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Commit db304854 authored by Ying Xue's avatar Ying Xue Committed by David S. Miller
Browse files

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: default avatarYing Xue <ying.xue@windriver.com>
Signed-off-by: default avatarThomas Graf <tgraf@suug.ch>
Acked-by: default avatarThomas Graf <tgraf@suug.ch>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 54c5b7d3

include/linux/rhashtable.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

lib/rhashtable.c

+82 −15
Original line number Diff line number Diff line
@@ -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 @@ void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key, 
}

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),