable_compare(void *ptr, void *arg)
-{
-	struct rhashtable_compare_arg *x = arg;
-	struct rhashtable *ht = x->ht;
-
-	return !memcmp(ptr + ht->p.key_offset, x->key, ht->p.key_len);
-}
-
 /**
  * rhashtable_lookup - lookup key in hash table
  * @ht:		hash table
@@ -565,14 +516,7 @@ static bool rhashtable_compare(void *ptr, void *arg)
  */
 void *rhashtable_lookup(struct rhashtable *ht, const void *key)
 {
-	struct rhashtable_compare_arg arg = {
-		.ht = ht,
-		.key = key,
-	};
-
-	BUG_ON(!ht->p.key_len);
-
-	return rhashtable_lookup_compare(ht, key, &rhashtable_compare, &arg);
+	return rhashtable_lookup_fast(ht, key, ht->p);
 }
 EXPORT_SYMBOL_GPL(rhashtable_lookup);
 
@@ -591,7 +535,8 @@ EXPORT_SYMBOL_GPL(rhashtable_lookup);
  * Returns the first entry on which the compare function returned true.
  */
 void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key,
-				bool (*compare)(void *, void *), void *arg)
+				bool (*compare)(void *, void *),
+				void *arg)
 {
 	const struct bucket_table *tbl;
 	struct rhash_head *he;
@@ -601,7 +546,7 @@ void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key,
 
 	tbl = rht_dereference_rcu(ht->tbl, ht);
 restart:
-	hash = key_hashfn(ht, tbl, key);
+	hash = rht_key_hashfn(ht, tbl, key, ht->p);
 	rht_for_each_rcu(he, tbl, hash) {
 		if (!compare(rht_obj(ht, he), arg))
 			continue;
@@ -643,15 +588,7 @@ EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);
  */
 bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj)
 {
-	struct rhashtable_compare_arg arg = {
-		.ht = ht,
-		.key = rht_obj(ht, obj) + ht->p.key_offset,
-	};
-
-	BUG_ON(!ht->p.key_len);
-
-	return rhashtable_lookup_compare_insert(ht, obj, &rhashtable_compare,
-						&arg);
+	return rhashtable_lookup_insert_fast(ht, obj, ht->p);
 }
 EXPORT_SYMBOL_GPL(rhashtable_lookup_insert);
 
@@ -927,8 +864,8 @@ int rhashtable_init(struct rhashtable *ht,
 
 	size = HASH_DEFAULT_SIZE;
 
-	if ((params->key_len && !params->hashfn) ||
-	    (!params->key_len && !params->obj_hashfn))
+	if ((!(params->key_len && params->hashfn) && !params->obj_hashfn) ||
+	    (params->obj_hashfn && !params->obj_cmpfn))
 		return -EINVAL;
 
 	if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))