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Date: Sat, 31 Jan 2015 21:23:29 +1100
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org
Subject: [RFC] rhashtable: rhashtable_rehash
Here is a totally untested patch that illustrates what I want to
do with rehash.
Note that this depends on the hash rnd patch I just sent.
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 4c3da1f..ebd5e44 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -79,9 +79,9 @@ static u32 rht_bucket_index(const struct bucket_table *tbl, u32 hash)
return hash & (tbl->size - 1);
}
-static u32 obj_raw_hashfn(const struct rhashtable *ht, const void *ptr)
+static u32 obj_raw_hashfn(const struct rhashtable *ht,
+ struct bucket_table *tbl, const void *ptr)
{
- struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
u32 hash;
if (unlikely(!ht->p.key_len))
@@ -93,9 +93,9 @@ static u32 obj_raw_hashfn(const struct rhashtable *ht, const void *ptr)
return hash >> HASH_RESERVED_SPACE;
}
-static u32 key_hashfn(struct rhashtable *ht, const void *key, u32 len)
+static u32 key_hashfn(struct rhashtable *ht, struct bucket_table *tbl,
+ const void *key, u32 len)
{
- struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
u32 hash;
hash = ht->p.hashfn(key, len, tbl->hash_rnd);
@@ -295,6 +295,89 @@ static void link_old_to_new(struct bucket_table *new_tbl,
spin_unlock_bh(new_bucket_lock);
}
+static void rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
+{
+ struct *old_tbl = rht_dereference(ht->tbl, ht);
+ struct *new_tbl = rht_dereference(ht->future_tbl, ht);
+ struct rhash_head *head, *next, *entry;
+ struct rhash_head __rcu **pprev;
+ spinlock_t *new_bucket_lock;
+ unsigned int new_hash;
+
+ pprev = &old_tbl->buckets[old_hash];
+ rht_for_each(entry, old_tbl, old_hash) {
+ next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
+
+ if (rht_is_a_nulls(next))
+ break;
+
+ pprev = &entry->next;
+ }
+
+ new_hash = head_hashfn(ht, new_tbl, entry);
+
+ new_bucket_lock = bucket_lock(new_tbl, new_hash);
+
+ spin_lock(new_bucket_lock);
+ head = rht_dereference_bucket(new_tbl->buckets[new_hash],
+ new_tbl, new_hash);
+
+ if (rht_is_a_nulls(head))
+ INIT_RHT_NULLS_HEAD(entry->next, ht, hash);
+ else
+ RCU_INIT_POINTER(entry->next, head);
+
+ rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
+ spin_unlock(new_bucket_lock);
+
+ rcu_assign_pointer(*pprev, next);
+}
+
+static void rhashtable_rehash_chain(struct rhashtable *ht,
+ unsigned int old_hash)
+{
+ struct *old_tbl = rht_dereference(ht->tbl, ht);
+ spinlock_t *old_bucket_lock;
+
+ old_bucket_lock = bucket_lock(old_tbl, old_hash);
+
+ spin_lock_bh(old_bucket_lock);
+ while (!rht_is_a_nulls(rht_dereference_bucket(
+ old_tbl->buckets[old_hash], old_tbl, old_hash)))
+ rhashtable_rehash_one(ht, old_hash);
+ spin_unlock_bh(old_bucket_lock);
+}
+
+static void rhashtable_rehash(struct rhashtable *ht,
+ struct bucket_table *new_tbl)
+{
+ struct *old_tbl = rht_dereference(ht->tbl, ht);
+
+ get_random_bytes(&new_tbl->hash_rnd, sizeof(new_tbl->hash_rnd));
+
+ /* Make insertions go into the new, empty table right away. Deletions
+ * and lookups will be attempted in both tables until we synchronize.
+ * The synchronize_rcu() guarantees for the new table to be picked up
+ * so no new additions go into the old table while we relink.
+ */
+ rcu_assign_pointer(ht->future_tbl, new_tbl);
+ synchronize_rcu();
+
+ for (old_hash = 0; i < old_tbl->size; old_hash++)
+ rhashtable_rehash_chain(ht, old_hash);
+
+ /* Publish the new table pointer. */
+ rcu_assign_pointer(ht->tbl, new_tbl);
+
+ /* Wait for readers. All new readers will see the new
+ * table, and thus no references to the old table will
+ * remain.
+ */
+ synchronize_rcu();
+
+ bucket_table_free(old_tbl);
+}
+
/**
* rhashtable_expand - Expand hash table while allowing concurrent lookups
* @ht: the hash table to expand
@@ -327,72 +410,8 @@ int rhashtable_expand(struct rhashtable *ht)
atomic_inc(&ht->shift);
- /* Make insertions go into the new, empty table right away. Deletions
- * and lookups will be attempted in both tables until we synchronize.
- * The synchronize_rcu() guarantees for the new table to be picked up
- * so no new additions go into the old table while we relink.
- */
- rcu_assign_pointer(ht->future_tbl, new_tbl);
- synchronize_rcu();
-
- /* For each new bucket, search the corresponding old bucket for the
- * first entry that hashes to the new bucket, and link the end of
- * newly formed bucket chain (containing entries added to future
- * table) to that entry. Since all the entries which will end up in
- * the new bucket appear in the same old bucket, this constructs an
- * entirely valid new hash table, but with multiple buckets
- * "zipped" together into a single imprecise chain.
- */
- for (new_hash = 0; new_hash < new_tbl->size; new_hash++) {
- old_hash = rht_bucket_index(old_tbl, new_hash);
- old_bucket_lock = bucket_lock(old_tbl, old_hash);
-
- spin_lock_bh(old_bucket_lock);
- rht_for_each(he, old_tbl, old_hash) {
- if (head_hashfn(ht, new_tbl, he) == new_hash) {
- link_old_to_new(new_tbl, new_hash, he);
- break;
- }
- }
- spin_unlock_bh(old_bucket_lock);
- }
-
- /* Publish the new table pointer. Lookups may now traverse
- * the new table, but they will not benefit from any
- * additional efficiency until later steps unzip the buckets.
- */
- rcu_assign_pointer(ht->tbl, new_tbl);
-
- /* Unzip interleaved hash chains */
- while (!complete && !ht->being_destroyed) {
- /* Wait for readers. All new readers will see the new
- * table, and thus no references to the old table will
- * remain.
- */
- synchronize_rcu();
-
- /* For each bucket in the old table (each of which
- * contains items from multiple buckets of the new
- * table): ...
- */
- complete = true;
- for (old_hash = 0; old_hash < old_tbl->size; old_hash++) {
- struct rhash_head *head;
-
- old_bucket_lock = bucket_lock(old_tbl, old_hash);
- spin_lock_bh(old_bucket_lock);
-
- hashtable_chain_unzip(ht, new_tbl, old_tbl, old_hash);
- head = rht_dereference_bucket(old_tbl->buckets[old_hash],
- old_tbl, old_hash);
- if (!rht_is_a_nulls(head))
- complete = false;
-
- spin_unlock_bh(old_bucket_lock);
- }
- }
+ rhashtable_rehash(ht, new_tbl);
- bucket_table_free(old_tbl);
return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_expand);
@@ -425,57 +444,7 @@ int rhashtable_shrink(struct rhashtable *ht)
if (new_tbl == NULL)
return -ENOMEM;
- rcu_assign_pointer(ht->future_tbl, new_tbl);
- synchronize_rcu();
-
- /* Link the first entry in the old bucket to the end of the
- * bucket in the new table. As entries are concurrently being
- * added to the new table, lock down the new bucket. As we
- * always divide the size in half when shrinking, each bucket
- * in the new table maps to exactly two buckets in the old
- * table.
- *
- * As removals can occur concurrently on the old table, we need
- * to lock down both matching buckets in the old table.
- */
- for (new_hash = 0; new_hash < new_tbl->size; new_hash++) {
- old_bucket_lock1 = bucket_lock(tbl, new_hash);
- old_bucket_lock2 = bucket_lock(tbl, new_hash + new_tbl->size);
- new_bucket_lock = bucket_lock(new_tbl, new_hash);
-
- spin_lock_bh(old_bucket_lock1);
-
- /* Depending on the lock per buckets mapping, the bucket in
- * the lower and upper region may map to the same lock.
- */
- if (old_bucket_lock1 != old_bucket_lock2) {
- spin_lock_bh_nested(old_bucket_lock2, RHT_LOCK_NESTED);
- spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED2);
- } else {
- spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED);
- }
-
- rcu_assign_pointer(*bucket_tail(new_tbl, new_hash),
- tbl->buckets[new_hash]);
- rcu_assign_pointer(*bucket_tail(new_tbl, new_hash),
- tbl->buckets[new_hash + new_tbl->size]);
-
- spin_unlock_bh(new_bucket_lock);
- if (old_bucket_lock1 != old_bucket_lock2)
- spin_unlock_bh(old_bucket_lock2);
- spin_unlock_bh(old_bucket_lock1);
- }
-
- /* Publish the new, valid hash table */
- rcu_assign_pointer(ht->tbl, new_tbl);
- atomic_dec(&ht->shift);
-
- /* Wait for readers. No new readers will have references to the
- * old hash table.
- */
- synchronize_rcu();
-
- bucket_table_free(tbl);
+ rhashtable_rehash(ht, new_tbl);
return 0;
}
Cheers,
--
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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