2 * Resizable, Scalable, Concurrent Hash Table
4 * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
5 * Copyright (c) 2014 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 #ifndef _LINUX_RHASHTABLE_H
18 #define _LINUX_RHASHTABLE_H
20 #include <linux/compiler.h>
21 #include <linux/errno.h>
22 #include <linux/jhash.h>
23 #include <linux/list_nulls.h>
24 #include <linux/workqueue.h>
25 #include <linux/mutex.h>
26 #include <linux/rcupdate.h>
29 * The end of the chain is marked with a special nulls marks which has
30 * the following format:
32 * +-------+-----------------------------------------------------+-+
34 * +-------+-----------------------------------------------------+-+
36 * Base (4 bits) : Reserved to distinguish between multiple tables.
37 * Specified via &struct rhashtable_params.nulls_base.
38 * Hash (27 bits): Full hash (unmasked) of first element added to bucket
39 * 1 (1 bit) : Nulls marker (always set)
41 * The remaining bits of the next pointer remain unused for now.
43 #define RHT_BASE_BITS 4
44 #define RHT_HASH_BITS 27
45 #define RHT_BASE_SHIFT RHT_HASH_BITS
47 /* Base bits plus 1 bit for nulls marker */
48 #define RHT_HASH_RESERVED_SPACE (RHT_BASE_BITS + 1)
51 struct rhash_head __rcu *next;
55 * struct bucket_table - Table of hash buckets
56 * @size: Number of hash buckets
57 * @rehash: Current bucket being rehashed
58 * @hash_rnd: Random seed to fold into hash
59 * @locks_mask: Mask to apply before accessing locks[]
60 * @locks: Array of spinlocks protecting individual buckets
61 * @walkers: List of active walkers
62 * @rcu: RCU structure for freeing the table
63 * @future_tbl: Table under construction during rehashing
64 * @buckets: size * hash buckets
70 unsigned int locks_mask;
72 struct list_head walkers;
75 struct bucket_table __rcu *future_tbl;
77 struct rhash_head __rcu *buckets[] ____cacheline_aligned_in_smp;
81 * struct rhashtable_compare_arg - Key for the function rhashtable_compare
83 * @key: Key to compare against
85 struct rhashtable_compare_arg {
86 struct rhashtable *ht;
90 typedef u32 (*rht_hashfn_t)(const void *data, u32 len, u32 seed);
91 typedef u32 (*rht_obj_hashfn_t)(const void *data, u32 seed);
92 typedef int (*rht_obj_cmpfn_t)(struct rhashtable_compare_arg *arg,
98 * struct rhashtable_params - Hash table construction parameters
99 * @nelem_hint: Hint on number of elements, should be 75% of desired size
100 * @key_len: Length of key
101 * @key_offset: Offset of key in struct to be hashed
102 * @head_offset: Offset of rhash_head in struct to be hashed
103 * @max_size: Maximum size while expanding
104 * @min_size: Minimum size while shrinking
105 * @nulls_base: Base value to generate nulls marker
106 * @locks_mul: Number of bucket locks to allocate per cpu (default: 128)
107 * @hashfn: Hash function (default: jhash2 if !(key_len % 4), or jhash)
108 * @obj_hashfn: Function to hash object
109 * @obj_cmpfn: Function to compare key with object
111 struct rhashtable_params {
116 unsigned int max_size;
117 unsigned int min_size;
121 rht_obj_hashfn_t obj_hashfn;
122 rht_obj_cmpfn_t obj_cmpfn;
126 * struct rhashtable - Hash table handle
128 * @nelems: Number of elements in table
129 * @key_len: Key length for hashfn
130 * @p: Configuration parameters
131 * @run_work: Deferred worker to expand/shrink asynchronously
132 * @mutex: Mutex to protect current/future table swapping
133 * @being_destroyed: True if table is set up for destruction
136 struct bucket_table __rcu *tbl;
138 bool being_destroyed;
139 unsigned int key_len;
140 struct rhashtable_params p;
141 struct work_struct run_work;
146 * struct rhashtable_walker - Hash table walker
147 * @list: List entry on list of walkers
148 * @tbl: The table that we were walking over
150 struct rhashtable_walker {
151 struct list_head list;
152 struct bucket_table *tbl;
156 * struct rhashtable_iter - Hash table iterator, fits into netlink cb
157 * @ht: Table to iterate through
158 * @p: Current pointer
159 * @walker: Associated rhashtable walker
160 * @slot: Current slot
161 * @skip: Number of entries to skip in slot
163 struct rhashtable_iter {
164 struct rhashtable *ht;
165 struct rhash_head *p;
166 struct rhashtable_walker *walker;
171 static inline unsigned long rht_marker(const struct rhashtable *ht, u32 hash)
173 return NULLS_MARKER(ht->p.nulls_base + hash);
176 #define INIT_RHT_NULLS_HEAD(ptr, ht, hash) \
177 ((ptr) = (typeof(ptr)) rht_marker(ht, hash))
179 static inline bool rht_is_a_nulls(const struct rhash_head *ptr)
181 return ((unsigned long) ptr & 1);
184 static inline unsigned long rht_get_nulls_value(const struct rhash_head *ptr)
186 return ((unsigned long) ptr) >> 1;
189 static inline void *rht_obj(const struct rhashtable *ht,
190 const struct rhash_head *he)
192 return (char *)he - ht->p.head_offset;
195 static inline unsigned int rht_bucket_index(const struct bucket_table *tbl,
198 return (hash >> RHT_HASH_RESERVED_SPACE) & (tbl->size - 1);
201 static inline unsigned int rht_key_hashfn(
202 struct rhashtable *ht, const struct bucket_table *tbl,
203 const void *key, const struct rhashtable_params params)
207 /* params must be equal to ht->p if it isn't constant. */
208 if (!__builtin_constant_p(params.key_len))
209 hash = ht->p.hashfn(key, ht->key_len, tbl->hash_rnd);
210 else if (params.key_len) {
211 unsigned key_len = params.key_len;
214 hash = params.hashfn(key, key_len, tbl->hash_rnd);
215 else if (key_len & (sizeof(u32) - 1))
216 hash = jhash(key, key_len, tbl->hash_rnd);
218 hash = jhash2(key, key_len / sizeof(u32),
221 unsigned key_len = ht->p.key_len;
224 hash = params.hashfn(key, key_len, tbl->hash_rnd);
226 hash = jhash(key, key_len, tbl->hash_rnd);
229 return rht_bucket_index(tbl, hash);
232 static inline unsigned int rht_head_hashfn(
233 struct rhashtable *ht, const struct bucket_table *tbl,
234 const struct rhash_head *he, const struct rhashtable_params params)
236 const char *ptr = rht_obj(ht, he);
238 return likely(params.obj_hashfn) ?
239 rht_bucket_index(tbl, params.obj_hashfn(ptr, tbl->hash_rnd)) :
240 rht_key_hashfn(ht, tbl, ptr + params.key_offset, params);
244 * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
246 * @tbl: current table
248 static inline bool rht_grow_above_75(const struct rhashtable *ht,
249 const struct bucket_table *tbl)
251 /* Expand table when exceeding 75% load */
252 return atomic_read(&ht->nelems) > (tbl->size / 4 * 3) &&
253 (!ht->p.max_size || tbl->size < ht->p.max_size);
257 * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
259 * @tbl: current table
261 static inline bool rht_shrink_below_30(const struct rhashtable *ht,
262 const struct bucket_table *tbl)
264 /* Shrink table beneath 30% load */
265 return atomic_read(&ht->nelems) < (tbl->size * 3 / 10) &&
266 tbl->size > ht->p.min_size;
269 /* The bucket lock is selected based on the hash and protects mutations
270 * on a group of hash buckets.
272 * A maximum of tbl->size/2 bucket locks is allocated. This ensures that
273 * a single lock always covers both buckets which may both contains
274 * entries which link to the same bucket of the old table during resizing.
275 * This allows to simplify the locking as locking the bucket in both
276 * tables during resize always guarantee protection.
278 * IMPORTANT: When holding the bucket lock of both the old and new table
279 * during expansions and shrinking, the old bucket lock must always be
282 static inline spinlock_t *rht_bucket_lock(const struct bucket_table *tbl,
285 return &tbl->locks[hash & tbl->locks_mask];
288 #ifdef CONFIG_PROVE_LOCKING
289 int lockdep_rht_mutex_is_held(struct rhashtable *ht);
290 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash);
292 static inline int lockdep_rht_mutex_is_held(struct rhashtable *ht)
297 static inline int lockdep_rht_bucket_is_held(const struct bucket_table *tbl,
302 #endif /* CONFIG_PROVE_LOCKING */
304 int rhashtable_init(struct rhashtable *ht,
305 const struct rhashtable_params *params);
307 int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
308 struct rhash_head *obj,
309 struct bucket_table *old_tbl);
311 int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter);
312 void rhashtable_walk_exit(struct rhashtable_iter *iter);
313 int rhashtable_walk_start(struct rhashtable_iter *iter) __acquires(RCU);
314 void *rhashtable_walk_next(struct rhashtable_iter *iter);
315 void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases(RCU);
317 void rhashtable_destroy(struct rhashtable *ht);
319 #define rht_dereference(p, ht) \
320 rcu_dereference_protected(p, lockdep_rht_mutex_is_held(ht))
322 #define rht_dereference_rcu(p, ht) \
323 rcu_dereference_check(p, lockdep_rht_mutex_is_held(ht))
325 #define rht_dereference_bucket(p, tbl, hash) \
326 rcu_dereference_protected(p, lockdep_rht_bucket_is_held(tbl, hash))
328 #define rht_dereference_bucket_rcu(p, tbl, hash) \
329 rcu_dereference_check(p, lockdep_rht_bucket_is_held(tbl, hash))
331 #define rht_entry(tpos, pos, member) \
332 ({ tpos = container_of(pos, typeof(*tpos), member); 1; })
335 * rht_for_each_continue - continue iterating over hash chain
336 * @pos: the &struct rhash_head to use as a loop cursor.
337 * @head: the previous &struct rhash_head to continue from
338 * @tbl: the &struct bucket_table
339 * @hash: the hash value / bucket index
341 #define rht_for_each_continue(pos, head, tbl, hash) \
342 for (pos = rht_dereference_bucket(head, tbl, hash); \
343 !rht_is_a_nulls(pos); \
344 pos = rht_dereference_bucket((pos)->next, tbl, hash))
347 * rht_for_each - iterate over hash chain
348 * @pos: the &struct rhash_head to use as a loop cursor.
349 * @tbl: the &struct bucket_table
350 * @hash: the hash value / bucket index
352 #define rht_for_each(pos, tbl, hash) \
353 rht_for_each_continue(pos, (tbl)->buckets[hash], tbl, hash)
356 * rht_for_each_entry_continue - continue iterating over hash chain
357 * @tpos: the type * to use as a loop cursor.
358 * @pos: the &struct rhash_head to use as a loop cursor.
359 * @head: the previous &struct rhash_head to continue from
360 * @tbl: the &struct bucket_table
361 * @hash: the hash value / bucket index
362 * @member: name of the &struct rhash_head within the hashable struct.
364 #define rht_for_each_entry_continue(tpos, pos, head, tbl, hash, member) \
365 for (pos = rht_dereference_bucket(head, tbl, hash); \
366 (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
367 pos = rht_dereference_bucket((pos)->next, tbl, hash))
370 * rht_for_each_entry - iterate over hash chain of given type
371 * @tpos: the type * to use as a loop cursor.
372 * @pos: the &struct rhash_head to use as a loop cursor.
373 * @tbl: the &struct bucket_table
374 * @hash: the hash value / bucket index
375 * @member: name of the &struct rhash_head within the hashable struct.
377 #define rht_for_each_entry(tpos, pos, tbl, hash, member) \
378 rht_for_each_entry_continue(tpos, pos, (tbl)->buckets[hash], \
382 * rht_for_each_entry_safe - safely iterate over hash chain of given type
383 * @tpos: the type * to use as a loop cursor.
384 * @pos: the &struct rhash_head to use as a loop cursor.
385 * @next: the &struct rhash_head to use as next in loop cursor.
386 * @tbl: the &struct bucket_table
387 * @hash: the hash value / bucket index
388 * @member: name of the &struct rhash_head within the hashable struct.
390 * This hash chain list-traversal primitive allows for the looped code to
391 * remove the loop cursor from the list.
393 #define rht_for_each_entry_safe(tpos, pos, next, tbl, hash, member) \
394 for (pos = rht_dereference_bucket((tbl)->buckets[hash], tbl, hash), \
395 next = !rht_is_a_nulls(pos) ? \
396 rht_dereference_bucket(pos->next, tbl, hash) : NULL; \
397 (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
399 next = !rht_is_a_nulls(pos) ? \
400 rht_dereference_bucket(pos->next, tbl, hash) : NULL)
403 * rht_for_each_rcu_continue - continue iterating over rcu hash chain
404 * @pos: the &struct rhash_head to use as a loop cursor.
405 * @head: the previous &struct rhash_head to continue from
406 * @tbl: the &struct bucket_table
407 * @hash: the hash value / bucket index
409 * This hash chain list-traversal primitive may safely run concurrently with
410 * the _rcu mutation primitives such as rhashtable_insert() as long as the
411 * traversal is guarded by rcu_read_lock().
413 #define rht_for_each_rcu_continue(pos, head, tbl, hash) \
414 for (({barrier(); }), \
415 pos = rht_dereference_bucket_rcu(head, tbl, hash); \
416 !rht_is_a_nulls(pos); \
417 pos = rcu_dereference_raw(pos->next))
420 * rht_for_each_rcu - iterate over rcu hash chain
421 * @pos: the &struct rhash_head to use as a loop cursor.
422 * @tbl: the &struct bucket_table
423 * @hash: the hash value / bucket index
425 * This hash chain list-traversal primitive may safely run concurrently with
426 * the _rcu mutation primitives such as rhashtable_insert() as long as the
427 * traversal is guarded by rcu_read_lock().
429 #define rht_for_each_rcu(pos, tbl, hash) \
430 rht_for_each_rcu_continue(pos, (tbl)->buckets[hash], tbl, hash)
433 * rht_for_each_entry_rcu_continue - continue iterating over rcu hash chain
434 * @tpos: the type * to use as a loop cursor.
435 * @pos: the &struct rhash_head to use as a loop cursor.
436 * @head: the previous &struct rhash_head to continue from
437 * @tbl: the &struct bucket_table
438 * @hash: the hash value / bucket index
439 * @member: name of the &struct rhash_head within the hashable struct.
441 * This hash chain list-traversal primitive may safely run concurrently with
442 * the _rcu mutation primitives such as rhashtable_insert() as long as the
443 * traversal is guarded by rcu_read_lock().
445 #define rht_for_each_entry_rcu_continue(tpos, pos, head, tbl, hash, member) \
446 for (({barrier(); }), \
447 pos = rht_dereference_bucket_rcu(head, tbl, hash); \
448 (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
449 pos = rht_dereference_bucket_rcu(pos->next, tbl, hash))
452 * rht_for_each_entry_rcu - iterate over rcu hash chain of given type
453 * @tpos: the type * to use as a loop cursor.
454 * @pos: the &struct rhash_head to use as a loop cursor.
455 * @tbl: the &struct bucket_table
456 * @hash: the hash value / bucket index
457 * @member: name of the &struct rhash_head within the hashable struct.
459 * This hash chain list-traversal primitive may safely run concurrently with
460 * the _rcu mutation primitives such as rhashtable_insert() as long as the
461 * traversal is guarded by rcu_read_lock().
463 #define rht_for_each_entry_rcu(tpos, pos, tbl, hash, member) \
464 rht_for_each_entry_rcu_continue(tpos, pos, (tbl)->buckets[hash],\
467 static inline int rhashtable_compare(struct rhashtable_compare_arg *arg,
470 struct rhashtable *ht = arg->ht;
471 const char *ptr = obj;
473 return memcmp(ptr + ht->p.key_offset, arg->key, ht->p.key_len);
477 * rhashtable_lookup_fast - search hash table, inlined version
479 * @key: the pointer to the key
480 * @params: hash table parameters
482 * Computes the hash value for the key and traverses the bucket chain looking
483 * for a entry with an identical key. The first matching entry is returned.
485 * Returns the first entry on which the compare function returned true.
487 static inline void *rhashtable_lookup_fast(
488 struct rhashtable *ht, const void *key,
489 const struct rhashtable_params params)
491 struct rhashtable_compare_arg arg = {
495 const struct bucket_table *tbl;
496 struct rhash_head *he;
501 tbl = rht_dereference_rcu(ht->tbl, ht);
503 hash = rht_key_hashfn(ht, tbl, key, params);
504 rht_for_each_rcu(he, tbl, hash) {
505 if (params.obj_cmpfn ?
506 params.obj_cmpfn(&arg, rht_obj(ht, he)) :
507 rhashtable_compare(&arg, rht_obj(ht, he)))
510 return rht_obj(ht, he);
513 /* Ensure we see any new tables. */
516 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
524 static inline int __rhashtable_insert_fast(
525 struct rhashtable *ht, const void *key, struct rhash_head *obj,
526 const struct rhashtable_params params)
528 struct rhashtable_compare_arg arg = {
533 struct bucket_table *tbl, *new_tbl;
534 struct rhash_head *head;
540 tbl = rht_dereference_rcu(ht->tbl, ht);
542 /* All insertions must grab the oldest table containing
543 * the hashed bucket that is yet to be rehashed.
546 hash = rht_head_hashfn(ht, tbl, obj, params);
547 lock = rht_bucket_lock(tbl, hash);
550 if (tbl->rehash <= hash)
553 spin_unlock_bh(lock);
554 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
557 new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
558 if (unlikely(new_tbl)) {
559 err = rhashtable_insert_slow(ht, key, obj, new_tbl);
566 rht_for_each(head, tbl, hash) {
567 if (unlikely(!(params.obj_cmpfn ?
568 params.obj_cmpfn(&arg, rht_obj(ht, head)) :
569 rhashtable_compare(&arg, rht_obj(ht, head)))))
576 head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
578 RCU_INIT_POINTER(obj->next, head);
580 rcu_assign_pointer(tbl->buckets[hash], obj);
582 atomic_inc(&ht->nelems);
583 if (rht_grow_above_75(ht, tbl))
584 schedule_work(&ht->run_work);
587 spin_unlock_bh(lock);
594 * rhashtable_insert_fast - insert object into hash table
596 * @obj: pointer to hash head inside object
597 * @params: hash table parameters
599 * Will take a per bucket spinlock to protect against mutual mutations
600 * on the same bucket. Multiple insertions may occur in parallel unless
601 * they map to the same bucket lock.
603 * It is safe to call this function from atomic context.
605 * Will trigger an automatic deferred table resizing if the size grows
606 * beyond the watermark indicated by grow_decision() which can be passed
607 * to rhashtable_init().
609 static inline int rhashtable_insert_fast(
610 struct rhashtable *ht, struct rhash_head *obj,
611 const struct rhashtable_params params)
613 return __rhashtable_insert_fast(ht, NULL, obj, params);
617 * rhashtable_lookup_insert_fast - lookup and insert object into hash table
619 * @obj: pointer to hash head inside object
620 * @params: hash table parameters
622 * Locks down the bucket chain in both the old and new table if a resize
623 * is in progress to ensure that writers can't remove from the old table
624 * and can't insert to the new table during the atomic operation of search
625 * and insertion. Searches for duplicates in both the old and new table if
626 * a resize is in progress.
628 * This lookup function may only be used for fixed key hash table (key_len
629 * parameter set). It will BUG() if used inappropriately.
631 * It is safe to call this function from atomic context.
633 * Will trigger an automatic deferred table resizing if the size grows
634 * beyond the watermark indicated by grow_decision() which can be passed
635 * to rhashtable_init().
637 static inline int rhashtable_lookup_insert_fast(
638 struct rhashtable *ht, struct rhash_head *obj,
639 const struct rhashtable_params params)
641 const char *key = rht_obj(ht, obj);
643 BUG_ON(ht->p.obj_hashfn);
645 return __rhashtable_insert_fast(ht, key + ht->p.key_offset, obj,
650 * rhashtable_lookup_insert_key - search and insert object to hash table
654 * @obj: pointer to hash head inside object
655 * @params: hash table parameters
657 * Locks down the bucket chain in both the old and new table if a resize
658 * is in progress to ensure that writers can't remove from the old table
659 * and can't insert to the new table during the atomic operation of search
660 * and insertion. Searches for duplicates in both the old and new table if
661 * a resize is in progress.
663 * Lookups may occur in parallel with hashtable mutations and resizing.
665 * Will trigger an automatic deferred table resizing if the size grows
666 * beyond the watermark indicated by grow_decision() which can be passed
667 * to rhashtable_init().
669 * Returns zero on success.
671 static inline int rhashtable_lookup_insert_key(
672 struct rhashtable *ht, const void *key, struct rhash_head *obj,
673 const struct rhashtable_params params)
675 BUG_ON(!ht->p.obj_hashfn || !key);
677 return __rhashtable_insert_fast(ht, key, obj, params);
680 static inline int __rhashtable_remove_fast(
681 struct rhashtable *ht, struct bucket_table *tbl,
682 struct rhash_head *obj, const struct rhashtable_params params)
684 struct rhash_head __rcu **pprev;
685 struct rhash_head *he;
690 hash = rht_head_hashfn(ht, tbl, obj, params);
691 lock = rht_bucket_lock(tbl, hash);
695 pprev = &tbl->buckets[hash];
696 rht_for_each(he, tbl, hash) {
702 rcu_assign_pointer(*pprev, obj->next);
707 spin_unlock_bh(lock);
713 * rhashtable_remove_fast - remove object from hash table
715 * @obj: pointer to hash head inside object
716 * @params: hash table parameters
718 * Since the hash chain is single linked, the removal operation needs to
719 * walk the bucket chain upon removal. The removal operation is thus
720 * considerable slow if the hash table is not correctly sized.
722 * Will automatically shrink the table via rhashtable_expand() if the
723 * shrink_decision function specified at rhashtable_init() returns true.
725 * Returns zero on success, -ENOENT if the entry could not be found.
727 static inline int rhashtable_remove_fast(
728 struct rhashtable *ht, struct rhash_head *obj,
729 const struct rhashtable_params params)
731 struct bucket_table *tbl;
736 tbl = rht_dereference_rcu(ht->tbl, ht);
738 /* Because we have already taken (and released) the bucket
739 * lock in old_tbl, if we find that future_tbl is not yet
740 * visible then that guarantees the entry to still be in
741 * the old tbl if it exists.
743 while ((err = __rhashtable_remove_fast(ht, tbl, obj, params)) &&
744 (tbl = rht_dereference_rcu(tbl->future_tbl, ht)))
750 atomic_dec(&ht->nelems);
751 if (rht_shrink_below_30(ht, tbl))
752 schedule_work(&ht->run_work);
760 #endif /* _LINUX_RHASHTABLE_H */