rhashtable: Shrink to fit

 * rhashtable_shrink - Shrink hash table while allowing concurrent lookups

 * @ht:		the hash table to shrink

 *

 * 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.

 * This function shrinks the hash table to fit, i.e., the smallest

 * size would not cause it to expand right away automatically.

 *

 * The caller must ensure that no concurrent resizing occurs by holding

 * ht->mutex.

int rhashtable_shrink(struct rhashtable *ht)

{

	struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);

	unsigned size = roundup_pow_of_two(atomic_read(&ht->nelems) * 3 / 2);

	ASSERT_RHT_MUTEX(ht);

	new_tbl = bucket_table_alloc(ht, old_tbl->size / 2);

	if (size < ht->p.min_size)

		size = ht->p.min_size;

	if (old_tbl->size <= size)

		return 0;

	new_tbl = bucket_table_alloc(ht, size);

	if (new_tbl == NULL)

		return -ENOMEM;