[ltt-dev] [PATCH 4/6] rculfhash: Change lazy shrink strategy

[Mathieu Desnoyers]

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> We can aggressively grow a ht,

What allows us to state that agressive grow is OK ?

> but we should conservatively shrink a ht.
> 
> When we try to shrink the ht after a deletion,
> but if a growing is required after it, we should
> stop this shrink.
> 
> But it is more complicated to implement it, so we use more
> conservative strategy to shrink a ht to gain simple code:
> 
> We stop to (lazy) shrink when we found growing is
> in progress.
> 
> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> ---
>  rculfhash.c |   29 ++++++++++++++++++++++++++++-
>  1 files changed, 28 insertions(+), 1 deletions(-)
> 
> diff --git a/rculfhash.c b/rculfhash.c
> index c12ee10..5ff832d 100644
> --- a/rculfhash.c
> +++ b/rculfhash.c
> @@ -1797,6 +1797,33 @@ void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
>  	if (!(ht->flags & CDS_LFHT_AUTO_RESIZE))
>  		return;
>  
> -	resize_target_update_count(ht, count);
> +	count = max(count, ht->min_alloc_size);
> +	if (count == size)
> +		return;
> +
> +	if (count > size) { /* lazy grow */
> +		if (resize_target_grow(ht, count) >= count)
> +			return;
> +	} else { /* lazy shrink */
> +		for (;;) {
> +			unsigned long s;
> +
> +			s = uatomic_cmpxchg(&ht->t.resize_target, size, count);

you could remove the empty lines in this code segment.

> +
> +			if (s == size)
> +				break;
> +
> +			/* growing is/(was just) in progress */
> +			if (s > size)
> +				return;
> +
> +			/* some other thread do shrink for me*/

missing space above.

> +			if (s <= count)
> +				return;

Keeping the behavior of size check (change to patch 2) will probably
affect this.

Thanks,

Mathieu

> +
> +			size = s;
> +		}
> +	}
> +
>  	__cds_lfht_resize_lazy_launch(ht);
>  }
> -- 
> 1.7.4.4
> 

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