[Devel] [PATCH rh7 v3 2/2] tcache: speedup tcaches operations on empty tcache.

[Kirill Tkhai]

On 13.12.2016 15:39, Andrey Ryabinin wrote:
> If tcache is empty we can bail out immediately from
> tcache_cleancache_[get_page, invalidate_page,invalidate_inode]().
> As a fast way of identifying empty tcache this patch adds global atomic
> counter of tcache nodes.
> 
> https://jira.sw.ru/browse/PSBM-56475
> 
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>

Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>

> ---
> 
> Changes since v1:
> 	- switch to long counter to prevent possible overflows
> Changes since v2:
> 	- use *_dec() insrtead of bogus _inc() in tcache_node_release_fn()
> 	in v2 version
> 
>  mm/tcache.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/mm/tcache.c b/mm/tcache.c
> index cec5a4e..c7613b2 100644
> --- a/mm/tcache.c
> +++ b/mm/tcache.c
> @@ -98,6 +98,8 @@ struct tcache_pool {
>  	struct tcache_pool_nodeinfo	nodeinfo[0];
>  };
>  
> +static atomic_long_t nr_tcache_nodes;
> +
>  /*
>   * Tcache nodes correspond to inodes. A node is created automatically when a
>   * new page is added to the cache (cleancache_put_page) and destroyed either
> @@ -561,6 +563,7 @@ retry:
>  		node->pool = pool;
>  		node->key = *key;
>  		atomic_long_inc(&pool->nr_nodes);
> +		atomic_long_inc(&nr_tcache_nodes);
>  		__tcache_insert_node(&tree->root, node, rb_link, rb_parent);
>  	}
>  	spin_unlock_irqrestore(&tree->lock, flags);
> @@ -590,6 +593,7 @@ static void tcache_node_release_fn(struct kref *kref)
>  	__tcache_delete_node(&tree->root, node);
>  	spin_unlock(&tree->lock);
>  
> +	atomic_long_dec(&nr_tcache_nodes);
>  	atomic_long_dec(&node->pool->nr_nodes);
>  	kfree(node);
>  }
> @@ -1168,6 +1172,9 @@ static int tcache_cleancache_get_page(int pool_id,
>  	struct tcache_node *node;
>  	struct page *cache_page = NULL;
>  
> +	if (!atomic_long_read(&nr_tcache_nodes))
> +		return -1;
> +
>  	node = tcache_get_node_and_pool(pool_id, &key, false);
>  	if (node) {
>  		cache_page = tcache_detach_page(node, index, true);
> @@ -1192,6 +1199,9 @@ static void tcache_cleancache_invalidate_page(int pool_id,
>  	struct tcache_node *node;
>  	struct page *page;
>  
> +	if (!atomic_long_read(&nr_tcache_nodes))
> +		return;
> +
>  	node = tcache_get_node_and_pool(pool_id, &key, false);
>  	if (node) {
>  		page = tcache_detach_page(node, index, false);
> @@ -1206,6 +1216,9 @@ static void tcache_cleancache_invalidate_inode(int pool_id,
>  {
>  	struct tcache_pool *pool;
>  
> +	if (!atomic_long_read(&nr_tcache_nodes))
> +		return;
> +
>  	pool = tcache_get_pool(pool_id);
>  	if (pool) {
>  		tcache_invalidate_node(pool, &key);
>