rhashtable: Add immediate rehash during insertion
This patch reintroduces immediate rehash during insertion. If
we find during insertion that the table is full or the chain
length exceeds a set limit (currently 16 but may be disabled
with insecure_elasticity) then we will force an immediate rehash.
The rehash will contain an expansion if the table utilisation
exceeds 75%.
If this rehash fails then the insertion will fail. Otherwise the
insertion will be reattempted in the new hash table.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index e8ffcdb..f9ecf32 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -103,6 +103,7 @@
* @max_size: Maximum size while expanding
* @min_size: Minimum size while shrinking
* @nulls_base: Base value to generate nulls marker
+ * @insecure_elasticity: Set to true to disable chain length checks
* @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
@@ -116,6 +117,7 @@
unsigned int max_size;
unsigned int min_size;
u32 nulls_base;
+ bool insecure_elasticity;
size_t locks_mul;
rht_hashfn_t hashfn;
rht_obj_hashfn_t obj_hashfn;
@@ -127,6 +129,7 @@
* @tbl: Bucket table
* @nelems: Number of elements in table
* @key_len: Key length for hashfn
+ * @elasticity: Maximum chain length before rehash
* @p: Configuration parameters
* @run_work: Deferred worker to expand/shrink asynchronously
* @mutex: Mutex to protect current/future table swapping
@@ -137,6 +140,7 @@
atomic_t nelems;
bool being_destroyed;
unsigned int key_len;
+ unsigned int elasticity;
struct rhashtable_params p;
struct work_struct run_work;
struct mutex mutex;
@@ -266,6 +270,17 @@
tbl->size > ht->p.min_size;
}
+/**
+ * rht_grow_above_100 - returns true if nelems > table-size
+ * @ht: hash table
+ * @tbl: current table
+ */
+static inline bool rht_grow_above_100(const struct rhashtable *ht,
+ const struct bucket_table *tbl)
+{
+ return atomic_read(&ht->nelems) > tbl->size;
+}
+
/* The bucket lock is selected based on the hash and protects mutations
* on a group of hash buckets.
*
@@ -307,6 +322,7 @@
int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
struct rhash_head *obj,
struct bucket_table *old_tbl);
+int rhashtable_insert_rehash(struct rhashtable *ht);
int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter);
void rhashtable_walk_exit(struct rhashtable_iter *iter);
@@ -529,12 +545,14 @@
.ht = ht,
.key = key,
};
- int err = -EEXIST;
struct bucket_table *tbl, *new_tbl;
struct rhash_head *head;
spinlock_t *lock;
+ unsigned elasticity;
unsigned hash;
+ int err;
+restart:
rcu_read_lock();
tbl = rht_dereference_rcu(ht->tbl, ht);
@@ -557,20 +575,34 @@
new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
if (unlikely(new_tbl)) {
err = rhashtable_insert_slow(ht, key, obj, new_tbl);
+ if (err == -EAGAIN)
+ goto slow_path;
goto out;
}
- if (!key)
- goto skip_lookup;
+ if (unlikely(rht_grow_above_100(ht, tbl))) {
+slow_path:
+ spin_unlock_bh(lock);
+ rcu_read_unlock();
+ err = rhashtable_insert_rehash(ht);
+ if (err)
+ return err;
+ goto restart;
+ }
+
+ err = -EEXIST;
+ elasticity = ht->elasticity;
rht_for_each(head, tbl, hash) {
- if (unlikely(!(params.obj_cmpfn ?
+ if (key &&
+ unlikely(!(params.obj_cmpfn ?
params.obj_cmpfn(&arg, rht_obj(ht, head)) :
rhashtable_compare(&arg, rht_obj(ht, head)))))
goto out;
+ if (!--elasticity)
+ goto slow_path;
}
-skip_lookup:
err = 0;
head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 220a11a..7686c1e 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -375,21 +375,76 @@
schedule_work(&ht->run_work);
}
+static bool rhashtable_check_elasticity(struct rhashtable *ht,
+ struct bucket_table *tbl,
+ unsigned hash)
+{
+ unsigned elasticity = ht->elasticity;
+ struct rhash_head *head;
+
+ rht_for_each(head, tbl, hash)
+ if (!--elasticity)
+ return true;
+
+ return false;
+}
+
+int rhashtable_insert_rehash(struct rhashtable *ht)
+{
+ struct bucket_table *old_tbl;
+ struct bucket_table *new_tbl;
+ struct bucket_table *tbl;
+ unsigned int size;
+ int err;
+
+ old_tbl = rht_dereference_rcu(ht->tbl, ht);
+ tbl = rhashtable_last_table(ht, old_tbl);
+
+ size = tbl->size;
+
+ if (rht_grow_above_75(ht, tbl))
+ size *= 2;
+ /* More than two rehashes (not resizes) detected. */
+ else if (WARN_ON(old_tbl != tbl && old_tbl->size == size))
+ return -EBUSY;
+
+ new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC);
+ if (new_tbl == NULL)
+ return -ENOMEM;
+
+ err = rhashtable_rehash_attach(ht, tbl, new_tbl);
+ if (err) {
+ bucket_table_free(new_tbl);
+ if (err == -EEXIST)
+ err = 0;
+ } else
+ schedule_work(&ht->run_work);
+
+ return err;
+}
+EXPORT_SYMBOL_GPL(rhashtable_insert_rehash);
+
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;
+ int err;
tbl = rhashtable_last_table(ht, tbl);
hash = head_hashfn(ht, tbl, obj);
spin_lock_nested(rht_bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
+ err = -EEXIST;
if (key && rhashtable_lookup_fast(ht, key, ht->p))
goto exit;
+ err = -EAGAIN;
+ if (rhashtable_check_elasticity(ht, tbl, hash) ||
+ rht_grow_above_100(ht, tbl))
+ goto exit;
+
err = 0;
head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
@@ -678,6 +733,9 @@
ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
+ if (!params->insecure_elasticity)
+ ht->elasticity = 16;
+
if (params->locks_mul)
ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
else
