From f89bd6f87a53ce5a7d60662429591ebac2745c10 Mon Sep 17 00:00:00 2001 From: Thomas Graf Date: Fri, 2 Jan 2015 23:00:21 +0100 Subject: 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 Signed-off-by: David S. Miller --- lib/rhashtable.c | 37 ++++++++++++++++++++++++++++++------- 1 file changed, 30 insertions(+), 7 deletions(-) (limited to 'lib') diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 312e3437c7bc..cbad192d3b3d 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 @@ static u32 obj_raw_hashfn(const struct rhashtable *ht, const void *ptr) 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 @@ static u32 key_hashfn(struct rhashtable *ht, const void *key, u32 len) 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 @@ static struct rhash_head __rcu **bucket_tail(struct bucket_table *tbl, u32 n) 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 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht, { 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 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht, return NULL; } + for (i = 0; i < nbuckets; i++) + INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i); + return tbl; } @@ -221,7 +229,7 @@ static void hashtable_chain_unzip(const struct rhashtable *ht, /* 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 @@ static void hashtable_chain_unzip(const struct rhashtable *ht, /* 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 @@ int rhashtable_expand(struct rhashtable *ht) */ 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 @@ static void rht_deferred_worker(struct work_struct *work) 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 @@ void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj) 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 @@ static size_t rounded_hashtable_size(struct rhashtable_params *params) * .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 @@ int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params) (!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 @@ static int __init test_rht_init(void) .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, }; -- cgit v1.2.3