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Diffstat (limited to 'lib/rhashtable.c')
| -rw-r--r-- | lib/rhashtable.c | 797 |
1 files changed, 797 insertions, 0 deletions
diff --git a/lib/rhashtable.c b/lib/rhashtable.c new file mode 100644 index 000000000000..e6940cf16628 --- /dev/null +++ b/lib/rhashtable.c @@ -0,0 +1,797 @@ +/* + * Resizable, Scalable, Concurrent Hash Table + * + * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch> + * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net> + * + * Based on the following paper: + * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf + * + * Code partially derived from nft_hash + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/log2.h> +#include <linux/slab.h> +#include <linux/vmalloc.h> +#include <linux/mm.h> +#include <linux/hash.h> +#include <linux/random.h> +#include <linux/rhashtable.h> +#include <linux/log2.h> + +#define HASH_DEFAULT_SIZE 64UL +#define HASH_MIN_SIZE 4UL + +#define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT)) + +#ifdef CONFIG_PROVE_LOCKING +int lockdep_rht_mutex_is_held(const struct rhashtable *ht) +{ + return ht->p.mutex_is_held(); +} +EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held); +#endif + +/** + * rht_obj - cast hash head to outer object + * @ht: hash table + * @he: hashed node + */ +void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he) +{ + return (void *) he - ht->p.head_offset; +} +EXPORT_SYMBOL_GPL(rht_obj); + +static u32 __hashfn(const struct rhashtable *ht, const void *key, + u32 len, u32 hsize) +{ + u32 h; + + h = ht->p.hashfn(key, len, ht->p.hash_rnd); + + return h & (hsize - 1); +} + +/** + * rhashtable_hashfn - compute hash for key of given length + * @ht: hash table to compuate for + * @key: pointer to key + * @len: length of key + * + * Computes the hash value using the hash function provided in the 'hashfn' + * of struct rhashtable_params. The returned value is guaranteed to be + * smaller than the number of buckets in the hash table. + */ +u32 rhashtable_hashfn(const struct rhashtable *ht, const void *key, u32 len) +{ + struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht); + + return __hashfn(ht, key, len, tbl->size); +} +EXPORT_SYMBOL_GPL(rhashtable_hashfn); + +static u32 obj_hashfn(const struct rhashtable *ht, const void *ptr, u32 hsize) +{ + if (unlikely(!ht->p.key_len)) { + u32 h; + + h = ht->p.obj_hashfn(ptr, ht->p.hash_rnd); + + return h & (hsize - 1); + } + + return __hashfn(ht, ptr + ht->p.key_offset, ht->p.key_len, hsize); +} + +/** + * rhashtable_obj_hashfn - compute hash for hashed object + * @ht: hash table to compuate for + * @ptr: pointer to hashed object + * + * Computes the hash value using the hash function `hashfn` respectively + * 'obj_hashfn' depending on whether the hash table is set up to work with + * a fixed length key. The returned value is guaranteed to be smaller than + * the number of buckets in the hash table. + */ +u32 rhashtable_obj_hashfn(const struct rhashtable *ht, void *ptr) +{ + struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht); + + return obj_hashfn(ht, ptr, tbl->size); +} +EXPORT_SYMBOL_GPL(rhashtable_obj_hashfn); + +static u32 head_hashfn(const struct rhashtable *ht, + const struct rhash_head *he, u32 hsize) +{ + return obj_hashfn(ht, rht_obj(ht, he), hsize); +} + +static struct bucket_table *bucket_table_alloc(size_t nbuckets, gfp_t flags) +{ + struct bucket_table *tbl; + size_t size; + + size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]); + tbl = kzalloc(size, flags); + if (tbl == NULL) + tbl = vzalloc(size); + + if (tbl == NULL) + return NULL; + + tbl->size = nbuckets; + + return tbl; +} + +static void bucket_table_free(const struct bucket_table *tbl) +{ + kvfree(tbl); +} + +/** + * rht_grow_above_75 - returns true if nelems > 0.75 * table-size + * @ht: hash table + * @new_size: new table size + */ +bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size) +{ + /* Expand table when exceeding 75% load */ + return ht->nelems > (new_size / 4 * 3); +} +EXPORT_SYMBOL_GPL(rht_grow_above_75); + +/** + * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size + * @ht: hash table + * @new_size: new table size + */ +bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size) +{ + /* Shrink table beneath 30% load */ + return ht->nelems < (new_size * 3 / 10); +} +EXPORT_SYMBOL_GPL(rht_shrink_below_30); + +static void hashtable_chain_unzip(const struct rhashtable *ht, + const struct bucket_table *new_tbl, + struct bucket_table *old_tbl, size_t n) +{ + struct rhash_head *he, *p, *next; + unsigned int h; + + /* Old bucket empty, no work needed. */ + p = rht_dereference(old_tbl->buckets[n], ht); + if (!p) + return; + + /* Advance the old bucket pointer one or more times until it + * reaches a node that doesn't hash to the same bucket as the + * previous node p. Call the previous node p; + */ + h = head_hashfn(ht, p, new_tbl->size); + rht_for_each(he, p->next, ht) { + if (head_hashfn(ht, he, new_tbl->size) != h) + break; + p = he; + } + RCU_INIT_POINTER(old_tbl->buckets[n], p->next); + + /* Find the subsequent node which does hash to the same + * bucket as node P, or NULL if no such node exists. + */ + next = NULL; + if (he) { + rht_for_each(he, he->next, ht) { + if (head_hashfn(ht, he, new_tbl->size) == h) { + next = he; + break; + } + } + } + + /* Set p's next pointer to that subsequent node pointer, + * bypassing the nodes which do not hash to p's bucket + */ + RCU_INIT_POINTER(p->next, next); +} + +/** + * rhashtable_expand - Expand hash table while allowing concurrent lookups + * @ht: the hash table to expand + * @flags: allocation flags + * + * A secondary bucket array is allocated and the hash entries are migrated + * while keeping them on both lists until the end of the RCU grace period. + * + * This function may only be called in a context where it is safe to call + * synchronize_rcu(), e.g. not within a rcu_read_lock() section. + * + * The caller must ensure that no concurrent table mutations take place. + * It is however valid to have concurrent lookups if they are RCU protected. + */ +int rhashtable_expand(struct rhashtable *ht, gfp_t flags) +{ + struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht); + struct rhash_head *he; + unsigned int i, h; + bool complete; + + ASSERT_RHT_MUTEX(ht); + + if (ht->p.max_shift && ht->shift >= ht->p.max_shift) + return 0; + + new_tbl = bucket_table_alloc(old_tbl->size * 2, flags); + if (new_tbl == NULL) + return -ENOMEM; + + ht->shift++; + + /* For each new bucket, search the corresponding old bucket + * for the first entry that hashes to the new bucket, and + * link the new bucket to that entry. Since all the entries + * which will end up in the new bucket appear in the same + * old bucket, this constructs an entirely valid new hash + * table, but with multiple buckets "zipped" together into a + * single imprecise chain. + */ + for (i = 0; i < new_tbl->size; i++) { + h = i & (old_tbl->size - 1); + rht_for_each(he, old_tbl->buckets[h], ht) { + if (head_hashfn(ht, he, new_tbl->size) == i) { + RCU_INIT_POINTER(new_tbl->buckets[i], he); + break; + } + } + } + + /* Publish the new table pointer. Lookups may now traverse + * the new table, but they will not benefit from any + * additional efficiency until later steps unzip the buckets. + */ + rcu_assign_pointer(ht->tbl, new_tbl); + + /* Unzip interleaved hash chains */ + do { + /* Wait for readers. All new readers will see the new + * table, and thus no references to the old table will + * remain. + */ + synchronize_rcu(); + + /* For each bucket in the old table (each of which + * contains items from multiple buckets of the new + * table): ... + */ + complete = true; + for (i = 0; i < old_tbl->size; i++) { + hashtable_chain_unzip(ht, new_tbl, old_tbl, i); + if (old_tbl->buckets[i] != NULL) + complete = false; + } + } while (!complete); + + bucket_table_free(old_tbl); + return 0; +} +EXPORT_SYMBOL_GPL(rhashtable_expand); + +/** + * rhashtable_shrink - Shrink hash table while allowing concurrent lookups + * @ht: the hash table to shrink + * @flags: allocation flags + * + * This function may only be called in a context where it is safe to call + * synchronize_rcu(), e.g. not within a rcu_read_lock() section. + * + * The caller must ensure that no concurrent table mutations take place. + * It is however valid to have concurrent lookups if they are RCU protected. + */ +int rhashtable_shrink(struct rhashtable *ht, gfp_t flags) +{ + struct bucket_table *ntbl, *tbl = rht_dereference(ht->tbl, ht); + struct rhash_head __rcu **pprev; + unsigned int i; + + ASSERT_RHT_MUTEX(ht); + + if (tbl->size <= HASH_MIN_SIZE) + return 0; + + ntbl = bucket_table_alloc(tbl->size / 2, flags); + if (ntbl == NULL) + return -ENOMEM; + + ht->shift--; + + /* Link each bucket in the new table to the first bucket + * in the old table that contains entries which will hash + * to the new bucket. + */ + for (i = 0; i < ntbl->size; i++) { + ntbl->buckets[i] = tbl->buckets[i]; + + /* Link each bucket in the new table to the first bucket + * in the old table that contains entries which will hash + * to the new bucket. + */ + for (pprev = &ntbl->buckets[i]; *pprev != NULL; + pprev = &rht_dereference(*pprev, ht)->next) + ; + RCU_INIT_POINTER(*pprev, tbl->buckets[i + ntbl->size]); + } + + /* Publish the new, valid hash table */ + rcu_assign_pointer(ht->tbl, ntbl); + + /* Wait for readers. No new readers will have references to the + * old hash table. + */ + synchronize_rcu(); + + bucket_table_free(tbl); + + return 0; +} +EXPORT_SYMBOL_GPL(rhashtable_shrink); + +/** + * rhashtable_insert - insert object into hash hash table + * @ht: hash table + * @obj: pointer to hash head inside object + * @flags: allocation flags (table expansion) + * + * Will automatically grow the table via rhashtable_expand() if the the + * grow_decision function specified at rhashtable_init() returns true. + * + * The caller must ensure that no concurrent table mutations occur. It is + * however valid to have concurrent lookups if they are RCU protected. + */ +void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj, + gfp_t flags) +{ + struct bucket_table *tbl = rht_dereference(ht->tbl, ht); + u32 hash; + + ASSERT_RHT_MUTEX(ht); + + hash = head_hashfn(ht, obj, tbl->size); + RCU_INIT_POINTER(obj->next, tbl->buckets[hash]); + rcu_assign_pointer(tbl->buckets[hash], obj); + ht->nelems++; + + if (ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size)) + rhashtable_expand(ht, flags); +} +EXPORT_SYMBOL_GPL(rhashtable_insert); + +/** + * rhashtable_remove_pprev - remove object from hash table given previous element + * @ht: hash table + * @obj: pointer to hash head inside object + * @pprev: pointer to previous element + * @flags: allocation flags (table expansion) + * + * Identical to rhashtable_remove() but caller is alreayd aware of the element + * in front of the element to be deleted. This is in particular useful for + * deletion when combined with walking or lookup. + */ +void rhashtable_remove_pprev(struct rhashtable *ht, struct rhash_head *obj, + struct rhash_head **pprev, gfp_t flags) +{ + struct bucket_table *tbl = rht_dereference(ht->tbl, ht); + + ASSERT_RHT_MUTEX(ht); + + RCU_INIT_POINTER(*pprev, obj->next); + ht->nelems--; + + if (ht->p.shrink_decision && + ht->p.shrink_decision(ht, tbl->size)) + rhashtable_shrink(ht, flags); +} +EXPORT_SYMBOL_GPL(rhashtable_remove_pprev); + +/** + * rhashtable_remove - remove object from hash table + * @ht: hash table + * @obj: pointer to hash head inside object + * @flags: allocation flags (table expansion) + * + * Since the hash chain is single linked, the removal operation needs to + * walk the bucket chain upon removal. The removal operation is thus + * considerable slow if the hash table is not correctly sized. + * + * Will automatically shrink the table via rhashtable_expand() if the the + * shrink_decision function specified at rhashtable_init() returns true. + * + * The caller must ensure that no concurrent table mutations occur. It is + * however valid to have concurrent lookups if they are RCU protected. + */ +bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj, + gfp_t flags) +{ + struct bucket_table *tbl = rht_dereference(ht->tbl, ht); + struct rhash_head __rcu **pprev; + struct rhash_head *he; + u32 h; + + ASSERT_RHT_MUTEX(ht); + + h = head_hashfn(ht, obj, tbl->size); + + pprev = &tbl->buckets[h]; + rht_for_each(he, tbl->buckets[h], ht) { + if (he != obj) { + pprev = &he->next; + continue; + } + + rhashtable_remove_pprev(ht, he, pprev, flags); + return true; + } + + return false; +} +EXPORT_SYMBOL_GPL(rhashtable_remove); + +/** + * rhashtable_lookup - lookup key in hash table + * @ht: hash table + * @key: pointer to key + * + * Computes the hash value for the key and traverses the bucket chain looking + * for a entry with an identical key. The first matching entry is returned. + * + * This lookup function may only be used for fixed key hash table (key_len + * paramter set). It will BUG() if used inappropriately. + * + * Lookups may occur in parallel with hash mutations as long as the lookup is + * guarded by rcu_read_lock(). The caller must take care of this. + */ +void *rhashtable_lookup(const struct rhashtable *ht, const void *key) +{ + const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht); + struct rhash_head *he; + u32 h; + + BUG_ON(!ht->p.key_len); + + h = __hashfn(ht, key, ht->p.key_len, tbl->size); + rht_for_each_rcu(he, tbl->buckets[h], ht) { + if (memcmp(rht_obj(ht, he) + ht->p.key_offset, key, + ht->p.key_len)) + continue; + return (void *) he - ht->p.head_offset; + } + + return NULL; +} +EXPORT_SYMBOL_GPL(rhashtable_lookup); + +/** + * rhashtable_lookup_compare - search hash table with compare function + * @ht: hash table + * @hash: hash value of desired entry + * @compare: compare function, must return true on match + * @arg: argument passed on to compare function + * + * Traverses the bucket chain behind the provided hash value and calls the + * specified compare function for each entry. + * + * Lookups may occur in parallel with hash mutations as long as the lookup is + * guarded by rcu_read_lock(). The caller must take care of this. + * + * Returns the first entry on which the compare function returned true. + */ +void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash, + bool (*compare)(void *, void *), void *arg) +{ + const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht); + struct rhash_head *he; + + if (unlikely(hash >= tbl->size)) + return NULL; + + rht_for_each_rcu(he, tbl->buckets[hash], ht) { + if (!compare(rht_obj(ht, he), arg)) + continue; + return (void *) he - ht->p.head_offset; + } + + return NULL; +} +EXPORT_SYMBOL_GPL(rhashtable_lookup_compare); + +static size_t rounded_hashtable_size(unsigned int nelem) +{ + return max(roundup_pow_of_two(nelem * 4 / 3), HASH_MIN_SIZE); +} + +/** + * rhashtable_init - initialize a new hash table + * @ht: hash table to be initialized + * @params: configuration parameters + * + * Initializes a new hash table based on the provided configuration + * parameters. A table can be configured either with a variable or + * fixed length key: + * + * Configuration Example 1: Fixed length keys + * struct test_obj { + * int key; + * void * my_member; + * struct rhash_head node; + * }; + * + * struct rhashtable_params params = { + * .head_offset = offsetof(struct test_obj, node), + * .key_offset = offsetof(struct test_obj, key), + * .key_len = sizeof(int), + * .hashfn = arch_fast_hash, + * .mutex_is_held = &my_mutex_is_held, + * }; + * + * Configuration Example 2: Variable length keys + * struct test_obj { + * [...] + * struct rhash_head node; + * }; + * + * u32 my_hash_fn(const void *data, u32 seed) + * { + * struct test_obj *obj = data; + * + * return [... hash ...]; + * } + * + * struct rhashtable_params params = { + * .head_offset = offsetof(struct test_obj, node), + * .hashfn = arch_fast_hash, + * .obj_hashfn = my_hash_fn, + * .mutex_is_held = &my_mutex_is_held, + * }; + */ +int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params) +{ + struct bucket_table *tbl; + size_t size; + + size = HASH_DEFAULT_SIZE; + + if ((params->key_len && !params->hashfn) || + (!params->key_len && !params->obj_hashfn)) + return -EINVAL; + + if (params->nelem_hint) + size = rounded_hashtable_size(params->nelem_hint); + + tbl = bucket_table_alloc(size, GFP_KERNEL); + if (tbl == NULL) + return -ENOMEM; + + memset(ht, 0, sizeof(*ht)); + ht->shift = ilog2(tbl->size); + memcpy(&ht->p, params, sizeof(*params)); + RCU_INIT_POINTER(ht->tbl, tbl); + + if (!ht->p.hash_rnd) + get_random_bytes(&ht->p.hash_rnd, sizeof(ht->p.hash_rnd)); + + return 0; +} +EXPORT_SYMBOL_GPL(rhashtable_init); + +/** + * rhashtable_destroy - destroy hash table + * @ht: the hash table to destroy + * + * Frees the bucket array. + */ +void rhashtable_destroy(const struct rhashtable *ht) +{ + const struct bucket_table *tbl = rht_dereference(ht->tbl, ht); + + bucket_table_free(tbl); +} +EXPORT_SYMBOL_GPL(rhashtable_destroy); + +/************************************************************************** + * Self Test + **************************************************************************/ + +#ifdef CONFIG_TEST_RHASHTABLE + +#define TEST_HT_SIZE 8 +#define TEST_ENTRIES 2048 +#define TEST_PTR ((void *) 0xdeadbeef) +#define TEST_NEXPANDS 4 + +static int test_mutex_is_held(void) +{ + return 1; +} + +struct test_obj { + void *ptr; + int value; + struct rhash_head node; +}; + +static int __init test_rht_lookup(struct rhashtable *ht) +{ + unsigned int i; + + for (i = 0; i < TEST_ENTRIES * 2; i++) { + struct test_obj *obj; + bool expected = !(i % 2); + u32 key = i; + + obj = rhashtable_lookup(ht, &key); + + if (expected && !obj) { + pr_warn("Test failed: Could not find key %u\n", key); + return -ENOENT; + } else if (!expected && obj) { + pr_warn("Test failed: Unexpected entry found for key %u\n", + key); + return -EEXIST; + } else if (expected && obj) { + if (obj->ptr != TEST_PTR || obj->value != i) { + pr_warn("Test failed: Lookup value mismatch %p!=%p, %u!=%u\n", + obj->ptr, TEST_PTR, obj->value, i); + return -EINVAL; + } + } + } + + return 0; +} + +static void test_bucket_stats(struct rhashtable *ht, + struct bucket_table *tbl, + bool quiet) +{ + unsigned int cnt, i, total = 0; + struct test_obj *obj; + + for (i = 0; i < tbl->size; i++) { + cnt = 0; + + if (!quiet) + pr_info(" [%#4x/%zu]", i, tbl->size); + + rht_for_each_entry_rcu(obj, tbl->buckets[i], node) { + cnt++; + total++; + if (!quiet) + pr_cont(" [%p],", obj); + } + + if (!quiet) + pr_cont("\n [%#x] first element: %p, chain length: %u\n", + i, tbl->buckets[i], cnt); + } + + pr_info(" Traversal complete: counted=%u, nelems=%zu, entries=%d\n", + total, ht->nelems, TEST_ENTRIES); +} + +static int __init test_rhashtable(struct rhashtable *ht) +{ + struct bucket_table *tbl; + struct test_obj *obj, *next; + int err; + unsigned int i; + + /* + * Insertion Test: + * Insert TEST_ENTRIES into table with all keys even numbers + */ + pr_info(" Adding %d keys\n", TEST_ENTRIES); + for (i = 0; i < TEST_ENTRIES; i++) { + struct test_obj *obj; + + obj = kzalloc(sizeof(*obj), GFP_KERNEL); + if (!obj) { + err = -ENOMEM; + goto error; + } + + obj->ptr = TEST_PTR; + obj->value = i * 2; + + rhashtable_insert(ht, &obj->node, GFP_KERNEL); + } + + rcu_read_lock(); + tbl = rht_dereference_rcu(ht->tbl, ht); + test_bucket_stats(ht, tbl, true); + test_rht_lookup(ht); + rcu_read_unlock(); + + for (i = 0; i < TEST_NEXPANDS; i++) { + pr_info(" Table expansion iteration %u...\n", i); + rhashtable_expand(ht, GFP_KERNEL); + + rcu_read_lock(); + pr_info(" Verifying lookups...\n"); + test_rht_lookup(ht); + rcu_read_unlock(); + } + + for (i = 0; i < TEST_NEXPANDS; i++) { + pr_info(" Table shrinkage iteration %u...\n", i); + rhashtable_shrink(ht, GFP_KERNEL); + + rcu_read_lock(); + pr_info(" Verifying lookups...\n"); + test_rht_lookup(ht); + rcu_read_unlock(); + } + + pr_info(" Deleting %d keys\n", TEST_ENTRIES); + for (i = 0; i < TEST_ENTRIES; i++) { + u32 key = i * 2; + + obj = rhashtable_lookup(ht, &key); + BUG_ON(!obj); + + rhashtable_remove(ht, &obj->node, GFP_KERNEL); + kfree(obj); + } + + return 0; + +error: + tbl = rht_dereference_rcu(ht->tbl, ht); + for (i = 0; i < tbl->size; i++) + rht_for_each_entry_safe(obj, next, tbl->buckets[i], ht, node) + kfree(obj); + + return err; +} + +static int __init test_rht_init(void) +{ + struct rhashtable ht; + struct rhashtable_params params = { + .nelem_hint = TEST_HT_SIZE, + .head_offset = offsetof(struct test_obj, node), + .key_offset = offsetof(struct test_obj, value), + .key_len = sizeof(int), + .hashfn = arch_fast_hash, + .mutex_is_held = &test_mutex_is_held, + .grow_decision = rht_grow_above_75, + .shrink_decision = rht_shrink_below_30, + }; + int err; + + pr_info("Running resizable hashtable tests...\n"); + + err = rhashtable_init(&ht, ¶ms); + if (err < 0) { + pr_warn("Test failed: Unable to initialize hashtable: %d\n", + err); + return err; + } + + err = test_rhashtable(&ht); + + rhashtable_destroy(&ht); + + return err; +} + +subsys_initcall(test_rht_init); + +#endif /* CONFIG_TEST_RHASHTABLE */ |