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

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Message-ID: <20171129152902.7y6xir6nrrzukgoi@linux-n805>
Date:   Wed, 29 Nov 2017 07:29:02 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Waiman Long <longman@...hat.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.com>,
        Jeff Layton <jlayton@...chiereds.net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andi Kleen <andi@...stfloor.org>,
        Dave Chinner <dchinner@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v8 1/6] lib/dlock-list: Distributed and lock-protected
 lists

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@...hat.com>
>Reviewed-by: Jan Kara <jack@...e.cz>

Reviewed-by: Davidlohr Bueso <dbueso@...e.de>