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)
41 /* The bucket lock is selected based on the hash and protects mutations
42 * on a group of hash buckets.
44 * A maximum of tbl->size/2 bucket locks is allocated. This ensures that
45 * a single lock always covers both buckets which may both contains
46 * entries which link to the same bucket of the old table during resizing.
47 * This allows to simplify the locking as locking the bucket in both
48 * tables during resize always guarantee protection.
50 * IMPORTANT: When holding the bucket lock of both the old and new table
51 * during expansions and shrinking, the old bucket lock must always be
54 static spinlock_t *bucket_lock(const struct bucket_table *tbl, u32 hash)
56 return &tbl->locks[hash & tbl->locks_mask];
59 static void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he)
61 return (void *) he - ht->p.head_offset;
64 static u32 rht_bucket_index(const struct bucket_table *tbl, u32 hash)
66 return (hash >> HASH_RESERVED_SPACE) & (tbl->size - 1);
69 static u32 key_hashfn(struct rhashtable *ht, const struct bucket_table *tbl,
72 return rht_bucket_index(tbl, ht->p.hashfn(key, ht->p.key_len,
76 static u32 head_hashfn(struct rhashtable *ht,
77 const struct bucket_table *tbl,
78 const struct rhash_head *he)
80 const char *ptr = rht_obj(ht, he);
82 return likely(ht->p.key_len) ?
83 key_hashfn(ht, tbl, ptr + ht->p.key_offset) :
84 rht_bucket_index(tbl, ht->p.obj_hashfn(ptr, tbl->hash_rnd));
87 #ifdef CONFIG_PROVE_LOCKING
88 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
90 int lockdep_rht_mutex_is_held(struct rhashtable *ht)
92 return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
94 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
96 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
98 spinlock_t *lock = bucket_lock(tbl, hash);
100 return (debug_locks) ? lockdep_is_held(lock) : 1;
102 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
104 #define ASSERT_RHT_MUTEX(HT)
108 static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl)
110 unsigned int i, size;
111 #if defined(CONFIG_PROVE_LOCKING)
112 unsigned int nr_pcpus = 2;
114 unsigned int nr_pcpus = num_possible_cpus();
117 nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
118 size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);
120 /* Never allocate more than 0.5 locks per bucket */
121 size = min_t(unsigned int, size, tbl->size >> 1);
123 if (sizeof(spinlock_t) != 0) {
125 if (size * sizeof(spinlock_t) > PAGE_SIZE)
126 tbl->locks = vmalloc(size * sizeof(spinlock_t));
129 tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
133 for (i = 0; i < size; i++)
134 spin_lock_init(&tbl->locks[i]);
136 tbl->locks_mask = size - 1;
141 static void bucket_table_free(const struct bucket_table *tbl)
149 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
150 size_t nbuckets, u32 hash_rnd)
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);
166 tbl->hash_rnd = hash_rnd;
168 if (alloc_bucket_locks(ht, tbl) < 0) {
169 bucket_table_free(tbl);
173 for (i = 0; i < nbuckets; i++)
174 INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
180 * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
182 * @tbl: current table
184 static bool rht_grow_above_75(const struct rhashtable *ht,
185 const struct bucket_table *tbl)
187 /* Expand table when exceeding 75% load */
188 return atomic_read(&ht->nelems) > (tbl->size / 4 * 3) &&
189 (!ht->p.max_shift || tbl->shift < ht->p.max_shift);
193 * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
195 * @tbl: current table
197 static bool rht_shrink_below_30(const struct rhashtable *ht,
198 const struct bucket_table *tbl)
200 /* Shrink table beneath 30% load */
201 return atomic_read(&ht->nelems) < (tbl->size * 3 / 10) &&
202 tbl->shift > ht->p.min_shift;
205 static int rhashtable_rehash_one(struct rhashtable *ht, unsigned old_hash)
207 struct bucket_table *new_tbl = rht_dereference(ht->future_tbl, ht);
208 struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
209 struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
211 struct rhash_head *head, *next, *entry;
212 spinlock_t *new_bucket_lock;
215 rht_for_each(entry, old_tbl, old_hash) {
217 next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
219 if (rht_is_a_nulls(next))
222 pprev = &entry->next;
228 new_hash = head_hashfn(ht, new_tbl, entry);
230 new_bucket_lock = bucket_lock(new_tbl, new_hash);
232 spin_lock_nested(new_bucket_lock, RHT_LOCK_NESTED);
233 head = rht_dereference_bucket(new_tbl->buckets[new_hash],
236 if (rht_is_a_nulls(head))
237 INIT_RHT_NULLS_HEAD(entry->next, ht, new_hash);
239 RCU_INIT_POINTER(entry->next, head);
241 rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
242 spin_unlock(new_bucket_lock);
244 rcu_assign_pointer(*pprev, next);
250 static void rhashtable_rehash_chain(struct rhashtable *ht, unsigned old_hash)
252 struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
253 spinlock_t *old_bucket_lock;
255 old_bucket_lock = bucket_lock(old_tbl, old_hash);
257 spin_lock_bh(old_bucket_lock);
258 while (!rhashtable_rehash_one(ht, old_hash))
260 spin_unlock_bh(old_bucket_lock);
263 static void rhashtable_rehash(struct rhashtable *ht,
264 struct bucket_table *new_tbl)
266 struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
269 get_random_bytes(&new_tbl->hash_rnd, sizeof(new_tbl->hash_rnd));
271 /* Make insertions go into the new, empty table right away. Deletions
272 * and lookups will be attempted in both tables until we synchronize.
273 * The synchronize_rcu() guarantees for the new table to be picked up
274 * so no new additions go into the old table while we relink.
276 rcu_assign_pointer(ht->future_tbl, new_tbl);
278 /* Ensure the new table is visible to readers. */
281 for (old_hash = 0; old_hash < old_tbl->size; old_hash++)
282 rhashtable_rehash_chain(ht, old_hash);
284 /* Publish the new table pointer. */
285 rcu_assign_pointer(ht->tbl, new_tbl);
287 /* Wait for readers. All new readers will see the new
288 * table, and thus no references to the old table will
293 bucket_table_free(old_tbl);
297 * rhashtable_expand - Expand hash table while allowing concurrent lookups
298 * @ht: the hash table to expand
300 * A secondary bucket array is allocated and the hash entries are migrated.
302 * This function may only be called in a context where it is safe to call
303 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
305 * The caller must ensure that no concurrent resizing occurs by holding
308 * It is valid to have concurrent insertions and deletions protected by per
309 * bucket locks or concurrent RCU protected lookups and traversals.
311 int rhashtable_expand(struct rhashtable *ht)
313 struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
315 ASSERT_RHT_MUTEX(ht);
317 new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, old_tbl->hash_rnd);
321 rhashtable_rehash(ht, new_tbl);
324 EXPORT_SYMBOL_GPL(rhashtable_expand);
327 * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
328 * @ht: the hash table to shrink
330 * This function may only be called in a context where it is safe to call
331 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
333 * The caller must ensure that no concurrent resizing occurs by holding
336 * The caller must ensure that no concurrent table mutations take place.
337 * It is however valid to have concurrent lookups if they are RCU protected.
339 * It is valid to have concurrent insertions and deletions protected by per
340 * bucket locks or concurrent RCU protected lookups and traversals.
342 int rhashtable_shrink(struct rhashtable *ht)
344 struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
346 ASSERT_RHT_MUTEX(ht);
348 new_tbl = bucket_table_alloc(ht, old_tbl->size / 2, old_tbl->hash_rnd);
352 rhashtable_rehash(ht, new_tbl);
355 EXPORT_SYMBOL_GPL(rhashtable_shrink);
357 static void rht_deferred_worker(struct work_struct *work)
359 struct rhashtable *ht;
360 struct bucket_table *tbl;
361 struct rhashtable_walker *walker;
363 ht = container_of(work, struct rhashtable, run_work);
364 mutex_lock(&ht->mutex);
365 if (ht->being_destroyed)
368 tbl = rht_dereference(ht->tbl, ht);
370 list_for_each_entry(walker, &ht->walkers, list)
371 walker->resize = true;
373 if (rht_grow_above_75(ht, tbl))
374 rhashtable_expand(ht);
375 else if (rht_shrink_below_30(ht, tbl))
376 rhashtable_shrink(ht);
378 mutex_unlock(&ht->mutex);
381 static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
382 bool (*compare)(void *, void *), void *arg)
384 struct bucket_table *tbl, *old_tbl;
385 struct rhash_head *head;
386 bool no_resize_running;
392 old_tbl = rht_dereference_rcu(ht->tbl, ht);
393 hash = head_hashfn(ht, old_tbl, obj);
395 spin_lock_bh(bucket_lock(old_tbl, hash));
397 /* Because we have already taken the bucket lock in old_tbl,
398 * if we find that future_tbl is not yet visible then that
399 * guarantees all other insertions of the same entry will
400 * also grab the bucket lock in old_tbl because until the
401 * rehash completes ht->tbl won't be changed.
403 tbl = rht_dereference_rcu(ht->future_tbl, ht);
404 if (tbl != old_tbl) {
405 hash = head_hashfn(ht, tbl, obj);
406 spin_lock_nested(bucket_lock(tbl, hash), RHT_LOCK_NESTED);
410 rhashtable_lookup_compare(ht, rht_obj(ht, obj) + ht->p.key_offset,
416 no_resize_running = tbl == old_tbl;
418 head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
420 if (rht_is_a_nulls(head))
421 INIT_RHT_NULLS_HEAD(obj->next, ht, hash);
423 RCU_INIT_POINTER(obj->next, head);
425 rcu_assign_pointer(tbl->buckets[hash], obj);
427 atomic_inc(&ht->nelems);
428 if (no_resize_running && rht_grow_above_75(ht, tbl))
429 schedule_work(&ht->run_work);
432 if (tbl != old_tbl) {
433 hash = head_hashfn(ht, tbl, obj);
434 spin_unlock(bucket_lock(tbl, hash));
437 hash = head_hashfn(ht, old_tbl, obj);
438 spin_unlock_bh(bucket_lock(old_tbl, hash));
446 * rhashtable_insert - insert object into hash table
448 * @obj: pointer to hash head inside object
450 * Will take a per bucket spinlock to protect against mutual mutations
451 * on the same bucket. Multiple insertions may occur in parallel unless
452 * they map to the same bucket lock.
454 * It is safe to call this function from atomic context.
456 * Will trigger an automatic deferred table resizing if the size grows
457 * beyond the watermark indicated by grow_decision() which can be passed
458 * to rhashtable_init().
460 void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj)
462 __rhashtable_insert(ht, obj, NULL, NULL);
464 EXPORT_SYMBOL_GPL(rhashtable_insert);
466 static bool __rhashtable_remove(struct rhashtable *ht,
467 struct bucket_table *tbl,
468 struct rhash_head *obj)
470 struct rhash_head __rcu **pprev;
471 struct rhash_head *he;
476 hash = head_hashfn(ht, tbl, obj);
477 lock = bucket_lock(tbl, hash);
481 pprev = &tbl->buckets[hash];
482 rht_for_each(he, tbl, hash) {
488 rcu_assign_pointer(*pprev, obj->next);
493 spin_unlock_bh(lock);
499 * rhashtable_remove - remove object from hash table
501 * @obj: pointer to hash head inside object
503 * Since the hash chain is single linked, the removal operation needs to
504 * walk the bucket chain upon removal. The removal operation is thus
505 * considerable slow if the hash table is not correctly sized.
507 * Will automatically shrink the table via rhashtable_expand() if the
508 * shrink_decision function specified at rhashtable_init() returns true.
510 * The caller must ensure that no concurrent table mutations occur. It is
511 * however valid to have concurrent lookups if they are RCU protected.
513 bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj)
515 struct bucket_table *tbl, *old_tbl;
520 old_tbl = rht_dereference_rcu(ht->tbl, ht);
521 ret = __rhashtable_remove(ht, old_tbl, obj);
523 /* Because we have already taken (and released) the bucket
524 * lock in old_tbl, if we find that future_tbl is not yet
525 * visible then that guarantees the entry to still be in
526 * old_tbl if it exists.
528 tbl = rht_dereference_rcu(ht->future_tbl, ht);
529 if (!ret && old_tbl != tbl)
530 ret = __rhashtable_remove(ht, tbl, obj);
533 bool no_resize_running = tbl == old_tbl;
535 atomic_dec(&ht->nelems);
536 if (no_resize_running && rht_shrink_below_30(ht, tbl))
537 schedule_work(&ht->run_work);
544 EXPORT_SYMBOL_GPL(rhashtable_remove);
546 struct rhashtable_compare_arg {
547 struct rhashtable *ht;
551 static bool rhashtable_compare(void *ptr, void *arg)
553 struct rhashtable_compare_arg *x = arg;
554 struct rhashtable *ht = x->ht;
556 return !memcmp(ptr + ht->p.key_offset, x->key, ht->p.key_len);
560 * rhashtable_lookup - lookup key in hash table
562 * @key: pointer to key
564 * Computes the hash value for the key and traverses the bucket chain looking
565 * for a entry with an identical key. The first matching entry is returned.
567 * This lookup function may only be used for fixed key hash table (key_len
568 * parameter set). It will BUG() if used inappropriately.
570 * Lookups may occur in parallel with hashtable mutations and resizing.
572 void *rhashtable_lookup(struct rhashtable *ht, const void *key)
574 struct rhashtable_compare_arg arg = {
579 BUG_ON(!ht->p.key_len);
581 return rhashtable_lookup_compare(ht, key, &rhashtable_compare, &arg);
583 EXPORT_SYMBOL_GPL(rhashtable_lookup);
586 * rhashtable_lookup_compare - search hash table with compare function
588 * @key: the pointer to the key
589 * @compare: compare function, must return true on match
590 * @arg: argument passed on to compare function
592 * Traverses the bucket chain behind the provided hash value and calls the
593 * specified compare function for each entry.
595 * Lookups may occur in parallel with hashtable mutations and resizing.
597 * Returns the first entry on which the compare function returned true.
599 void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key,
600 bool (*compare)(void *, void *), void *arg)
602 const struct bucket_table *tbl, *old_tbl;
603 struct rhash_head *he;
608 tbl = rht_dereference_rcu(ht->tbl, ht);
609 hash = key_hashfn(ht, tbl, key);
611 rht_for_each_rcu(he, tbl, hash) {
612 if (!compare(rht_obj(ht, he), arg))
615 return rht_obj(ht, he);
618 /* Ensure we see any new tables. */
622 tbl = rht_dereference_rcu(ht->future_tbl, ht);
623 if (unlikely(tbl != old_tbl))
629 EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);
632 * rhashtable_lookup_insert - lookup and insert object into hash table
634 * @obj: pointer to hash head inside object
636 * Locks down the bucket chain in both the old and new table if a resize
637 * is in progress to ensure that writers can't remove from the old table
638 * and can't insert to the new table during the atomic operation of search
639 * and insertion. Searches for duplicates in both the old and new table if
640 * a resize is in progress.
642 * This lookup function may only be used for fixed key hash table (key_len
643 * parameter set). It will BUG() if used inappropriately.
645 * It is safe to call this function from atomic context.
647 * Will trigger an automatic deferred table resizing if the size grows
648 * beyond the watermark indicated by grow_decision() which can be passed
649 * to rhashtable_init().
651 bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj)
653 struct rhashtable_compare_arg arg = {
655 .key = rht_obj(ht, obj) + ht->p.key_offset,
658 BUG_ON(!ht->p.key_len);
660 return rhashtable_lookup_compare_insert(ht, obj, &rhashtable_compare,
663 EXPORT_SYMBOL_GPL(rhashtable_lookup_insert);
666 * rhashtable_lookup_compare_insert - search and insert object to hash table
667 * with compare function
669 * @obj: pointer to hash head inside object
670 * @compare: compare function, must return true on match
671 * @arg: argument passed on to compare function
673 * Locks down the bucket chain in both the old and new table if a resize
674 * is in progress to ensure that writers can't remove from the old table
675 * and can't insert to the new table during the atomic operation of search
676 * and insertion. Searches for duplicates in both the old and new table if
677 * a resize is in progress.
679 * Lookups may occur in parallel with hashtable mutations and resizing.
681 * Will trigger an automatic deferred table resizing if the size grows
682 * beyond the watermark indicated by grow_decision() which can be passed
683 * to rhashtable_init().
685 bool rhashtable_lookup_compare_insert(struct rhashtable *ht,
686 struct rhash_head *obj,
687 bool (*compare)(void *, void *),
690 BUG_ON(!ht->p.key_len);
692 return __rhashtable_insert(ht, obj, compare, arg);
694 EXPORT_SYMBOL_GPL(rhashtable_lookup_compare_insert);
697 * rhashtable_walk_init - Initialise an iterator
698 * @ht: Table to walk over
699 * @iter: Hash table Iterator
701 * This function prepares a hash table walk.
703 * Note that if you restart a walk after rhashtable_walk_stop you
704 * may see the same object twice. Also, you may miss objects if
705 * there are removals in between rhashtable_walk_stop and the next
706 * call to rhashtable_walk_start.
708 * For a completely stable walk you should construct your own data
709 * structure outside the hash table.
711 * This function may sleep so you must not call it from interrupt
712 * context or with spin locks held.
714 * You must call rhashtable_walk_exit if this function returns
717 int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)
724 iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL);
728 INIT_LIST_HEAD(&iter->walker->list);
729 iter->walker->resize = false;
731 mutex_lock(&ht->mutex);
732 list_add(&iter->walker->list, &ht->walkers);
733 mutex_unlock(&ht->mutex);
737 EXPORT_SYMBOL_GPL(rhashtable_walk_init);
740 * rhashtable_walk_exit - Free an iterator
741 * @iter: Hash table Iterator
743 * This function frees resources allocated by rhashtable_walk_init.
745 void rhashtable_walk_exit(struct rhashtable_iter *iter)
747 mutex_lock(&iter->ht->mutex);
748 list_del(&iter->walker->list);
749 mutex_unlock(&iter->ht->mutex);
752 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
755 * rhashtable_walk_start - Start a hash table walk
756 * @iter: Hash table iterator
758 * Start a hash table walk. Note that we take the RCU lock in all
759 * cases including when we return an error. So you must always call
760 * rhashtable_walk_stop to clean up.
762 * Returns zero if successful.
764 * Returns -EAGAIN if resize event occured. Note that the iterator
765 * will rewind back to the beginning and you may use it immediately
766 * by calling rhashtable_walk_next.
768 int rhashtable_walk_start(struct rhashtable_iter *iter)
772 if (iter->walker->resize) {
775 iter->walker->resize = false;
781 EXPORT_SYMBOL_GPL(rhashtable_walk_start);
784 * rhashtable_walk_next - Return the next object and advance the iterator
785 * @iter: Hash table iterator
787 * Note that you must call rhashtable_walk_stop when you are finished
790 * Returns the next object or NULL when the end of the table is reached.
792 * Returns -EAGAIN if resize event occured. Note that the iterator
793 * will rewind back to the beginning and you may continue to use it.
795 void *rhashtable_walk_next(struct rhashtable_iter *iter)
797 const struct bucket_table *tbl;
798 struct rhashtable *ht = iter->ht;
799 struct rhash_head *p = iter->p;
802 tbl = rht_dereference_rcu(ht->tbl, ht);
805 p = rht_dereference_bucket_rcu(p->next, tbl, iter->slot);
809 for (; iter->slot < tbl->size; iter->slot++) {
810 int skip = iter->skip;
812 rht_for_each_rcu(p, tbl, iter->slot) {
819 if (!rht_is_a_nulls(p)) {
822 obj = rht_obj(ht, p);
832 if (iter->walker->resize) {
836 iter->walker->resize = false;
837 return ERR_PTR(-EAGAIN);
842 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
845 * rhashtable_walk_stop - Finish a hash table walk
846 * @iter: Hash table iterator
848 * Finish a hash table walk.
850 void rhashtable_walk_stop(struct rhashtable_iter *iter)
855 EXPORT_SYMBOL_GPL(rhashtable_walk_stop);
857 static size_t rounded_hashtable_size(struct rhashtable_params *params)
859 return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
860 1UL << params->min_shift);
864 * rhashtable_init - initialize a new hash table
865 * @ht: hash table to be initialized
866 * @params: configuration parameters
868 * Initializes a new hash table based on the provided configuration
869 * parameters. A table can be configured either with a variable or
872 * Configuration Example 1: Fixed length keys
876 * struct rhash_head node;
879 * struct rhashtable_params params = {
880 * .head_offset = offsetof(struct test_obj, node),
881 * .key_offset = offsetof(struct test_obj, key),
882 * .key_len = sizeof(int),
884 * .nulls_base = (1U << RHT_BASE_SHIFT),
887 * Configuration Example 2: Variable length keys
890 * struct rhash_head node;
893 * u32 my_hash_fn(const void *data, u32 seed)
895 * struct test_obj *obj = data;
897 * return [... hash ...];
900 * struct rhashtable_params params = {
901 * .head_offset = offsetof(struct test_obj, node),
903 * .obj_hashfn = my_hash_fn,
906 int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
908 struct bucket_table *tbl;
912 size = HASH_DEFAULT_SIZE;
914 if ((params->key_len && !params->hashfn) ||
915 (!params->key_len && !params->obj_hashfn))
918 if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
921 params->min_shift = max_t(size_t, params->min_shift,
922 ilog2(HASH_MIN_SIZE));
924 if (params->nelem_hint)
925 size = rounded_hashtable_size(params);
927 memset(ht, 0, sizeof(*ht));
928 mutex_init(&ht->mutex);
929 memcpy(&ht->p, params, sizeof(*params));
930 INIT_LIST_HEAD(&ht->walkers);
932 if (params->locks_mul)
933 ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
935 ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
937 get_random_bytes(&hash_rnd, sizeof(hash_rnd));
939 tbl = bucket_table_alloc(ht, size, hash_rnd);
943 atomic_set(&ht->nelems, 0);
945 RCU_INIT_POINTER(ht->tbl, tbl);
946 RCU_INIT_POINTER(ht->future_tbl, tbl);
948 INIT_WORK(&ht->run_work, rht_deferred_worker);
952 EXPORT_SYMBOL_GPL(rhashtable_init);
955 * rhashtable_destroy - destroy hash table
956 * @ht: the hash table to destroy
958 * Frees the bucket array. This function is not rcu safe, therefore the caller
959 * has to make sure that no resizing may happen by unpublishing the hashtable
960 * and waiting for the quiescent cycle before releasing the bucket array.
962 void rhashtable_destroy(struct rhashtable *ht)
964 ht->being_destroyed = true;
966 cancel_work_sync(&ht->run_work);
968 mutex_lock(&ht->mutex);
969 bucket_table_free(rht_dereference(ht->tbl, ht));
970 mutex_unlock(&ht->mutex);
972 EXPORT_SYMBOL_GPL(rhashtable_destroy);