[ltt-dev] [PATCH 05/10 round10] add max_size arguemnt

[Mathieu Desnoyers]

arguemnt -> argument

I think we need to discuss the semantic of max_size: here, you propose
that max_size is just the number of buckets, but it does not limit the
ability of the table to contain more elements than max_size.

IMHO, it would be nice to have max_size limit the number of elements
that the table can accept, e.g. ensuring that insertion fails if the
number of elements gets over the max_size threshold. It might not need
to be an exact thing though, just giving an approximated upper limit
might be fine (using the split-counters), as long as it is documented.

Thanks,

Mathieu

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> ---
>  rculfhash.c            |   17 +++++++++++++++++
>  tests/test_urcu_hash.c |    2 +-
>  urcu/rculfhash.h       |    9 ++++++---
>  3 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/rculfhash.c b/rculfhash.c
> index 2df133c..b7be893 100644
> --- a/rculfhash.c
> +++ b/rculfhash.c
> @@ -266,6 +266,7 @@ struct cds_lfht {
>  	struct rcu_table t;
>  	unsigned long min_alloc_order;
>  	unsigned long min_alloc_size;
> +	unsigned long max_size;
>  	int flags;
>  	/*
>  	 * We need to put the work threads offline (QSBR) when taking this
> @@ -1351,6 +1352,7 @@ void cds_lfht_create_bucket(struct cds_lfht *ht, unsigned long size)
>  
>  struct cds_lfht *_cds_lfht_new(unsigned long init_size,
>  			unsigned long min_alloc_size,
> +			unsigned long max_size,
>  			int flags,
>  			void (*cds_lfht_call_rcu)(struct rcu_head *head,
>  					void (*func)(struct rcu_head *head)),
> @@ -1369,11 +1371,22 @@ struct cds_lfht *_cds_lfht_new(unsigned long init_size,
>  	/* min_alloc_size must be power of two */
>  	if (!min_alloc_size || (min_alloc_size & (min_alloc_size - 1)))
>  		return NULL;
> +
>  	/* init_size must be power of two */
>  	if (!init_size || (init_size & (init_size - 1)))
>  		return NULL;
> +
> +	if (!max_size)
> +		max_size = 1UL << (MAX_TABLE_ORDER - 1);
> +
> +	/* max_size must be power of two */
> +	if (!max_size || (max_size & (max_size - 1)))
> +		return NULL;
> +
>  	min_alloc_size = max(min_alloc_size, MIN_TABLE_SIZE);
>  	init_size = max(init_size, MIN_TABLE_SIZE);
> +	max_size = max(max_size, min_alloc_size);
> +	init_size = min(init_size, max_size);
>  	ht = calloc(1, sizeof(struct cds_lfht));
>  	assert(ht);
>  	ht->flags = flags;
> @@ -1393,6 +1406,7 @@ struct cds_lfht *_cds_lfht_new(unsigned long init_size,
>  	ht->t.resize_target = 1UL << order;
>  	ht->min_alloc_size = min_alloc_size;
>  	ht->min_alloc_order = get_count_order_ulong(min_alloc_size);
> +	ht->max_size = max_size;
>  	cds_lfht_create_bucket(ht, 1UL << order);
>  	ht->t.size = 1UL << order;
>  	return ht;
> @@ -1752,6 +1766,7 @@ void resize_target_update_count(struct cds_lfht *ht,
>  				unsigned long count)
>  {
>  	count = max(count, MIN_TABLE_SIZE);
> +	count = min(count, ht->max_size);
>  	uatomic_set(&ht->t.resize_target, count);
>  }
>  
> @@ -1809,6 +1824,7 @@ void cds_lfht_resize_lazy_grow(struct cds_lfht *ht, unsigned long size, int grow
>  {
>  	unsigned long target_size = size << growth;
>  
> +	target_size = min(target_size, ht->max_size);
>  	if (resize_target_grow(ht, target_size) >= target_size)
>  		return;
>  
> @@ -1827,6 +1843,7 @@ void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
>  	if (!(ht->flags & CDS_LFHT_AUTO_RESIZE))
>  		return;
>  	count = max(count, MIN_TABLE_SIZE);
> +	count = min(count, ht->max_size);
>  	if (count == size)
>  		return;		/* Already the right size, no resize needed */
>  	if (count > size) {	/* lazy grow */
> diff --git a/tests/test_urcu_hash.c b/tests/test_urcu_hash.c
> index b9e3e81..2961177 100644
> --- a/tests/test_urcu_hash.c
> +++ b/tests/test_urcu_hash.c
> @@ -967,7 +967,7 @@ int main(int argc, char **argv)
>  	 * thread from the point of view of resize.
>  	 */
>  	rcu_register_thread();
> -	test_ht = cds_lfht_new(init_hash_size, min_hash_alloc_size,
> +	test_ht = cds_lfht_new(init_hash_size, min_hash_alloc_size, (1UL << 18),
>  			(opt_auto_resize ? CDS_LFHT_AUTO_RESIZE : 0) |
>  			CDS_LFHT_ACCOUNTING, NULL);
>        	ret = populate_hash();
> diff --git a/urcu/rculfhash.h b/urcu/rculfhash.h
> index c13d3df..2eefd2c 100644
> --- a/urcu/rculfhash.h
> +++ b/urcu/rculfhash.h
> @@ -98,6 +98,7 @@ enum {
>   */
>  struct cds_lfht *_cds_lfht_new(unsigned long init_size,
>  			unsigned long min_alloc_size,
> +			unsigned long max_size,
>  			int flags,
>  			void (*cds_lfht_call_rcu)(struct rcu_head *head,
>  				void (*func)(struct rcu_head *head)),
> @@ -112,8 +113,9 @@ struct cds_lfht *_cds_lfht_new(unsigned long init_size,
>  
>  /*
>   * cds_lfht_new - allocate a hash table.
> - * @init_size: number of nodes to allocate initially. Must be power of two.
> - * @min_alloc_size: the smallest allocation size to use. Must be power of two.
> + * @init_size: number of buckets to allocate initially. Must be power of two.
> + * @min_alloc_size: the smallest allocation buckets size to use. Must be power of two.
> + * @max_size: the max size of buckets for future growing. Must be power of two.
>   * @flags: hash table creation flags (can be combined with bitwise or: '|').
>   *           0: no flags.
>   *           CDS_LFHT_AUTO_RESIZE: automatically resize hash table.
> @@ -134,10 +136,11 @@ struct cds_lfht *_cds_lfht_new(unsigned long init_size,
>  static inline
>  struct cds_lfht *cds_lfht_new(unsigned long init_size,
>  			unsigned long min_alloc_size,
> +			unsigned long max_size,
>  			int flags,
>  			pthread_attr_t *attr)
>  {
> -	return _cds_lfht_new(init_size, min_alloc_size, flags,
> +	return _cds_lfht_new(init_size, min_alloc_size, max_size, flags,
>  			call_rcu, synchronize_rcu, rcu_read_lock,
>  			rcu_read_unlock, rcu_thread_offline,
>  			rcu_thread_online, rcu_register_thread,
> -- 
> 1.7.4.4
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com