rhashtable: Disable automatic shrinking by default

Introduce a new bool automatic_shrinking to require the
user to explicitly opt-in to automatic shrinking of tables.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/rhashtable.h

@@ -2,7 +2,7 @@
  * Resizable, Scalable, Concurrent Hash Table
  *
  * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
- * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch>
+ * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
  * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
  *
  * Code partially derived from nft_hash
@@ -104,6 +104,7 @@ struct rhashtable;
  * @min_size: Minimum size while shrinking
  * @nulls_base: Base value to generate nulls marker
  * @insecure_elasticity: Set to true to disable chain length checks
+ * @automatic_shrinking: Enable automatic shrinking of tables
  * @locks_mul: Number of bucket locks to allocate per cpu (default: 128)
  * @hashfn: Hash function (default: jhash2 if !(key_len % 4), or jhash)
  * @obj_hashfn: Function to hash object
@@ -118,6 +119,7 @@ struct rhashtable_params {
 	unsigned int		min_size;
 	u32			nulls_base;
 	bool			insecure_elasticity;
+	bool			automatic_shrinking;
 	size_t			locks_mul;
 	rht_hashfn_t		hashfn;
 	rht_obj_hashfn_t	obj_hashfn;
@@ -784,7 +786,8 @@ static inline int rhashtable_remove_fast(
 		goto out;
 
 	atomic_dec(&ht->nelems);
-	if (rht_shrink_below_30(ht, tbl))
+	if (unlikely(ht->p.automatic_shrinking &&
+		     rht_shrink_below_30(ht, tbl)))
 		schedule_work(&ht->run_work);
 
 out:

lib/rhashtable.c

@@ -367,7 +367,7 @@ static void rht_deferred_worker(struct work_struct *work)
 
 	if (rht_grow_above_75(ht, tbl))
 		rhashtable_expand(ht);
-	else if (rht_shrink_below_30(ht, tbl))
+	else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl))
 		rhashtable_shrink(ht);
 
 	err = rhashtable_rehash_table(ht);

net/netfilter/nft_hash.c

@@ -172,6 +172,7 @@ static const struct rhashtable_params nft_hash_params = {
 	.head_offset = offsetof(struct nft_hash_elem, node),
 	.key_offset = offsetof(struct nft_hash_elem, key),
 	.hashfn = jhash,
+	.automatic_shrinking = true,
 };
 
 static int nft_hash_init(const struct nft_set *set,

net/netlink/af_netlink.c

@@ -3142,6 +3142,7 @@ static const struct rhashtable_params netlink_rhashtable_params = {
 	.obj_hashfn = netlink_hash,
 	.obj_cmpfn = netlink_compare,
 	.max_size = 65536,
+	.automatic_shrinking = true,
 };
 
 static int __init netlink_proto_init(void)

net/tipc/socket.c

@@ -2297,6 +2297,7 @@ static const struct rhashtable_params tsk_rht_params = {
 	.key_len = sizeof(u32), /* portid */
 	.max_size = 1048576,
 	.min_size = 256,
+	.automatic_shrinking = true,
 };
 
 int tipc_sk_rht_init(struct net *net)