/*
* Resizable, Scalable, Concurrent Hash Table
*
- * 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>
*
* Based on the following paper:
enum {
RHT_LOCK_NORMAL,
RHT_LOCK_NESTED,
- RHT_LOCK_NESTED2,
};
/* 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.
nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);
- /* Never allocate more than one lock per bucket */
- size = min_t(unsigned int, size, tbl->size);
+ /* Never allocate more than 0.5 locks per bucket */
+ size = min_t(unsigned int, size, tbl->size >> 1);
if (sizeof(spinlock_t) != 0) {
#ifdef CONFIG_NUMA
}
EXPORT_SYMBOL_GPL(rht_shrink_below_30);
-static void hashtable_chain_unzip(const struct rhashtable *ht,
+static void lock_buckets(struct bucket_table *new_tbl,
+ struct bucket_table *old_tbl, unsigned int hash)
+ __acquires(old_bucket_lock)
+{
+ spin_lock_bh(bucket_lock(old_tbl, hash));
+ if (new_tbl != old_tbl)
+ spin_lock_bh_nested(bucket_lock(new_tbl, hash),
+ RHT_LOCK_NESTED);
+}
+
+static void unlock_buckets(struct bucket_table *new_tbl,
+ struct bucket_table *old_tbl, unsigned int hash)
+ __releases(old_bucket_lock)
+{
+ if (new_tbl != old_tbl)
+ spin_unlock_bh(bucket_lock(new_tbl, hash));
+ spin_unlock_bh(bucket_lock(old_tbl, hash));
+}
+
+/**
+ * Unlink entries on bucket which hash to different bucket.
+ *
+ * Returns true if no more work needs to be performed on the bucket.
+ */
+static bool hashtable_chain_unzip(const struct rhashtable *ht,
const struct bucket_table *new_tbl,
struct bucket_table *old_tbl,
size_t old_hash)
{
struct rhash_head *he, *p, *next;
- spinlock_t *new_bucket_lock, *new_bucket_lock2 = NULL;
unsigned int new_hash, new_hash2;
ASSERT_BUCKET_LOCK(old_tbl, old_hash);
p = rht_dereference_bucket(old_tbl->buckets[old_hash], old_tbl,
old_hash);
if (rht_is_a_nulls(p))
- return;
+ return false;
- new_hash = new_hash2 = head_hashfn(ht, new_tbl, p);
- new_bucket_lock = bucket_lock(new_tbl, new_hash);
+ new_hash = head_hashfn(ht, new_tbl, p);
+ ASSERT_BUCKET_LOCK(new_tbl, new_hash);
/* Advance the old bucket pointer one or more times until it
* reaches a node that doesn't hash to the same bucket as the
*/
rht_for_each_continue(he, p->next, old_tbl, old_hash) {
new_hash2 = head_hashfn(ht, new_tbl, he);
+ ASSERT_BUCKET_LOCK(new_tbl, new_hash2);
+
if (new_hash != new_hash2)
break;
p = he;
}
rcu_assign_pointer(old_tbl->buckets[old_hash], p->next);
- spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED);
-
- /* If we have encountered an entry that maps to a different bucket in
- * the new table, lock down that bucket as well as we might cut off
- * the end of the chain.
- */
- new_bucket_lock2 = bucket_lock(new_tbl, new_hash);
- if (new_bucket_lock != new_bucket_lock2)
- spin_lock_bh_nested(new_bucket_lock2, RHT_LOCK_NESTED2);
-
/* Find the subsequent node which does hash to the same
* bucket as node P, or NULL if no such node exists.
*/
*/
rcu_assign_pointer(p->next, next);
- if (new_bucket_lock != new_bucket_lock2)
- spin_unlock_bh(new_bucket_lock2);
- spin_unlock_bh(new_bucket_lock);
+ p = rht_dereference_bucket(old_tbl->buckets[old_hash], old_tbl,
+ old_hash);
+
+ return !rht_is_a_nulls(p);
}
static void link_old_to_new(struct bucket_table *new_tbl,
unsigned int new_hash, struct rhash_head *entry)
{
- spinlock_t *new_bucket_lock;
-
- new_bucket_lock = bucket_lock(new_tbl, new_hash);
-
- spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED);
rcu_assign_pointer(*bucket_tail(new_tbl, new_hash), entry);
- spin_unlock_bh(new_bucket_lock);
}
/**
{
struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
struct rhash_head *he;
- spinlock_t *old_bucket_lock;
unsigned int new_hash, old_hash;
bool complete = false;
*/
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);
+ lock_buckets(new_tbl, old_tbl, new_hash);
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);
+ unlock_buckets(new_tbl, old_tbl, new_hash);
}
/* Publish the new table pointer. Lookups may now traverse
*/
complete = true;
for (old_hash = 0; old_hash < old_tbl->size; old_hash++) {
- struct rhash_head *head;
+ lock_buckets(new_tbl, old_tbl, old_hash);
- 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))
+ if (hashtable_chain_unzip(ht, new_tbl, old_tbl,
+ old_hash))
complete = false;
- spin_unlock_bh(old_bucket_lock);
+ unlock_buckets(new_tbl, old_tbl, old_hash);
}
}
int rhashtable_shrink(struct rhashtable *ht)
{
struct bucket_table *new_tbl, *tbl = rht_dereference(ht->tbl, ht);
- spinlock_t *new_bucket_lock, *old_bucket_lock1, *old_bucket_lock2;
unsigned int new_hash;
ASSERT_RHT_MUTEX(ht);
* 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);
- }
+ lock_buckets(new_tbl, tbl, new_hash);
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);
+ unlock_buckets(new_tbl, tbl, new_hash);
}
/* Publish the new, valid hash table */
*/
void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj)
{
- struct bucket_table *tbl;
- spinlock_t *lock;
+ struct bucket_table *tbl, *old_tbl;
unsigned hash;
rcu_read_lock();
tbl = rht_dereference_rcu(ht->future_tbl, ht);
+ old_tbl = rht_dereference_rcu(ht->tbl, ht);
hash = head_hashfn(ht, tbl, obj);
- lock = bucket_lock(tbl, hash);
- spin_lock_bh(lock);
+ lock_buckets(tbl, old_tbl, hash);
__rhashtable_insert(ht, obj, tbl, hash);
- spin_unlock_bh(lock);
+ unlock_buckets(tbl, old_tbl, hash);
rcu_read_unlock();
}
*/
bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj)
{
- struct bucket_table *tbl;
+ struct bucket_table *tbl, *new_tbl, *old_tbl;
struct rhash_head __rcu **pprev;
struct rhash_head *he;
- spinlock_t *lock;
- unsigned int hash;
+ unsigned int hash, new_hash;
bool ret = false;
rcu_read_lock();
- tbl = rht_dereference_rcu(ht->tbl, ht);
- hash = head_hashfn(ht, tbl, obj);
-
- lock = bucket_lock(tbl, hash);
- spin_lock_bh(lock);
+ tbl = old_tbl = rht_dereference_rcu(ht->tbl, ht);
+ new_tbl = rht_dereference_rcu(ht->future_tbl, ht);
+ new_hash = head_hashfn(ht, new_tbl, obj);
+ lock_buckets(new_tbl, old_tbl, new_hash);
restart:
+ hash = rht_bucket_index(tbl, new_hash);
pprev = &tbl->buckets[hash];
rht_for_each(he, tbl, hash) {
if (he != obj) {
* resizing. Thus traversing both is fine and the added cost is
* very rare.
*/
- if (tbl != rht_dereference_rcu(ht->future_tbl, ht)) {
- spin_unlock_bh(lock);
-
- tbl = rht_dereference_rcu(ht->future_tbl, ht);
- hash = head_hashfn(ht, tbl, obj);
-
- lock = bucket_lock(tbl, hash);
- spin_lock_bh(lock);
+ if (tbl != new_tbl) {
+ tbl = new_tbl;
goto restart;
}
- spin_unlock_bh(lock);
+ unlock_buckets(new_tbl, old_tbl, new_hash);
if (ret) {
atomic_dec(&ht->nelems);
void *arg)
{
struct bucket_table *new_tbl, *old_tbl;
- spinlock_t *new_bucket_lock, *old_bucket_lock;
- u32 new_hash, old_hash;
+ u32 new_hash;
bool success = true;
BUG_ON(!ht->p.key_len);
rcu_read_lock();
-
old_tbl = rht_dereference_rcu(ht->tbl, ht);
- old_hash = head_hashfn(ht, old_tbl, obj);
- old_bucket_lock = bucket_lock(old_tbl, old_hash);
- spin_lock_bh(old_bucket_lock);
-
new_tbl = rht_dereference_rcu(ht->future_tbl, ht);
new_hash = head_hashfn(ht, new_tbl, obj);
- new_bucket_lock = bucket_lock(new_tbl, new_hash);
- if (unlikely(old_tbl != new_tbl))
- spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED);
+
+ lock_buckets(new_tbl, old_tbl, new_hash);
if (rhashtable_lookup_compare(ht, rht_obj(ht, obj) + ht->p.key_offset,
compare, arg)) {
__rhashtable_insert(ht, obj, new_tbl, new_hash);
exit:
- if (unlikely(old_tbl != new_tbl))
- spin_unlock_bh(new_bucket_lock);
- spin_unlock_bh(old_bucket_lock);
-
+ unlock_buckets(new_tbl, old_tbl, new_hash);
rcu_read_unlock();
return success;
projects / users / dwmw2 / linux.git / commitdiff