rhashtable: Supports for nulls marker
In order to allow for wider usage of rhashtable, use a special nulls
marker to terminate each chain. The reason for not using the existing
nulls_list is that the prev pointer usage would not be valid as entries
can be linked in two different buckets at the same time.
The 4 nulls base bits can be set through the rhashtable_params structure
like this:
struct rhashtable_params params = {
[...]
.nulls_base = (1U << RHT_BASE_SHIFT),
};
This reduces the hash length from 32 bits to 27 bits.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 312e343..cbad192 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -28,6 +28,9 @@
#define HASH_MIN_SIZE 4UL
#define BUCKET_LOCKS_PER_CPU 128UL
+/* Base bits plus 1 bit for nulls marker */
+#define HASH_RESERVED_SPACE (RHT_BASE_BITS + 1)
+
enum {
RHT_LOCK_NORMAL,
RHT_LOCK_NESTED,
@@ -86,7 +89,7 @@
hash = ht->p.hashfn(ptr + ht->p.key_offset, ht->p.key_len,
ht->p.hash_rnd);
- return hash;
+ return hash >> HASH_RESERVED_SPACE;
}
static u32 key_hashfn(struct rhashtable *ht, const void *key, u32 len)
@@ -95,6 +98,7 @@
u32 hash;
hash = ht->p.hashfn(key, len, ht->p.hash_rnd);
+ hash >>= HASH_RESERVED_SPACE;
return rht_bucket_index(tbl, hash);
}
@@ -111,7 +115,7 @@
struct rhash_head __rcu **pprev;
for (pprev = &tbl->buckets[n];
- rht_dereference_bucket(*pprev, tbl, n);
+ !rht_is_a_nulls(rht_dereference_bucket(*pprev, tbl, n));
pprev = &rht_dereference_bucket(*pprev, tbl, n)->next)
;
@@ -164,6 +168,7 @@
{
struct bucket_table *tbl;
size_t size;
+ int i;
size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
tbl = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
@@ -180,6 +185,9 @@
return NULL;
}
+ for (i = 0; i < nbuckets; i++)
+ INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
+
return tbl;
}
@@ -221,7 +229,7 @@
/* Old bucket empty, no work needed. */
p = rht_dereference_bucket(old_tbl->buckets[old_hash], old_tbl,
old_hash);
- if (!p)
+ if (rht_is_a_nulls(p))
return;
new_hash = new_hash2 = head_hashfn(ht, new_tbl, p);
@@ -252,8 +260,8 @@
/* Find the subsequent node which does hash to the same
* bucket as node P, or NULL if no such node exists.
*/
- next = NULL;
- if (he) {
+ INIT_RHT_NULLS_HEAD(next, ht, old_hash);
+ if (!rht_is_a_nulls(he)) {
rht_for_each_continue(he, he->next, old_tbl, old_hash) {
if (head_hashfn(ht, new_tbl, he) == new_hash) {
next = he;
@@ -369,11 +377,15 @@
*/
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);
- if (old_tbl->buckets[old_hash] != NULL)
+ 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);
@@ -498,6 +510,7 @@
void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj)
{
struct bucket_table *tbl;
+ struct rhash_head *head;
spinlock_t *lock;
unsigned hash;
@@ -508,7 +521,12 @@
lock = bucket_lock(tbl, hash);
spin_lock_bh(lock);
- RCU_INIT_POINTER(obj->next, tbl->buckets[hash]);
+ head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
+ if (rht_is_a_nulls(head))
+ INIT_RHT_NULLS_HEAD(obj->next, ht, hash);
+ else
+ RCU_INIT_POINTER(obj->next, head);
+
rcu_assign_pointer(tbl->buckets[hash], obj);
spin_unlock_bh(lock);
@@ -709,6 +727,7 @@
* .key_offset = offsetof(struct test_obj, key),
* .key_len = sizeof(int),
* .hashfn = jhash,
+ * .nulls_base = (1U << RHT_BASE_SHIFT),
* };
*
* Configuration Example 2: Variable length keys
@@ -741,6 +760,9 @@
(!params->key_len && !params->obj_hashfn))
return -EINVAL;
+ if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
+ return -EINVAL;
+
params->min_shift = max_t(size_t, params->min_shift,
ilog2(HASH_MIN_SIZE));
@@ -974,6 +996,7 @@
.key_offset = offsetof(struct test_obj, value),
.key_len = sizeof(int),
.hashfn = jhash,
+ .nulls_base = (3U << RHT_BASE_SHIFT),
.grow_decision = rht_grow_above_75,
.shrink_decision = rht_shrink_below_30,
};