2 * Resizable, Scalable, Concurrent Hash Table
4 * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
5 * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
6 * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
8 * Code partially derived from nft_hash
9 * Rewritten with rehash code from br_multicast plus single list
10 * pointer as suggested by Josh Triplett
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 4U
31 #define BUCKET_LOCKS_PER_CPU 128UL
33 static u32
head_hashfn(struct rhashtable
*ht
,
34 const struct bucket_table
*tbl
,
35 const struct rhash_head
*he
)
37 return rht_head_hashfn(ht
, tbl
, he
, ht
->p
);
40 #ifdef CONFIG_PROVE_LOCKING
41 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
43 int lockdep_rht_mutex_is_held(struct rhashtable
*ht
)
45 return (debug_locks
) ? lockdep_is_held(&ht
->mutex
) : 1;
47 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held
);
49 int lockdep_rht_bucket_is_held(const struct bucket_table
*tbl
, u32 hash
)
51 spinlock_t
*lock
= rht_bucket_lock(tbl
, hash
);
53 return (debug_locks
) ? lockdep_is_held(lock
) : 1;
55 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held
);
57 #define ASSERT_RHT_MUTEX(HT)
61 static int alloc_bucket_locks(struct rhashtable
*ht
, struct bucket_table
*tbl
,
65 #if defined(CONFIG_PROVE_LOCKING)
66 unsigned int nr_pcpus
= 2;
68 unsigned int nr_pcpus
= num_possible_cpus();
71 nr_pcpus
= min_t(unsigned int, nr_pcpus
, 32UL);
72 size
= roundup_pow_of_two(nr_pcpus
* ht
->p
.locks_mul
);
74 /* Never allocate more than 0.5 locks per bucket */
75 size
= min_t(unsigned int, size
, tbl
->size
>> 1);
77 if (sizeof(spinlock_t
) != 0) {
79 if (size
* sizeof(spinlock_t
) > PAGE_SIZE
&&
81 tbl
->locks
= vmalloc(size
* sizeof(spinlock_t
));
84 tbl
->locks
= kmalloc_array(size
, sizeof(spinlock_t
),
88 for (i
= 0; i
< size
; i
++)
89 spin_lock_init(&tbl
->locks
[i
]);
91 tbl
->locks_mask
= size
- 1;
96 static void bucket_table_free(const struct bucket_table
*tbl
)
104 static void bucket_table_free_rcu(struct rcu_head
*head
)
106 bucket_table_free(container_of(head
, struct bucket_table
, rcu
));
109 static struct bucket_table
*bucket_table_alloc(struct rhashtable
*ht
,
113 struct bucket_table
*tbl
= NULL
;
117 size
= sizeof(*tbl
) + nbuckets
* sizeof(tbl
->buckets
[0]);
118 if (size
<= (PAGE_SIZE
<< PAGE_ALLOC_COSTLY_ORDER
) ||
120 tbl
= kzalloc(size
, gfp
| __GFP_NOWARN
| __GFP_NORETRY
);
121 if (tbl
== NULL
&& gfp
== GFP_KERNEL
)
126 tbl
->size
= nbuckets
;
128 if (alloc_bucket_locks(ht
, tbl
, gfp
) < 0) {
129 bucket_table_free(tbl
);
133 INIT_LIST_HEAD(&tbl
->walkers
);
135 get_random_bytes(&tbl
->hash_rnd
, sizeof(tbl
->hash_rnd
));
137 for (i
= 0; i
< nbuckets
; i
++)
138 INIT_RHT_NULLS_HEAD(tbl
->buckets
[i
], ht
, i
);
143 static struct bucket_table
*rhashtable_last_table(struct rhashtable
*ht
,
144 struct bucket_table
*tbl
)
146 struct bucket_table
*new_tbl
;
150 tbl
= rht_dereference_rcu(tbl
->future_tbl
, ht
);
156 static int rhashtable_rehash_one(struct rhashtable
*ht
, unsigned old_hash
)
158 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
159 struct bucket_table
*new_tbl
= rhashtable_last_table(ht
,
160 rht_dereference_rcu(old_tbl
->future_tbl
, ht
));
161 struct rhash_head __rcu
**pprev
= &old_tbl
->buckets
[old_hash
];
163 struct rhash_head
*head
, *next
, *entry
;
164 spinlock_t
*new_bucket_lock
;
167 rht_for_each(entry
, old_tbl
, old_hash
) {
169 next
= rht_dereference_bucket(entry
->next
, old_tbl
, old_hash
);
171 if (rht_is_a_nulls(next
))
174 pprev
= &entry
->next
;
180 new_hash
= head_hashfn(ht
, new_tbl
, entry
);
182 new_bucket_lock
= rht_bucket_lock(new_tbl
, new_hash
);
184 spin_lock_nested(new_bucket_lock
, SINGLE_DEPTH_NESTING
);
185 head
= rht_dereference_bucket(new_tbl
->buckets
[new_hash
],
188 if (rht_is_a_nulls(head
))
189 INIT_RHT_NULLS_HEAD(entry
->next
, ht
, new_hash
);
191 RCU_INIT_POINTER(entry
->next
, head
);
193 rcu_assign_pointer(new_tbl
->buckets
[new_hash
], entry
);
194 spin_unlock(new_bucket_lock
);
196 rcu_assign_pointer(*pprev
, next
);
202 static void rhashtable_rehash_chain(struct rhashtable
*ht
, unsigned old_hash
)
204 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
205 spinlock_t
*old_bucket_lock
;
207 old_bucket_lock
= rht_bucket_lock(old_tbl
, old_hash
);
209 spin_lock_bh(old_bucket_lock
);
210 while (!rhashtable_rehash_one(ht
, old_hash
))
213 spin_unlock_bh(old_bucket_lock
);
216 static int rhashtable_rehash_attach(struct rhashtable
*ht
,
217 struct bucket_table
*old_tbl
,
218 struct bucket_table
*new_tbl
)
220 /* Protect future_tbl using the first bucket lock. */
221 spin_lock_bh(old_tbl
->locks
);
223 /* Did somebody beat us to it? */
224 if (rcu_access_pointer(old_tbl
->future_tbl
)) {
225 spin_unlock_bh(old_tbl
->locks
);
229 /* Make insertions go into the new, empty table right away. Deletions
230 * and lookups will be attempted in both tables until we synchronize.
232 rcu_assign_pointer(old_tbl
->future_tbl
, new_tbl
);
234 /* Ensure the new table is visible to readers. */
237 spin_unlock_bh(old_tbl
->locks
);
242 static int rhashtable_rehash_table(struct rhashtable
*ht
)
244 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
245 struct bucket_table
*new_tbl
;
246 struct rhashtable_walker
*walker
;
249 new_tbl
= rht_dereference(old_tbl
->future_tbl
, ht
);
253 for (old_hash
= 0; old_hash
< old_tbl
->size
; old_hash
++)
254 rhashtable_rehash_chain(ht
, old_hash
);
256 /* Publish the new table pointer. */
257 rcu_assign_pointer(ht
->tbl
, new_tbl
);
259 spin_lock(&ht
->lock
);
260 list_for_each_entry(walker
, &old_tbl
->walkers
, list
)
262 spin_unlock(&ht
->lock
);
264 /* Wait for readers. All new readers will see the new
265 * table, and thus no references to the old table will
268 call_rcu(&old_tbl
->rcu
, bucket_table_free_rcu
);
270 return rht_dereference(new_tbl
->future_tbl
, ht
) ? -EAGAIN
: 0;
274 * rhashtable_expand - Expand hash table while allowing concurrent lookups
275 * @ht: the hash table to expand
277 * A secondary bucket array is allocated and the hash entries are migrated.
279 * This function may only be called in a context where it is safe to call
280 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
282 * The caller must ensure that no concurrent resizing occurs by holding
285 * It is valid to have concurrent insertions and deletions protected by per
286 * bucket locks or concurrent RCU protected lookups and traversals.
288 static int rhashtable_expand(struct rhashtable
*ht
)
290 struct bucket_table
*new_tbl
, *old_tbl
= rht_dereference(ht
->tbl
, ht
);
293 ASSERT_RHT_MUTEX(ht
);
295 old_tbl
= rhashtable_last_table(ht
, old_tbl
);
297 new_tbl
= bucket_table_alloc(ht
, old_tbl
->size
* 2, GFP_KERNEL
);
301 err
= rhashtable_rehash_attach(ht
, old_tbl
, new_tbl
);
303 bucket_table_free(new_tbl
);
309 * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
310 * @ht: the hash table to shrink
312 * This function shrinks the hash table to fit, i.e., the smallest
313 * size would not cause it to expand right away automatically.
315 * The caller must ensure that no concurrent resizing occurs by holding
318 * The caller must ensure that no concurrent table mutations take place.
319 * It is however valid to have concurrent lookups if they are RCU protected.
321 * It is valid to have concurrent insertions and deletions protected by per
322 * bucket locks or concurrent RCU protected lookups and traversals.
324 static int rhashtable_shrink(struct rhashtable
*ht
)
326 struct bucket_table
*new_tbl
, *old_tbl
= rht_dereference(ht
->tbl
, ht
);
327 unsigned size
= roundup_pow_of_two(atomic_read(&ht
->nelems
) * 3 / 2);
330 ASSERT_RHT_MUTEX(ht
);
332 if (size
< ht
->p
.min_size
)
333 size
= ht
->p
.min_size
;
335 if (old_tbl
->size
<= size
)
338 if (rht_dereference(old_tbl
->future_tbl
, ht
))
341 new_tbl
= bucket_table_alloc(ht
, size
, GFP_KERNEL
);
345 err
= rhashtable_rehash_attach(ht
, old_tbl
, new_tbl
);
347 bucket_table_free(new_tbl
);
352 static void rht_deferred_worker(struct work_struct
*work
)
354 struct rhashtable
*ht
;
355 struct bucket_table
*tbl
;
358 ht
= container_of(work
, struct rhashtable
, run_work
);
359 mutex_lock(&ht
->mutex
);
360 if (ht
->being_destroyed
)
363 tbl
= rht_dereference(ht
->tbl
, ht
);
364 tbl
= rhashtable_last_table(ht
, tbl
);
366 if (rht_grow_above_75(ht
, tbl
))
367 rhashtable_expand(ht
);
368 else if (rht_shrink_below_30(ht
, tbl
))
369 rhashtable_shrink(ht
);
371 err
= rhashtable_rehash_table(ht
);
374 mutex_unlock(&ht
->mutex
);
377 schedule_work(&ht
->run_work
);
380 static bool rhashtable_check_elasticity(struct rhashtable
*ht
,
381 struct bucket_table
*tbl
,
384 unsigned elasticity
= ht
->elasticity
;
385 struct rhash_head
*head
;
387 rht_for_each(head
, tbl
, hash
)
394 int rhashtable_insert_rehash(struct rhashtable
*ht
)
396 struct bucket_table
*old_tbl
;
397 struct bucket_table
*new_tbl
;
398 struct bucket_table
*tbl
;
402 old_tbl
= rht_dereference_rcu(ht
->tbl
, ht
);
403 tbl
= rhashtable_last_table(ht
, old_tbl
);
407 if (rht_grow_above_75(ht
, tbl
))
409 /* More than two rehashes (not resizes) detected. */
410 else if (WARN_ON(old_tbl
!= tbl
&& old_tbl
->size
== size
))
413 new_tbl
= bucket_table_alloc(ht
, size
, GFP_ATOMIC
);
417 err
= rhashtable_rehash_attach(ht
, tbl
, new_tbl
);
419 bucket_table_free(new_tbl
);
423 schedule_work(&ht
->run_work
);
427 EXPORT_SYMBOL_GPL(rhashtable_insert_rehash
);
429 int rhashtable_insert_slow(struct rhashtable
*ht
, const void *key
,
430 struct rhash_head
*obj
,
431 struct bucket_table
*tbl
)
433 struct rhash_head
*head
;
437 tbl
= rhashtable_last_table(ht
, tbl
);
438 hash
= head_hashfn(ht
, tbl
, obj
);
439 spin_lock_nested(rht_bucket_lock(tbl
, hash
), SINGLE_DEPTH_NESTING
);
442 if (key
&& rhashtable_lookup_fast(ht
, key
, ht
->p
))
446 if (rhashtable_check_elasticity(ht
, tbl
, hash
) ||
447 rht_grow_above_100(ht
, tbl
))
452 head
= rht_dereference_bucket(tbl
->buckets
[hash
], tbl
, hash
);
454 RCU_INIT_POINTER(obj
->next
, head
);
456 rcu_assign_pointer(tbl
->buckets
[hash
], obj
);
458 atomic_inc(&ht
->nelems
);
461 spin_unlock(rht_bucket_lock(tbl
, hash
));
465 EXPORT_SYMBOL_GPL(rhashtable_insert_slow
);
468 * rhashtable_walk_init - Initialise an iterator
469 * @ht: Table to walk over
470 * @iter: Hash table Iterator
472 * This function prepares a hash table walk.
474 * Note that if you restart a walk after rhashtable_walk_stop you
475 * may see the same object twice. Also, you may miss objects if
476 * there are removals in between rhashtable_walk_stop and the next
477 * call to rhashtable_walk_start.
479 * For a completely stable walk you should construct your own data
480 * structure outside the hash table.
482 * This function may sleep so you must not call it from interrupt
483 * context or with spin locks held.
485 * You must call rhashtable_walk_exit if this function returns
488 int rhashtable_walk_init(struct rhashtable
*ht
, struct rhashtable_iter
*iter
)
495 iter
->walker
= kmalloc(sizeof(*iter
->walker
), GFP_KERNEL
);
499 mutex_lock(&ht
->mutex
);
500 iter
->walker
->tbl
= rht_dereference(ht
->tbl
, ht
);
501 list_add(&iter
->walker
->list
, &iter
->walker
->tbl
->walkers
);
502 mutex_unlock(&ht
->mutex
);
506 EXPORT_SYMBOL_GPL(rhashtable_walk_init
);
509 * rhashtable_walk_exit - Free an iterator
510 * @iter: Hash table Iterator
512 * This function frees resources allocated by rhashtable_walk_init.
514 void rhashtable_walk_exit(struct rhashtable_iter
*iter
)
516 mutex_lock(&iter
->ht
->mutex
);
517 if (iter
->walker
->tbl
)
518 list_del(&iter
->walker
->list
);
519 mutex_unlock(&iter
->ht
->mutex
);
522 EXPORT_SYMBOL_GPL(rhashtable_walk_exit
);
525 * rhashtable_walk_start - Start a hash table walk
526 * @iter: Hash table iterator
528 * Start a hash table walk. Note that we take the RCU lock in all
529 * cases including when we return an error. So you must always call
530 * rhashtable_walk_stop to clean up.
532 * Returns zero if successful.
534 * Returns -EAGAIN if resize event occured. Note that the iterator
535 * will rewind back to the beginning and you may use it immediately
536 * by calling rhashtable_walk_next.
538 int rhashtable_walk_start(struct rhashtable_iter
*iter
)
541 struct rhashtable
*ht
= iter
->ht
;
543 mutex_lock(&ht
->mutex
);
545 if (iter
->walker
->tbl
)
546 list_del(&iter
->walker
->list
);
550 mutex_unlock(&ht
->mutex
);
552 if (!iter
->walker
->tbl
) {
553 iter
->walker
->tbl
= rht_dereference_rcu(ht
->tbl
, ht
);
559 EXPORT_SYMBOL_GPL(rhashtable_walk_start
);
562 * rhashtable_walk_next - Return the next object and advance the iterator
563 * @iter: Hash table iterator
565 * Note that you must call rhashtable_walk_stop when you are finished
568 * Returns the next object or NULL when the end of the table is reached.
570 * Returns -EAGAIN if resize event occured. Note that the iterator
571 * will rewind back to the beginning and you may continue to use it.
573 void *rhashtable_walk_next(struct rhashtable_iter
*iter
)
575 struct bucket_table
*tbl
= iter
->walker
->tbl
;
576 struct rhashtable
*ht
= iter
->ht
;
577 struct rhash_head
*p
= iter
->p
;
581 p
= rht_dereference_bucket_rcu(p
->next
, tbl
, iter
->slot
);
585 for (; iter
->slot
< tbl
->size
; iter
->slot
++) {
586 int skip
= iter
->skip
;
588 rht_for_each_rcu(p
, tbl
, iter
->slot
) {
595 if (!rht_is_a_nulls(p
)) {
598 obj
= rht_obj(ht
, p
);
605 /* Ensure we see any new tables. */
608 iter
->walker
->tbl
= rht_dereference_rcu(tbl
->future_tbl
, ht
);
609 if (iter
->walker
->tbl
) {
612 return ERR_PTR(-EAGAIN
);
621 EXPORT_SYMBOL_GPL(rhashtable_walk_next
);
624 * rhashtable_walk_stop - Finish a hash table walk
625 * @iter: Hash table iterator
627 * Finish a hash table walk.
629 void rhashtable_walk_stop(struct rhashtable_iter
*iter
)
632 struct rhashtable
*ht
;
633 struct bucket_table
*tbl
= iter
->walker
->tbl
;
640 spin_lock(&ht
->lock
);
641 if (tbl
->rehash
< tbl
->size
)
642 list_add(&iter
->walker
->list
, &tbl
->walkers
);
644 iter
->walker
->tbl
= NULL
;
645 spin_unlock(&ht
->lock
);
652 EXPORT_SYMBOL_GPL(rhashtable_walk_stop
);
654 static size_t rounded_hashtable_size(const struct rhashtable_params
*params
)
656 return max(roundup_pow_of_two(params
->nelem_hint
* 4 / 3),
657 (unsigned long)params
->min_size
);
660 static u32
rhashtable_jhash2(const void *key
, u32 length
, u32 seed
)
662 return jhash2(key
, length
, seed
);
666 * rhashtable_init - initialize a new hash table
667 * @ht: hash table to be initialized
668 * @params: configuration parameters
670 * Initializes a new hash table based on the provided configuration
671 * parameters. A table can be configured either with a variable or
674 * Configuration Example 1: Fixed length keys
678 * struct rhash_head node;
681 * struct rhashtable_params params = {
682 * .head_offset = offsetof(struct test_obj, node),
683 * .key_offset = offsetof(struct test_obj, key),
684 * .key_len = sizeof(int),
686 * .nulls_base = (1U << RHT_BASE_SHIFT),
689 * Configuration Example 2: Variable length keys
692 * struct rhash_head node;
695 * u32 my_hash_fn(const void *data, u32 seed)
697 * struct test_obj *obj = data;
699 * return [... hash ...];
702 * struct rhashtable_params params = {
703 * .head_offset = offsetof(struct test_obj, node),
705 * .obj_hashfn = my_hash_fn,
708 int rhashtable_init(struct rhashtable
*ht
,
709 const struct rhashtable_params
*params
)
711 struct bucket_table
*tbl
;
714 size
= HASH_DEFAULT_SIZE
;
716 if ((!params
->key_len
&& !params
->obj_hashfn
) ||
717 (params
->obj_hashfn
&& !params
->obj_cmpfn
))
720 if (params
->nulls_base
&& params
->nulls_base
< (1U << RHT_BASE_SHIFT
))
723 if (params
->nelem_hint
)
724 size
= rounded_hashtable_size(params
);
726 memset(ht
, 0, sizeof(*ht
));
727 mutex_init(&ht
->mutex
);
728 spin_lock_init(&ht
->lock
);
729 memcpy(&ht
->p
, params
, sizeof(*params
));
731 if (params
->min_size
)
732 ht
->p
.min_size
= roundup_pow_of_two(params
->min_size
);
734 if (params
->max_size
)
735 ht
->p
.max_size
= rounddown_pow_of_two(params
->max_size
);
737 ht
->p
.min_size
= max(ht
->p
.min_size
, HASH_MIN_SIZE
);
739 if (!params
->insecure_elasticity
)
742 if (params
->locks_mul
)
743 ht
->p
.locks_mul
= roundup_pow_of_two(params
->locks_mul
);
745 ht
->p
.locks_mul
= BUCKET_LOCKS_PER_CPU
;
747 ht
->key_len
= ht
->p
.key_len
;
748 if (!params
->hashfn
) {
749 ht
->p
.hashfn
= jhash
;
751 if (!(ht
->key_len
& (sizeof(u32
) - 1))) {
752 ht
->key_len
/= sizeof(u32
);
753 ht
->p
.hashfn
= rhashtable_jhash2
;
757 tbl
= bucket_table_alloc(ht
, size
, GFP_KERNEL
);
761 atomic_set(&ht
->nelems
, 0);
763 RCU_INIT_POINTER(ht
->tbl
, tbl
);
765 INIT_WORK(&ht
->run_work
, rht_deferred_worker
);
769 EXPORT_SYMBOL_GPL(rhashtable_init
);
772 * rhashtable_destroy - destroy hash table
773 * @ht: the hash table to destroy
775 * Frees the bucket array. This function is not rcu safe, therefore the caller
776 * has to make sure that no resizing may happen by unpublishing the hashtable
777 * and waiting for the quiescent cycle before releasing the bucket array.
779 void rhashtable_destroy(struct rhashtable
*ht
)
781 ht
->being_destroyed
= true;
783 cancel_work_sync(&ht
->run_work
);
785 mutex_lock(&ht
->mutex
);
786 bucket_table_free(rht_dereference(ht
->tbl
, ht
));
787 mutex_unlock(&ht
->mutex
);
789 EXPORT_SYMBOL_GPL(rhashtable_destroy
);