Re: [PATCH v8 1/6] lib/dlock-list: Distributed and lock-protected lists

[Davidlohr Bueso]

On Tue, 31 Oct 2017, Waiman Long wrote:

> Linked list is used everywhere in the Linux kernel. However, if many
> threads are trying to add or delete entries into the same linked list,
> it can create a performance bottleneck.
>
> This patch introduces a new list APIs that provide a set of distributed
> lists (one per CPU), each of which is protected by its own spinlock.
> To the callers, however, the set of lists acts like a single
> consolidated list.  This allows list entries insertion and deletion
> operations to happen in parallel instead of being serialized with a
> global list and lock.
>
> List entry insertion is strictly per cpu. List deletion, however, can
> happen in a cpu other than the one that did the insertion. So we still
> need lock to protect the list. Because of that, there may still be
> a small amount of contention when deletion is being done.
>
> A new header file include/linux/dlock-list.h will be added with the
> associated dlock_list_head and dlock_list_node structures. The following
> functions are provided to manage the per-cpu list:
>
> 1. int alloc_dlock_list_heads(struct dlock_list_heads *dlist)
> 2. void free_dlock_list_heads(struct dlock_list_heads *dlist)
> 3. void dlock_list_add(struct dlock_list_node *node,
> 		        struct dlock_list_heads *dlist)
> 4. void dlock_list_del(struct dlock_list *node)
>
> Iteration of all the list entries within a dlock list array
> is done by calling either the dlist_for_each_entry() or
> dlist_for_each_entry_safe() macros. They correspond to the
> list_for_each_entry() and list_for_each_entry_safe() macros
> respectively. The iteration states are keep in a dlock_list_iter
> structure that is passed to the iteration macros.
>
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> Reviewed-by: Jan Kara <jack@xxxxxxx>

Reviewed-by: Davidlohr Bueso <dbueso@xxxxxxx>