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
)
64 #if defined(CONFIG_PROVE_LOCKING)
65 unsigned int nr_pcpus
= 2;
67 unsigned int nr_pcpus
= num_possible_cpus();
70 nr_pcpus
= min_t(unsigned int, nr_pcpus
, 32UL);
71 size
= roundup_pow_of_two(nr_pcpus
* ht
->p
.locks_mul
);
73 /* Never allocate more than 0.5 locks per bucket */
74 size
= min_t(unsigned int, size
, tbl
->size
>> 1);
76 if (sizeof(spinlock_t
) != 0) {
78 if (size
* sizeof(spinlock_t
) > PAGE_SIZE
)
79 tbl
->locks
= vmalloc(size
* sizeof(spinlock_t
));
82 tbl
->locks
= kmalloc_array(size
, sizeof(spinlock_t
),
86 for (i
= 0; i
< size
; i
++)
87 spin_lock_init(&tbl
->locks
[i
]);
89 tbl
->locks_mask
= size
- 1;
94 static void bucket_table_free(const struct bucket_table
*tbl
)
102 static void bucket_table_free_rcu(struct rcu_head
*head
)
104 bucket_table_free(container_of(head
, struct bucket_table
, rcu
));
107 static struct bucket_table
*bucket_table_alloc(struct rhashtable
*ht
,
110 struct bucket_table
*tbl
= NULL
;
114 size
= sizeof(*tbl
) + nbuckets
* sizeof(tbl
->buckets
[0]);
115 if (size
<= (PAGE_SIZE
<< PAGE_ALLOC_COSTLY_ORDER
))
116 tbl
= kzalloc(size
, GFP_KERNEL
| __GFP_NOWARN
| __GFP_NORETRY
);
122 tbl
->size
= nbuckets
;
124 if (alloc_bucket_locks(ht
, tbl
) < 0) {
125 bucket_table_free(tbl
);
129 INIT_LIST_HEAD(&tbl
->walkers
);
131 get_random_bytes(&tbl
->hash_rnd
, sizeof(tbl
->hash_rnd
));
133 for (i
= 0; i
< nbuckets
; i
++)
134 INIT_RHT_NULLS_HEAD(tbl
->buckets
[i
], ht
, i
);
139 static int rhashtable_rehash_one(struct rhashtable
*ht
, unsigned old_hash
)
141 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
142 struct bucket_table
*new_tbl
=
143 rht_dereference(old_tbl
->future_tbl
, ht
) ?: old_tbl
;
144 struct rhash_head __rcu
**pprev
= &old_tbl
->buckets
[old_hash
];
146 struct rhash_head
*head
, *next
, *entry
;
147 spinlock_t
*new_bucket_lock
;
150 rht_for_each(entry
, old_tbl
, old_hash
) {
152 next
= rht_dereference_bucket(entry
->next
, old_tbl
, old_hash
);
154 if (rht_is_a_nulls(next
))
157 pprev
= &entry
->next
;
163 new_hash
= head_hashfn(ht
, new_tbl
, entry
);
165 new_bucket_lock
= rht_bucket_lock(new_tbl
, new_hash
);
167 spin_lock_nested(new_bucket_lock
, SINGLE_DEPTH_NESTING
);
168 head
= rht_dereference_bucket(new_tbl
->buckets
[new_hash
],
171 if (rht_is_a_nulls(head
))
172 INIT_RHT_NULLS_HEAD(entry
->next
, ht
, new_hash
);
174 RCU_INIT_POINTER(entry
->next
, head
);
176 rcu_assign_pointer(new_tbl
->buckets
[new_hash
], entry
);
177 spin_unlock(new_bucket_lock
);
179 rcu_assign_pointer(*pprev
, next
);
185 static void rhashtable_rehash_chain(struct rhashtable
*ht
, unsigned old_hash
)
187 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
188 spinlock_t
*old_bucket_lock
;
190 old_bucket_lock
= rht_bucket_lock(old_tbl
, old_hash
);
192 spin_lock_bh(old_bucket_lock
);
193 while (!rhashtable_rehash_one(ht
, old_hash
))
196 spin_unlock_bh(old_bucket_lock
);
199 static void rhashtable_rehash(struct rhashtable
*ht
,
200 struct bucket_table
*new_tbl
)
202 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
203 struct rhashtable_walker
*walker
;
206 /* Make insertions go into the new, empty table right away. Deletions
207 * and lookups will be attempted in both tables until we synchronize.
209 rcu_assign_pointer(old_tbl
->future_tbl
, new_tbl
);
211 /* Ensure the new table is visible to readers. */
214 for (old_hash
= 0; old_hash
< old_tbl
->size
; old_hash
++)
215 rhashtable_rehash_chain(ht
, old_hash
);
217 /* Publish the new table pointer. */
218 rcu_assign_pointer(ht
->tbl
, new_tbl
);
220 list_for_each_entry(walker
, &old_tbl
->walkers
, list
)
223 /* Wait for readers. All new readers will see the new
224 * table, and thus no references to the old table will
227 call_rcu(&old_tbl
->rcu
, bucket_table_free_rcu
);
231 * rhashtable_expand - Expand hash table while allowing concurrent lookups
232 * @ht: the hash table to expand
234 * A secondary bucket array is allocated and the hash entries are migrated.
236 * This function may only be called in a context where it is safe to call
237 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
239 * The caller must ensure that no concurrent resizing occurs by holding
242 * It is valid to have concurrent insertions and deletions protected by per
243 * bucket locks or concurrent RCU protected lookups and traversals.
245 int rhashtable_expand(struct rhashtable
*ht
)
247 struct bucket_table
*new_tbl
, *old_tbl
= rht_dereference(ht
->tbl
, ht
);
249 ASSERT_RHT_MUTEX(ht
);
251 new_tbl
= bucket_table_alloc(ht
, old_tbl
->size
* 2);
255 rhashtable_rehash(ht
, new_tbl
);
258 EXPORT_SYMBOL_GPL(rhashtable_expand
);
261 * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
262 * @ht: the hash table to shrink
264 * This function may only be called in a context where it is safe to call
265 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
267 * The caller must ensure that no concurrent resizing occurs by holding
270 * The caller must ensure that no concurrent table mutations take place.
271 * It is however valid to have concurrent lookups if they are RCU protected.
273 * It is valid to have concurrent insertions and deletions protected by per
274 * bucket locks or concurrent RCU protected lookups and traversals.
276 int rhashtable_shrink(struct rhashtable
*ht
)
278 struct bucket_table
*new_tbl
, *old_tbl
= rht_dereference(ht
->tbl
, ht
);
280 ASSERT_RHT_MUTEX(ht
);
282 new_tbl
= bucket_table_alloc(ht
, old_tbl
->size
/ 2);
286 rhashtable_rehash(ht
, new_tbl
);
289 EXPORT_SYMBOL_GPL(rhashtable_shrink
);
291 static void rht_deferred_worker(struct work_struct
*work
)
293 struct rhashtable
*ht
;
294 struct bucket_table
*tbl
;
296 ht
= container_of(work
, struct rhashtable
, run_work
);
297 mutex_lock(&ht
->mutex
);
298 if (ht
->being_destroyed
)
301 tbl
= rht_dereference(ht
->tbl
, ht
);
303 if (rht_grow_above_75(ht
, tbl
))
304 rhashtable_expand(ht
);
305 else if (rht_shrink_below_30(ht
, tbl
))
306 rhashtable_shrink(ht
);
308 mutex_unlock(&ht
->mutex
);
311 int rhashtable_insert_slow(struct rhashtable
*ht
, const void *key
,
312 struct rhash_head
*obj
,
313 struct bucket_table
*tbl
)
315 struct rhash_head
*head
;
319 hash
= head_hashfn(ht
, tbl
, obj
);
320 spin_lock_nested(rht_bucket_lock(tbl
, hash
), SINGLE_DEPTH_NESTING
);
322 if (key
&& rhashtable_lookup_fast(ht
, key
, ht
->p
))
327 head
= rht_dereference_bucket(tbl
->buckets
[hash
], tbl
, hash
);
329 RCU_INIT_POINTER(obj
->next
, head
);
331 rcu_assign_pointer(tbl
->buckets
[hash
], obj
);
333 atomic_inc(&ht
->nelems
);
336 spin_unlock(rht_bucket_lock(tbl
, hash
));
340 EXPORT_SYMBOL_GPL(rhashtable_insert_slow
);
343 * rhashtable_walk_init - Initialise an iterator
344 * @ht: Table to walk over
345 * @iter: Hash table Iterator
347 * This function prepares a hash table walk.
349 * Note that if you restart a walk after rhashtable_walk_stop you
350 * may see the same object twice. Also, you may miss objects if
351 * there are removals in between rhashtable_walk_stop and the next
352 * call to rhashtable_walk_start.
354 * For a completely stable walk you should construct your own data
355 * structure outside the hash table.
357 * This function may sleep so you must not call it from interrupt
358 * context or with spin locks held.
360 * You must call rhashtable_walk_exit if this function returns
363 int rhashtable_walk_init(struct rhashtable
*ht
, struct rhashtable_iter
*iter
)
370 iter
->walker
= kmalloc(sizeof(*iter
->walker
), GFP_KERNEL
);
374 mutex_lock(&ht
->mutex
);
375 iter
->walker
->tbl
= rht_dereference(ht
->tbl
, ht
);
376 list_add(&iter
->walker
->list
, &iter
->walker
->tbl
->walkers
);
377 mutex_unlock(&ht
->mutex
);
381 EXPORT_SYMBOL_GPL(rhashtable_walk_init
);
384 * rhashtable_walk_exit - Free an iterator
385 * @iter: Hash table Iterator
387 * This function frees resources allocated by rhashtable_walk_init.
389 void rhashtable_walk_exit(struct rhashtable_iter
*iter
)
391 mutex_lock(&iter
->ht
->mutex
);
392 if (iter
->walker
->tbl
)
393 list_del(&iter
->walker
->list
);
394 mutex_unlock(&iter
->ht
->mutex
);
397 EXPORT_SYMBOL_GPL(rhashtable_walk_exit
);
400 * rhashtable_walk_start - Start a hash table walk
401 * @iter: Hash table iterator
403 * Start a hash table walk. Note that we take the RCU lock in all
404 * cases including when we return an error. So you must always call
405 * rhashtable_walk_stop to clean up.
407 * Returns zero if successful.
409 * Returns -EAGAIN if resize event occured. Note that the iterator
410 * will rewind back to the beginning and you may use it immediately
411 * by calling rhashtable_walk_next.
413 int rhashtable_walk_start(struct rhashtable_iter
*iter
)
416 struct rhashtable
*ht
= iter
->ht
;
418 mutex_lock(&ht
->mutex
);
420 if (iter
->walker
->tbl
)
421 list_del(&iter
->walker
->list
);
425 mutex_unlock(&ht
->mutex
);
427 if (!iter
->walker
->tbl
) {
428 iter
->walker
->tbl
= rht_dereference_rcu(ht
->tbl
, ht
);
434 EXPORT_SYMBOL_GPL(rhashtable_walk_start
);
437 * rhashtable_walk_next - Return the next object and advance the iterator
438 * @iter: Hash table iterator
440 * Note that you must call rhashtable_walk_stop when you are finished
443 * Returns the next object or NULL when the end of the table is reached.
445 * Returns -EAGAIN if resize event occured. Note that the iterator
446 * will rewind back to the beginning and you may continue to use it.
448 void *rhashtable_walk_next(struct rhashtable_iter
*iter
)
450 struct bucket_table
*tbl
= iter
->walker
->tbl
;
451 struct rhashtable
*ht
= iter
->ht
;
452 struct rhash_head
*p
= iter
->p
;
456 p
= rht_dereference_bucket_rcu(p
->next
, tbl
, iter
->slot
);
460 for (; iter
->slot
< tbl
->size
; iter
->slot
++) {
461 int skip
= iter
->skip
;
463 rht_for_each_rcu(p
, tbl
, iter
->slot
) {
470 if (!rht_is_a_nulls(p
)) {
473 obj
= rht_obj(ht
, p
);
480 iter
->walker
->tbl
= rht_dereference_rcu(tbl
->future_tbl
, ht
);
481 if (iter
->walker
->tbl
) {
484 return ERR_PTR(-EAGAIN
);
493 EXPORT_SYMBOL_GPL(rhashtable_walk_next
);
496 * rhashtable_walk_stop - Finish a hash table walk
497 * @iter: Hash table iterator
499 * Finish a hash table walk.
501 void rhashtable_walk_stop(struct rhashtable_iter
*iter
)
504 struct rhashtable
*ht
;
505 struct bucket_table
*tbl
= iter
->walker
->tbl
;
512 mutex_lock(&ht
->mutex
);
513 if (tbl
->rehash
< tbl
->size
)
514 list_add(&iter
->walker
->list
, &tbl
->walkers
);
516 iter
->walker
->tbl
= NULL
;
517 mutex_unlock(&ht
->mutex
);
524 EXPORT_SYMBOL_GPL(rhashtable_walk_stop
);
526 static size_t rounded_hashtable_size(const struct rhashtable_params
*params
)
528 return max(roundup_pow_of_two(params
->nelem_hint
* 4 / 3),
529 (unsigned long)params
->min_size
);
533 * rhashtable_init - initialize a new hash table
534 * @ht: hash table to be initialized
535 * @params: configuration parameters
537 * Initializes a new hash table based on the provided configuration
538 * parameters. A table can be configured either with a variable or
541 * Configuration Example 1: Fixed length keys
545 * struct rhash_head node;
548 * struct rhashtable_params params = {
549 * .head_offset = offsetof(struct test_obj, node),
550 * .key_offset = offsetof(struct test_obj, key),
551 * .key_len = sizeof(int),
553 * .nulls_base = (1U << RHT_BASE_SHIFT),
556 * Configuration Example 2: Variable length keys
559 * struct rhash_head node;
562 * u32 my_hash_fn(const void *data, u32 seed)
564 * struct test_obj *obj = data;
566 * return [... hash ...];
569 * struct rhashtable_params params = {
570 * .head_offset = offsetof(struct test_obj, node),
572 * .obj_hashfn = my_hash_fn,
575 int rhashtable_init(struct rhashtable
*ht
,
576 const struct rhashtable_params
*params
)
578 struct bucket_table
*tbl
;
581 size
= HASH_DEFAULT_SIZE
;
583 if ((!(params
->key_len
&& params
->hashfn
) && !params
->obj_hashfn
) ||
584 (params
->obj_hashfn
&& !params
->obj_cmpfn
))
587 if (params
->nulls_base
&& params
->nulls_base
< (1U << RHT_BASE_SHIFT
))
590 if (params
->nelem_hint
)
591 size
= rounded_hashtable_size(params
);
593 memset(ht
, 0, sizeof(*ht
));
594 mutex_init(&ht
->mutex
);
595 memcpy(&ht
->p
, params
, sizeof(*params
));
597 if (params
->min_size
)
598 ht
->p
.min_size
= roundup_pow_of_two(params
->min_size
);
600 if (params
->max_size
)
601 ht
->p
.max_size
= rounddown_pow_of_two(params
->max_size
);
603 ht
->p
.min_size
= max(ht
->p
.min_size
, HASH_MIN_SIZE
);
605 if (params
->locks_mul
)
606 ht
->p
.locks_mul
= roundup_pow_of_two(params
->locks_mul
);
608 ht
->p
.locks_mul
= BUCKET_LOCKS_PER_CPU
;
610 tbl
= bucket_table_alloc(ht
, size
);
614 atomic_set(&ht
->nelems
, 0);
616 RCU_INIT_POINTER(ht
->tbl
, tbl
);
618 INIT_WORK(&ht
->run_work
, rht_deferred_worker
);
622 EXPORT_SYMBOL_GPL(rhashtable_init
);
625 * rhashtable_destroy - destroy hash table
626 * @ht: the hash table to destroy
628 * Frees the bucket array. This function is not rcu safe, therefore the caller
629 * has to make sure that no resizing may happen by unpublishing the hashtable
630 * and waiting for the quiescent cycle before releasing the bucket array.
632 void rhashtable_destroy(struct rhashtable
*ht
)
634 ht
->being_destroyed
= true;
636 cancel_work_sync(&ht
->run_work
);
638 mutex_lock(&ht
->mutex
);
639 bucket_table_free(rht_dereference(ht
->tbl
, ht
));
640 mutex_unlock(&ht
->mutex
);
642 EXPORT_SYMBOL_GPL(rhashtable_destroy
);