[sheepdog] [PATCH] sheep: refactor object cache

[Liu Yuan]

On Tue, Dec 24, 2013 at 11:11:58AM +0900, Hitoshi Mitake wrote:

'refactor object cache' title is so big. Please write what your patches actually
did.

> This patch removes a confusing variable "in_push" of object cache. The
> most important change is removing a usleep() wait based on the
> variable.
> 
> Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
> ---
>  sheep/object_cache.c |   19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/sheep/object_cache.c b/sheep/object_cache.c
> index 10a051c..546f781 100644
> --- a/sheep/object_cache.c
> +++ b/sheep/object_cache.c
> @@ -61,7 +61,7 @@ struct object_cache {
>  	struct list_head lru_head; /* Per VDI LRU list for reclaimer */
>  	struct list_head dirty_head; /* Dirty objects linked to this list */
>  	int push_efd; /* Used to synchronize between pusher and push threads */
> -	uatomic_bool in_push; /* Whether if pusher is running */
> +	pthread_mutex_t push_mutex; /* mutex for pushing cache */
>  
>  	struct sd_lock lock; /* Cache lock */
>  };
> @@ -224,11 +224,11 @@ static void do_background_push(struct work *work)
>  	struct push_work *pw = container_of(work, struct push_work, work);
>  	struct object_cache *oc = pw->oc;
>  
> -	if (!uatomic_set_true(&oc->in_push))
> +	if (pthread_mutex_trylock(&oc->push_mutex) == EBUSY)
>  		return;
>  
>  	object_cache_push(oc);
> -	uatomic_set_false(&oc->in_push);
> +	pthread_mutex_unlock(&oc->push_mutex);
>  }
>  
>  static void background_push_done(struct work *work)
> @@ -263,13 +263,11 @@ static void add_to_dirty_list(struct object_cache_entry *entry)
>  	list_add_tail(&entry->dirty_list, &oc->dirty_head);
>  	/* FIXME read sys->status atomically */
>  	if (uatomic_add_return(&oc->dirty_count, 1) > MAX_DIRTY_OBJECT_COUNT
> -	    && !uatomic_is_true(&oc->in_push)
>  	    && sys->cinfo.status == SD_STATUS_OK)
>  		kick_background_pusher(oc);
>  }
>  
> -static inline void
> -free_cache_entry(struct object_cache_entry *entry)
> +static inline void free_cache_entry(struct object_cache_entry *entry)
>  {
>  	struct object_cache *oc = entry->oc;
>  
> @@ -638,6 +636,8 @@ not_found:
>  
>  		sd_init_lock(&cache->lock);
>  		hlist_add_head(&cache->hash, head);
> +
> +		pthread_mutex_init(&cache->push_mutex, NULL);
>  	} else {
>  		cache = NULL;
>  	}
> @@ -1191,11 +1191,10 @@ int object_cache_flush_vdi(uint32_t vid)
>  	 * that dirty bits produced while it is waiting are guaranteed
>  	 * to be pushed back
>  	 */
> -	while (!uatomic_set_true(&cache->in_push))
> -		usleep(100000);
> -
> +	pthread_mutex_lock(&cache->push_mutex);
>  	ret = object_cache_push(cache);
> -	uatomic_set_false(&cache->in_push);
> +	pthread_mutex_unlock(&cache->push_mutex);

pthread_mutex_*** can fail sometimes, I'd like you add a sd_mutex helpers which
can check ret value like sd_lock and use it in this patch.

Thanks
Yuan