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rhashtable: kill ht->shift atomic operations

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Commit c0c09bfdc4 ("rhashtable: avoid unnecessary wakeup for worker
queue") changed ht->shift to be atomic, which is actually unnecessary.

Instead of leaving the current shift in the core rhashtable structure,
it can be cached inside the individual bucket tables.

There, it will only be initialized once during a new table allocation
in the shrink/expansion slow path, and from then onward it stays immutable
for the rest of the bucket table liftime.

That allows shift to be non-atomic. The patch also moves hash_rnd
management into the table setup. The rhashtable structure now consumes
3 instead of 4 cachelines.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ying Xue <ying.xue@windriver.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Daniel Borkmann 2015-03-12 15:28:40 +01:00 committed by David S. Miller
parent 9497df88ab
commit a5b6846f9e
2 changed files with 28 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/rhashtable.h
View File

@ -50,6 +50,7 @@ struct rhash_head {
* struct bucket_table - Table of hash buckets
* @size: Number of hash buckets
* @hash_rnd: Random seed to fold into hash
* @shift: Current size (1 << shift)
* @locks_mask: Mask to apply before accessing locks[]
* @locks: Array of spinlocks protecting individual buckets
* @buckets: size * hash buckets
@ -57,6 +58,7 @@ struct rhash_head {
struct bucket_table {
size_t size;
u32 hash_rnd;
u32 shift;
unsigned int locks_mask;
spinlock_t *locks;
@ -99,7 +101,6 @@ struct rhashtable_params {
* @tbl: Bucket table
* @future_tbl: Table under construction during expansion/shrinking
* @nelems: Number of elements in table
* @shift: Current size (1 << shift)
* @p: Configuration parameters
* @run_work: Deferred worker to expand/shrink asynchronously
* @mutex: Mutex to protect current/future table swapping
@ -110,12 +111,11 @@ struct rhashtable {
struct bucket_table __rcu *tbl;
struct bucket_table __rcu *future_tbl;
atomic_t nelems;
atomic_t shift;
bool being_destroyed;
struct rhashtable_params p;
struct work_struct run_work;
struct mutex mutex;
struct list_head walkers;
bool being_destroyed;
};
/**

55
lib/rhashtable.c
View File

@ -147,7 +147,7 @@ static void bucket_table_free(const struct bucket_table *tbl)
}
static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
size_t nbuckets)
size_t nbuckets, u32 hash_rnd)
{
struct bucket_table *tbl = NULL;
size_t size;
@ -162,6 +162,8 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
return NULL;
tbl->size = nbuckets;
tbl->shift = ilog2(nbuckets);
tbl->hash_rnd = hash_rnd;
if (alloc_bucket_locks(ht, tbl) < 0) {
bucket_table_free(tbl);
@ -177,25 +179,27 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
/**
* rht_grow_above_75 - returns true if nelems > 0.75 * table-size
* @ht: hash table
* @new_size: new table size
* @tbl: current table
*/
static bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size)
static bool rht_grow_above_75(const struct rhashtable *ht,
const struct bucket_table *tbl)
{
/* Expand table when exceeding 75% load */
return atomic_read(&ht->nelems) > (new_size / 4 * 3) &&
(!ht->p.max_shift || atomic_read(&ht->shift) < ht->p.max_shift);
return atomic_read(&ht->nelems) > (tbl->size / 4 * 3) &&
(!ht->p.max_shift || tbl->shift < ht->p.max_shift);
}
/**
* rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
* @ht: hash table
* @new_size: new table size
* @tbl: current table
*/
static bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size)
static bool rht_shrink_below_30(const struct rhashtable *ht,
const struct bucket_table *tbl)
{
/* Shrink table beneath 30% load */
return atomic_read(&ht->nelems) < (new_size * 3 / 10) &&
(atomic_read(&ht->shift) > ht->p.min_shift);
return atomic_read(&ht->nelems) < (tbl->size * 3 / 10) &&
tbl->shift > ht->p.min_shift;
}
static int rhashtable_rehash_one(struct rhashtable *ht, unsigned old_hash)
@ -310,16 +314,11 @@ int rhashtable_expand(struct rhashtable *ht)
ASSERT_RHT_MUTEX(ht);
new_tbl = bucket_table_alloc(ht, old_tbl->size * 2);
new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, old_tbl->hash_rnd);
if (new_tbl == NULL)
return -ENOMEM;
new_tbl->hash_rnd = old_tbl->hash_rnd;
atomic_inc(&ht->shift);
rhashtable_rehash(ht, new_tbl);
return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_expand);
@ -342,20 +341,15 @@ EXPORT_SYMBOL_GPL(rhashtable_expand);
*/
int rhashtable_shrink(struct rhashtable *ht)
{
struct bucket_table *new_tbl, *tbl = rht_dereference(ht->tbl, ht);
struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
ASSERT_RHT_MUTEX(ht);
new_tbl = bucket_table_alloc(ht, tbl->size / 2);
new_tbl = bucket_table_alloc(ht, old_tbl->size / 2, old_tbl->hash_rnd);
if (new_tbl == NULL)
return -ENOMEM;
new_tbl->hash_rnd = tbl->hash_rnd;
atomic_dec(&ht->shift);
rhashtable_rehash(ht, new_tbl);
return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_shrink);
@ -376,9 +370,9 @@ static void rht_deferred_worker(struct work_struct *work)
list_for_each_entry(walker, &ht->walkers, list)
walker->resize = true;
if (rht_grow_above_75(ht, tbl->size))
if (rht_grow_above_75(ht, tbl))
rhashtable_expand(ht);
else if (rht_shrink_below_30(ht, tbl->size))
else if (rht_shrink_below_30(ht, tbl))
rhashtable_shrink(ht);
unlock:
mutex_unlock(&ht->mutex);
@ -431,7 +425,7 @@ static bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
rcu_assign_pointer(tbl->buckets[hash], obj);
atomic_inc(&ht->nelems);
if (no_resize_running && rht_grow_above_75(ht, tbl->size))
if (no_resize_running && rht_grow_above_75(ht, tbl))
schedule_work(&ht->run_work);
exit:
@ -539,7 +533,7 @@ bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj)
bool no_resize_running = tbl == old_tbl;
atomic_dec(&ht->nelems);
if (no_resize_running && rht_shrink_below_30(ht, tbl->size))
if (no_resize_running && rht_shrink_below_30(ht, tbl))
schedule_work(&ht->run_work);
}
@ -913,6 +907,7 @@ int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
{
struct bucket_table *tbl;
size_t size;
u32 hash_rnd;
size = HASH_DEFAULT_SIZE;
@ -939,14 +934,14 @@ int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
else
ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
tbl = bucket_table_alloc(ht, size);
get_random_bytes(&hash_rnd, sizeof(hash_rnd));
tbl = bucket_table_alloc(ht, size, hash_rnd);
if (tbl == NULL)
return -ENOMEM;
get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
atomic_set(&ht->nelems, 0);
atomic_set(&ht->shift, ilog2(tbl->size));
RCU_INIT_POINTER(ht->tbl, tbl);
RCU_INIT_POINTER(ht->future_tbl, tbl);