Re: [PATCH 7/9] lib: radix-tree: update callback for changing leaf nodes

[Jan Kara]

On Thu 17-11-16 14:31:34, Johannes Weiner wrote:
> Support handing __radix_tree_replace() a callback that gets invoked
> for all leaf nodes that change or get freed as a result of the slot
> replacement, to assist users tracking nodes with node->private_list.
> 
> This prepares for putting page cache shadow entries into the radix
> tree root again and drastically simplifying the shadow tracking.
> 
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/dax.c                   |  3 ++-
>  include/linux/radix-tree.h |  4 +++-
>  lib/radix-tree.c           | 42 +++++++++++++++++++++++++++++-------------
>  mm/shmem.c                 |  3 ++-
>  4 files changed, 36 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 85930c2a2749..6916ed37d463 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -649,7 +649,8 @@ static void *dax_insert_mapping_entry(struct address_space *mapping,
>  
>  		ret = __radix_tree_lookup(page_tree, index, &node, &slot);
>  		WARN_ON_ONCE(ret != entry);
> -		__radix_tree_replace(page_tree, node, slot, new_entry);
> +		__radix_tree_replace(page_tree, node, slot,
> +				     new_entry, NULL, NULL);
>  	}
>  	if (vmf->flags & FAULT_FLAG_WRITE)
>  		radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index 2d1b9b8be983..15c972ea9510 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -263,9 +263,11 @@ void *__radix_tree_lookup(struct radix_tree_root *root, unsigned long index,
>  			  struct radix_tree_node **nodep, void ***slotp);
>  void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
>  void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
> +typedef void (*radix_tree_update_node_t)(struct radix_tree_node *, void *);
>  void __radix_tree_replace(struct radix_tree_root *root,
>  			  struct radix_tree_node *node,
> -			  void **slot, void *item);
> +			  void **slot, void *item,
> +			  radix_tree_update_node_t update_node, void *private);
>  void radix_tree_replace_slot(struct radix_tree_root *root,
>  			     void **slot, void *item);
>  bool __radix_tree_delete_node(struct radix_tree_root *root,
> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index 5d8930f3b3d8..df4ff18dd63c 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -325,7 +325,6 @@ static void radix_tree_node_rcu_free(struct rcu_head *head)
>  		tag_clear(node, i, 0);
>  
>  	node->slots[0] = NULL;
> -	node->count = 0;
>  
>  	kmem_cache_free(radix_tree_node_cachep, node);
>  }
> @@ -542,7 +541,9 @@ static int radix_tree_extend(struct radix_tree_root *root,
>   *	radix_tree_shrink    -    shrink radix tree to minimum height
>   *	@root		radix tree root
>   */
> -static inline bool radix_tree_shrink(struct radix_tree_root *root)
> +static inline bool radix_tree_shrink(struct radix_tree_root *root,
> +				     radix_tree_update_node_t update_node,
> +				     void *private)
>  {
>  	bool shrunk = false;
>  
> @@ -597,8 +598,12 @@ static inline bool radix_tree_shrink(struct radix_tree_root *root)
>  		 * also results in a stale slot). So tag the slot as indirect
>  		 * to force callers to retry.
>  		 */
> -		if (!radix_tree_is_internal_node(child))
> +		node->count = 0;
> +		if (!radix_tree_is_internal_node(child)) {
>  			node->slots[0] = RADIX_TREE_RETRY;
> +			if (update_node)
> +				update_node(node, private);
> +		}
>  
>  		radix_tree_node_free(node);
>  		shrunk = true;
> @@ -608,7 +613,8 @@ static inline bool radix_tree_shrink(struct radix_tree_root *root)
>  }
>  
>  static bool delete_node(struct radix_tree_root *root,
> -			struct radix_tree_node *node)
> +			struct radix_tree_node *node,
> +			radix_tree_update_node_t update_node, void *private)
>  {
>  	bool deleted = false;
>  
> @@ -617,7 +623,8 @@ static bool delete_node(struct radix_tree_root *root,
>  
>  		if (node->count) {
>  			if (node == entry_to_node(root->rnode))
> -				deleted |= radix_tree_shrink(root);
> +				deleted |= radix_tree_shrink(root, update_node,
> +							     private);
>  			return deleted;
>  		}
>  
> @@ -880,17 +887,20 @@ static void replace_slot(struct radix_tree_root *root,
>  
>  /**
>   * __radix_tree_replace		- replace item in a slot
> - * @root:	radix tree root
> - * @node:	pointer to tree node
> - * @slot:	pointer to slot in @node
> - * @item:	new item to store in the slot.
> + * @root:		radix tree root
> + * @node:		pointer to tree node
> + * @slot:		pointer to slot in @node
> + * @item:		new item to store in the slot.
> + * @update_node:	callback for changing leaf nodes
> + * @private:		private data to pass to @update_node
>   *
>   * For use with __radix_tree_lookup().  Caller must hold tree write locked
>   * across slot lookup and replacement.
>   */
>  void __radix_tree_replace(struct radix_tree_root *root,
>  			  struct radix_tree_node *node,
> -			  void **slot, void *item)
> +			  void **slot, void *item,
> +			  radix_tree_update_node_t update_node, void *private)
>  {
>  	/*
>  	 * This function supports replacing exceptional entries and
> @@ -900,7 +910,13 @@ void __radix_tree_replace(struct radix_tree_root *root,
>  	replace_slot(root, node, slot, item,
>  		     !node && slot != (void **)&root->rnode);
>  
> -	delete_node(root, node);
> +	if (!node)
> +		return;
> +
> +	if (update_node)
> +		update_node(node, private);
> +
> +	delete_node(root, node, update_node, private);
>  }
>  
>  /**
> @@ -1585,7 +1601,7 @@ unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
>  bool __radix_tree_delete_node(struct radix_tree_root *root,
>  			      struct radix_tree_node *node)
>  {
> -	return delete_node(root, node);
> +	return delete_node(root, node, NULL, NULL);
>  }
>  
>  static inline void delete_sibling_entries(struct radix_tree_node *node,
> @@ -1642,7 +1658,7 @@ void *radix_tree_delete_item(struct radix_tree_root *root,
>  		node_tag_clear(root, node, tag, offset);
>  
>  	delete_sibling_entries(node, node_to_entry(slot), offset);
> -	__radix_tree_replace(root, node, slot, NULL);
> +	__radix_tree_replace(root, node, slot, NULL, NULL, NULL);
>  
>  	return entry;
>  }
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 7f3a08df25c9..62ac381069fc 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -311,7 +311,8 @@ static int shmem_radix_tree_replace(struct address_space *mapping,
>  		return -ENOENT;
>  	if (item != expected)
>  		return -ENOENT;
> -	__radix_tree_replace(&mapping->page_tree, node, pslot, replacement);
> +	__radix_tree_replace(&mapping->page_tree, node, pslot,
> +			     replacement, NULL, NULL);
>  	return 0;
>  }
>  
> -- 
> 2.10.2
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR