2 * Resizable, Scalable, Concurrent Hash Table
4 * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
5 * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
7 * Based on the following paper:
8 * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
10 * Code partially derived from nft_hash
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License version 2 as
14 * published by the Free Software Foundation.
17 #include <linux/kernel.h>
18 #include <linux/init.h>
19 #include <linux/log2.h>
20 #include <linux/sched.h>
21 #include <linux/slab.h>
22 #include <linux/vmalloc.h>
24 #include <linux/jhash.h>
25 #include <linux/random.h>
26 #include <linux/rhashtable.h>
27 #include <linux/err.h>
29 #define HASH_DEFAULT_SIZE 64UL
30 #define HASH_MIN_SIZE 4UL
31 #define BUCKET_LOCKS_PER_CPU 128UL
33 /* Base bits plus 1 bit for nulls marker */
34 #define HASH_RESERVED_SPACE (RHT_BASE_BITS + 1)
36 /* The bucket lock is selected based on the hash and protects mutations
37 * on a group of hash buckets.
39 * A maximum of tbl->size/2 bucket locks is allocated. This ensures that
40 * a single lock always covers both buckets which may both contains
41 * entries which link to the same bucket of the old table during resizing.
42 * This allows to simplify the locking as locking the bucket in both
43 * tables during resize always guarantee protection.
45 * IMPORTANT: When holding the bucket lock of both the old and new table
46 * during expansions and shrinking, the old bucket lock must always be
49 static spinlock_t *bucket_lock(const struct bucket_table *tbl, u32 hash)
51 return &tbl->locks[hash & tbl->locks_mask];
54 static void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he)
56 return (void *) he - ht->p.head_offset;
59 static u32 rht_bucket_index(const struct bucket_table *tbl, u32 hash)
61 return (hash >> HASH_RESERVED_SPACE) & (tbl->size - 1);
64 static u32 key_hashfn(struct rhashtable *ht, const struct bucket_table *tbl,
67 return rht_bucket_index(tbl, ht->p.hashfn(key, ht->p.key_len,
71 static u32 head_hashfn(struct rhashtable *ht,
72 const struct bucket_table *tbl,
73 const struct rhash_head *he)
75 const char *ptr = rht_obj(ht, he);
77 return likely(ht->p.key_len) ?
78 key_hashfn(ht, tbl, ptr + ht->p.key_offset) :
79 rht_bucket_index(tbl, ht->p.obj_hashfn(ptr, tbl->hash_rnd));
82 #ifdef CONFIG_PROVE_LOCKING
83 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
85 int lockdep_rht_mutex_is_held(struct rhashtable *ht)
87 return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
89 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
91 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
93 spinlock_t *lock = bucket_lock(tbl, hash);
95 return (debug_locks) ? lockdep_is_held(lock) : 1;
97 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
99 #define ASSERT_RHT_MUTEX(HT)
103 static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl)
105 unsigned int i, size;
106 #if defined(CONFIG_PROVE_LOCKING)
107 unsigned int nr_pcpus = 2;
109 unsigned int nr_pcpus = num_possible_cpus();
112 nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
113 size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);
115 /* Never allocate more than 0.5 locks per bucket */
116 size = min_t(unsigned int, size, tbl->size >> 1);
118 if (sizeof(spinlock_t) != 0) {
120 if (size * sizeof(spinlock_t) > PAGE_SIZE)
121 tbl->locks = vmalloc(size * sizeof(spinlock_t));
124 tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
128 for (i = 0; i < size; i++)
129 spin_lock_init(&tbl->locks[i]);
131 tbl->locks_mask = size - 1;
136 static void bucket_table_free(const struct bucket_table *tbl)
144 static void bucket_table_free_rcu(struct rcu_head *head)
146 bucket_table_free(container_of(head, struct bucket_table, rcu));
149 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
152 struct bucket_table *tbl = NULL;
156 size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
157 if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
158 tbl = kzalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY);
164 tbl->size = nbuckets;
165 tbl->shift = ilog2(nbuckets);
167 if (alloc_bucket_locks(ht, tbl) < 0) {
168 bucket_table_free(tbl);
172 INIT_LIST_HEAD(&tbl->walkers);
174 get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
176 for (i = 0; i < nbuckets; i++)
177 INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
183 * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
185 * @tbl: current table
187 static bool rht_grow_above_75(const struct rhashtable *ht,
188 const struct bucket_table *tbl)
190 /* Expand table when exceeding 75% load */
191 return atomic_read(&ht->nelems) > (tbl->size / 4 * 3) &&
192 (!ht->p.max_shift || tbl->shift < ht->p.max_shift);
196 * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
198 * @tbl: current table
200 static bool rht_shrink_below_30(const struct rhashtable *ht,
201 const struct bucket_table *tbl)
203 /* Shrink table beneath 30% load */
204 return atomic_read(&ht->nelems) < (tbl->size * 3 / 10) &&
205 tbl->shift > ht->p.min_shift;
208 static int rhashtable_rehash_one(struct rhashtable *ht, unsigned old_hash)
210 struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
211 struct bucket_table *new_tbl =
212 rht_dereference(old_tbl->future_tbl, ht) ?: old_tbl;
213 struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
215 struct rhash_head *head, *next, *entry;
216 spinlock_t *new_bucket_lock;
219 rht_for_each(entry, old_tbl, old_hash) {
221 next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
223 if (rht_is_a_nulls(next))
226 pprev = &entry->next;
232 new_hash = head_hashfn(ht, new_tbl, entry);
234 new_bucket_lock = bucket_lock(new_tbl, new_hash);
236 spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);
237 head = rht_dereference_bucket(new_tbl->buckets[new_hash],
240 if (rht_is_a_nulls(head))
241 INIT_RHT_NULLS_HEAD(entry->next, ht, new_hash);
243 RCU_INIT_POINTER(entry->next, head);
245 rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
246 spin_unlock(new_bucket_lock);
248 rcu_assign_pointer(*pprev, next);
254 static void rhashtable_rehash_chain(struct rhashtable *ht, unsigned old_hash)
256 struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
257 spinlock_t *old_bucket_lock;
259 old_bucket_lock = bucket_lock(old_tbl, old_hash);
261 spin_lock_bh(old_bucket_lock);
262 while (!rhashtable_rehash_one(ht, old_hash))
265 spin_unlock_bh(old_bucket_lock);
268 static void rhashtable_rehash(struct rhashtable *ht,
269 struct bucket_table *new_tbl)
271 struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
272 struct rhashtable_walker *walker;
275 /* Make insertions go into the new, empty table right away. Deletions
276 * and lookups will be attempted in both tables until we synchronize.
278 rcu_assign_pointer(old_tbl->future_tbl, new_tbl);
280 /* Ensure the new table is visible to readers. */
283 for (old_hash = 0; old_hash < old_tbl->size; old_hash++)
284 rhashtable_rehash_chain(ht, old_hash);
286 /* Publish the new table pointer. */
287 rcu_assign_pointer(ht->tbl, new_tbl);
289 list_for_each_entry(walker, &old_tbl->walkers, list)
292 /* Wait for readers. All new readers will see the new
293 * table, and thus no references to the old table will
296 call_rcu(&old_tbl->rcu, bucket_table_free_rcu);
300 * rhashtable_expand - Expand hash table while allowing concurrent lookups
301 * @ht: the hash table to expand
303 * A secondary bucket array is allocated and the hash entries are migrated.
305 * This function may only be called in a context where it is safe to call
306 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
308 * The caller must ensure that no concurrent resizing occurs by holding
311 * It is valid to have concurrent insertions and deletions protected by per
312 * bucket locks or concurrent RCU protected lookups and traversals.
314 int rhashtable_expand(struct rhashtable *ht)
316 struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
318 ASSERT_RHT_MUTEX(ht);
320 new_tbl = bucket_table_alloc(ht, old_tbl->size * 2);
324 rhashtable_rehash(ht, new_tbl);
327 EXPORT_SYMBOL_GPL(rhashtable_expand);
330 * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
331 * @ht: the hash table to shrink
333 * This function may only be called in a context where it is safe to call
334 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
336 * The caller must ensure that no concurrent resizing occurs by holding
339 * The caller must ensure that no concurrent table mutations take place.
340 * It is however valid to have concurrent lookups if they are RCU protected.
342 * It is valid to have concurrent insertions and deletions protected by per
343 * bucket locks or concurrent RCU protected lookups and traversals.
345 int rhashtable_shrink(struct rhashtable *ht)
347 struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
349 ASSERT_RHT_MUTEX(ht);
351 new_tbl = bucket_table_alloc(ht, old_tbl->size / 2);
355 rhashtable_rehash(ht, new_tbl);
358 EXPORT_SYMBOL_GPL(rhashtable_shrink);
360 static void rht_deferred_worker(struct work_struct *work)
362 struct rhashtable *ht;
363 struct bucket_table *tbl;
365 ht = container_of(work, struct rhashtable, run_work);
366 mutex_lock(&ht->mutex);
367 if (ht->being_destroyed)
370 tbl = rht_dereference(ht->tbl, ht);
372 if (rht_grow_above_75(ht, tbl))
373 rhashtable_expand(ht);
374 else if (rht_shrink_below_30(ht, tbl))
375 rhashtable_shrink(ht);
377 mutex_unlock(&ht->mutex);
380 static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
381 bool (*compare)(void *, void *), void *arg)
383 struct bucket_table *tbl, *old_tbl;
384 struct rhash_head *head;
385 bool no_resize_running;
391 old_tbl = rht_dereference_rcu(ht->tbl, ht);
392 hash = head_hashfn(ht, old_tbl, obj);
394 spin_lock_bh(bucket_lock(old_tbl, hash));
396 /* Because we have already taken the bucket lock in old_tbl,
397 * if we find that future_tbl is not yet visible then that
398 * guarantees all other insertions of the same entry will
399 * also grab the bucket lock in old_tbl because until the
400 * rehash completes ht->tbl won't be changed.
402 tbl = rht_dereference_rcu(old_tbl->future_tbl, ht) ?: old_tbl;
403 if (tbl != old_tbl) {
404 hash = head_hashfn(ht, tbl, obj);
405 spin_lock_nested(bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
409 rhashtable_lookup_compare(ht, rht_obj(ht, obj) + ht->p.key_offset,
415 no_resize_running = tbl == old_tbl;
417 head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
419 if (rht_is_a_nulls(head))
420 INIT_RHT_NULLS_HEAD(obj->next, ht, hash);
422 RCU_INIT_POINTER(obj->next, head);
424 rcu_assign_pointer(tbl->buckets[hash], obj);
426 atomic_inc(&ht->nelems);
427 if (no_resize_running && rht_grow_above_75(ht, tbl))
428 schedule_work(&ht->run_work);
431 if (tbl != old_tbl) {
432 hash = head_hashfn(ht, tbl, obj);
433 spin_unlock(bucket_lock(tbl, hash));
436 hash = head_hashfn(ht, old_tbl, obj);
437 spin_unlock_bh(bucket_lock(old_tbl, hash));
445 * rhashtable_insert - insert object into hash table
447 * @obj: pointer to hash head inside object
449 * Will take a per bucket spinlock to protect against mutual mutations
450 * on the same bucket. Multiple insertions may occur in parallel unless
451 * they map to the same bucket lock.
453 * It is safe to call this function from atomic context.
455 * Will trigger an automatic deferred table resizing if the size grows
456 * beyond the watermark indicated by grow_decision() which can be passed
457 * to rhashtable_init().
459 void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj)
461 __rhashtable_insert(ht, obj, NULL, NULL);
463 EXPORT_SYMBOL_GPL(rhashtable_insert);
465 static bool __rhashtable_remove(struct rhashtable *ht,
466 struct bucket_table *tbl,
467 struct rhash_head *obj)
469 struct rhash_head __rcu **pprev;
470 struct rhash_head *he;
475 hash = head_hashfn(ht, tbl, obj);
476 lock = bucket_lock(tbl, hash);
480 pprev = &tbl->buckets[hash];
481 rht_for_each(he, tbl, hash) {
487 rcu_assign_pointer(*pprev, obj->next);
492 spin_unlock_bh(lock);
498 * rhashtable_remove - remove object from hash table
500 * @obj: pointer to hash head inside object
502 * Since the hash chain is single linked, the removal operation needs to
503 * walk the bucket chain upon removal. The removal operation is thus
504 * considerable slow if the hash table is not correctly sized.
506 * Will automatically shrink the table via rhashtable_expand() if the
507 * shrink_decision function specified at rhashtable_init() returns true.
509 * The caller must ensure that no concurrent table mutations occur. It is
510 * however valid to have concurrent lookups if they are RCU protected.
512 bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj)
514 struct bucket_table *tbl, *old_tbl;
519 old_tbl = rht_dereference_rcu(ht->tbl, ht);
520 ret = __rhashtable_remove(ht, old_tbl, obj);
522 /* Because we have already taken (and released) the bucket
523 * lock in old_tbl, if we find that future_tbl is not yet
524 * visible then that guarantees the entry to still be in
525 * old_tbl if it exists.
527 tbl = rht_dereference_rcu(old_tbl->future_tbl, ht) ?: old_tbl;
528 if (!ret && old_tbl != tbl)
529 ret = __rhashtable_remove(ht, tbl, obj);
532 bool no_resize_running = tbl == old_tbl;
534 atomic_dec(&ht->nelems);
535 if (no_resize_running && rht_shrink_below_30(ht, tbl))
536 schedule_work(&ht->run_work);
543 EXPORT_SYMBOL_GPL(rhashtable_remove);
545 struct rhashtable_compare_arg {
546 struct rhashtable *ht;
550 static bool rhashtable_compare(void *ptr, void *arg)
552 struct rhashtable_compare_arg *x = arg;
553 struct rhashtable *ht = x->ht;
555 return !memcmp(ptr + ht->p.key_offset, x->key, ht->p.key_len);
559 * rhashtable_lookup - lookup key in hash table
561 * @key: pointer to key
563 * Computes the hash value for the key and traverses the bucket chain looking
564 * for a entry with an identical key. The first matching entry is returned.
566 * This lookup function may only be used for fixed key hash table (key_len
567 * parameter set). It will BUG() if used inappropriately.
569 * Lookups may occur in parallel with hashtable mutations and resizing.
571 void *rhashtable_lookup(struct rhashtable *ht, const void *key)
573 struct rhashtable_compare_arg arg = {
578 BUG_ON(!ht->p.key_len);
580 return rhashtable_lookup_compare(ht, key, &rhashtable_compare, &arg);
582 EXPORT_SYMBOL_GPL(rhashtable_lookup);
585 * rhashtable_lookup_compare - search hash table with compare function
587 * @key: the pointer to the key
588 * @compare: compare function, must return true on match
589 * @arg: argument passed on to compare function
591 * Traverses the bucket chain behind the provided hash value and calls the
592 * specified compare function for each entry.
594 * Lookups may occur in parallel with hashtable mutations and resizing.
596 * Returns the first entry on which the compare function returned true.
598 void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key,
599 bool (*compare)(void *, void *), void *arg)
601 const struct bucket_table *tbl;
602 struct rhash_head *he;
607 tbl = rht_dereference_rcu(ht->tbl, ht);
609 hash = key_hashfn(ht, tbl, key);
610 rht_for_each_rcu(he, tbl, hash) {
611 if (!compare(rht_obj(ht, he), arg))
614 return rht_obj(ht, he);
617 /* Ensure we see any new tables. */
620 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
627 EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);
630 * rhashtable_lookup_insert - lookup and insert object into hash table
632 * @obj: pointer to hash head inside object
634 * Locks down the bucket chain in both the old and new table if a resize
635 * is in progress to ensure that writers can't remove from the old table
636 * and can't insert to the new table during the atomic operation of search
637 * and insertion. Searches for duplicates in both the old and new table if
638 * a resize is in progress.
640 * This lookup function may only be used for fixed key hash table (key_len
641 * parameter set). It will BUG() if used inappropriately.
643 * It is safe to call this function from atomic context.
645 * Will trigger an automatic deferred table resizing if the size grows
646 * beyond the watermark indicated by grow_decision() which can be passed
647 * to rhashtable_init().
649 bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj)
651 struct rhashtable_compare_arg arg = {
653 .key = rht_obj(ht, obj) + ht->p.key_offset,
656 BUG_ON(!ht->p.key_len);
658 return rhashtable_lookup_compare_insert(ht, obj, &rhashtable_compare,
661 EXPORT_SYMBOL_GPL(rhashtable_lookup_insert);
664 * rhashtable_lookup_compare_insert - search and insert object to hash table
665 * with compare function
667 * @obj: pointer to hash head inside object
668 * @compare: compare function, must return true on match
669 * @arg: argument passed on to compare function
671 * Locks down the bucket chain in both the old and new table if a resize
672 * is in progress to ensure that writers can't remove from the old table
673 * and can't insert to the new table during the atomic operation of search
674 * and insertion. Searches for duplicates in both the old and new table if
675 * a resize is in progress.
677 * Lookups may occur in parallel with hashtable mutations and resizing.
679 * Will trigger an automatic deferred table resizing if the size grows
680 * beyond the watermark indicated by grow_decision() which can be passed
681 * to rhashtable_init().
683 bool rhashtable_lookup_compare_insert(struct rhashtable *ht,
684 struct rhash_head *obj,
685 bool (*compare)(void *, void *),
688 BUG_ON(!ht->p.key_len);
690 return __rhashtable_insert(ht, obj, compare, arg);
692 EXPORT_SYMBOL_GPL(rhashtable_lookup_compare_insert);
695 * rhashtable_walk_init - Initialise an iterator
696 * @ht: Table to walk over
697 * @iter: Hash table Iterator
699 * This function prepares a hash table walk.
701 * Note that if you restart a walk after rhashtable_walk_stop you
702 * may see the same object twice. Also, you may miss objects if
703 * there are removals in between rhashtable_walk_stop and the next
704 * call to rhashtable_walk_start.
706 * For a completely stable walk you should construct your own data
707 * structure outside the hash table.
709 * This function may sleep so you must not call it from interrupt
710 * context or with spin locks held.
712 * You must call rhashtable_walk_exit if this function returns
715 int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)
722 iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL);
726 mutex_lock(&ht->mutex);
727 iter->walker->tbl = rht_dereference(ht->tbl, ht);
728 list_add(&iter->walker->list, &iter->walker->tbl->walkers);
729 mutex_unlock(&ht->mutex);
733 EXPORT_SYMBOL_GPL(rhashtable_walk_init);
736 * rhashtable_walk_exit - Free an iterator
737 * @iter: Hash table Iterator
739 * This function frees resources allocated by rhashtable_walk_init.
741 void rhashtable_walk_exit(struct rhashtable_iter *iter)
743 mutex_lock(&iter->ht->mutex);
744 if (iter->walker->tbl)
745 list_del(&iter->walker->list);
746 mutex_unlock(&iter->ht->mutex);
749 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
752 * rhashtable_walk_start - Start a hash table walk
753 * @iter: Hash table iterator
755 * Start a hash table walk. Note that we take the RCU lock in all
756 * cases including when we return an error. So you must always call
757 * rhashtable_walk_stop to clean up.
759 * Returns zero if successful.
761 * Returns -EAGAIN if resize event occured. Note that the iterator
762 * will rewind back to the beginning and you may use it immediately
763 * by calling rhashtable_walk_next.
765 int rhashtable_walk_start(struct rhashtable_iter *iter)
767 struct rhashtable *ht = iter->ht;
769 mutex_lock(&ht->mutex);
771 if (iter->walker->tbl)
772 list_del(&iter->walker->list);
776 mutex_unlock(&ht->mutex);
778 if (!iter->walker->tbl) {
779 iter->walker->tbl = rht_dereference_rcu(ht->tbl, ht);
785 EXPORT_SYMBOL_GPL(rhashtable_walk_start);
788 * rhashtable_walk_next - Return the next object and advance the iterator
789 * @iter: Hash table iterator
791 * Note that you must call rhashtable_walk_stop when you are finished
794 * Returns the next object or NULL when the end of the table is reached.
796 * Returns -EAGAIN if resize event occured. Note that the iterator
797 * will rewind back to the beginning and you may continue to use it.
799 void *rhashtable_walk_next(struct rhashtable_iter *iter)
801 struct bucket_table *tbl = iter->walker->tbl;
802 struct rhashtable *ht = iter->ht;
803 struct rhash_head *p = iter->p;
807 p = rht_dereference_bucket_rcu(p->next, tbl, iter->slot);
811 for (; iter->slot < tbl->size; iter->slot++) {
812 int skip = iter->skip;
814 rht_for_each_rcu(p, tbl, iter->slot) {
821 if (!rht_is_a_nulls(p)) {
824 obj = rht_obj(ht, p);
831 iter->walker->tbl = rht_dereference_rcu(tbl->future_tbl, ht);
832 if (iter->walker->tbl) {
835 return ERR_PTR(-EAGAIN);
844 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
847 * rhashtable_walk_stop - Finish a hash table walk
848 * @iter: Hash table iterator
850 * Finish a hash table walk.
852 void rhashtable_walk_stop(struct rhashtable_iter *iter)
854 struct rhashtable *ht;
855 struct bucket_table *tbl = iter->walker->tbl;
864 mutex_lock(&ht->mutex);
865 if (tbl->rehash < tbl->size)
866 list_add(&iter->walker->list, &tbl->walkers);
868 iter->walker->tbl = NULL;
869 mutex_unlock(&ht->mutex);
873 EXPORT_SYMBOL_GPL(rhashtable_walk_stop);
875 static size_t rounded_hashtable_size(struct rhashtable_params *params)
877 return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
878 1UL << params->min_shift);
882 * rhashtable_init - initialize a new hash table
883 * @ht: hash table to be initialized
884 * @params: configuration parameters
886 * Initializes a new hash table based on the provided configuration
887 * parameters. A table can be configured either with a variable or
890 * Configuration Example 1: Fixed length keys
894 * struct rhash_head node;
897 * struct rhashtable_params params = {
898 * .head_offset = offsetof(struct test_obj, node),
899 * .key_offset = offsetof(struct test_obj, key),
900 * .key_len = sizeof(int),
902 * .nulls_base = (1U << RHT_BASE_SHIFT),
905 * Configuration Example 2: Variable length keys
908 * struct rhash_head node;
911 * u32 my_hash_fn(const void *data, u32 seed)
913 * struct test_obj *obj = data;
915 * return [... hash ...];
918 * struct rhashtable_params params = {
919 * .head_offset = offsetof(struct test_obj, node),
921 * .obj_hashfn = my_hash_fn,
924 int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
926 struct bucket_table *tbl;
929 size = HASH_DEFAULT_SIZE;
931 if ((params->key_len && !params->hashfn) ||
932 (!params->key_len && !params->obj_hashfn))
935 if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
938 params->min_shift = max_t(size_t, params->min_shift,
939 ilog2(HASH_MIN_SIZE));
941 if (params->nelem_hint)
942 size = rounded_hashtable_size(params);
944 memset(ht, 0, sizeof(*ht));
945 mutex_init(&ht->mutex);
946 memcpy(&ht->p, params, sizeof(*params));
948 if (params->locks_mul)
949 ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
951 ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
953 tbl = bucket_table_alloc(ht, size);
957 atomic_set(&ht->nelems, 0);
959 RCU_INIT_POINTER(ht->tbl, tbl);
961 INIT_WORK(&ht->run_work, rht_deferred_worker);
965 EXPORT_SYMBOL_GPL(rhashtable_init);
968 * rhashtable_destroy - destroy hash table
969 * @ht: the hash table to destroy
971 * Frees the bucket array. This function is not rcu safe, therefore the caller
972 * has to make sure that no resizing may happen by unpublishing the hashtable
973 * and waiting for the quiescent cycle before releasing the bucket array.
975 void rhashtable_destroy(struct rhashtable *ht)
977 ht->being_destroyed = true;
979 cancel_work_sync(&ht->run_work);
981 mutex_lock(&ht->mutex);
982 bucket_table_free(rht_dereference(ht->tbl, ht));
983 mutex_unlock(&ht->mutex);
985 EXPORT_SYMBOL_GPL(rhashtable_destroy);