From db30485408326a6f466a843b291b23535f63eda0 Mon Sep 17 00:00:00 2001 From: Ying Xue Date: Wed, 7 Jan 2015 13:41:54 +0800 Subject: [PATCH] rhashtable: involve rhashtable_lookup_insert routine Involve a new function called rhashtable_lookup_insert() which makes lookup and insertion atomic under bucket lock protection, helping us avoid to introduce an extra lock when we search and insert an object into hash table. Signed-off-by: Ying Xue Signed-off-by: Thomas Graf Acked-by: Thomas Graf Signed-off-by: David S. Miller --- include/linux/rhashtable.h | 1 + lib/rhashtable.c | 97 ++++++++++++++++++++++++++++++++------ 2 files changed, 83 insertions(+), 15 deletions(-) diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h index de1459c74c4d..73c913f31574 100644 --- a/include/linux/rhashtable.h +++ b/include/linux/rhashtable.h @@ -168,6 +168,7 @@ int rhashtable_shrink(struct rhashtable *ht); void *rhashtable_lookup(struct rhashtable *ht, const void *key); void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key, bool (*compare)(void *, void *), void *arg); +bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj); void rhashtable_destroy(struct rhashtable *ht); diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 20006854fce0..4430233c4e11 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -505,8 +505,26 @@ static void rhashtable_wakeup_worker(struct rhashtable *ht) schedule_delayed_work(&ht->run_work, 0); } +static void __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj, + struct bucket_table *tbl, u32 hash) +{ + struct rhash_head *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); + + atomic_inc(&ht->nelems); + + rhashtable_wakeup_worker(ht); +} + /** - * rhashtable_insert - insert object into hash hash table + * rhashtable_insert - insert object into hash table * @ht: hash table * @obj: pointer to hash head inside object * @@ -523,7 +541,6 @@ static void rhashtable_wakeup_worker(struct rhashtable *ht) void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj) { struct bucket_table *tbl; - struct rhash_head *head; spinlock_t *lock; unsigned hash; @@ -534,19 +551,9 @@ void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj) lock = bucket_lock(tbl, hash); spin_lock_bh(lock); - 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); + __rhashtable_insert(ht, obj, tbl, hash); spin_unlock_bh(lock); - atomic_inc(&ht->nelems); - - rhashtable_wakeup_worker(ht); - rcu_read_unlock(); } EXPORT_SYMBOL_GPL(rhashtable_insert); @@ -560,7 +567,7 @@ EXPORT_SYMBOL_GPL(rhashtable_insert); * walk the bucket chain upon removal. The removal operation is thus * considerable slow if the hash table is not correctly sized. * - * Will automatically shrink the table via rhashtable_expand() if the the + * Will automatically shrink the table via rhashtable_expand() if the * shrink_decision function specified at rhashtable_init() returns true. * * The caller must ensure that no concurrent table mutations occur. It is @@ -641,7 +648,7 @@ static bool rhashtable_compare(void *ptr, void *arg) * for a entry with an identical key. The first matching entry is returned. * * This lookup function may only be used for fixed key hash table (key_len - * paramter set). It will BUG() if used inappropriately. + * parameter set). It will BUG() if used inappropriately. * * Lookups may occur in parallel with hashtable mutations and resizing. */ @@ -702,6 +709,66 @@ restart: } EXPORT_SYMBOL_GPL(rhashtable_lookup_compare); +/** + * rhashtable_lookup_insert - lookup and insert object into hash table + * @ht: hash table + * @obj: pointer to hash head inside object + * + * Locks down the bucket chain in both the old and new table if a resize + * is in progress to ensure that writers can't remove from the old table + * and can't insert to the new table during the atomic operation of search + * and insertion. Searches for duplicates in both the old and new table if + * a resize is in progress. + * + * This lookup function may only be used for fixed key hash table (key_len + * parameter set). It will BUG() if used inappropriately. + * + * It is safe to call this function from atomic context. + * + * Will trigger an automatic deferred table resizing if the size grows + * beyond the watermark indicated by grow_decision() which can be passed + * to rhashtable_init(). + */ +bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj) +{ + struct bucket_table *new_tbl, *old_tbl; + spinlock_t *new_bucket_lock, *old_bucket_lock; + u32 new_hash, old_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); + + if (rhashtable_lookup(ht, rht_obj(ht, obj) + ht->p.key_offset)) { + success = false; + goto exit; + } + + __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); + + rcu_read_unlock(); + + return success; +} +EXPORT_SYMBOL_GPL(rhashtable_lookup_insert); + static size_t rounded_hashtable_size(struct rhashtable_params *params) { return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),