/*
* 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>
#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
static void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he)
{
return (void *) he - ht->p.head_offset;
}
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 compute 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 compute 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 (ht->shift <= ht->p.min_shift)
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 __rcu **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(struct rhashtable_params *params)
{
return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
1UL << params->min_shift);
}
/**
* 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;
params->min_shift = max_t(size_t, params->min_shift,
ilog2(HASH_MIN_SIZE));
if (params->nelem_hint)
size = rounded_hashtable_size(params);
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. This function is not rcu safe, therefore the caller
* has to make sure that no resizing may happen by unpublishing the hashtable
* and waiting for the quiescent cycle before releasing the bucket array.
*/
void rhashtable_destroy(const struct rhashtable *ht)
{
bucket_table_free(ht->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 */
